NBSIR 75-655

Report No. 5

Analysis of Findings of Four

Tank-Car Accident Reports

C. G. Interrante, J. G. Early and G. E. Hicho

Mechanical Properties

Metallurgy Division

Institute for Materials

National Bureau of Sta Washington, D. C. 20i

January 1975

Summary Report

Interrante, C. G. , Early, J. G. , Hicho, G. E.,

Analysis of findings of four tank-car accident

reports, DOT Report No. FRA-OR&D/75-50,

70 pages (Available as PB/251-097 from the

National Technical Information Service,

Springfield, VA, 22l6l, Jan. 1975).

g 5 f R 1 ^

31.

Prepared for Federal Railroad Administration

Department of Transportation

Washington, D. C. 20591

NBSIR 75-655

Report No. 5

ANALYSIS OF FINDINGS OF FOUR

TANK-CAR ACCIDENT REPORTS

C. G. Interrante, J. G. Early and G. E. Hicho

Mechanical Properties Section

Metal lurgy Division

Institute for Materials Research

National Bureau of Standards

Washington. D. C. 20234

January 1 975

Summary Report

Prepared for Federal Railroad Administration

Department of Transportation

Washington, D. C. 2D 59

1

o«

U. S. DEPARTMENT OF COMMERCE. Frederick B. Dent. Secretary

NATIONAL BUREAU OF STANDARDS. R. chard Mr. Roberts. Doctor

TABLE OF CONTENTS

Page

1. PREFACE iv

2. INTRODUCTION 1

2.1 Background 1

2.2 Purpose 1

2.3 Scope of this Report 1

3. FINDINGS 2

3.1 Specified Properties 3

3.1.1 Chemical composition 3

3.1.2 Tensile properties 6

3.1.3 Bend-test performance 9

3.1.4 Welding practice 11

3.2 Measurements not Specified 12

3.2.1 Hardness test results 12

3.2.2 Macroscopic observations 14

3.2.3 Microscopic observations 18

4. SUMMARY OF FINDINGS 21

5. GENERAL DISCUSSIONS 23

5.1 Effect of Inclusions on Mechanical Properties 23

5.2 Anisotropy of Mechanical Properties 24

5.3 Observations of Unusual and Undesirable Features... 25

in Samples From Three Head Plates

5.4 South Byron Shell Plate Steel 26

5.5 Abusive Service Requirements 28

6. CONCLUSIONS 29

7. REFERENCES 31

l
TABLES

1. Identification of Samples Taken from Tank Cars

2. Summary of Compositional Findings

3. Summary of Tensile Test Results

4. Abbreviated Summary of Bend Test Results

5. Summary of Observations Related to Welding Practice ...

6. Hardness Results

7. Macroscopic Observations

8. Observed Ferrite Grain Size Values

9. Inclusion Ratings by ASTM E-4 5 Method A for Five Plates

Used for Studies of Mechanical Properties

10. QTM Inclusion Content Ratings in Area Percent for Five

Steel Plate Samples

11. Comparisons of Results of Inclusion Ratings by

Various Criteria

v. FIGURES

1. Comparison of Longitudinal and Transverse Ductility

of AAR TC128 Steels of Various Strength Levels ......

2. Profile View of Crescent City Sample FRA-3 in the

B Plane

3. Weld Cross-Section Taken from Callao Sample K-ll at the

Weld Between Shell Courses 4 and 5

4. Montage of Microstructure Through the Cross-Section of

Callao Head Plate K-l with Hardness Values Shown

for Specific Areas

5. Comparison of Tensile Strength and Hardness of the

AAR TC128 and ASTM A212 Steels Tested

6. Profile Views of Fractures Taken from Crescent City

Accident

7. Profile Views of Fractures Taken from the Callao and

South Byron Accidents
FIGURES (Continued)

8. Micros tructure of the Belle Sample

9. Drawing Showing the Three Mutually Perpendicular

Planes Associated With the Rolling Diection in

A Plate

10. Microstructure of the South Byron Shell Plate Sample,

As Observed on Three Mutually Perpendicular Planes .

11. Microstructure of the Crescent City Shell Plate Sample

FRA-2, as Observed on Three Mutually Perpendicular

Planes

12. Microstructure of the Callao Head Plate K-l, as

Observed on Three Mutually Perpendicular Planes ....

13. Microstructure of the Callao Shell Plate K-5, as

Observed on Three Mutually Perpendicular Planes .... APPENDIX A - Specifications AAR M128-65, -69 and -70;

ASTM A212-65 •. . APPENDIX B

APPENDIX C

APPENDIX D

- Summary of Chemical Compositions

- Summary of Bend Test Results . .

.

- Guided Bend Test Jig
ANALYSIS OF FINDINGS FROM FOUR TANK-CAR ACCIDENT REPORTS"

1. PREFACE

A comprehensive overview of the findings and metallurgical

analyses of tests conducted at the National Bureau of Standards on samples of tank-car materials submitted by the Federal Railroad

Administration is presented. The submitted samples were taken

from tank cars which had been involved in accidents during the

period January 1970 to January 1971. The testing conducted

during the metallurgical analyses included full chemical analyses,

ambient temperature tensile tests on longitudinal and transverse

specimens, quantitative metallography to determine ferrite grain

size, pearl ite colony size, and inclusion content, size, and shape,

hardness tests, bend tests on longitudinal and transverse specimens,

and a very comprehensive program of impact testing, which is

covered in a separate report on Impact Properties.

The data, which are presented in the Findings section of this

report and which are summarized and discussed in the Summary

and in the General Discussions, represent a valuable body of

information from which the Conclusions were drawn. These summaries

and conclusions on the properties of these steels, and the

metallurgical factors affecting these properties, when taken in

conjunction with the service requirements and the observed behaviors

of the materials during the actual service failures, can be useful

in making recommendations as to approaches to improved materials

and improved specifications for the plate materials for tank cars.

While some attempt is made to relate the findings of laboratory

tests of the materials to observations made at the accident sites and

to the appearances of the fractures of the failed pieces submitted to

the Bureau, the principle objectives are not to establish a cause of

the failure for each of the five failed tank cars from which samples were submitted; rather, the intent is to determine if the plate

samples conformed with the specifications to which the tank cars had

been fabricated and to gather information pertinent to the question

of the suitability of these materials for use as the plate materials

of tank cars. Some departures from the requirements were found in

these tests, mainly in the areas of chemical composition and bend

requirements. These findings as well as others, such as those

related to welding practices and those obtained through quantitative

metallography, lead to some questions concerning the specifications

for the materials and the possible means by which materials with

improved performance under abusive service conditions may be specified

in the light of an overall understanding of the problems and of

the current materials technology.

iv
Report No. 5

Analysis of Findings from Four Tank-Car Accident Reports

2. INTRODUCTION

2.1 Background

Failures involving tank cars carrying hazardous materials have

prompted the Federal Railroad Administration (FRA) to sponsor research

studies aimed at the development of knowledge that could be used to

prevent or minimize the sometimes catastrophic effects of these failures.

As part of these studies, the FRA has requested that the National Bureau

of Standards (NBS) conduct metallurgical analyses on steel samples

taken from tank cars that were failed in four of the accidents which

occurred during the period January 1970 to January 1971.

2.2 Purpose

The principal purpose of the metallurgical analyses was to determine

if the steel samples conformed with the specifications to which the tank cars had reportedly been fabricated. Another objective was to gather

information pertinent to the question of the suitability of the specifications for steels used as plate material of tank cars carrying hazardous

materials. Thus, the information developed in the analyses of tank car samples is useful as a basis for understanding both the mechanical

properties of the steels when fabricated as tank cars and the pertinent

metallurgical factors that govern these properties, and this information

may ultimately lead to a better understanding of and perhaps improvements

of the mechanical integrity of tank cars, particularly under abusive

service conditions.

2.3 Scope of the Report

The results summarized in this report of the metallurgical analyses

conducted by NBS on steel samples taken from failed tank cars includes

the findings of four accident reports* "

, each of which gives information on one or more steel plate samples taken from one failed tank car at each accident site, except for the Crescent City site from

which samples were taken from two failed cars.

1
As shown in Table 1, a total of 19 steel samples were submitted

by FRA for the$e analyses. Each sample represents either a single

plate of steel or two plates with a weldment joining the plates.

Shell plates, cold-formed and hot-formed head plates are included.

Three different grades of steel are represented: AAR TC128-A-69,

AAR TC128-B-65, and ASTM A212-B-65. The pertinent specifications for

these grades are given in Appendix A.

We note that in the specifications for plate materials for these

tank cars, properties are specified for plates in the as-rolled condition

and the plate samples taken for these studies were in the as-formed

and stress-relieved condition. Furthermore, in the accidents, these

plates could have received some reforming and/or heating during and

following the failures of the tank cars. Therefore, the plates used

for studies of the mechanical properties were plates selected to have

(1) only minor or negligible amounts of reforming and (2) paint present

on the surface, which indicates that the plate was not subject to

excessively high temperatures. With these as prerequisites for the

plates selected for studies of mechanical properties, it is believed that

the observations and properties reported in the four reports that are here

summarized are germane to the plates in the tank cars in service, except

where noted otherwise.

3. FINDINGS

In this report, two categories of findings are given: (1) Those

relating directly to the specifications to which the tank cars were

constructed—presented in section 3.1, these findings indicate

whether or not the steels and the fabricational procedures meet the

requirements of the specification on chemical compositions, tensile

properties, bend behaviors, and welding practice; and (2) those measurements

and observations not specified but which relate to the question of the

suitability of the steels for use as the plate material of tank cars--this

second category, given as section 3.2, is somewhat more complex and in some instances more subjective and qualitative; it involves measurements of

mechanical properties, such as hardness, and other measurements and

observations, such as thickness measurements and metal lographic observations

of the microstructures, the types of inclusions and the percentage

content of inclusions.

Each of these topics is presented and discussed here in the

findings section of this report. The findings are then summarized

and some general discussions, which may relate findings of more than one of these topics, are given. Finally, recommendations are made,

based on the findings and analyses given here.

For some plates, more than one sample was taken to represent the plate.

2
Although some references to the results of impact tests are made in

this summary, a full summary of impact test results is presented as a separate report on the findings and significance of the impact tests

conducted at NBS.

3.1 Specified Properties

3.1.1 Chemical Composition

Check chemical analyses were conducted by the Analytical Chemistry

Division of NBS to determine whether or not the chemical composition of

the plate samples taken from the failed tank cars conformed to the

applicable specifications.

Specifications of the chemical requirements for the AAR TC128

steels and the ASTM A212-B steel are given as ladle analyses for various

elements. Ladle analyses represent the liquid composition of the heat

of steel from which plates are ultimately formed. Differences between

ladle analyses and check analyses from finished plates represent chemical

segregation. Chemical segregation occurs not only between ingots but

also within an ingot, and therefore the location of the check analysis

sample is very important.

A general procedure was followed regarding the location of the

samples for check chemical analyses and the chemical detection

techniques employed. Samples for chemical analysis were taken from

the quarterthickness position in the plate or weld, as specified in

ASTM Method E59-67 which treats the sampling of steel for determination

of chemical composition. Optical emission spectrometric analysis was used for the determination of manganese (Mn), phosphorus (P), sulfur (S),

silicon (Si), vanadium (V), copper (Cu), nickel (Ni), chromium (Cr),

molybdenum (Mo), aluminum (Al), titanium (Ti), niobium (Nb), and

zirconium (Zr). Carbon (C) was determined by combustion-thermal- * conductivity analysis. Exceptions to this general procedure occurred.

