A UNITED STATES DEPARTMENT OF COMMERCE

PUBLICATION

NAT L INST. OF STAND & TECH

11 IlilllUI AlllQb aUDEMb

NBS SPECIAL PUBLICATION 260-43

U.S.

DEPARTMENT

OF

COMMERCE

National

Bureau

of

Standards

Standard Reference Materials:

PREPARATION AND

HOMOGENEITY CHARACTERIZATION

OF AN AUSTENITIC

IRON-CHROMIUM-NICKEL ALLOY
NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards' was established by an act of Congress March 3, 1901. The Bureau's overall goal is to strengthen and advance the Nation's science and

technology and facilitate their effective application for public benefit. To this end, the

Bureau conducts research and provides: (1) a basis for the Nation's physical measure- ment system, (2) scientific and technological services for industry and government, (3) a technical basis for equity in trade, and (4) technical services to promote public safety.

The Bureau consists of the Institute for Basic Standards, the Institute for Materials

Research, the Institute for Applied Technology, the Center for Computer Sciences and

Technology, and the Office for Information Programs.

THE INSTITUTE FOR BASIC STANDARDS provides the central basis within the

United States of a complete and consistent system of physical measurement; coordinates

that system with measurement systems of other nations; and furnishes essential services

leading to accurate and uniform physical measurements throughout the Nation's scientific community, industry, and commerce. The Institute consists of a Center for Radiation Research, an Office of Measurement Services and the following divisions:

Applied Mathematics—Electricity—Heat—Mechanics—Optical Physics—^Linac

Radiation^—Nuclear Radiation^—Applied Radiation^—Quantum Electronics^

Electromagnetics''—^Time and Frequency^—Laboratory Astrophysics^—Cryogenics^.

THE INSTITUTE FOR MATERIALS RESEARCH conducts materials research leading to improved methods of measurement, standards, and data on the properties of

well-characterized materials needed by industry, commerce, educational institutions, and

Government; provides advisory and research services to other Government agencies;

and develops, produces, and distributes standard reference materials. The Institute consists of the Office of Standard Reference Materials and the following divisions:

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THE INSTITUTE FOR APPLIED TECHNOLOGY provides technical services to pro- mote the use of available technology and to facilitate technological innovation in industry and Government; cooperates with public and private organizations leading to the

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and effective utilization of automatic data processing equipment; and serves as the principal focus within the executive branch for the development of Federal standards for

automatic data processing equipment, techniques, and computer languages. The Center

consists of the following offices and divisions:

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THE OFFICE FOR INFORMATION PROGRAMS promotes optimum dissemination

and accessibility of scientific information generated within NBS and other agencies of

the Federal Government; promotes the development of the National Standard Reference

Data System and a system of information analysis centers dealing with the broader

aspects of the National Measurement System; provides appropriate services to ensure

that the NBS staff has optimum accessibility to the scientific information of the world,

and directs the public information activities of the Bureau. The Office consists of the

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1 Headquarters and Laboratories at Gaithersburg, Maryland, unless otherwise noted ; mailing address Washington, D.C. 202.34.

2 Part of the Center for Radiation Research.

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* Part of the Center for Building Technology.
•IS'hbilSi :. APR 2 9 1974

Standard Reference Materials:

Preparation and

Homogeneity Characterization of an

Austenitic Iron-Chromium-Nickel Alloy

Harvey Yakowitz and Arthur W. Ruff

Metallurgy Division

and

Robert E. Michaelis

Office of Standard Reference Materials

Institute for Materials Research

National Bureau of Standards

Washington, D.C. 20234

U.S. DEPARTMENT OF COMMERCE, Peter G. Peterson, Secretary

NATIONAL BUREAU OF STANDARDS, Lawrence M. Kushner, Acfing Director,

Issued November 1972
Library of Congress Catalog Card Number: 72-600312

National Bureau of Standards Special Publication 260-43

Nat. Bur. Stand. (U.S.), Spec. Publ. 260-43, 19 pages (Nov. 1972)

CODEN: XNBSAV

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402

(Order by SD Catalog No. C13.10:260-43). Price 45 cents.
PREFACE

Standard Reference Materials (SRM's) as defined by the

National Bureau of Standards are "well-characterized materials, produced in quantity, that calibrate a measurement

system to assure compatibility of measurement in the nation."

