NBSIR 87-3598

Weldability of A Leaded Carbon

Steel

J. G. Early and J. H. Smith

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

Institute for Materials Science and Engineering

Metallurgy Division

Gaithersburg, MD 20899

June 1987

Final Report

Prepared for United States Coast Guard

Department of Transportation

Washington, DC 20590

NBSIR 87-3598

WELDABILITY OF A LEADED CARBON

STEEL

J. G. Early and J. H. Smith

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

Institute for Materials Science and Engineering

Metallurgy Division

Gaithersburg, MD 20899

June 1987

Final Report

Prepared for United States Coast Guard

Department of Transportation

Washington, DC 20590

INTRODUCTION

To determine if acceptable quality welds could be made using leaded carbon

steel, a limited program was conducted to evaluate the properties of welds

made on AISI 12L14 steel. The welds were evaluated by conducting bend tests,

hardness tests, and metallographic examinations. The welding procedures were

varied by using three different butt weld geometries which are expected to

simulate various weld metal cooling rates that would be expected when welding

components of different sizes.

MATERIALS AND TESTS

Cold finished bar stock of AISI 12L14 steel was used as the base metal and

was separately evaluated by hardness tests, tensile tests, bend tests, and

metallographic examination to provide baseline data for comparison with the

welded samples. The heat chemical analysis of the 12L14 bar stock was

reported by the producer as: (weight percent) carbon 0.08; manganese 1.01;

phosphorous 0.06; and sulhur 0.31. The lead content was reported to be in

the range 0.15 to 0.35 weight percent. The AISI-SAE specification

requirement for 12L14 steel is: (weight percent) carbon 0.15 max.; manganese

0.85 to 1.15; phosphorous 0.04 to 0.09; sulfur 0.26 to 0.35; and lead 0.15 to

0.35.

Welded specimens were reported by Parker-Hannif in Inc. to have been prepared

by the metal-inert gas (MIG) welding procedure with As-28/ER705-6 AWS 5.18

filler metal. The three different weld geometries that were made (1/4-inch

bevel joint, 3/8-inch bevel joint, and nominal 1/2-inch "J" joint) are shown

in Figure 1. The resulting weldments were not full penetration.

All bar stock material below the root of each weld was removed by a band saw. In all cases, the weld reinforcement was ground flush with the bar stock

surface to remove any weld undercut. The as -welded samples were finished by

surface grinding to obtain the appropriate test specimen dimensions. For all

face bend specimens the final test specimen thickness was obtained by

grinding the root weld surface, while for all root bend specimens the face

weld surface was ground. The test specimen dimensions are described in

sections QW-466.2 and QW-466.3 of Section IX of the ASME Boiler and Pressure

Vessel Code, 1983 Edition. The face bend, root bend, and side bend specimens

with the "J" joint were finished to the standard 3/8-inch thickness. The

face bend, root bend, and side bend specimens with the 3/8-inch bevel joint

were finished to the standard 3/ 16-inch thickness. The face bend and root

bend specimens with the 1/4-inch bevel joint were finished to a non-standard

thickness of 0.1 -inch because the weld penetration was insufficient for

preparing a 3/16-inch thickness specimen. By optical inspection, all welds

appeared to be sound and no weld defects were visible in any of the finished

bend test specimens.

1
Bend tests were conducted using two fixture geometries: a guided-bend roller

jig as described in section QW-466.2 and a guided-bend wrap-around jig as described in section QW 466.3 of section IX of the ASME Boiler and Pressure

Vessel Code, 1983 Edition. The spacing between the roller jig shoulders and

the radius of the forming mandrel are controlled by the thickness of the test

specimen and are defined in section 466.1 of Section IX. The exact

dimensions of the spacing used in each of the specimen sizes tested is shown

in Tables I, II, and III. Additional face bend and root bend tests were

carried out on specimens made from the 3/8-inch bevel joint and 1/2-inch "J"

weld joint using a wrapped bend test fixture instead of the guided bend test

fixture to control better the strain produced in the bend tests.