A complete summary of the chemical compositions as determined by

the NBS check analyses is listed in Appendix B along with the applicable

specifications (min, max, range) and the available producers '. .ladl

e

analyses. Ten steel plate samples are grouped on the basis of the

specification to which they were produced: Four are ASTM A212-B-65

*Exceptions: (i) In the Belle, W. Va. accident, the sample taken for

chemical analysis was removed from the surface of the plate rather than

from the quarterthickness position. The phosphorus content was determined

by photometric analysis (ASTM E3S0) and the sulfur by combustion-ti tration

analysis (ASTM E395). (ii) In the Callao, Mo. accident, optical emission

spectroscopy was used to determine all of the elements, including carbon.

3
steels, five are AAR TC128-B-65 steels, and one is an AAR TC128-A-69

steel. Each check analysis represents a separate steel plate except

for the shell plate samples FRA-1 and FRA-2, which were taken from the same plate. In addition to these plate samples, one analysis of a weldment (Callao, K-2) is given.

These analyses show that the check analyses for 3 of the 10

plates, for all specified elements, meet the chemical requirements of

the applicable specification, and that all of the producers' ladle

analyses - only 5 were available - are within the specifications. Thus

for brevity, the present discussion will concern only (1) those

analyses of elements with compositions outside of the specified range

and (2) other analyses that in some other way are considered

significant. See Table 2 for a summary of significant compositional

findings.

We note that product analysis tolerances are not given in the

specifications applicable to the three grades of steel. Thus, the

question of how much the composition can vary, under a specified

minimum or over a specified maximum limit, is an open question. To

make a judgment on this question, it is useful to refer to ASTM

Specification A6-70, which governs general delivery requirements of

rolled steel plates and other shapes for structural uses. This

specification allows the purchaser to make a check analysis of finished

material representing each heat: Sampling of the finished material

must be done in accordance with ASTM Method E59, and the chemical

composition of the material shall conform to the requirements of the

product specification, subject to the applicable product analysis

tolerances given in A6-70. These tolerances were used in interpreting

our findings on check analyses. However, the specified sample

locations could not be followed because our plate samples were not

taken from the ends (top and bottom) of the plate.

Carbon - In general, the carbon level in the check analyses of

all 10 plate samples was close to or above the maximum limit of the

specified ladle analyses. As shown in Table 2, check analyses of one plate of A212-B steel, four plates of TC128-B-65, and one plate of

TC128-A-69 steel revealed carbon contents in excess of specification

limits by amounts varying from 0.01 to 0.05 weight percent. The

analysis tolerance for carbon, as given in ASTM A6-70 for carbon-steel

plates, permits a check analysis to be 0.04 percent by weight over the

maximum specified ladle analysis. Using this ASTM criterion, only

plate sample FRA-3 of AAR TC128-B-65 steel, taken from the Crescent

City accident, falls outside the tolerance limit and thereby fails to

meet the specification requirement. The other four TC128 steel plates

and the three A212 steel plates meet the requirements. The

consistently high level of carbon, measured in our 10 test samples and

in the 5 ladle analyses, indicates that steel producers work to the top

of the permissible range for carbon and that this is done to assure

that the strength requirements will be met.

4
Manganese - The check analyses for manganese have a greater

variability than those for carbon, although the manganese contents of

only 3 of the 10 plate samples are above the specified maximum. One

plate of A212-B steel (Crescent City) and 2 plates of TC128-B steel

(Crescent City and South Byron) exceed the specification limits in

amounts ranging from 0.01 to 0.05 percent by weight, as shown in Table

2. Using the criteria of ASTM A6-70, the analysis tolerance for

manganese is 0.04 percent by weight over the maximum specification

limit. By the argument given above for carbon, only one TC128-B plate

sample, FRA-3 (Crescent City), exceeds the maximum allowed chemical

variation. The two other plates, a TC128-B steel (South Byron) and a A212-B steel (Crescent City), meet the compositional requirements.

Sulphur and Phosphorus - Check analyses for sulfur and phosphorus

indicate that, although all of the plate samples are within the

specified maximum limits, one or both of the elements are close to

their limits for four steels: 1 plate of A212 steel (Crescent City), 2

plates of TC128-B-65 steel (Crescent City and South Byron), and 1 plate

of TC128-A-69 steel (Belle), as shown in Table 2. The sulfur contents

of the Crescent City shell plate samples FRA-5, FRA-3 and the A-head

portion of FRA-2 were 0.047, 0.04 and 0.03 weight percent, respectively,

and the South Byron plate sample contained 0.04 weight percent sulfur.

All of these sulfur contents are near but within the specified maximum

limit of 0.05 weight percent. The phosphorus levels of the Belle plate

sample and plate sample FRA-3 (Crescent City) were 0.03 and 0.027

weight percent respectively; while these values are considerably higher

than those determined in all other plate samples, they are within the

specified maximum of 0.04 weight percent phosphorus.

Ueoxidation Practice - Specifications TCI 28-65 and TCI 28-69

require a fine-grain steelmaking practice, while specification A212-B

allows either coarse- or fine-grain practice. The check analyses for

aluminum and/or vanadium showed that all of the plate samples except

two had been produced to fine-grain practice. The levels of aluminum

and/or vanadium present in one sample, A-head, FRA-2 (Crescent City),

of the four A212 steel plates and in one sample, K-5 (Callao), of the

six TC128 steel plates (see Table 2), indicate that the steels for

these two plates were produced in accordance with coarse-grain practice.

Therefore, the TC128-B steel sample, K-5 (Callao), was not produced in

accordance with fine-grain practice required by the specification.

* The aluminum and/or vanadium check analyses indicate whether the steel was deoxidized by a combination of silicon and one or both of these

grain-refining deoxidizers. When these elements are present only at

very low levels, a fine-grain dioxidation practice was not used.

5
3.1.2 Tensile Properties

A complete summary of the tensile test results from three head

plate samples, three shell plate samples, and three weld samples—all taken

from the four accidents--is shown in Table 3. Tension specimens were

prepared in accordance with the appropriate product specification and

tested in accordance with ASTM Methods and Definitions A370-71 .

Test Specimens - The tension test specimens, 0.250 inches in

diameter with a 1-inch-gage length, were taken as closely as possible

from the quarterthickness position of the plate. Longitudinal and

transverse specimens were tested for each plate and weldment, except

only transverse tensile specimens w$re taken from the head plate of

FRA-2 due to insufficient material.

* The General Conditions for Delivery section of the specifications

for AAR TCI 28-69, AAR TCI 28-65, and ASTM A212-65 tank-car steels require

that materials furnished to these specifications must conform to the

applicable requirements of ASTM Specifications A20-67 and A20-65 respectively.

Specifications A20-67 and A20-65 require for plates 1-1/2 inch and under

in thickness, tension test specimens shall be Standard Rectangular Tension

Test Specimens with 8-inch-gage length and for plates over 1-1/2 inches

in thickness, tension test specimens shall be Standard Round Tension Test

Specimens with 2-inch-gage length, 0.505 inches in diameter. For

plates up to 4 inches in thickness, Standard Rectangular Test Specimens

with 8-inch-gage length can be used if testing machine capacity exists.

However, both A20-67 and A20-65 require the tests to be conducted in

accordance with the ASTM Methods and Definitions A370, for the Mechanical

Testing of Steel Products. ASTM A370-68 allows Standard Round Tension

Test Specimens and Small Size Specimens proportional to the Standard

Round Specimen to be used when it is necessary to test material from which

the Standard Rectangular Test Specimens of 8-inch- and 2-inch-gage length

cannot be prepared. Because the amount of plate material available for

machining test samples was sometimes limited in our studies, it would not

always have been feasible to prepare the Standard Rectangular Tension

Specimens. The Standard Round Tension Test Specimen, 0.505 inches in

diameter, has a 2-inch-gage length, thus allowing direct comparison between

test result and specification; however, the threaded end section requires

a diameter of 3/4 inches, which exceeds the plate thickness of the head

and shell plates tested. Thus, for test consistency from plate to plate,

the tensile test specimens were machined to standard 0.250-inch-diameter

round test specimens with a 1-inch-gage length.

*A1 though the specifications ASTM A212-65, AAR TCI 28-65, and AAR TC128-69

do not specify test specimen orientation, ASTM A370-71 does specify that

wrought steel products are usually tested in the longitudinal direction

but that where size permits and service justifies it, transverse testing

is done.

6
Strength Levels - The measured values of tensile strength and yield

strength for four of the six plate samples tested were within the

specification limits. The two plate samples outside the specified

limits were the South Byron shell plate sample (an AAR TCI 28-65 steel)

and the Belle head plate sample (an AAR TC128-69 steel). For the South

Byron sample, the longitudinal and transverse tensile-strength values

exceeded (by up to 2%) the specified maximum limit, but the yield-strength

values met the requirements and were well above the specification minimum

level. For the Belle sample, the longitudinal yield-strength values were below (by up to 8%) the specified minimum yield strength.

Yield point phenomena, as measured by a distinct yield point or a lower-yield point, were observed in both longitudinal and transverse

specimens in four of the six plate samples but were not seen in any of

the specimens from the AAR TCI 28-69 Belle head-plate sample or in three

of the four specimens from the AAR TC128-65 Callao (K-l) head-plate

sample. The presence or absence of yield-point phenomena can provide

information on the recent thermal mechanical history of the test sample.

Tensile Ductility - Tensile ductility data for all six plate samples

were measured by percent elongation in a 1-inch-gage length and by percent

reduction in area at the fracture. For all plates tested, the ductility

as measured by percent elongation exceeded the minimum specification

requirements. For the TC128 steels the longitudinal ductility was approximately 10 percent higher than the transverse ductility; for one A212 steel tested, this value is only 4 percent. This latter finding indicates

the degree of the anisotropy of tensile ductility of the plates and

grades of steel tested. This result is illustrated in Figure 1 where

percent elongation is plotted against the ultimate tensile strength for

all AAR TCI 28 steels tested. The graph includes both head and shell

plate specimens and illustrates that the anisotropy is independent of

whether the test specimens were from head or shell plates.

Reduction-i n-area measurements are not specified in either

ASTM A212-65 or AAR Ml 28, but they provide a useful check of the

elongation results, as percent-reduction-in-area measurements are independent of the gage length of the specimen. The trends for reductionin-area data given in Table 3 are similar to those for elongation data.

Wei dments - The three weldment samples (one weld of ASTM A212

plates and two welds of AAR-TC128 plates) have acceptable elongation

values, and their tensile- and yield-strength levels meet the minimum

requirements for the plates, indicating that the joint efficiency is

1.0 for all welds tested.

7
Ferrite Grain Size - Also tabulated (in Table 3) for the six

steels on which tensile data were taken are the ferri te-grain-size

determinations as measured in accordance with ASTM Ell 2 Method

of Uetermining Average Grain Size in Metals. The effects of grain

size on yield strength, hardenabil i ty , and toughness has long been known.

Three of the plate samples have ferrite grain size numbers in the

range of 7 or 8. One plate sample of A212-B steel that was not

produced to fine-grain practice (FRA-2, A-head, Crescent City),

has a ferrite grain size of 6 and is coarser than the other five plates,

which were made to fine-grain practice. One plate sample has a uniformly finer grain size than the others, the Belle sample

(a AAR-TC128 steel), which contains sufficient vanadium to satisfy

the requirements for Grade A of the Ml 28 specification. Lastly, a hot-formed head plate (K-l, A-head, Callao) of TC128-B steel has a variable microstructure with ferrite grain sizes varying from 7 to 9

through the thickness of the plate.

