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REFERENCE publications

NBS SPECIAL PUBLICATION 260-73

U.S. DEPARTMENT OF COMMERCE / National Bureau of Standards

A STANDARD REFERENCE MATERIAL

CONTAINING NOMINALLY

FIFTEEN PERCENT AUSTEN ITE (SRM 486)
NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards' was established by an act of Congress on 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 measurement system, (2) scientific and technological services lor industry and government, (3) a technical basis for equity in trade, and (4) technical services to promote public safety. The Bureau's technical work is per- formed by the National Measurement Laboratory, the National Engineering Laboratory, and

the Institute for Computer Sciences and Technology. THE NATIONAL MEASUREMENT LABORATORY provides the national system ot physical and chemical and materials measurement; coordinates the system with measurement

systems of other nations and furnishes essential services leading to accurate and uniform

physical and chemical measurement throughout the Nation's scientific community, industry, and commerce; conducts materials research leading to improved methods of measurement,

standards, and data on the properties of materials needed by industry, commerce, educational

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Standard Reference Materials:

A STANDARD REFERENCE MATERIAL CONTAINING

NOMINALLY FIFTEEN PERCENT AUSTENITE (SRM 486)

C. G. Interrante and G. E. Hicho

National Measurement Laboratory

National Bureau of Standards Washington, DC 20234

U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director Issued January 1982
Library of Congress Catalog Card Number: 81-600173

National Bureau of Standards Special Publication 260-73

Nat. Bur. Stand. (U.S.). Spec. Publ. 260-73. 34 pages (Jan. 1982) CODEN: XNBSAV

U.S. GOVERNMENT PRINTING OFFICE WASHINGTON: 1982

For sale by the Superintendent of Documents. U.S. Government Printing Oil ice. Washington. DC 20402

Price (Add 25 percent for other than U.S. mailing)
PREFACE

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

National Bureau of Standards are we 1 1- char a c t e r i z ed materials

produced in quantity and certified for one or more physical

or chemical properties. They are used to assure the accuracy

and compatibility of measurements throughout 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. They are also used

extensively in the fields of environmental and clinical analysis. In many applications, traceability of quality control

and measurement processes to the national measurement system

are 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 different phases of the preparation, measurement, certif ication, and use 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.

These papers also should 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 authors. 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

George A. Uriano, Chief

Office of Standard Reference Materials

iii
OTHER NBS PUBLICATIONS IN THIS SERIES

Catalog of NBS Standard Reference Materials (1981-83 edition), R. W. Seward, ed., NBS

Spec. Publ. 260 (November 1981). Michaelis, R. E., and Wyman, L. L. Standard

Reference Materials: Preparation of White Cast

Iron Spectrochemical Standards. NBS Misc. Publ. 260-1 (June 1964). COM 74- 1 1 06 1 **

Michaelis, R. E., Wyman, L. L., and Flitsch, R., Standard Reference Materials: Preparation of NBS Copper-Base Spectrochemical Standards. NBS Misc. Publ. 260-2 (October 1964). COM74-

1 1063**

Michaelis, R. E., Yakowitz, H., and Moore, G. A., Standard Reference Materials: Metallographic

Characterization of an NBS Spectrometric LowAlloy Steel Standard. NBS Misc. Publ. 260-3 (October 1964). COM74-1 1060** Hague, J. L. Mears, T. W., and Michaelis, R. E., Standard Reference Materials: Sources of

Information, NBS Misc. Publ. 260-4 (February

1965). COM74-11059

Alvarez, R., and Flitsch R., Standard Reference

Materials: Accuracy of Solution X-Ray Spectrometric Analysis of Copper-Base Alloys. NBS

Misc. Publ. 260-5 (March 1965). PB168068**

Shultz, J. L, Standard Reference Materials: Methods for the Chemical Analysis of White

Cast Iron Standards, NBS Misc. Publ. 260-6

(July 1975). COM74-11068**

Bell, R. K., Standard Reference Materials: Methods for the Chemical Analysis of NBS

Copper-Base Spectrochemical Standards. NBS

Misc. Publ. 260-7 (October 1965). COM74-

11067** Richmond, M.S., Standard Reference Materials: Analysis of Uranium Concentrates at the