All hardness tests on base metal and on the weldments were performed on ground specimens prepared in the same manner as the face or root bend

specimens. Metallographic analysis was performed on specimens taken frojn the

bend specimens. Tensile tests performed on the base metal were conducted on 3/4-inch and 1-1/2-inch bar stock of cold-finished type 12L14 steel.

RESULTS AND DISCUSSION

Base-metal guided bend tests were conducted on the 12L14 steel bar stock for

comparison with the weld metal tests. The test specimens of base metal were

3/8- inch thick and were bent around a 1-1/2-inch diameter mandrel. As shown

in Table III, the base metal specimens successfully passed the guided bend

test with no evidence of cracking. These results show that the AISI 12L14

base metal steel has adequate ductility to pass a bend test when tested

around a 4t diameter mandrel.

Tensile tests were previously conducted on 3/4- inch and 1-1/2-inch thick

sections of cold-rolled bar stock of 12L14 [1], As shown in Table IV, the

base metal had an ultimate tensile strength of 74,000 to 76,000 psi and a yield strength of 68,000 to 71,000 psi. Hardness measurements were made on both the base metal from welded samples as well as from the cold-rolled bar

stock used in the tensile tests for comparison with the weld metal. As shown

in Table IV, the average hardness of the base metal from bend-test specimens

was HRB 85 (Rockwell B scale) and the hardness of the cold-rolled bar stock

ranged from HRB 81 to 87. Using a reported [2] empirical relationship betwen

hardness and ultimate tensile strength for carbon steels, the measured

ultimate strength range of 74 to 76 ksi was in good agreement with the range

of 73 to 83 ksi predicted from the measured hardness. Thus, for 12L14 steel,

the hardness -strength correleation is applicable.

Guided bend tests were conducted on 3/8-inch thick root bend, face bend, and

side bend specimens taken from the 1/2-inch "J" weld joint geometry. These

were bent around a 1-1/2 inch diameter mandrel. As shown in Table I, all of

the specimens (root, face and side bend) failed by cracking along the heataffected zone (HAZ) of the weldment before completing the full bend test (as

shown in Figure 2). The same size specimens were then tested as root-bend

and face-bend specimens using the wrapped bend test fixture. This was done

because it was recognized that in the guided bend test, the test specimen

does not always stay in close contact with the forming mandrel and the

2
specimen may go slightly "pointy" at the maximum bend point. When this

happens, the maximum true strain in the specimen will be drastically higher

than the expected strain for the specimen thickness and mandrel diameter used

in the test. The wrapped bend test avoids this problem and creates a well

controlled and known strain in the specimen because the specimen is made to

conform to the mandrel at all times. All of the specimens tested with the

wrapped-bend-test fixture also cracked at the HAZ boundary in the same manner

as the specimens tested with the guided-bend-test fixture. This indicates

that the specimens cracked because of reduced ductility (at least when

compared with the base metal) in the HAZ of the weld metal and not because of

any unusually large strains produced in the guided bend test.

Guided bend tests were also conducted on 3/16-inch thick face bend specimens

taken from the 3/8-inch thick bevel weld joint geometry. These were bent

around a 3/4- inch diameter mandrel. As shown in Table II, the specimens

failed by cracking along the heat-affected zone (HAZ) of the weldment before

completing the full bend test (as shown in Figure 2). The same specimen

geometries were then tested as face bend and root bend specimens using the

wrapped bend test fixture. These specimens also cracked at the HAZ boundary

in the same manner as the specimens tested with the guided bend fixture.

This indicates that the weldments produced with the procedures used for the

3/8-inch bevel joint geometry also had reduced ductility compared with the

base metal and did not pass the bend test.

Although the 0.1-inch-thick face-bend and root-bend specimens taken from the

1/4-inch bevel joint geometry were not tested at this time, they are also not

expected to have sufficient ductility to pass the bend test around a 4t

diameter mandrel because strain levels are similar to those produced in the

3/ 8 -inch specimens.