* The ferrite grain size is not specified in either ASTM A212 of AAR M128,

but indirect reference is made to austenite grain size through the specification requirement of coarse- or fine-grain practice, i.e., the

austenite grain size existing just before cooling through the transformation

temperature shall be fine or coarse. ASTM A212 allows either fine- or coarse-grain practice while AAR M128 specifies fine-grain practice only.

The micros tructures of both ASTM A212 and AAR TCI 28 steels consist of

proeutectoid ferrite and pearl ite, and the coarseness of the pearl ite

colonies (surrounded by ferrite at the prior austenite grain boundaries)

can represent the grain size of the austenite, prior to its transformation,

to ferrite and pearl ite. However, there is a problem in attempting to

correlate ferrite grain size with deoxidation practice for steels which

are not reaustenitized after hot rolling (i.e., shell plates and coldformed head plates). A fine-grain practice can reliably control the austenitic grain size of reaustenitized steel provided that excessively high

austenitizing temperatures are not used. The grain size for hot-rolled

steels (even when produced to fine-grain practice) may be coarse if the

rolling finishing temperature is high, as it frequently is. Thus a specification of fine-grain practice will not consistently result in

fine-grained steel, unless the plates are normalized after rolling or unless the finishing temperature for hot rolling (or the reausteni tizi ng

temperature allowed for hot forming) can be specified and rigidly controlled

in a manner that always results in a fine-grained austenite.

8
Ferrite grain size is primarily controlled by the prior

austenite grain size and by the cooling rate through the transformation

temperature. Thus it is affected by deoxidation practice, the

finishing temperature of rolling or forming operations, and the rate

of cooling after these operations.

3.1.3 Bend-Tests Performance

Bend tests were conducted on 24 specimens of plate steels and

on 4 specimens of weldments. A complete summary of these test results

is given in Appendix C.

For tests of plate steels, pairs of longitudinal and transverse

bend specimens were prepared and tested. Bend tests were conducted in

accordance with the requirements of ASTM Designation A370-68 Standard

Methods and Definitions for Mechanical Testing of Steel Products.

Specimens of 3/8-inch thickness were bent through an inside diameter

of 3/4 inches, so as to provide a ratio of bend diameter (d) to

thickness (t) equal to 2, as required for the ASTM A212 and the

AAR TC128 steels tested. Tests of transverse specimens are not required.

For the weldments, side-bend specimens were tested and a less severe bend

ratio of 4 was used to meet the test conditions given in the methods of

ASTM E190-64 for the guided-bend test for ductility of welds. The

apparatus used for all bend tests is that given in Appendix W of the AAR

Specifications for Tank Cars and given here as Appendix D.

* Dimensions of all test specimens were 3/8-inch thick X 1-1/2 inch

wide X 6-inch long, except that the width of the side-bend specimens

for welds is the plate thickness.

* The width of the bend specimens significantly affects the bend ductility.

Dieter^ 'has reported that ductility, in terms of the bend angle before

cracking occurs in a material in bending, decreases with increasing values

of the width to thickness ratio, w/t, until a terminal level is achieved

at a w/t equal to about 8. As this ratio of w/t increases, the ratio of

the transverse stress to the circumferential stress also increases and

the bend ductility of the specimen decreases. Therefore, in order to

have a bend test specimen of "intermediate" severity, the w/t ratio of

4 was chosen for the bend specimens tested at NBS. However, we note that

adherence to ASTM Specification A20, referred to in both of the steel

plate specifications, would permit a specimen thickness equal to the

plate thickness. The width is 1-1/2 inches. Thus, the width to thickness

ratio for 5/8-inch thick plates (w/t) would equal approximately 2.4; this

test may be a test at a severity level different from that conducted

by NBS, as the w/t ratio of the NBS tests was 4.0 with a 1-1/2-inch

wide by 3/8-inch thick specimen.

9
The results of bend tests for a total of 28 specimens are given

in Table 4 in an abreviated form. Fourteen specimens from three

accident sites (including four side-bend weld specimens from two of

these sites) passed the required bend test, whereas six shell-plate

specimens, including two specimens of the required longitudinal

orientation, from the South Byron accident failed the required bend test.

Bend tests are used to assess surface quality and ductility,

and the failures of all six of the standard South Byron bend specimens

indicate that ductility of this steel may be inadequate, and this

conclusion seems consistent with the results of tensile tests in

which the steel met the elongation requirement by only a small margin

but it is not consistent^ 'with the results of the mill bend tests

required for delivery of the plate. This is discussed in section 5.4.

Six additional South Byron shell -plate specimens were tested at

non-standard d/t ratios. Two of these failed in tests more severe

(d/t= 1.7) than the specification requirement and four of these passed

in tests less severe (d/t = 4.0) than the specification requirements.

Two additional bend specimens taken from the Callao head plate were tested in a non-standard manner after one longitudinal specimen

and one transverse specimen passed the required bend test with the

outside surface of the tank car being the outer curve of the bend. In these two non-standard tests, the specimens were tested with the

outside surface of the tank car being the inner curve of the bend.

The transverse head-plate-sample K2-6 failed this test. Cracks were

visible at an angle of bend of approximately 120°. With further

bending, the cracks extended until the specimen fractured into two

pieces at 180° of bend. While this failure is not considered a failure

of the bend requirement for this steel, the failure is instructive.

This transverse specimen failed at a relatively low bend angle of

120°and the longitudinal specimen did not fail, indicating that the

tendency for bend-test failure will be greater for transverse bend

specimens.* Furthermore, the steel of the failed specimen was different

from the steel for specimens tested in the standard manner in that the

outer curve of the bend represented the steel near the center of the

plate for the non-standard test whereas it represented the plate

surface in the standard test. In addition, the inclusion content near

the mid- thickness and center of the plate is greater than that near

the plate surfaces. Thus, these tests indicate that the tendency to

fail in the bend test increases with the inclusion content, which is to some extent dependent upon the thickness location within the plate,

and that in these steels transverse specimens have less bend ductility

than longitudinal specimens.

* This finding is consistent with the results of the failures of the six

South Byron standard bend tests. The two longitudinal specimens failed

by crazing only, whereas all four transverse specimens failed at

relatively low angles of bend.

10
3.1.4 Welding Practice

The specifications for the steels used in the tank cars of the

four accident reports state that "Welding technique is of fundamental

importance and it is presupposed that welding procedures will be in

accordance with good practice" (M128 specifications) and "Welding

technique, etc in accordance with approved methods" (A212

specifications). Accordingly, weldments submitted to NBS for these

metallurgical analyses were examined and tested to gather information

on the methods and practices used in welding of the tank cars.

Of the 19 plate samples submitted to NBS, six contained weldments

and two additional plates contained a weld heat affected zone (HAZ)

with little or no weld metal. These eight plates were visually

examined and various tests were made on their weldments and HAZ

regions. The visual examinations included inspection of fractures

related to the weldment or its HAZ and examination for the alignment of

the plates being welded. On three of these weldments, the tests were

extensive and included side-bend tests, tensile tests, and selected

hardness tests. The three weldments examined in this detailed way

include two weldments that joined the "A" head plate to the first shell course of a tank car; one of these weldments joined two A212-B steel

plates (sample FRA-2), and the other one joined TC128-B steel plates

(sample K-2). The third weldment joined one shell course to another

shell course of TC128-B steel (sample K-8). In addition, chemical

analyses were made on one weldment and impact tests (not reported here) were made on selected weld-metal and HAZ specimens taken from three of

these plates. The results of these examinations and tests are summarized in Table 5.

For the three weldments most extensively tested, with side-bend

tests, tensile tests and measurements of hardness, the results indicate

that: (1) The ductility of these weldments is good. All passed the

bend test and the ductility in tensile tests exceeded the elongation

requirements of the plates being joined. (2) The joint efficiency of

the weldments was 1.0, i.e., the strength of the weldment meets or exceeds the required strength for the plates that it joins. (3) The

hardness of these weldments is satisfactory, being uniformly hard

enough in the weld-metal region to match the strength requirements of

the plate steels and being soft enough in the HAZ region to indicate

that the plates were properly stress relieved after welding.

Each of the two plate samples that contained an HAZ but little or

no weld metal, samples K-6 (Callao) and FRA-2 (Crescent City),

contained a region in which a crack propagated along a heat affected

zone, a tendency which would be expected to increase with increasing

values of HAZ hardness. For TC128 steel, the maximum measured Knoop

hardness in the HAZ corresponds to that of steel with tensile strength

of about 117Ksi. This value is not excessive in comparison with the

tensile strength of about 90 Ksi of unaffected base metal.

11
The fracture of FRA-3 (Crescent City) may have contributed to

the failure of tank car designation SOEX 3219. This was concluded

upon finding a region of high hardness (Rr28) and a secondary crack.

These were observed near the surface of the plate sample at a location

near the fracture. This region is believed to be an HAZ of a welded

attachment that was improperly stress relieved. See Figure 2.

The region of higher hardness in the HAZ of this weldment would be

expected to have limited ductility and the presence of the secondary

crack is illustrative of this point. However, it is also possible

that the cracking started outside of the HAZ region and followed the

HAZ only because of the less favorable stress state due to the

joint contour.

Six of the eight weld related samples contained weldments that were visually examined for plate alignment. The alignment for five of

the six plates was satisfactory, but the sixth plate, sample K-ll,

(Callao) was not properly aligned and it contained an unusually wide

circumferential weldment. This was the weld between shell courses

4 and 5 of TC GATX 94451. A section taken from this weldment, shown

in Figure 3 indicates that this weldment contains a total of seven weld

passes: It has four large weld passes presumed to be submerged-arc welds

and three small passes. Two of the large passes were the first to be

deposited, one from each side of the weld groove. Then, the other two

large passes were deposited on one side of this weldment while three

small passes were deposited on the other side of the weldment. It appears

that these later 5 passes were deposited to smooth out the discontinuity

of a misalignment of the plates that arose after the first two passes had

been deposited. The offset of these plates in this region was measured

at NBS to be about 0.203 inches and this value exceeds, by 0.047 inches,

the tolerance prescribed in the AAR SPECIFICATIONS FOR TANK CARS,

January 1, 1970 Ld. (Appendix W, Table 15.03(a). This is an example

of poor welding practice.

3.2 Measurements not Specified

3.2.1 Hardness Test Results

Hardness is not a specification requirement, but hardness measurements

can be very instructive in metallurgical analyses. Hardness measurements

were taken on 19 specimens from 11 plate samples. The results of these

measurements are given in Table 6. For all the samples except the Belle

head-plate sample, the measurements were taken on planes perpendicular to

the plate surfaces. On the Belle sample these were taken on a plane

parallel to the surface of the plate. Most of the hardness measurements

were Rockwell B measurements, but one set of Brinell measurements were

taken and three sets of Knoop hardness measurements were taken, two in

heat-affected-zone (HAZ) regions and one set through the thickness of a plate steel sample.

12
The hardness results indicate that for the steels investigated,

the hardness throughout each plate sample (with the exception of the

head plate from the Callao accident) is generally uniform. The results

also show that the average hardness is R

R 80.2 for the ASTM A212 steels

tested and Rp 92.8 for the AAR TC128 steels tested. The A212 steels have

average hardness values of 80.3 for the shell plate and 79.9 for the

head plate. For the AAR TC128 steels the averages are Rg 93.1, and

Rg 92.3, respectively, for the shell and head plates.

Hardness measurements taken on the "mixed" micros tructure shown in

Figure 4, a mi crostructure which varies greatly from the outside to the

inside of the head plate, clearly points up this mi crostructural

dissparity. The average hardness near the outside, where the

microstructure is finer is about Rg 88, whereas near the inside surface

where the microstructure is coarser, the average hardness is about Rg 94.