National Bureau of Standards. NBS Misc. Publ. 260-8 (December 1965). COM74-1 1066** Anspach, S. C, Cavallo, L. M. Garfinkel, S. B. Hutchinson, J. M. R., and Smith, C. N., Standard Reference Materials: Half Lives of Materials Used in the Preparation of Standard Reference Materials of Nineteen Radioactive Nuclides

Issued by the National Bureau of Standards NBS Misc. Publ. 260-9 (November 1965). COM74-11065**

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

Michaelis, R. E., Standard Reference Materials: Homogeneity Characterization on NBS Spectrometric Standards II: Cartridge Brass and LowAlloy Steel, NBS Misc. Publ. 260-10 (December

1965). COM74-11064**

Napolitano, A., and Hawkins, E. G., Standard Reference Materials: Viscosity of Standard

Lead-Silica Glass, NBS Misc. Publ. 260-11 (November 1966). NBS Misc. Publ. 260-11** Yakowitz, H., Vieth, D. L., and Michaelis, R. E., Standard Reference Materials: Homogeneity

Characterization of NBS Spectrometric Standards III: White Cast Iron and Stainless Steel Powder Compact, NBS Misc. Publ. 260-12

(September 1966). NBS Misc. Publ. 260-12** Spijkerman, J. L., Snediker, D. K., Ruegg, F. C,

and DeVoe, J. R., Standard Reference Materials: Mossbauer Spectroscopy Standard for the Chemical Shift of Iron Compounds, NBS Misc. Publ. 260-13 (July 1967). NBS Misc. Publ.

260-13** Menis, O., and Sterling, J. T., Standard Reference

Materials: Determination of Oxygen in Ferrous

Materials - SRM 1090, 1091, and 1092, NBS

Misc. Publ. 260-14 (September 1966). NBS Misc.

Publ. 260-14**

Passaglia, E., and Shouse, P. J. Standard Refer- ence Materials: Recommended Method of Use

of Standard Light-Sensitive Paper for Calibrating Carbon Arcs Used in Testing Textiles for Colorfastness to Light, NBS Misc. Publ. 260-15 (June 1967). (Replaced by NBS Spec. Publ.

260-41.) Yakowitz, H., Michaelis, R. E., and Vieth, D. L., Standard Reference Materials: Homogeneity

Characterization of NBS Spectrometric Standards IV: Preparation and Microprobe Characterization of W-20% MO Alloy Fabricated by Powder Metallurgical Methods, NBS Spec.

Publ. 260-16 (January 1969). COM74-1 1062** Catanzaro, E. J., Champion, C. E., Garner, E. L., Marinenko, G., Sappenfield, K. M., and Shields, W. R., Standard Reference Materials: Boric

Acid; Isotopic and Assay Standard Reference

Materials, NBS Spec. Publ. 260-17 (February

1970). Out of Print

iv
Geller, S. B., Mantek, P.A., and Cleveland, N.

G., Standard Reference Materials: Calibration of NBS Secondary Standard Magnetic Tape (Computer Amplitude Reference) Using the Reference Tape Amplitude Measurement

"Process A, "NBS Spec. Publ. 260-18 (November

1969). (See NBS Spec. Publ. 260-29.) Paule, R. C, and Mandel, J., Standard Reference

Materials: Analysis of Interlaboratory Measurements on the Vapor Pressure of Gold (Certifica- tion of Standard Reference Material 745). NBS

Spec. Publ. 260-19 (January 1970). PB190071**

Paule, R. C, and Mandel, J., Standard Reference

Materials: Analysis of Interlaboratory Measurements on the Vapor Pressures of Cadmium and

Silver, NBS Spec. Publ. 260-21 (January 1971). COM74-11359**

Yakowitz, H., Fiori, C. E., and Michaelis, R. E., Standard Reference Materials: Homogeneity

Characterization of Fe-3 Si Alloy, NBS Spec.

Publ. 260-22 (February 1971). COM74-1 1357** Napolitano, A., and Hawkins, E. G., Standard

Reference Materials: Viscosity of a Standard

Borosilicate Glass, NBS Spec. Publ. 260-23 (December 1970). COM7 1-00 157**

Sappenfield, K. M., Marineko, G., and Hague, J. L., Standard Reference Materials: Comparison

of Redox Standards, NBS Spec. Publ. 260-24 (January 1972). COM72-50058**

Hicho, G. E., Yakowitz, H., Rasberry, S. D., and

Michaelis, R. E., Standard Reference Materials: A Standard Reference Material Containing

Nominally Four Percent Austenite, NBS Spec.