Hardness profile measurements were taken across the weld metal, HAZ, and base

metal of a bend specimen taken from the 1/2-inch "J" weld geometry. As

shown in Table IV, the average hardness of the weld metal was HRB 92

(Rockwell B scale) which corresponds to a tensile strength of about 93,000

psi. This is considerably higher than the average hardness of HRB 85 in the

base metal which corresponds to a tensile strength of about 79,000 psi. This

may explain why the bend specimens all failed in the HAZ. With the strongly

overmatching strength of the weld metal, the ductility of the weld metal, and

even more so the HAZ, may be so reduced relative to that of the base metal

that the strain to fracture in the HAZ is too low to pass the bend test.

This suggests that to successfully weld the leaded carbon steels, the welding

procedures and welding electrode should be modified so that the weld metal is

at best only slightly stronger than the base metal so that the finished weld

can pass the bend test. The failure to pass the bend test does not appear to

be related to the leaded carbon steel, but only to the strongly overmatching

strength of the weld metal.

To understand further the welding behavior of the leaded carbon steel, a limited metallographic analysis was conducted on the base metal and the weld

metal. As shown in Figure 3, the microstructure of the base metal consisted

of a ferrite matrix with manganese sulfide inclusions uniformly distributed

throughout. Small areas of pearlite were scattered between the ferrite grains

3
as shown in Figure 4. By contrast, the weld metal/HAZ interface showed

almost a complete absence of manganese sulfide inclusions in the fusion zone,

as shown in Figure 5. This indicates limited melting of the base metal and a very narrow HAZ. Limited EDAX analysis was conducted of the base metal to

confirm the identity of the inclusions observed by optical microscopy. As

shown in Figures 6 and 7, the X-ray results confirm that the inclusions are

MnS. Very small particles that were not visible by optical microscopy were

found with the electron microscope and, as shown in Figure 8, were identified

by EDAX examination to be primarily lead. No detailed examination was done

at this time to determine the effect of welding on the size or distribution

of the lead particles.

CONCLUSIONS

(1) Sound welds were produced in the leaded steel (AISI 12L14) using

welding procedures currently used for unleaded carbon steels.

(2) The welding procedures used and the welding electrodes used produced

a weld metal with a highly overmatching strength so that the

ductility of the HAZ was reduced to the point where the welded steel

could not pass the conventional ductility (bend) tests.

(3) The inability of these particular welds to pass the bend test is not

attributed to the use of leaded steel but is more likely due to the

particular welding procedure and welding electrodes used to make

these specific welds.

REFERENCES

1. Early, J.G., "Mechanical Properties of a Leaded, Resulfurized,

Rephospherized Steel in Various Thermo/Mechanical Conditions" NBSIR 84-

2839, January 1984.

2. Society for Automotive Engineers (SAE) Standard J417-83 "Hardness Tests

and Hardness Number Conversions."