Hardness measurements alone are difficult to assess since hardness

is not a well-defined property. However, empirical relations between

hardness and tensile strength exist for most carbon steel

s

fi

x One such

correlation is shown as the continuous curve of Figure 5. ' Also plotted

are the average measured values of hardness for the six plate steels

tested in the four accident reports. The NBS data and the empirical

curve compare as favorably as might be expected for this type of

correlation, and the Figure points up that hardness can be a useful

gage of tensile strength. However, hardness is most useful in metallurgical

analyses as a tool for gaging variability of mechanical properties within

a given material

.

Hardness measurements taken on the heat-affected zone (HAZ) of

the Callao plate sample K-8 indicate that as expected, the HAZ hardness is

appreciably greater than the hardness of the unaffected base metal of

this AAR TC128 steel. Regions of higher hardness, such as those found

in the HAZ of weldments, could either act as sites of crack initiation

under overload conditions or they could provide paths for easier

crack propagation under unusual combinations of stress and weld geometry.

Further, residual stresses in as-welded structures may be just as important as microstructure (or hardness) in causing crack initiation

or propagation in certain regions. Therefore thermal stress relief is

beneficial to both hardness and stress reduction.

Figure 2 shows a cross sectional view of TC128-B sample FRA-3

and a "white" area, marked A, which was believed to be a weld HAZ.

The average Knoop hardness value in Region A was 295, which converts

to Rp 28. The average Knoop hardness of an area remote from the HAZ was Z38, which converts to Rg 97. These results indicate that region A

is significantly higher in hardness than the hardness of/the surrounding

base metal in sample FRA-3. In addition, it is believed^ ' that this

13
hardness value is abnormally high and higher than the hardness that

would be obtained in a weld HAZ in this steel after a stress-relief

treatment at the recommended temperatures of 1100 to 1200 F. A

metal lographic analysis showed that the unaffected base metal of sample

FRA-3 contained spherical carbide precipitates which indicated that the

bulk of this sample had been stress-relieved at relatively high temperatures.

Thus, it is concluded that Region A of Figure 2 in sample FRA-3 is an HAZ of some head plate attachment, which was not given a proper post-weld

stress-relief heat treatment, perhaps because it was produced after the

stress-relief treatment. In service, this local site would have a much

greater potential for crack initiation when compared with properly

stress-relieved metal.

3.2.2 Macroscopic Observations

A total of 11 plate samples taken from 4 accident sites were examined.

Three plates were ASTM A212-B-65 steel, six were AAR TC128-B-65 steel,

and one was AAR TC128-A-69 steel. Thirty-one different areas of the

fracture surfaces of these plate samples were examined to determine

the type and condition of paint on the outside plate surfaces and to

classify the observed fracture modes. Fracture profile sections

taken from each of the 31 selected sites and classified on the basis

of the following four profile types: (1) NP, fracture face is nearly

perpendicular to the plate surfaces; (2) shear, fracture face inclined

approximately 45 degrees to the plate surfaces; (3) mixed, a combination

of types (1) and (2); and (4) lamellar tearing, fracture face contains

steps or ledges that are parallel to the plate surfaces. Examples

of each of these modes are shown in Figures 6 and 7, and a complete

summary of the modes observed and other macroscopic observations is

given in Table 7.

Plate thickness measurements were also taken at 24 of the 31

selected areas. These measurements were made along a line perpendicular

to the fracture surface (at appropriate intervals) until the measured

thickness became constant. Plate thickness was measured and

the percent reduction in plate thickness was calculated for the region near the fracture surface. These plate thinning calculational

results are given in Table 7 along with data on the 50% shear transition

temperature determined from Charpy V-Notch (CVN) tests on 6 of the 11 plate

The plate thinning percentage was based on the measured full plate

thickness rather than the nominal plate thickness so as to provide a more accurate parameter for gaging the extent of deformation near

the fracture.

14
samples taken from the four accident reports*. The last two columns in

Table 7 give the ambient temperature for each of the accidents and an estimate of the temperature of the steel sample at time of failure, based

on an evaluation of the other data in the table. These data, combined

with the plate appearance and fracture mode data, are shown in Table 7.

The presence and condition of paint on the outside surface of the

plate samples is indicative of whether the plate was subjected

to fire. This indication can be used, along with the ambient temperature

at the time of failure, in interpreting the signficance of other observations such as the fracture mode, the percent plate thinning, and the

50%-shear transition temperature.

Only three plates, as is indicated in Table 7, gave evidence of

having been subjected to fire in the accident. These three plates are from the Crescent City (two tank cars) and South Byron accidents, both of

which involved fires and explosions of the tank cars. The South Byron

plate was covered with paint that had blistered but not charred,

indicating a moderate exposure to fire. Plates FRA-4 and FRA-5 from the

Crescent City accident had, respectively, white powder and no paint on their surfaces, indicating a substantial exposure to fire.

The majority of the samples from the other two (Callao and Belle)

accidents, as shown in Table 7, have fracture, modes that are predominately

brittle with fractures that propagated in planes nearly perpendicular to

the plate surfaces, i.e., the NP mode, whereas the samples from the

Crescent City and South Byron accidents have fracture modes that are generally of the shear and mixed type, indicating a more ductile failure.

The tank cars involved in the Crescent City accident, SOEX 3037 and

SOEX 3219, eventually exploded after being heated by a fire. Tank car 3037 contained plate samples FRA-1, FRA-2, and FRA-5, all ASTM A212-B

steels, and tank car 3219 contained plate samples FRA-3 and FRA-4, both

AAR TC128-B steels. The appearances of the fractures on the ASTM A212-B

and AAR TC128-B plate samples are consistent with both the paint * observations on the plate surface and with the. impact test results.

*Results of impact tests on these steels are discussed in a separate report.

We have no data on the thermal behavior of the paint that was used on these two tank cars.

15
Neither the outside surface of FRA-2 near the fracture surface nor any part of the plate surface of FRA-5 contained any paint residue. The

fractures of these plates were of the ductile shear type with 13-percent

plate thinning for the shell portion of FRA-2 and 23-percent thinning for

FRA-5. These results indicate that fracture occurred at an elevated

temperature. The 50%-shear transition temperatures of both the shell and

head parts of FRA-2 (not determined for FRA-5) are relatively high, about

85 F and 140 F respectively, being well above the ambient temperature of

53 F. Thus, it is concluded that these plates at the time of failure

were heated significantly above the ambient temperature, probably in excess of 200 F. The fracture of plate FRA-1, taken from another

location in the shell plate that contained the shell plate portion of

FRA-2, was brittle in appearance with only one-percent reduction in

thickness and evidence of a red paint or primer on the plate surface.

This plate was therefore probably not heated substantially at the time of

failure , a conclusion which is in agreement with the fact that the

CVN-50%-shear temperature of this shell plate was about 85 F, a temperature well above that of the ambient air.

Two of the three AAR TC128-B-65 steel samples, FRA-3 and FRA-4,

contained, respectively, lamellar tearing and shear fractures (shown in

Figures 6a and 6b) with thinning near the fracture being about 0.5 and 10

percent. The presence of paint on the surface of FRA-3, coupled with the

negligible plate thinning at the fracture surface, suggests that this

plate fractured at temperatures within the ductile-brittle transition

region. The presence of paint residue and significant plate thinning of

FRA-4 suggests that this plate fractured at temperatures above the

transition temperature. CVN test data are not available for these plates.

The third plate sample of AAR TC128-B-65 steel believed to have

been subjected to heat from a fire is from the South Byron accident.

Examination of this shell plate sample shows that the paint was blistered,

but there is little or no evidence of paint charring. The best estimate

of the thermal behavior of the paint indicates that charring would occur

at roughly 400 to 450 F, and the paint would be completely burned off

at 600 F.* Based on this estimate, it appears that the surface of the

sample could not have exceeded 450 F and that the actual temperature

was between the ambient temperature of 68 F and about 400 F.

*A telephone conversation on 7-6-71 between Q. Banks (FRA) Washington, D.C.

and C. Graves (GATX) Sharon, Pa. provided this estimate.

16
The fracture surface of the South Byron plate reveals a fracture

mode which changes from one end of the fracture line (type NP), through

a transition region (mixed type), to the other end (shear type) indicating

that the temperature of this steel at the time of fracture was in the

transition region. The 50%-shear transition temperature for this plate

is about 32 F as measured by CVN tests. Plate thinning measurements in areas of each fracture mode type ranged from three to six percent with

the greatest thinning in the shear fracture region. Thus it is probable

that a portion of the plate fractured at a temperature at which the

resistance to fracture propagation is near the maximum for this particular

plate. This temperature, called the upper-shelf temperature, was determined from the CVN tests to be approximately 80 F or higher. It is therefore concluded based on all of these observations that the

plate temperature at the time of failure was above the ambient but

presumed to be closer to the ambient temperature than to 400 F.

The remaining five plate samples were taken from two accidents in

which the failures were the result of severe impact loads. Samples

from these tank cars were not heated either before or after the

failure. These include four plates of AAR TC128-B-65 steel from the

Callao site and one plate of AAR TC128-A-69 from the Belle site.

Plate samples K-l,, K-3, K-5, K-6, K-7, K-9, K-10, and K-12, from

the four Callao plates contained a predominance of NP type fractures,

indicating that fracture occured at temperatures below the ductilebrittle transition temperature. The 50%-shear temperature, as measured

by CVN tests, for the head plate, sample K-l, and for one shell plate

(samples K-3, K-5, and K-6), are, respectively, about 90 F and 55 F. These transition temperatures are well above the ambient temperature of

15 F, indicating brittle fracture would be expected. This conclusion

is supported by the measurements of plate thickness which indicate that

plate thinning is two percent or less.

The single plate sample of AAR TC128-A-69 steel, taken from the

Belle head plate, failed at an ambient temperature of -2 F. The

fracture surface of this sample indicates a mixed failure mode of

primarily type NP with shear lips at the plate surfaces. This mode

indicates that the temperature of the plate at failure was within the

ductile-brittle transition and below the 50%-shear transition temperature.

The 50%-shear temperature for this plate sample, measured by CVN tests,

is between -12 F and -35 F. CVN test results suggest that at the

ambient temperature the steel would be on the upper shelf with a 70-100% shear fracture appearance. A probable explanation for these

conflicting observations is given in the accident report: Prior to the

accident, a crack existed near the HAZ of the weld between the

stiffener plate and the head plate, and the impact of the accident

caused this pre-existing crack to propagate partly into the head plate

but primarily along the HAZ of the weld. Due to lack of material, CVN

tests of HAZ specimens were not conducted; thus, the plate impact data

is not representative of the HAZ and cannot be directly correlated with

the mode of fracture.

17
3.2.3 Microscopic Observations

The metal lographic studies include observations of microstructures

and inclusions and ratings of grain size and inclusion content. None

of these observations and ratings are requirements of the specifications

for A212 and TCI 28 steels. Grain size was rated by optical comparison

using the standard grain size charts given in ASTM E112. Inclusion

content was rated both by the method prescribed in ASTM E45, which

uses the JK charts for the four basic types of inclusions, and by a quantitative television microscope (QTM) method, which rates the

inclusion content as an area percent of the section being rated.

ASTM E45 is used to rate the relative quantity of each of four

types of inclusions: Type A, sulfide; Type B, alumina; Type C, silicate;

Type D, globular oxide. Within each type there are subtypes of thin

and heavy; the heavy usually applies to heavy-section forgings.

The worst field per 100 fields of inclusions of each type in any area (of 0.250-square inches) rated is given on a scale of 0

to 5. Zero represents nearly none and 5 represents the largest

amount on this scale.