SRM's are widely used as primary standards in many diverse

fields in science, industry, and technology, both within the

United States and throughout the world. In many industries

traceability of their quality control process to the national

measurement system is carried out through the mechanism and

use of SRM's. For many of the nation's scientists and technologists it is therefore of more than passing interest to

know the details of the measurements made at NBS in arriving

at the certified values of the SRM's produced. An NBS series

of papers, of which this publication is a member, called the

NBS Special Publication - 260 Series is reserved for this

purpose

This 260 Series is dedicated to the dissemination of

information on all phases of the preparation, measurement,

and certification of NBS-SRM's. In general, much more detail will be found in these papers than is generally allowed,

or desirable, in scientific journal articles. This enables

the user to assess the validity and accuracy of the measurement processes employed, to judge the statistical analysis,

and to learn details of techniques and methods utilized for

work entailing the greatest care and accuracy. It is also

hoped that these papers will provide sufficient additional

information not found on the certificate so that new applications in diverse fields not foreseen at the time the SRM

was originally issued will be sought and found.

Inquiries concerning the technical content of this

paper should be directed to the author (s). Other questions

concerned with the availability, delivery, price, and so

forth will receive prompt attention from:

Office of Standard Reference Materials

National Bureau of Standards

Washington, D.C. 20234

J. Paul Call, Chief

Office of Standard Reference Materials
CONTENTS

PAGE

I. INTRODUCTION 2

II. PREPARATION OF THE ALLOY 2

III. PREPARATION FOR MICROPROBE ANALYSIS 3

IV. HOMOGENEITY CHARACTERIZATION 4

V. ELECTRON PROBE MICROANALYSIS 6

VI. CONCLUSIONS 7

VII. REFERENCES 10

LIST OF TABLES

I. Electron Probe Microanalysis Results for Fe

,

Cr and Ni in SRM 479. Standards were pure

Fe, Cr and Ni . True concentrations in weight

fractions: Fe = 0.710: Cr = 0.183; Ni = 0.017 9

LIST OF FIGURES

I. Microstructure observed on a transverse

surface after polishing and etching.

Magnification 160X 11

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Materials: Preparation and Homogeneity

Characterization of an Austenitic IronChromium-Nickel Alloy. (In preparation)

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STANDARD REFERENCE MATERIALS:

PREPARATION AND HOMOGENEITY CHARACTERIZATION OF

AN AUSTENITIC IRON-CHROMIUM-NICKEL ALLOY

H. Yakowitz, A. W. Ruff and R. E. Michaelis

Institute for Materials Research

National Bureau of Standards

Washington, D. C. 20234

An alloy of weight fraction 0.710 iron, 0.183

chromium and 0.107 nickel was characterized

at the micrometer level of spatial resolution

by means of electron probe microanalysis. This

alloy, designated SRM 479, is of suitable homogeneity for use as a standard in microanalytical

techniques. The coefficient of variation for

each of the three elements is not more than 1.5%

based on about 800 analyses involving five different specimens. There is no statistically

significant variation in composition within

specimens or from specimen to specimen. Electron

probe microanalysis was carried out using different instrumental conditions and operators.

SRM 479 is supplied as a disk about 4.6mm diameter by Irom thick.

Key words: Austenitic stainless steel; electron probe microanalysis; Fe-Cr-Ni alloy; homogeneity testing; metallography;

stacking fault energy; Standard Reference Material.

1
1. INTRODUCTION

The National Bureau of Standards maintains a continuing

program to provide standards suitable for quantitative

microanalytical methods such as electron probe microanalysis,

spark source mass spectrometry, and laser probe analysis.

Several standard materials have already been certified under

this program [1-6] This report describes the methods and

results of homogeneity characterization of the first ternary

alloy to be so certified - an austenitic Fe-Cr-Ni alloy

designated SRM 479.

This alloy was produced at NBS as a research material

for a project concerned with the measurement of stacking

fault energies [7]. Those results indicated a high degree

of solute homogeneity on a microscopic level. Additional

thermomechanical treatment led to material of suitable

homogeneity for use in microanalytical methods of analysis.