Publ. 260-25 (February 1971). COM74-1 1356** Martin, J. F., Standard Reference Materials:

National Bureau of Standards-US Steel Corportion Joint Program for Determining Oxygen and Nitrogen in Steel, NBS Spec. Publ. 260-26

(February 1971). 85 cents* PB 81176620

Garner, E. L., Machlan, L. A., and Shields, W. R., Standard Reference Materials: Uranium

Isotopic Standard Reference Materials, NBS

Spec. Publ. 260-27 (April 1971). COM74-

11358**

Heinrich, K. F. J., Myklebust, R. L., Rasberry, S. D., and Michaelis, R. E., Standard Reference Materials: Preparation and Evaluation of SRM's 481 and 482 Gold-Silver and GoldCopper Alloys for Microanalysis, NBS Spec.

Publ. 260-28 (August 1971). COM7 1-50365**

Geller, S. B., Standard Reference Materials: Cali- bration of NBS Secondary Standard Magnetic Tape (Computer Amplitude Reference) Using

the Reference Tape Amplitude Measurement

"Process A-Model 2," NBS Spec. Publ. 260-29 (June 1971). COM71-50282

Gorozhanina, R. S., Freedman, A. Y., and

Shaievitch, A. B. (translated by M. C. Selby), Standard Reference Materials: Standard

Samples Issued in the USSR (A Translation from the Russian). NBS Spec. Publ. 260-30 (June

1971). COM71-50283**

Hust, J. G., and Sparks, L. L., Standard Reference

Materials: Thermal Conductivity of Electrolytic Iron SRM 734 from 4 to 300 K, NBS Spec. Publ. 260-31 (November 1971). COM71-50563**

Mavrodineanu, R., and Lazar, J. W., Standard

Reference Materials: Standard Quartz Cuvettes,

for High Accuracy Spectrophotometry, NBS

Spec. Publ. 260-32 (December 1973). 55 cents* SN003-003-012I3-1 Wagner, H. L., Standard Reference Materials: Comparison of Original and Supplemental

SRM 705, Narrow Molecular Weight Distri- bution Polystyrene, NBS Spec. Publ. 260-33 (May 1972). COM72-50526**

Sparks, L. L., and Hust, J. G., Standard Reference

Materials: Thermoelectric Voltage, NBS Spec.

Publ. 260-34, (April 1972). COM72-50371**

Sparks, L. L., and Hust, J. G., Standard Refer- ence Materials: Thermal Conductivity of

Austenitic Stainless Steel, SRM 735 from 5 to 280 K, NBS Spec. Publ. 260-35 (April 1972.) 35 cents* COM72-50368**

Cali, J. P., Mandel, J., Moore, L. J., and Young, D.

S., Standard Reference Materials: A Referee Method for the Determination of Calcium in Serum, NBS SRM 915, NBS Spec. Publ. 260-36 (May 1972). COM72-50527**

Shultz, J. I„Bell., R. K. Rains, T. C, and Menis,

O., Standard Reference Materials: Methods of Analysis of NBS Clay Standards, NBS Spec.

Publ. 260-37 (June 1972). COM72-50692**

Richmond, J. C, and Hsia, J. J., Standard Refer- ence Materials: Preparation and Calibration of Standards of Spectral Specular Reflectance, NBS Spec. Publ. 260-38 (May 1972). COM72-

50528**

Clark, A. F., Denson, V.A., Hust, J. G., and

Powell, R. L., Standard Reference Materials The Eddy Current Decay Method for Resistivity Characterization of High-Purity Metals, NBS

Spec. Publ. 260-39 (May 1972). COM72-50529**
McAdie, H. G., Garn, P.D., and Menis, O., Standard Reference Materials: Selection of Thermal

Analysis Temperature Standards Through a Cooperative Study (SRM 758, 759, 760), NBS

Spec. Publ. 260-40 (August 1972.) COM72-

50776** Wood, L. A., and Shouse, P. J., Standard

Reference Materials: Use of Standard LightSensitive Paper for Calibrating Carbon Arcs Used in Testing Textiles for Colorfastness to Light, NBS Spec. Publ. 260-41 (August 1972) COM72-50775**

Wagner, H. L. and Verdier, P. H., eds., Standard

Reference Materials: The Characterization of Linear Polyethylene, SRM 1475, NBS Spec. Publ. 260-42 (September 1972). COM72-