The QTM method rates the inclusion content as an area percentage

at each of two magnifications, X338 and XI 300, for specimens taken

from the South Byron sample, and at one magnification, X338, for

specimens taken from both the head and the shell plates of sample

FRA-2 from the Crescent City accident, and from samples K-l and K-5

from the Callao accident. The area percentage measurements were made at two quarterthickness locations and at the midthickness. In addition, for each 100 fields rated, the worst field and the number

of fields with inclusion area greater than 0.5 percent, were tabulated.

Microstructures - A total of 22 metal lographic samples sectioned

from 15 plates were examined for general mi crostructure. This was done on one surface taken normal to the plate surfaces, as shown

in Figure 8, which shows the mi crostructure of the Belle sample at

X100 and X240. The microstructures of several of the plates used for

studies of the mechanical properties were observed on three mutually

perpendicular surfaces oriented as shown in Figure 9. These microstructures are presented as Figures 10 through 13, respectively

representing the South Byron sample, Crescent City-sample FRA-2 (shell)

and Cal lao-samples K-l and K-5.

18
The microstructures shown represent the various microstructures

observed in the 15 plates. These microstructures are not unexpected

for carbon-manganese steels in the as-rolled condition, produced in

accordance with the specifications for grades A212-B and TC128-A & -B.

Each of the microstructures shows some banding, with the banding being

only moderate in shell plates K-5 and FRA-2, intermediate in the

South Byron shell plate, and substantial in head plates K-l and

Belle. The banded microstructure consists of alternate layers

(parallel to the plate surfaces) of proeutectoid ferrite and pearlite.

In unbanded microstructures, like most of that shown for plate K-5

in Figure 10, the ferrite and pearlite are more homogeneously

distributed.

The results of ratings by the QTM method are given for 18 specimens

taken from five plates in Table 10. The data indicate that for each

of the steels rated, the rated inclusion content is similar for the

quarterthickness and midthickness. The South Byron data, which were

taken at two magnifications (X338 and XI 300), indicate that the

area-percent values are about 10 percent greater at the higher

magnification. This is true for all except the worst field ratings,

which are somewhat more variable and which are about 30 percent

greater at higher magnification. The ratings at higher magnification

have greater accuracy due to higher resolution. However, the ratings

at lower magnification cover a greater area with fewer observations,

and they are considered sufficiently accurate for comparisons of

the five plate steels rated by QTM at X338.

Table 11 gives a summary of the results of the inclusion ratings

by ASTM Method A and by the QTM method at X338. Method A results for

Type A thin are given for comparison with the QTM results for overall

inclusion area percent, number of fields greater than 0.5%, and Worst

Field. The first four of the six steels listed were rated by both

ASTM method A and the QTM method. A comparison of the results by

each of the four criteria indicates that they all rank the steels in

a consistent manner. Thus, even for cases in which only one criterion

has been evaluated, the steel can be ranked.

We classify these steels into three arbitrary ranks: Rank 1 - moderate content; Rank 2 - intermediate content; and Rand 3 - high content.

Thus, the table ranks all six steels: Rank 1- A212-B shell of Crescent

City and A212-B head of Crescent City; Rank 2- TC128-B shell of Callao

and TC128-B head of Callao; Rank 3- TC128-B shell of South Byron and

TC128-A of Belle, /ganding augments the anisotropy of mechanical properties

due to inclusions. The mechanical properties of the unbanded steels

would thus be expected to be more isotropic, with the properties being

similar in the longitudinal and transverse directions (and perhaps, even

in the thickness direction) of the plate, particularly for steels with

low inclusion contents.

19
The size of the pearl ite colonies reflects the size of the prior

austenite grains from which the pearl ite and proeutectoid ferrite were

formed on cooling after hot rolling. In these photomicrographs, the

pearl ite is coarse in the South Bryron shell plate and in the FRA-2

shell plate. It is intermediate in the K-5 shell plate and in the

K-l head plate and fine in the Belle head plate. The pearlite colonies

of the cold-formed head plate steel of sample FRA-2 are much larger than

any of the other steels used in our mechanical properties studies; this

is consistent with the finding that this steel was not made to fine-grain

practice.

More important than the size of the pearlite colonies is the

ferrite grain size and the fraction of ferrite in the microstructure,

as the mechanical properties of steels with less tha«gO. 4-percent

carbon are more closely related to these parameters. ' The ratings

of ferrite grain size for 14 steel plates are given in Table 8.

The ASTM ferri te-grai n-size number of the five steels used for studies

of mechanical properties are as follows: Belle (8-9), South Byron (8),

Crescent City FRA-2 shell (7), Callao K-l (7-9), K-2 (8), K-5 (7).

The higher numbers represent the finer ferrite grains.

When other factors are held constant, a decrease in ferrite grain

size leads to an increase in yield strength, and toughness is generally

improved at a given level of strength. Toughness can also be improved

by increasing the fraction of ferrite, and this can be done by decreasing

the carbon content. In addition, some of the processing and compositional

variables can affect toughness by affecting ferrite grain size.

A microstructure of unexpectedly high variability was observed at one location in the TC128-B steel head-plate K-l of the Callao

accident. This variability of microstructure is shown in Figure 4,

a montage of X30 observations taken at various plate thickness

locations from the inside surface to the outside surface of the plate.

The microstructure of the inside locations is generally coarser, with

coarse ferrite (7) and large pearlite colonies, when compared with

that of the outside locations. The outside, with its finer microstructure, was observed to have better resistance to impact failures.

The microstructures observed at other locations within sample K-l,

and in sample K-2 from another part of the same head plate, were

similar to the coarser microstructure shown (in Figure 4) for the

inside of the plate. This variability of microstructure is generally

not desirable and it reflects variables associated with the hot-forming

process used in the fabrication of this head plate. This variability is

believed to give rise to nonuniform strength, ductility, and fracture

resistance. Hardness measurements (see Section 3.22), which reflect the

effect on strength and impact test results^ ' (to be presented in a separate report), were also greatly affected by the microstructural

variabi 1 ity.

20
Incl usion Measurements - Measurements of inclusions by both the

ASTM and the QTM methods were taken only on longitudinal planes. In Figure 9, the C plane is the longitudinal plane that contains the

principal rolling direction. Inclusions on this plane are shaped like

needles. The B plane is a transverse plane that contains the

cross-rolling direction. Inclusions on this plane appear shorter,

and they may appear as dots in plates that have little cross rolling.

The A plane is a short- transverse plane, parallel to the

plate surfaces. Inclusions on it have irregular shapes, but they

frequently contain one long dimension aligned in the principal

rolling direction.

Inclusion analyses by the ASTM Method were conducted on 14

samples taken from five plates taken from the four accidents. Results

of these ratings are summarized in Table 9, which shows that the principal

type of inclusion in all steels rated is Type A, sulfide. The sulfides were particularly prominent in the South Byron sample, rated 3 to 5

(in various specimens) and in the Belle sample, rated 3 to 4. Sulfides

were intermediate at 2 to 3 in both Crescent City-sample FRA-2 and

Cal lao-sample K-5, and they were only slightly less in Cal lao-sample K-l.

The table also indicates that the sample rated highest in sulfides,

South Byron, also rated highest in alumina and globular oxides (types B & D), and it was the only sample with any significant silicates, Type C.

4. SUMMARY OF FINDINGS

4.1 Check analyses of seven of the 10 plates analyzed failed to

meet the chemical compositional requirements for the ladle analysis

to which the steel had been produced, but all of the Producers'

ladle analyses (five were available) met the requirements.

4.2 The carbon level in check analyses was generally near the maximum

specified limit for ladle, and four check analyses exceeded this

ladle limit.

4.3 Three of the 10 check analyses for manganese exceeded the maximum

specified limit for ladle analysis.

4.4 Check analyses for sulfur and phosphorous indicated that one or both of these elements were near the maximum specified ladle

analysis for four of the 10 plate samples.

4.5 One of the 10 plates analyzed for chemical composition failed to

meet the requirement for deoxidation practice.

21
4.6 Specimens taken from two of the six plate samples tested had

strength levels outside of the requirements for strength level.

4.7 Although all six steels tested met the elongation requirements,

bend speciemens of one of these steels failed to meet the bend requirements.

4.8 The tensile test results of four TC128 steels indicated that the

ductility of these plates is anisotropic with longitudinal specimens

having 10 percent greater elongation than transverse specimens for

any tensile strength level from 85 to 105 Ksi. Bend test results

of two of these steels were consistent with and supportive of this finding.

4.9 ASTM ferrite grain size numbers of TC128 steels varied from 7 to 9,

and those of two A212 steels were 7 and 6, with the 6 representing a steel not produced to fine-grain practice. Only one of the TC128 steels

was known to have not been produced to fine-grain practice and it had an ASTM

ferrite grain size number of 7. The only other TCI 28 steel sample, on which

NBS made chemical anlysis, with this grain size was from a hot-formed

head-plate sample with a highly variable microstructure which apparently

resulted from excessive heating for hot forming.

4.10 Of six weldments examined for plate alignment, one weldment

failed the alignment requirement prescribed by AAR by an amount of

0.047 inches.

4.11 Three weldments tested had a joint efficiency of 1.0, and all

had acceptable ductility in bend and tensile tests. Two of these three were head/shell weldments and one was a shell/shell weldment. The

hardness results of the HAZ in each of these weldments indicated that

they were properly stress relieved.

4.12 Two additional samples contained weld HAZ regions along which

crack propagation had occurred. Hardness measurements of one of

these HAZ regions, located at a head plate attachment, indicated that

it had been improperly stress relieved.

4.13 Of the five tank cars involved in the four accidents from

which samples were taken, three of the cars had been heated (at

least in parts of the car) to temperatures above that of the

ambient air.

4.14 Plates believed to have been heated at the time of fracture

had fracture modes, generally of the shear mode and mixed

mode, indicating that the mode of failure was ductile in plates failed at

temperatures above that of the ambient air.

22
4.15 Plates believed to have been at the temperature of the ambient

air at the time of fracture generally had fractures that were predominantly nearly perpendicular to the plate surfaces, indicating

brittle failure of the steel.

4.16 The observed fracture mode on plates examined was consistent

with results of measurements of plate thinning near the fracture

and with results of impact test measurements.

4.17 A microstructure of unexpectedly high variablity was observed

at one location of the TC128-B steel head-plate sample K-l of the

Callao accident. This variability is believed to be generally not

desirable and it reflects variables (uncontrolled) in the hot-forming

process used for fabricating this head plate.

4.18 Inclusion content ratings indicate that for six steels rated,

two of the steels can be classified into each of three arbitrary ranks

of moderate, intermediate, and high.

5. GENERAL DISCUSSIONS

5.1 Effects of Inclusions on Mechanical Properties

In general, the mechanical properties of steels are unfavorably

affected by the presence of inclusions in steels. These effects can

be moderate to severe, and they become increasingly important as the

tensile strength is increased. The controlling factors are the

composition-\Shape, distribution, and volume percent of the inclusions in

the steel. ' These factors can be and are today controlled (at a price)

in normal steelmaking practice, and methods for improving the techniques

and for making them more economical are receiving attention both here and

abroad.

The inclusion contents of the six steel plate samples analyzed in

this report fell into three arbitrary ranks of steel quality with

two steels in each of the ranks: Rank 1 --moderate content: Rank 2--

intermediate content: Rank 3--high content. We note that this

distribution of inclusion contents is broad, but that none of the

specification requirements for the steels tested require special .

.

mill practice to control inclusion levels in these steels. Thus,

it is interesting to note that two of the six steels tested have

moderate inclusion contents, and these two were apparently produced

under normal mill practices.