The material preparation and the results of quantitative

electron probe microanalysis of the constituent three elements

will be presented in detail.

II. PREPARATION OF THE ALLOY

The alloy was melted by the arc fusion method using

appropriate amounts of the raw material in the form of chips

and small pieces. The raw material purities furnished by

the suppliers were: Ni-99 .98%, Cr-99 .95%, and Fe--99 .95%.

An inert gas atmosphere of argon, gettered by titanium, was

established within the furnace at a pressure of about 0.4

atmospheres. A non- consumable thoriated tungsten electrode

was used to melt the charge of approximately 55g. The ingot

was melted four times, twice on each side, and allowed to

solidify in a round depression in the cooled, copper base

plate, A final remelting was conducted in a well of

rectangular cross-section in the base plate to produce an

ingot about 15cm x 1cm x 1cm, The expected composition,

^Figures in brackets indicate the references at the end of this paper.

2
assuming no material loss, was 10.6% Ni , 18.8% Cr, 70.6% Fe.

A portion of the ingot was reserved for rolling thin

foil, a small amount for chemical analysis, and the remainder

fabricated for the present standard. Initially, the balance

of the ingot was annealed for 1 hr. at 1120 °C within a sealed

quartz tube containing helium at a pressure of 0.3 atmospheres.

The ingot was then swaged to about 60% reduction in diameter,

sealed again in quartz and homogenized for 5 days at 1120 °C.

Two subsequent swaging and annealing steps produced the final

round rod of 4.6mm diameter x 220mm long. On each occasion

the ends were cropped and the surface etched deeply in a

20% HNO^ + 3% HF solution. No liibrication was used during

the mechanical processing. Each heating treatment was

concluded "by quenching the sealed ingot into water. Five

disks, 1mm thick, were cut from the final rod at each end

and at the 1/4, 1/2, and 3/4 positions. These disks were

used for electron microprobe characterization of the material.

Chemical analysis performed on a representative portion of

the ingot indicated a composition of 10.7% Ni , 18.3% Cr,

0.012% C, the balance Fe.

SRM 479 is issued as a disk, approximately 1mm thick

X 4.6mm diameter, in the as-cut condition after electrical

discharge slicing. A typical microstructure found on a

metallographically prepared and etched transverse surface

is shown in Fig. 1. The as-deformed grain structure is

evident. Small pits and voids that were not completely removed in the processing treatments are to be seen in the

section. Inclusions were not detected in the specimens

examined.

III. PREPARATION FOR MICROPROBE ANALYSIS

This material was easily prepared for microprobe

examination. Mounted specimens were ground on water- lubricated Sic papers in the usual progression 80, 220, 400 and

600 grit size. Rough polishing was done on a canvas cloth

3
impregnated with Gym diamond particles. Fine polishing

was done on a Selvyt cloth impregnated with l/4]jm diamond

particles. Both rough and fine polishing were carried out

with the wheels rotating at 125 RPM. The specimen

was finished using a Gamal cloth impregnated with O.OSym

Al^O^, Wheel rotation was 150 RPM. Total time was about

30 minutes to complete specimen preparation. Unetched

specimens were characterized and analyzed with the electron

probe microanalyzer

.

IV. HOMOGENEITY CHARACTERIZATION

Five specimens were taken from the rod; one from each

end and one from the 1/4, 1/2 and 3/4 positions. The specimens were tested for homogeneity to determine whether any

significant composition gradients were present in both the

transverse and longitudinal directions of the rod.

Homogeneity testing was carried out with a microprobe

operating voltage of 20kV. The Ka radiation from all three

elements was monitored by spectrometers equipped with LiF

crystals and sealed proportional counters. The x-ray

emergence angle was 52.5°. Each element peak was found by

scanning the peak profile by hand. Monitor current was

adjusted to give about 25,000 counts per second on pure

iron. Under these conditions, a 40 second counting interval

on the specimen gave about 900,000 Fe counts, 340,00 0 Cr

counts and 270,000 Ni counts.