4
TABLE I . BEND TEST RESULTS FOR " J" -WELD SPECIMENS

SPECIMEN TEST SPECIMEN

NUMBER TYPE (a) TYPE COMMENTS

55-57 G ROOT CRACKED ALONG HAZ

50-49 G ROOT CRACKED ALONG HAZ

58-58 G FACE CRACKED ALONG HAZ

52-53 G SIDE CRACKED ALONG HAZ

56-56 W FACE CRACKED ALONG HAZ

52-51 W ROOT CRACKED ALONG HAZ

GUIDED BEND ROLLER JIG

FINISHED SPECIMEN THICKNESS = t = 3/8 INCH

FORMING MANDREL DIAMETER = 4t = 1-1/2 INCH

JIG SHOULDER SPACING = 6t + 1/8 INCH = 2-3/8 INCH

WRAPPED BEND JIG

FINISHED SPECIMEN THICKNESS = t = 3/8 INCH

FORMING MANDREL DIAMETER = 4t = 1-1/2 INCH

(a) G = GUIDED BEND

W = WRAPPED BEND
TABLE II. BEND TEST RESULTS FOR 3/8 INCH BEVEL WELD SPECIMENS

SPECIMEN TEST SPECIMEN

NUMBER TYPE (a) TYPE COMMENTS

37-38 G FACE CRACKED ALONG HAZ

33-34 W FACE CRACKED ALONG HAZ

34-35 W FACE CRACKED ALONG HAZ

39-40 W ROOT CRACKED ALONG HAZ

38-39 W ROOT CRACKED ALONG HAZ

GUIDED BEND ROLLER JIG

FINISHED SPECIMEN THICKNESS = t = 3/16 INCH

FORMING MANDREL DIAMETER = 4t = 3/4 INCH

JIG SHOULDER SPACING = 6t + 1/8 = 1-1/4 INCH

WRAPPED BEND JIG

FINISHED SPECIMEN THICKNESS = t = 3/16 INCH

FORMING MANDREL DIAMETER = 4t = 3/4 INCH

(a) G = GUIDED BEND

W = WRAPPED BEND
TABLE III. BEND TEST RESULTS FOR BASE METAL SPECIMENS

SPECIMEN

NUMBER

TEST

TYPE fa)

SPECIMEN

TYPE COMMENTS

1

2

G

G

BASE METAL NO CRACKS

BASE METAL NO CRACKS

FINISHED SPECIMEN THICKNESS = t = 3/8 INCH

FORMING MANDREL DIAMETER = 4t = 1-1/2 INCH

JIG SHOULDER SPACING = 6t + 1/8 = 2-3/8 INCH

(a) G = GUIDED BEND
TABLE IV. RESULTS OF HARDNESS MEASUREMENTS

SPECIMEN LOCATION

HARDNESS

HRB

MEASURED

ULTIMATE TENSILE

STRENGTH. KSI

ULTIMATE TENSILE

STRENGTH, KSI, FROM

HARDNESS CORRELATION

BEND BASE METAL 85 79

BEND WELD METAL 92 93

BAR STOCK 81 - 87 74 - 76 73 - 83
Figure 1. Weld Joint Geometries

a. 1/4 inch bevel

b. 3/8 inch bevel

c. "J" joint
Figure 2. Guided Bend Roller Test Specimens

a. 3/16 inch thick, 3/8 inch bevel joint, tensile surface

b. 3/8 inch thick, 1/2 inch "J" joint, tensile surface
250- jam

Unetched X200

Figure 3. Photomicrograph of AISI 12L14 Steel Base Metal

Manganese sulfide inclusions are distributed

throughout the microstructure.
Figure 4. Photomicrograph of AISI 12L14 Steel Base Metal

Light gray particles are manganese sulfide

inclusions. Dark areas between ferrite grains

are pearl ite.
Unetched X200

Figure 5. Photomicrograph of AISI 12L14 Steel Weld Metal/HAZ Interface

Almost complete absence of manganese sulfide inclusions

in the fusion zone (left half of photo)
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NBS-1T4A 1 REV. 2»ac) U.S. DEPT. OF COMM. » 1 . BIBLIOGRAPHIC DATA

SHEET (See instructions)

4. TITLE AND SUBTITLE

PUBLICATION OR

REPORT NO.

2. Performing Organ. Report NoJ 3. Publication Date

WELDABILITY OF LEADED CARBON STEEL

5. AUTHOR(S)

James G. Early and John H. Smith

6. PERFORMING ORGANIZATION (If joint or other than NBS, see instructions) 7. Contract/Grant No. national bureau of standards Z70099-2-06104

DEPARTMENT OF COMMERCE 8. Type of Report & Period Covered

WASHINGTON, D.C. 20234

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City. State, ZIP)

U. S. Coast Guard

Washington, DC 20234

10. SUPPLEMENTARY NOTES

| | Oocument describes a computer program; SF-185, FIPS Software Summary, is attached.

11. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here)

Samples of A1S1 12L14, leaded free maching steel were welded using

conventional metal-inert gas (MIG) welding procedures. The welds were

evaluated for soundness and mechanical properties. Hardness, ductility and

microstructure were evaluated to assess the integrity of the welds. Sound

welds were produced but the overmatching strength of the weld metal resulted

in failure in the HAZ.

12. KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolons)

Carbon steel; free machining steel; leaded steel; mechanical properties;

MIG welding; steel; welding; 12L14 steel.

13. AVAILABILITY

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20402.

1 1 Order From National Technical Information Service (NTIS), Springfield, VA. 22161

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