23
The principal type of inclusions in all six of the steels

analyzed at NBS is manganese sulfide, and the content of sulfides

in steel is proportional to the sulfur content. Various treatments

have proven effective in lowering the sulfur of steels. Treatments

such as those involving additives to the hot blast-furnace iron

permit the sulfur content of the finished steel to be in the range

of 0.005 to 0.010 percent by weight. These levels are to be compared

with the levels of the results of NBS laboratory check analyses for

sulfur given in this report for 10 steels and one weldment. These

contents vary from 0.012 to 0.04 percent by weight, and they meet the

specification requirement of 0.05 percent maximum. Steels with

lower sulfur contents are not only tougher but they have more isotropic

mechanical properties.

Other techniques, used to minimize the undersirable effects of

inclusions, control inclusion composition and shape. This is done

either by increased use of cross rolling of the plates or by using additi

in the refining of molten steel. Additives of rare earth metals or of

titanium are commonly used to form a type of inclusion with greatly

decreased tendencies for elongation during hot rolling. The result

of this improved composition and shape of inclusions is improved

product performance with less anisotropy and with improved transverse

ductility and toughness.

It is recognized that sulfur is a principal impurity of blast

furnace iron, that sulfur is difficult to remove in the commonly used

refining facilities, and that it is costly either to decrease the

sulfur level or to control the effects of sulfur in steels. We point

up the fact that the technology exists for lowering the sulfur content

to improve the quality of steels; this technology has undergone many

changes even in recent years, and it is one of the many alternatives

for improving the isotropy and fracture properties of steels.

5.2 Anisotropy of Mechanical Properties

The ductility of rolled steel plates tends to be greater in tests

of longitudinal specimens than in tests of transverse specimens. This was shown in Figure 1 for tensile tests of steels of various strength

levels. In general, longitudinal tensile ductility, as measured by

percent elongation, was about 10-percent greater than the transverse

ductility, Similarly, in bend tests the results given earlier showed

that the onset of cracking of transverse specimens occurred at smaller

angles of bend than that of longitudinal specimens (Appendix C).

24
The effect of this anisotropy on the tensile ductility as measured in tensile and bend tests is not so large as to give rise to

great concern to designers of tank cars. However, its effect on the

fracture process in general and on crack propagation behaviors in

particular can be much greater than the effect on ductility. Therefore,

anisotropy can be very significant and very important in a metallurgical

analysis of the materials used for tank cars subjected to abusive

service conditions, and our future efforts will be directed toward

providing a more complete understanding of its significance for the

plate materials used in the construction of tank cars.

(2)

In a metallurgical analysis^ 'of a steel shell plate taken from

tank car PPGX9990 involved in an accident near South Byron, New York,

it was concluded that the fracture of this car, which exploded after

being subject to fire, "...circumscribed the tank car because the shell

plate was anisotropic- (in mechanical properties) with lower resistance

to crack propagation in the circumferential direction of the tank car,

which was the (final) rolling direction of the plate." Because this

type of fracture separates a tank car into two sections, it promotes

"rocketing" of either or both sections. It is therefore considered

undesirable and more hazardous than alternative types of fracture, such

as punctures that leak but do not propagate or fractures that propagate

along the length of the tank car. Further, a tank car with improved

safety would result either from the use of materials that are more isotropic or from designs that preclude circumferential fracture.

5.3 Observations of Unusual and Undesirable Features in Samples From

Three Head Plates

Of the steel plate samples examined at NBS, five samples

contained small parts from three head plates. These are the Belle

sample, FRA-2 and FKA-3 from Crescent City, and K-l and K-2 from

Callao, each taken from a different tank car. Four of these five

head-plate samples (all except FRA-2 which apparently was heated prior

to fracture) had metallurgical anomalies considered to be deleterious

from the viewpoint of their relative resistance to fracture.

The Belle sample was believed to contain an HAZ crack that

existed before the final fracture. This was a part-through crack that

is believed to have contributed to the failure of the tank car. Further, this crack propagated for some distance along the HAZ of a weldment of a stiffener plate, and then it terminated in the unaffected

base metal of the head plate. This behavior indicates that the weld

HAZ had significantly lower resistance to crack propagation compared to

that of the unaffected base metal

.

25
Sample FRA-3 (from Crescent City) contained a hard zone with a secondary crack in a region believed to be an improperly stress-relieved

HAZ of a head-plate attachment. The hard zone is believed to have

contributed to the failure of this tank car, but it is possible that

geometrical effects of the weld were contributing to the failure.

From the Callao A-head plate, sample K-l had an undesirable

microstructure of unexpectedly high variability and sample K-2 had

a relatively coarse microstructure. This variability is believed to

reflect improperly controlled variables in the hot- forming process used

to fabricate this head plate. Hardness tests indicated that mechanical

properties are significantly affected by this mi crostructural variability,

and impact tests indicated that the variability has a marked effect on

the crack propagation behaviors of this steel.

These observations of various anomalies, two of which involved

welding practices and properties of weldments and one of which involved

hot-forming practices, indicate to us that for the tank cars involved

in the three accidents (four tank cars) from which these samples were

taken, the ability to withstand abusive service had been deteriorated.

These anomalous observations are particularly disconcerting when one recognizes that, in service, the two head plates of a tank car are generally more likely to be subject to abusive loading conditions than

are any of the many shell plates of a tank car.

5.4 South Byron Shell Plate Steel

The tank car involved in the South Byron, New York, accident

explosions. A circumferential type^of fracture separated the tank car into two sections and led to the propulsion of one of them. The

results of the metallurgical analysis of a sample of a fractured shell

plate from this car is both interesting and instructive.

The findings for this AAR TC128-B plate steel sample taken from

this summary report are as follows:

(a) carbon and manganese levels slightly exceed the maximum

specified limit.

(b) sulfur content is high and near the maximum specified limit.

(c) vanadium and aluminum levels indicate that the steel was produced in accordance with fine-grain practice by deoxidation with

a combination of silicon and both of these grain-refining deoxidizers.

failed in a manner resulting in tank car

26
(d) the plate sample contained the highest total inclusion

content of all plates tested; rated highest in sulfides, alumina

and globular oxides; and was the only plate with any significant

amount of sil icates. v

(e) measured tensile strength slightly exceeded the maximum

specified limit and was greater than that of any of the other plates

tested.

(f) measured yield strength was well above the specified minimum

value and greater than that of any of the other plates tested.

(g) tensile ductility, as measured by percent elongation, was slightly above the minimum specified value and lowest of all plates tested.

(h) all specimens tested failed the required bend test:

longitudinal specimens, which are required by the manufacturer of the

plate, failed by crazing of the external surface, and transverse

specimens, which are not required, fractured completely and at relatively

low angles of bend.

Based on the anlysis of these findings, it could reasonably be

concluded that this steel plate satisfied the intent of the material

requirements (although marginally) of the appropriate specification,

AAR Ml 28. However, specimens taken from this plate did fail the bend

test, which is a performance requirement, but met the other performance

requirements: yield strength, tensile strength, and percent elongation,

although the latter two are met only marginally. The probable

explanations for the test behavior of this plate sample are both

interesting and instructive.

The high tensile strength (maximum allowed) and the high yield

strength are probably a result of the high levels of carbon

and manganese. In the sample they are both at the maximum allowed.

The marginally low tensile ductility is consistent with the high

observed value of tensile strength.

The high total inclusion content, principally manganese sulfide

but including alumina, globular oxides and silicates, is consistent

with the high sulfur level and use of aluminum as a deoxidizer and

grain refiner. The use of aluminum in the steel deoxidation process

is known to result in the inclusions being morfix stri nger-1 i ke, rather

than globular as when silicon is used alone. '

27
The crazing of the surfaces of the longitudinal bend test

specimens is not unexpected because the surface experiences maximum

tensile stress and thus maximum strain, and because this plate had

higher inclusion content and lower measured values of elongation

and reduction of area than that of any of the other steels tested.

The transverse bend test specimens would be expected to be more sensitive to the inclusions present (total content, shape, and

distribution), and the complete fracture of these specimens is

consistent with the high inclusion content.

Although this plate marginally satisfied both the material and

performance requirements (bend test excepted) of the AAR Ml 28

specification, the cooperative effects of producing a steel at the

limits of compositional requirements for carbon, manganese, and sulfur,

yielded a plate with marginal properties. The mechanical properties

and other observations on this steel plate sample point up the strong

need for improvements in the control over the quality of steel used as plate material in tank cars.

5.5 Abusive Service Requirements

Railway tank car service failures occur principally after

exposure of tank cars to elevated temperatures and to severe impact

loads at ambient (and perhaps at elevated) temperatures. Each of.these

abusive service conditions can lead to hazardous ruptures. Thus, the

safety of tank cars under these abusive service conditions becomes an important question for consideration.

The problem of developing a tank car with superior safety is

particularly complex. Understanding must be developed on the

mechanisms of failures, the frequency of failure under various types of

abusive conditions, the properties of the materials used in

construction of existing tank cars, and the alternatives of materials

available for tank car service. In addition, many other factors must

be considered, such as cost of materials, the feasibility of

implementing various proposed design changes, and the cost of capital

equipment needed for such changes.

From the materials viewpoint, the tank-car construction industry

uses such large tonnages of steels that the requirement for steels with

improved properties can be a major stimulus to improve steel production

practice. It can also be a stimulus for the development of superior

and economical steels for this application.

28
NBS is undertaking to explore the currently available

materials that could be used as plate materials for tank cars. Steels with properties that are likely to lead to increased resistance

to hazardous failures will be selected as candidate steels.

Prerequisite to the development of a satisfactory compilation

of candidate steels is a satisfactory understanding of the materials

requirements. Some of this information will be made available through

the current studies at NBS, but other complementary information must

be collected. This includes:

1. For elevated-temperature abusive service conditions, expected

temperatures and time at temperature.

2. Minimum and median temperatures of ambient temperature service

fail ures

.

3. Frequency and location (in the tank cars) of ambient-temperature

service failures. A concise summary of this information along with other

pertinent information will be very useful and necessary for the reasons given above.

CONCLUSIONS

6.1 Materials with improved resistance to both ambient- and

elevated-temperature failure should be sought on a continuing basis

for use as plate materials in tank cars, so that the safety and

economy of these cars will be abreast of the technology of the times.

6.2 Among the alternatives for improving service performance of the

plate materials used for tank cars, consideration should be given to

the use of steels of uniformly good quality, as for example, by

decreasing the sulfur level below the 0.05 percent by weight now considered acceptable.

6.3 Steps should be taken to improve the fracture resistance of

head plate steels and all weldments of these steels. These should

include but not necessarily be limited to a thorough review of head

plate forming, welding, and stress-relief practices.

29
6.4 The decreased ductility and the marked decrease in fracture

resistance in the final rolling direction of plates used for tank cars

has been observed to promote an undesirable circumferencial fracture. A

tank car with improved safety would result either from the use of

materials (especially for shell plates) that are more isotropic or from

designs that preclude circumferencial fracture.

6.5 In specifications for the chemical compositional requirements,

tolerances should be clearly prescribed for chemical check analyses of

each of the specified elements.

AKNOWLEUGEMENT

The authors would like to thank Mr. D. E. Harne for his assistance

in making hardness measurements and in preparing the figures and tables

used in this report.

30
7 . REFERENCES

1. G. E. Hicho and C. H. Brady, "HAZARDOUS MATERIALS TANK CARS -

EVALUATION OF TANK CAR SHELL CONSTRUCTION MATERIAL", (Report

No. 1), NBS Report 312.01/14, September 28, 1970.