50944**

Yakowitz, H., Ruff, A. W., and Michaelis, R. E., Standard Reference Materials: Preparation and Homogeneity Characterization of an Austenitic Iron-Chromium-Nickel Alloy, NBS Spec. Publ. 260-43 (November 1972). COM73-50760**

Schooley, J. F., Soulen, R. J., Jr., and Evans, G. A.,

Jr., Standard Reference Materials: Preparation and Use of Superconductive Fixed Point

Devices, SRM 767, NBS Spec. Publ. 260-44 (December 1972). COM 73-50037**

Greifer, B., Maienthal, E. J. Rains, T. C, and

Rasberry, S. D., Standard Reference Materials: Powdered Lead-Based Paint, SRM 1579, NBS

Spec. Publ. 260-45 (March 1973). COM73-

50226**

Hust, J. G., and Giarratano, P. J., Standard Refer- ence Materials: Thermal Conductivity and

Electrical Resistivity Standard Reference Materials: Austenitic Stainless Steel, SRM's 735 and

798, from 4 to 1200 k, NBS Spec. Publ. 260-46 (March 1975). SN003-003-0 1278-5 Hust, J. G., Standard Reference Materials: Electrical Resistivity of Electrolytic Iron, SRM 797, and Austenitic Stainless Steel, SRM 798, from 5 to 280 K, NBS Spec. Publ. 260-47 (February

1974). COM74-50176** Mangum, B. W., and Wise, J. A., Standard Refer- ence Materials: Description and Use of Precision Thermometers for the Clinical Laboratory,

SRM 933 and SRM 934, NBS Spec. Publ. 260-48 (May 1974). 60 cents* SN003-003-0 1278-5 Carpenter, B. S., and Reimer, G. M., Standard Reference Materials Calibrated Glass Standards for Fission Track Use, NBS Spec. Publ. 260-49 (November 1974). COM 74-5 1185

Hust, J. G., and Giarratano, P. J., Standard Refer- ence Materials: Thermal Conductivity and Electrical Resistivity Standard Reference Materials:

Electrolytic Iron, SRM's 734 and 797 from 4 to 1000 K, NBS Spec. Publ. 260-50 (June 1975). $1.00* SN003-003-0 1425-7 Mavrodineanu, R., and Baldwin, J. R., Standard

Reference Materials: Glass Filters As a Standard Reference Material for Spectrophotometry;

Selection; Preparation; Certification; Use-SRM

930, NBS Spec. Publ. 260-51 (November 1975). $1.90* SN003-003-01481-8

Hust, J. G., and Giarratano, P. J., Standard Refer- ence Materials: Thermal Conductivity and Electrical Resistivity Standard Reference Materials 730 and 799, from 4 to 3000 K, NBS Spec. Publ. 260-52 (September 1975). $1.05* SN003-003-

01464-8 Durst, R. A., Standard Reference Materials: Standardization of pH Measurements, NBS

Spec. Publ. 260-53 (December 1975, Revised). $1.05 SN003-003-01551-2

Burke, R. W., and Mavrodineanu, R. Standard

Reference Materials: Certification and Use of Acidic Potassium Dichromate Solutions as an

Ultraviolet Absorbance Standard, NBS Spec.

Publ. 260-54 (August 1977). $3.00* SN003-003-

01828-7

Ditmars, D. A., Cezairliyan, A., Ishihara, S., and

Douglas, T. B., Standard Reference Materials: Enthalpy and Heat Capacity; Molybdenum

SRM 781, from 273 to 2800 K, NBS Spec. Publ. 260-55 (September 1977). $2.20* SN003-003-

01836-8

Powell, R. L., Sparks, L. L., and Hust, J. G., Standard Reference Materials: Standard

Thermocouple Materials, Pt.67: SRM 1967, NBS

Spec. Publ. 260-56 (February 1978). $2.20* SN003-003-0 18864

Cali, J. P. and Plebanski, T., Guide to United

States Reference Materials, NBS Spec. Publ. 260-57 (February 1978). $2.20* PB 277173

Barnes, J. D., and Martin, G. M., Standard Refer- ence Materials: Polyester Film for Oxygen Gas

Transmission Measurements SRM 1470, NBS

Spec. Publ. 260-58 (June 1979) $2.00* SN003-

003-02077 Chang, T., and Kahn, A. H., Standard Reference Materials: Electron Paramagnetic Resonance

Intensity Standard; SRM 2601, NBS Spec.