The homogeneity test on each transverse specimen face

consisted of collecting data along two diameters at right

angles to one another and four chords of the specimen; points

were spaced 200ym apart. The chord paths were one-fourth

of the specimen diameter and parallel to the diameters discussed above. The procedure was repeated twice on different

days with different orientation of the specimen. Approximately

160 points total were taken on each specimen.

4
In evaluating the results, the coefficient of variation

in percent, CV, was taken to be the most useful indicator

of homogeneity. The valxie of CV is defined as

IQOs

CV = ^ (%)

where s is the standard deviation, in counts, for a particular

data array Cs is obtained in the usual fashion) and N is the

average total number of counts

In no case was CV greater than 1.5% for any element

present. Therefore, a conservative estimate of CV for the

entire lot is 1.5% for all three elements, iron, chromium

and nickel.

On any given day of testing, at least two different

specimens were tested under the same experimental conditions.

These were checked by an "outside count" method [8] to see

whether, statistically, the two specimens were significantly

different. The specimens always passed the test. Hence, we

conclude that all five specimens tested are not statistically

different from one another in terms of composition.

The implications of the CV value of 1.5% must now be

considered. The width of a 99% confidence interval is

^ / n 100

where C^^^ is the true chemical weight fraction of element i

in SRM 479; CV is the coefficient of variation, 1.5% in this

99

case; n is the number of trials or analyses; and t , is the n-1

Student's t value for 99% confidence for (n-1) degrees of

freedom.

5
If "n" is arbitrarily made equal to sixteen in Eqn. (1)

,

then

^99 " - ^i ^'V^ (0.015) = + 0.0111 (2)

Hence, if one is willing to run sixteen separate points for

each element in SRM 479, the 99% confidence interval widths

and mean values would be

Iron = 0.710 + 0.0080

Chromiaim = 0.183 + 0.0020

Nickel = 0.107 + 0.0012

The time to collect data for sixteen points is not prohibitive,

being about 30 minutf=^s.

V. ELECTRON PROBE MICROANALYSIS

As a final test, four different microprobe operators

analyzed the specimens by means of electron probe microanalysis

using pure iron, chromium and nickel as standards. The 1/4,

1/2, 3/4 specimens were used for analyses. The first of

these was tested by analyst A, the second by B and the third

by C. Analyst D collected data from all three specimens.

Sixteen determinations were made for all elements . Results

were obtained with instrumental operating voltages of 15, 20,

25, and 30kV respectively. Count rates were set so that pure

iron gave about 12,000 counts per second to minimize coincidence loss uncertainties I9J . Instrument stability was

checked by obseirving monitor current variations during the

course of the analysis. Drift was less than one percent

for all runs. Data from standards were obtained both before

and after data from the specimen. No significant variation

of the data from standards was observed,

6
Raw data from standards and specimen were entered in

the microprobe data reduction program COR. This program

has been described in detail elsewhere [10] . The results

obtained are listed in Table I. These results show no

significant specimen-to-specimen variations and reaffirm

that the CV of 1.5% is reasonable. The analyses for iron

and nickel are within about 1% relative for all operating

voltages. The chromium analyses tend to be high, the most

likely cause being the large characteristic fluorscence

correction for chromium - about 20%. Errors in this correction have been discussed in detail by Heinrich and Yakowitz

[llj . The fluorescence yield factors for nickel and iron

may be the source of error in the case of the analyses in

Table I.

VI . CONCLUSIONS

The ternary alloy consisting of 0.710 iron, 0.183

chromium and 0.107 nickel as determined by chemical analysis,

is suitable for use as a microanalytical standard. This

alloy, SRjyt 479, has a chemical homogeneity, expressed as

coefficient of variation of not more than 1.5% for each

element present. The individual region for which this coefficient of variation is valid is approximately a 1.5ym

diameter sphere of the material. As an additional characterization, the stacking fault energy of this alloy has been

determined from electron transparent thin foils in the temperature range 25 °C to 325 °C by Latanision and Ruff [7]