2. C. G. Interrante and G. E. Hicho, "METALLURGICAL ANALYSIS

OF A STEEL SHELL PLATE TAKEN FROM A TANK CAR ACCIDENT NEAR

SOUTH BYRON, NEW YORK", (Report No. 2), NBS Report 312.01/35,

October 22, 1971.

3. C. G. Interrante, G. E. Hicho, and D. E. Harne, "A METALLURGICAL

ANALYSIS OF FIVE STEEL PLATES TAKEN FROM A TANK CAR ACCIDENT

NEAR CRESCENT CITY, ILLINOIS", (Report No. 3), N3S Report

312.01/39, March 10, 1972.

4. C. G. Interrante, G. E. Hicho, and D. E. Harne, "A METALLURGICAL

ANALYSIS OF ELEVEN STEEL PLATES TAKEN FROM A TANK CAR ACCIDENT

NEAR CALLAO, MISSOURI", (Report No. 4), NBS Report 312.01/51,

September 19, 1972.

5. G. E. Dieter, Mechanical Metallurgy , McGraw-Hill Book Co.,

New York City, 1961, pp. 557-562.

6. Army-Navy Approximate Hardness Tensile Strength Relationship

of Carbon and Low Alloy Steels ( AN-QQ-H-2 01 )

7. Handbook 268,. Modern Steels and Their properties , The

Bethlehem Steel Company, Bethlehem, Pennsylvania, 1949.

8. R. A. Grange, "Effect of Microstructural Banding in Steels",

Metallurgical Transactions , 1971, pp. 417-426.

9. R. M. Brick and A. Phillips, Structure and Properties of Alloys , McGraw-Hill Book Co. , New York City, 1949, p. 252.

10. Metals Handbook , The American Society for Metals, Cleveland,

Ohio, 1948, p. 450.

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A comparison of elongation data obtained from different sizes of

specimens of the same material can be made provided the ratio of

the gage length to cross-sectional dimensions is held constant.

Since the ratio of the square root of the cross-sectional area to the gage length is the same for the specimen with a 0.500-inchdiameter with a 2-inch-gage and for the specimen with a 0.250-inch

diameter with a 1-inch-gage length, the elongation data from the

1-inch-gage length specimen can be directly compared to the

specification requirement based on a 2-inch-gage length.

Although the specifications ASTM A212-65, AAR TC128-65, and

AAR TC128-69 do not specify test specimen orientation, ASTM A370-7

does specify that wrought steel products are usually tested in the

longitudinal direction but that where size permits and service

justifies it, transverse testing is done.

Not specified, either fine- or coarse-grain practice allowed.

Not specified.

The letter/number code refers to the specimen numbers as reported

in the particular accident report. Long, and Trans, refer to the

longitudinal and transverse specimen axis orientation with respect

to the principal rolling direction.

The number of letter/number codes given here refer to the specimen

numbers reported in the particular accident report. It is usually

difficult, in the case of head plates, to determine exactly the

principal plate rolling direction because of the probability of

extensive cross-rolling of the plate and the method of fabrication

of head plates. The usual procedure followed in the specific

accident reports was to relate the specimen orientation to either

a shell plate weld or to a crack propagation direction. In this

summary report, however, the orientation direction has been

assigned to the test data based on whether the specimens were aligned closer to what is believed to be either the principal

rolling direction (longitudinal) or normal (transverse) to the

principal rolling direction. The determination of the principal

rolling direction was based on percent elongation and percent

reduction in area data of shell plate specimens. Shell plate test

data, where there is little ambiguity in the determination of the

principal rolling direction, show that the values of percent

elongation and percent reduction in area of longitudinal test

specimens always exceeded the values for transverse test specimens

The longitudinal specimens taken from the weldment are all-weldmetal specimens with longitudinal axes that lie in the (circumferential) welding direction. The transverse specimens were machined perpendicular to the circumferential weld.

Not determined.

Specification AAR TC128-65 requires minimum elongation values for

8-inch-gage length specimens only. As it was not possible to use

the 8-inch-gage length specimens, some basis for comparing the

test results with 0.250-inch diameter, 1-inch-gage length round

specimens with the specification must be used. The basis selected

was to apply the specification AAR TC128-70 which requires

identical tensile and yield strength values as AAR TC128-65.

AAR TC128-70 further requires minimum elongation values for both

2- and 8-inch gage length, thus a direct comparison was made

between the 2-inch-gage length requirement and test data on 0.250-

inch diameter, 1-inch-gage length specimens. However, since

AAR TC128-70 calls for a minimum percent elongation of 16% in

8-inch-gage length and 19% in a 2-inch-gage length, while AAR

TC128-65 calls for a minimum percent elongation of 18% in an 8-

inch-gage length, the test results should clearly exceed the 19%

minimum to satisfy the intent of the specification.

Not specified, fine-grain practice required.

These elongation values reported in the particular accident

reports were in error. The corrected values are reported here.

The letter/number code refers to the specimen numbers reported in

the original accident report. Inclusion length measurements were

made to determine the principal rolling direction and the specimen

orientation was assigned based on these data.

Table 4. Abbreviated Summary of Bend Test Results

Steel

1 A212-B

TC128-B

TCI 2

8 -B

TC128-B

A212/A212

i TC128/TC128

TC128-B

Sample

Location

Shell

Shell

Shell

Head

Weldment

Weldment

Shell

Accident

Crescent City

South Byron

Callao

Callao

Crescent City

Callao

South Bryon

passed Failed

2

1(a)

2

2

4(b)

1(a)

2(c)

Specimen

Orientation

2 longitudinal

and 2 transverse

2 longitudinal

and 4 transverse

2 longitudinal

and 2 transverse

1 long. & 1 trans

1 longitudinal

and 1 transverse

side bend

side bend

4 longitudinal

and 2 transverse

(a) These two specimens were tested in a non-standard test with

the outer curve of the bend being the inner part (near midthickness) of the plate; the transverse specimen failed.

(b) Non-standard d/t ratio of 4 . 0 (2 longitudinal and 2

transverse specimens)

.

(c) Non-standard d/t ratio of 1.7 (longitudinal specimens).

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Table 6. Hardness Results

Steel Sample Head or Averages

Specification Accident Identification Shell Plate Rg

ASTM A212 -B Crescent City FRA-1 Shell 80 . 0

i ASTM A212 -B Crescent City FRA-2 Shell 78 . 8

ASTM A212 -B Crescent City FRA-2 r\A——Hplie ar\ dLl 79 . 8

ASTM A212 -B Crescent City FRA-5 Shell 82 .2

AAR TCI 2 8 -B Crescent City FRA-3 B-Head 93 . 5

AAR TCI 2 8 -B Crescent City FRA-4 Shell 94 . 3

AAR TC128 -B South Byron Sample A -A plane Shell 92 .1

AAR' TC128 -B South Byron Sample A -B plane Shell 92 . 5

AAR TC128 -B South Byron Sample A -c plane Shell 92 .4

AAR TC128 -B South Byron Sample B -B plane Shell 93 . 2

AAR TCI 2 8 -B South Byron Sample c -c plane Shell 97 .8

AAR TC128 -B South Byron Sample C -c plane Shell 196 .4*

AAR TC128 -B Callao K-l A-Head 90 . 6

AAR TC128 -B Callao K-2 A-Head 92 .3

AAR TC128 -B Callao K-5 Shell-1 89 .5

AAR TC128 -B Callao K-8 Shell-1 93 . 5

AAR TC128 -B Callao K-8 Shell-2 89 .3

AAR TC128 -A Belle ** Head 92 . 0

Weld Callao K-2 92 .8

Weld Callao K-8 92 . 0

HAZ Callao K-8 RC

24***

***

HAZ Crescent City FRA-3 Rc

28

* Brinell value

** Only one plate sample submitted.

*** Knoop hardness measurements were taken and converted to

Rockwell C values.

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Table 8. Observed Ferrite Grain Size Values

Ferrite

ASTM G.S. No.

Grade of

Steel

Belle*

South Byron*

Crescent City

Shell FRA-1

Shell FRA-2

Head FRA-2*

Shell FRA-3

Shell FRA-4

Shell FRA-5

Callao

Shell course 1

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Shell course 2

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Shell course 4

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A Head

K-l*

K-2

to 9

7

7

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9

8

7 to 8

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A212-B

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A212-B**

TC128-B

TC128-B

A212-B

TCI 2 8-

B

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TC128-B

TC128-B

TC128-B

TC128-B

Used in studies of mechanical properties.

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Ratings by Various Criteria.

Sulfide

Rating (thin)

Steel Method A,

Identification ASTM E-45

QTM Results at

Magnification X338

TC128-B, Shell,

South Byron

TC128-B, Shell,

Callao

3-5

2.7

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Overall

Area

Percent*

.40

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Area >0.5*

(Average)

29

15

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of QTM

Worse

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1.9

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Rank

TC12 8--B, Head,

Callao

2 .3-2.7 .35 21 1.0

TC128-A, Head,

Belle

3-4 ** ** * *

A212-B, Shell

Crescent City

A212-B, Head,

Crescent City

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A HEAD • SHELL

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60 70 80 90 100 110

Ultimate Tensile Strength - ksi

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of AAR TC128 Steels of Various Strength Levels.

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in the B plane.

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surface at A, and B shows a crack progressing

parallel to the plate surface. The region at

A has high hardness and is believed to be an

HAZ of a weld attachment. Etched: 1% nital

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Figure 8. Microstructure of the Belle Sample.

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B

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Appendix A

Specifications

AAR M128-65, -6 9 and -7 0; ASTM A212-65

JANUARY t, 1969 AAR APPENDIX M

Ml 23.00 Spceificotion for high strength carbon manga*

nese steel plates for tank cars - AAR TCI 28- 69.

Ml 28.01 Scope

(a) This specification covers two grades of high

strength carbon-manganese steel plate of flange quality. The maximum thickness shall be 1 inch. Moderately high manganese content, together with small amounts of other elements provide for high strength with limited carbon

content. The steel shall be made to fine gmin practice. Welding technique is of fundamental importance, and it

is presupposed that welding procedures will be ir. ac- cordance with good practice.

(b) The material shall be furnlnhed In the as rolled condition. When specified for low tenperature service the material nhal 1 be furnished

normalized to meet requirements of AST>I Specification A300-6S, Class 1, except that impact specimens

shall be Type A Charpy V -Notch as shovn in ASTM

Specification A370-67 and meet impact requirements

at the temperature specified in the tank car specification. Ml 28.02 General Conditions for Delivery

(a) Material furnished under this specification shall conform to the applicable requirements of ASTM Specification A20-67 titled, "General Requirements for De- livery of Steel Plates for Pressure Vessels."

(b) See M128.01(b) Ml 28.03 Process

(a) The steel shall be made by one or more of the fol- owing processes:

(1) Open-hearth,

(2) Electric furnace, or

(3) Basic oxygen. Ml 28.04 Chemical composition

(a) The steel shall conform to the requirements as to themical composition prescribed in Table M128.04(a).

TABLE Ml 28.04(a) CHEMICAL REQUIREMENTS

Ladle Analyis. Percent Dement

Grade A Grade B

Carbon Max. 0.25 0.25 Manganese, Max.

For plates *f* and

under in thickness 1.35 1.35 For plates over Jj" to 1* incl. in thickness 1.50 1.50 Phosphorus

Sulfur Max. 0.040 0.040 Max. 0.050 0.050

Silicon Max.

For plates 54" and

under in thickness 0.30 020

For plates over J£* to

1* incl. in thickness 0.50 0.50 Vanadium Min. 0.02 Copoer •/ Max. 0.35 Nickel »/ Max. 025

Chromium •/ Max. 0.25 Molybdenum »/ Max. 0.08

»/ These elements will be reported when requested by the

purchaser.