Publ. 260-59 (August 1978) $2.30* SN003-

003-01975-5 vi
Velapoldi, R. A., Paule, R. C, Schaffer, R., Mandel, J., and Moody, J. R., Standard Refer- ence Materials: A Reference Method for the Determination of Sodium in Serum, NBS Spec.

Publ. 260-60 (August 1978). $3.00* SN003-003

01978-0

Verdier, P. H., and Wagner. H. L., Standard Refer- ence Materials: The Characterization of Linear Polyethylene (SRM 1482, 1483, 1484), NBS

Spec. Publ. 260-61 (December 1978). $1.70* SN003-003-02006-1

Soulen, R. J., and Dove, R. B., Standard Reference

Materials: Temperature Reference Standard

for Use Below 0.5 K (SRM 768). NBS Spec.

Publ. 260-62 (April 1979). $2.30* SN003-003-

02047-8 Velapoldi, R. A., Paule, R. C, Schaffer, R., Mandel, J., Machlan, L. A., and Gramlich, J. W., Standard Reference Materials: A Reference Method for the Determination of Potassium in Serum. NBS Spec. Publ. 260-63 (May 1979). $3.75* SN003-003-02068

Velapoldi, R. A., and Mielenz, K.. D., Standard

Reference Materials: A Fluorescence Standard

Reference Material Quinine Sulfate Dihydrate (SRM 936), NBS Spec. Publ. 260-64 (January

1980). $4.25* SN003-003-02 148-2 Marinenko, R. B., Heinrich, K. F. J., and Ruegg,

F. C, Standard Reference Materials: Micro- Homogeneity Studies of NBS Standard Reference

Materials, NBS Research Materials, and Other Related Samples, NBS Spec. Publ. 260-65

(September 1979). $3.50* SN003-003-021 14-1 Venable, W. H., Jr. and Eckerle, K. L., Standard

Reference Materials: Didymium Glass Filters for Calibrating the Wavelength Scale of Spectro- photometers (SRM 2009, 2010, 2013), NBS Spec.

Publ. 260-66 (October 1979). $3.50* SN003-003-

02127-0

Velapoldi, R. A., Paule, R. C, Schaffer, R., Mandel,

J., Murphy, T. J., and Gramlich, J. W., Standard

Reference Materials: A Reference Method for the Determination of Chloride in Serum, NBS Spec.

Publ. 260-67 (November 1979). $3.75* SN003-

003-02136-9 Mavrodineanu, R. and Baldwin, J.R., Standard

Reference Materials: Metal-On-Quartz Filters as a Standard Reference Material for Spectrophoto- metry-SRM 2031, NBS Spec. Publ. 260-68

(April 1980). $4.25* SN003-003-02 167-9

Velapoldi, R. A., Paule, R. C, Schaffer, R., Mandel, J., Machlan, L. A., Garner, E. L., and

Rains, T. C, Standard Reference Materials: A

Reference Method for the Determination of Lithium in Serum, NBS Spec. Publ. 260-69 (July)

1980). $4.25* SN003-003-02214-4 Marinenko, R. B., Biancaniello, F., Boyer, P. A., Ruff, A. W., DeRobertis, L., Standard Reference

Materials: Preparation and Characterization of an Iron-Chromium-Nickel Alloy for Microanalysis, NBS Spec. Publ. 260-70 (May 1981). $2.50* Seward, R. W. and Mavrodineanu, R., Standard

Reference Materials: Summary of the Clinical Laboratory Standards Issued by the National Bureau of Standards, NBS Spec. Publ. 260-71

(in press). Reeder, D.J., Coxon, B., Enagonio, D., Christensen,

R. G., Schaffer, R., Howell, B. F., Paule, R. C,

Mandel, J., Standard Reference Materials: SRM

900, Antiepilepsy Drug Level Assay Standard, NBS Spec. Publ. 260-72 (June 1981). $4.25*

Interrante, C. G., and Hicho, G. E., Standard Refer- ence Materials: A Standard Reference Material Containing Nominally Fifteen Percent Austenite (SRM 486), NBS Spec. Publ. 260-73 (in press).