SRM 479 should be useful in the study of the fluorescence

correction in microprobe analyses. This material will also

be useful in any laboratory concerned with the quantitative

microanalysis of stainless steels. SRM 479 represents the

first ternary alloy to be certified under the homogeneity

characterization program of the NBS Office of Standard

Reference Materials

7
The authors thank Mr. D. P. Fickle for his efforts in

the preparation of SRM 479; Dr. K. F. J. Heinrich for use of

the electron microprobe; Mrs. M. M. Darr, Mr. C. E. Fiori and

Mr. R. L. Myklebust for electron probe microanalysis of SRM

479. Thanks are also due to Mr. Myklebust for aid in preparing the data for the computer. We thank Mr. R. A. Paulson

for the chemical analysis of SRM 479. Finally, we acknowledge

the initial characterization efforts of Dr. R. M. Latanision

CRIAS) as part of his NAS-NRC Postdoctoral Research Associateship .

8
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VII. REFERENCES

II] Michaelis, R. E., Yakowitz, H. and Moore, G. A., J. Res.,

Nat. Bur. Stand. (U.S.) 6 8A , 343 (1964).

[2] Yakowitz, H. , Vieth, D. L., Heinrich, K. F. J. and

Michaelis, R. E., Advances in X-ray Analysis 9_, 289

(1966) .

[3] Yakowitz, H., Vieth, D. L. and Michaelis, R. E. , Nat.

Bur. Stand. (U.S.) Spec. Publ. 260-12 (1966).

[4] Yakowitz, H. , Michaelis, R, E. and Vieth, D. L., Advances

in X-ray Analysis 12_, 418 (1969 ).

15] Yakowitz, H., Fiori, C. E. and Michaelis, R. E. , Nat.

Bur. Stand. (U.S.) Spec. Piabl. 260-22 (1971).

16] Heinrich, K. F. J., Myklebust, R. L. and Rasberry, S. D.,

Nat. Bur. Stand. (U.S.) Spec. Publ. 260-28 (1971).

17] Latanision, R. M. and Ruff, A. W. , Jr., Met. Trans. 2^,

505 (1971) .

18] Tukey, J. W. , Technometries 1, 31 (1959).

19] Heinrich, K. F. J., Vieth, D. L. and Yakowitz, H.

,

Advances in X-ray Analysis 9_, 208 (1966).

110] Heinrich, K. F. J., Henoc , J. and Myklebust, R. L., NBS

Tech Note (1973) , (in preparation)

.

III] Heinrich, K. F. J. and Yakowitz, H. , Mikrochim. Acta 5_,

905 C1968).

10
FIGURE I, Microstructure observed on a transverse

surface after polishing and etching.

Magnification 160X.

11

FORM NBS-114A (1-71)

U.S. DEPT. OF COMM. 1- PUBLICATION OR REPORT NO. 2VGdv"t Atc^Cs^ioS

BIBLIOGRAPHIC DATA ^BS SP 260-43

3. Recipient's Accession No.

4. TITLE AND SUBTITLE STANDARD REFERENCE MATERIALS : Preparation and Homogeneity Characterization of an

Austenitic Iron-Chromium-Nickel Alloy

5. Publication Date November 1972

6. Performing Organization Code

7. AUTHOR(S)

H. Yakowitz, A. W. Ruff, R. E. Michaelis

8. Performing Organization

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/ Work Unit No. 3020101

1. i^onuact/ orant ino.

12. Sponsoring Organization Name and Address

Same as No. 9.

13. Type of Report & Period

Covered

Final

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

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

bibliography or literature survey, mention it here.)

An alloy of weight fraction 0.710 iron, 0.183 chromium and 0.107

resolution by means of electron probe microanalysis. This alloy,

designated SRM 47 9, is of suitable homogeneity for use as a

standard in microanalytical techniques. The coefficient of

variation for each of the three elements is not more than 1.5%

based on about 800 analyses involving five different specimens.

There is no statistically significant variation in composition

within specimens or from specimen to specimen. Electron probe

microanalysis was carried out using different instrumental

conditions and operators. SRM 479 is supplied as a disc about

4.6mm diameter by Imra thick.

17. KEY WORDS (Alphabetical order, separated by semicolons) AuStenitic StainleSS Steel; eleCtrOn

probe microanalysis; Fe-Cr-Ni alloy; homogeneity testing; metallography; stacking fault energy; Standard Reference Material.

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