Ml 28.05 Tensile properties

(a) The material as represented by the test specimens

shall conform to the requirements as to tensile properties prescribed in Table M128.05(a).

TABLE Ml 78.05(a) TENSILE REQUIREMENTS

Property

Tensile strength, psi Yield point, psi Min.

Elongation in 8 inches percent \ Min.

Elongation in 2 inches percent Min.

Grade A and Grade B

81,000 to 101,000 50,000

16.0 V

19.0 V For material under Kg inch thick a reduction from the

specified percent of elongation of 1.25 percent shall be made for each decrease of i£ inch of thickness below

*•£ inch. For material over inch thick a reduction from

the specified percent elongation of 0.5 percent shall be made for each increase of V% inch of the thickness above

54 inch; this deduction shall not exceed 3 percent. Ml 23.06 Bending properties

(a) The bend test specimens shall stand being bent cold through 180° without cracking on the outside of the bent

portion through an inside diameter which shall have the

relation to the thickness of the specimen prescribed in Table M128.06(a). When the test is made on a specimen

reduced in thickness, the rolled surface shall be on the outer curve of the bend.

TABLE Ml 28.06(a) BEND DIAMETERS

Thickness of Material, Ratio of Bend Diameter

inches to Thickness of Specimen

1 and under 2

Ml 28.07 Test specimens

(a) Test specimens shall be prepared from the material

in the as-rolled condition. Ml 28.08 Number of tests (a) One tension test and one bend test shall be made

from each plate as-rolled. Note: The term "plate as rolled" used here refers to the unit plate rolled from a slab or directly from an ingot

in its relation to the location and number of specimens, not to its condition. Ml 28.09 Inspection (a) The inspector representing the purchaser shall have

free entry, at all times while the work on the contract of the purchaser is being performed, to all parts of the manufacturer's works which concern the manufacture of the

material ordered. The manufacturer shall afford the in- spector, free of charge, all reasonable facilities and neces- sary assistance to satisfy him that the material is being

furnished in accordance with these specifications. Tests and inspection shall be made at the place of manufacture

prior to shipment, unless otherwise specified. (b) The purchaser may make tests to cover the accept- ance or rejection of the material in his own laboratory or

elsewhere. Such tests shall be made at the expense of the purchaser. Ml 28.10 Rejection (a) Material represented by samples which fail to con- form to the requirements of these specifications will be

rejected.

< (b) Material which shows injurious defects subsequent

to its original inspection and acceptance at the manufacturer's works, or elsewhere, will be rejected, and the manufacturer shall be notified.

M12S.11 Rehearing

(a) Samples tested in accordance with these specifica- tions which represent, rejected material, 3hall be held for a period of fourteen days from date of the test report. In case of dissatisfaction with the results of the tests, the manufacturer may make claim for a rehearing within that

time.

Appendix A

Specifications

AAR M128-65, -69 and -70; ASTM A212-65

M128.00 SPECIFICATION FOR MICH STRENGTH

CARBON MANGANESE STEEL PLATES FOR

TANK CARS - AAR TC128-70.

M128.01 SCOPE

() This specification covers two grades of high

strength carbon-manganese steel plate of flange quality. The maximum thickness shall be 1 inch. Moderately high manganese content, together with small amounts of other elements provide for high strength with limited carbon content. The steel shall be made

to fine grain practice. Welding technique is of funda- mental Importance, and it is presupposed that welding procedure will be in accordance with good practice. (b) The material shall be furnished in the as- rolled condition. When specified for low temperature

service the material shall be furnished norm alized to meet requirements oj_ASTMJ>pecjficatioj)_A3JlflJi8.. Class 1, except that impact specimens shall be Type A

Charpv V-Notch assliown. in_AS;rj»l_Speciji^aiian_ A37Q-68 a nd meet i mpact requirements a t the temperature specified in the tank car specification.

M128.02 GENERAL CONDITIONS FOR

DELIVERY

(a) Material furnished under this specification

shall conform to the applicable requirements of ASTM Specification A20-69a titled, "General Re- quirements for Delivery of Steel Plates for Pressure

Vessels."

(b) SeeM128.01(b).

M128.03 PROCESS

(s) The steel shall be made by one or more of

tbe following processes:

(1) Open-hearth,

(2) Electric furnace, or

(3) Bask oxygen.

M128.04 CHEMICAL COMPOSITION

(a) The steel shall conform to the requirements

as to chemical composition prescribed in Tsble

M128.04(a). TABLE M128.04(a) CHEMICAL REQUIREMENTS

Element

Ladle Analysis, Percent Grade A Grade 8

Carbon Max. 0.25 0.25 Manganese, Max.

For plates 3/4" and

under In thickness 1.35 1.35 For plates over 3/4" 1" incl. in thickness 1.50 1.50 Phosphorus Max. 0.040 0.040

Sulfur Max. 0.050 0.050

Silicon Max. For pistes 3/4" and under in thickness 0.30 0.30 For plates over 3/4" to 1" Incl. In thickness 0.50 0.50 Vanadium a/ 0.02 Min. 0.08 Max. Copper a/ Max 0.35

Nickel a/ Max. 0.25 Chromium a/ Max. 0.25 Molybdenum a/ Max. 0.08

elements wi by the purchaser. be reported when requested

M128.05 TENSILE PROPERTIES

(a) The material as represented by the test speci- mens shall conform to the requirements as to tensile properties prescribed in Table M 128.05(a). TABLE M128.05(a) TENSILE REQUIREMENTS

Property Grade A and Grade B

Tensile strength, psi 81,000 to 101.000

Yield point, psi Min. 50,000

Elongation in 8 inches percent Min. 16.0 a/ Elongation In 2 inches percent Min. 19.0

a/ For material under 5/16 inch thick a reduction from the specified percent of elongation of 1.25 percent shall be made for each decrease of 1/32

Inch of thickness below 5/16 Inch. For material over 3/4 Inch thick a reduction from the speci- fied percent elongation of 0.5 percent shall be made for each increase of 1/8 inch of the thick- ness above 3/4 inch; this deduction shall not exceed 3 percent.

M128.06 BENDING PROPERTIES

(a) The bend test specimens shall stand being bent cold through 180° without cracking on the outside of the bent portion through an inside diameter which shall have the relation to the thickness of the specimen prescribed in Table Ml 28.06(a). When the

test Is made on a specimen reduced in thickness, the

rolled surface shall be on the outer curve of the bend. TABLE M128.06(a) BEND DIAMETERS

Thickness of Material, Inches Ratio of Bend Diameter

to Thickness of Specimen

1 and under 2

M128.07 TEST SPECIMENS

(a) Test specimens shall be prepared from the

material In the as-rolled condition.

M128.08 NUMBER OF TESTS

(a) One tension test and one bend test shall be made from each plate as rolled. Note: The term "plate as rolled" used here refers to the unit plate rolled from a slab or directly from

an Ingot In Its relation to the location and number of

specimens, not to its condition.

M128.09 INSPECTION

(a) The inspector representing the purchaser

shall have free entry, at ail times while the work on

the contract of the purchaser is being performed, to

all parts of the manufacturer's works which concern

the manufacture of the material ordered. The manufacturer shall afford the inspector, free of charge, all reasonable facilities and necessary assistance to satisfy him that the material is being furnished in accordance with these specifications. Tests and inspection shall be made at the place of manufacture prior to ship- ment, unless otherwise specified. (b) The purchaser may make tests to cover the acceptance or rejection of the material in his own

laboratory or elsewhere. Such tests shall be made at tbe expense of the purchaser.

11128.10 REJECTION

(a) Material represented by samples which fail to conform to the requitements of these specifications

will be rejected.

(b) Material which shows injurious defects subse- quent to its original inspection and acceptance at the manufacturer's works, or elsewhere, will be rejected, and the manufacturer shall be notified.

M128.ll REHEARING

(a) Samples tested in accordance with these

specifications which represent rejected material, shall be held for a period of fourteen days from date of the

test report. In case of dissatisfaction with the results of the tests, the manufacturer may make claim for a

rehearing within that time.

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Appendix D

Guided Bend Test Jig

Tapped Hole to suit

Testing Machine

Hardened Rollers, f$ dia

may be Substituted for

*

i/ig Shoulders — As required

THICKNESS OF A B C D SPECIMENS (in.) (in.) (in.) (in.) (in.)

3/8 a/ 1 1/2 2 3/8 1 3/16 a/

t a/ ht 2t 6t * 1/8 3t + 1/16 a/

1/8 b/ 2 1/16 1 1/32 2 3/8 1 3/16 b/

3/8 c/ 2 1/2 1 1/k 3 3/8 1 11/16 c/

t y 6 2/3t 3 l/3t 8 2/3t +1/8 l/3t + 1/16 d/

NOTES:

a/ Use for all materials not otherwise indicated,

b/ Use only for P-23 aluminum alloys.

cj Use only for P-25 aluminum alloys.

y Use only for P-25 aluminum alloys where thickness, t, is

less than 3/8 inch.

NBS-1 14A (REV. 7-73)

U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBS IR 75-655

2. Gov't Accession

No.

3. Recipient's Accession No.

4. TITLE AND SUBTITLE

Analysis of findings from Four Tank-Car Accident

Reports

Report No . 5

5. Publication Date Ja.nua.i7v . 197 5

6. Performing Organization Code

7. AUTHOR(S)

C. G. Interrante, J. G. Early and G. E. Hicho

8. Performing Organ. Report No. NBS IR 75-655

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No. 3120413

11. Contract/Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

Department of Transportation

Federal Railroad Administration

Washincrton, D. C. 2 05 91

13. Type of Report & Period Covered

Summary Report

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less (actual summary ol most significant information. If document includes a significant

bibliography or literature survey, mention it here.) A comprehensive overview of the findings and metallurgical analyses

of tests conducted at the National Bureau of Standards on samples of

tank-car materials submitted by the Federal Railroad Administration is

presented. The submitted samples were taken from tank cars which had

been involved in accidents during the period January 197 0 to January 197'.

The testing conducted during the metallurgical analyses included full

chemical analyses, ambient temperature tensile tests on longitudinal and

transverse specimens , quantitative metallography to determine f errite

grain size, pearlite colony size, and inclusion content, size, and shape

hardness tests, bend tests on longitudinal and transverse specimens, and

a very comprehensive program of impact testing, which is covered in a separate report on Impact Properties

.

The data, which are presented in the Findings Section of this report

and which are summarized and discussed in the Summary and in the General

Discussions , represent a valuable body of information from which the

Conclusions were drawn. These summaries and conclusions on the properties

of these steels, and the metallurgical factors affecting these properties

when taken in conjunction with the service requirements and the observed

behaviors of the materials during the actual service failures, can be

useful in making recommendations as to .approaches to improved materials

name; separated by semicolons

)

Anisotropy; carbon-manganese steels; hardness; inclusions; mechanical

properties; pressure-vessel steels; quantitative metallography; tankcar steels; tensile properties;

18. AVAILABILITY 1

' Unlimited

For Official Distribution. Do Not Release to NTIS

I Order From Sup. of Doc, U.S. Government Printing Office Washington, D.C. 20402, SD Cat. No. C13

| ! Order From National Technical Information Service (NTIS)

Springfield, Virginia 22151

19. SECURITY CLASS

(THIS REPORT)

UNCLASSIFIED

20. SECURITY CLASS

(THIS PAGE)

UNCLASSIFIED

21. NO. OF PAGES

69

22. Price

USCOMM-DC 29042-P74