* Send order with remittance to Superintendent

of Documents, US Government Printing Office, Washington, DC 20402. Remittance from

foreign countries should include an additional one-fourth of the purchase price for postage. ** May be ordered from: National Technical Information Services (NTIS). Springfield,

Virginia 22151.

vii
TABLE OF CONTENTS

Page ABSTRACT 1 INTRODUCTION 2 GENERAL DESCRIPTION OF SRM 3 PREPARATION OF THE COMPACTS k PREFERRED ORIENTATION 11 CHARACTERIZATION OF SRM U86 12 COMPARISON OF DIFFRACTION AND FLUORESCENCE RESULTS 22 CONCLUSIONS 25 ACKNOWLEDGMENTS 25 REFERENCES 25

LIST OF TABLES Page

1. Chemical Analysis of Stainless Steel Powder Particles h 2. Comparison of X-Ray Diffraction and X-ray Fluorescence

Measurements of Austenite Content for Six Specimens 23

LIST OF FIGURES

Page

1. Scanning electron micrographs of the powders 5 2. Fabrication and inspection of powder compacts 7

3. Appearance of as- polished compacts 10

h. Characterization procedures for SRM hQ6 13

5. Structure of etched compacts 17

6. Two compacts, as etched with modified Grosheck's reagent... 18

7. Calibration curve showing percent austenite by volume as a function of nickel-K counts 20

a

8. Histogram showing frequency of occurrence vs. austenite

content, for l62 certified copies 21

viii
A Standard Reference Material Containing

Nominally Fifteen Percent Austenite (SRM 486)

C. G. Interrante and G. E. Hicho Fracture and Deformation Division

Center for Materials Sciences

National Measurement Laboratory

National Bureau of Standards

Washington, D.C. 2023^

ABSTRACT

This Standard Reference Material, SRM-i+86, is intended for the calibration of x-ray diffraction equipment used in determining the

amount of retained austenite in ferrous materials. It was produced

using powder metallurgical techniques and known amounts of type 310 stainless steel powder (austenitic) and type ^-30 stainless steel powder (ferritic) to make a blend of 15 percent by weight (ih.'J percent by volume) austenite in ferrite. From a larger blend of these powders, powder for 17^- compacts was taken. Using 12 of these

compacts, a calibration curve was established for the certification

of the remaining compacts. The curve relates the nickel x-ray count rate of x-ray fluorescence measurements to the volume percentage of austenite as determined by quantitative microscopy measurements of area percentage. The austenite content of this SRM can be related

directly to the nickel count rate, because the nickel content of the austenitic powder (20.9 weight percent) is many times that of the ferritic powder (0.10 weight percent). The mean percentage austenite

for 162 certified standards is 1^.7 volume percent; this value exactly

equals the volume percentage of austenite powder in the original

blend. X-ray diffraction determinations of the austenite content are

in good agreement with the certified content of austenite. The SRM may be used as an x-ray diffraction standard for austenite or, in special cases, as an x-ray fluorescence standard for nickel content.

Keywords: Austenite in ferrite; austenite standard; electron

microprobe; powder metallurgy; quantitative microscopy; Standard Reference Material; x-ray diffraction; x-ray fluorescence analysis.

1
INTRODUCTION

This Standard Reference Material has been produced to provide a means for calibration of x-ray diffraction equipment. Standard

Reference Materials that contain known proportions of austenite in ferrite are required to assess the experimental and computational

techniques that are used in x-ray measurements of the austenite

content of ferrous materials. The austenite is present in ferritic

steels because it is sometimes retained in martensite that forms after quenching from the austenitic region. The amount of this retained

austenite can critically affect properties, fabricability, or service

performance. Thus, sometimes it is necessary to quantitatively

establish the austenite content. Measurements of the percentage

austenite in ferrous materials are made using a series of x-ray diffraction lines using a complex process that requires judgment in the application of correction factors for the effects of various

material factors and instrumental parameters. Thus, an austenite

determination is not made from first principles alone, and this Standard Reference Material can be a useful aid in the determination.

In a reference material used for these measurements, it is desired to have reasonable homogeneity and a minimum of metallurgical

confoundments, such as residual stress, preferred orientation, large

grain size, and twinning. To meet these requirements, the National

Bureau of Standards is in the process of producing a series of Standard

Reference Materials (.SRM's) containing various percentages of austenite

in ferrite. The first of these SRM's was issued in July of 1970 as SRM 1+85; it contained a nominal k percent austenite [l]. Both SRM 1+85 and the current issue, SRM 1+86, which contains a nominal 15 percent

austenite, were prepared by means of powder metallurgical methods.

The purpose of this report is to describe the methods used in the certification of the austenite content of the surface of each of 162 compacts prepared for use as SRM 1+86. For each compact, a separate

characterization of austenite content is required, because complete

homogeneous blending (of the austenite and ferrite powders used to make the compacts) cannot be achieved to the degree required for this

SRM. For this same reason, the certified value of each compact is valid only for the certified surface.

2
GENERAL DESCRIPTION OF SRM

This SRM contains two structurally different constituents that are highly stahle and require substantial changes in chemical composition

to affect a transformation of the structure. The constituents are a fully austenitic type 310 stainless steel powder (austenite) and a fully ferritic type U30 stainless steel powder (ferrite). The austenite

contains large amounts of nickel and chromium that render it austenitic,

even at nickel concentrations significantly below the 20 percent level

of the nominal composition for type 310 stainless steel. The ferrite

contains large amounts of chromium, hut almost no nickel. Much larger

concentrations of nickel would he required for this composition to become austenitic at room temperature. Hence, significant amounts of nickel diffusion could occur, during annealing or sintering of powder

compactions of these two constituents, without causing any significant

amount of transformation to alter the structure of either constituent.

This SRM was prepared from a blend of the austenite and ferrite

powders. The powders were compacted by various pressing and annealing

treatments. The compacts are 21 mm (0.83 in.) in diameter with a 2.h mm (0.09^+ in.) thickness. One surface is polished, and this surface

has been characterized with respect to austenite content. The lowest actual percentage austenite in the certified faces of these unetched

SRM's is 13.^ percent, and the highest value is l6.9 percent 1

. The mean for l62 SRM's prepared is ih.J volume percent. These compacts were taken from a larger blend of the powders that contained lh .

7

volume percent (.15.00 weight percent) austenite.

Care should be taken to avoid alterations of, or damage to, the certified surface. Research conducted on methods for preparation of this SRM has shown that alterations of the surface can render the SRM

useless, as for example: (l) Etching procedures have been shown to increase the nickel counts in x-ray fluorescence measurements by as much as 12 percent of the amount present; and (2) metal removal by

grinding was shown to change the austenite content of the surface by

as much as 5 percent of the amount present.

In the above "grinding" example, a controlled experiment was conducted on 23 compacts, using quantitative microscopy (QM) methods

to assess the austenite content. Metal was systematically removed

from the characterized surfaces of each of the 23 compacts. This was accomplished by hand-grinding and polishing to uniformly remove a

1 The SRM's with certified values outside of the range 13.8 to l6.2 were retained for use in research at NBS.
layer of only 0.08 mm (0.003 in.) of metal. Each compact was then characterized again. The resulting change in the austenite content

for a single compact ranged from -k to +5 percent of the amount present (-0.6 to +0.8 percent austenite). The mean change in austenite

content for the 23 compacts, after removal of this small amount of

metal, differed by only 0.05 percent austenite (final mean less original mean). However, the above noted changes observed in individual

compacts are significant—these changes are due to inhomogeneities

in the austenite powder compacts. The measured change in austenite

content for the 23 compacts has a standard deviation of 0.1+0 percent

austenite, which equals 2.7 percent of the average amount present. These values are significantly greater than estimates of the precision

based on duplicate measurements: 0.U5 percent relative ( 0.067 percent

austenite). Thus, the certified value does not apply if the certified

surface has been altered or damaged.

PREPARATION OF THE COMPACTS

The austenite and ferrite used to produce the compacts are stainless steel powders produced by water atomization. As shown in Fig. 1, the powders are irregularly shaped and uniformly sized. The figure gives scanning electron micrographs of each type of powder.

Figs, la and lb, respectively, represent the type 310 and 1+30 stainless

steel powders, taken at a magnification of l60X, that were used to make

the compacts.

Preliminary sizing was done by the producer of the powders and

final sizing was done with sieves at NBS. The austenitic powder was passed through a 270 mesh screen and was retained on a 325 mesh

screen. This sieving furnished particles in the size range of from

53 to kk micrometers. Similarly the ferritic powders were sized (-325 to +k00 mesh) to furnish particles of kk to 37 micrometers. The chemical analysis of the powders is given in Table 1. Table 1. Chemical Analysis of Stainless Steel Powder Particles (content

in weight percent). Elements 310 Stainless Steel 1+30 Stainless

Chromium 25.^3 16.19

Nickel 20.91 0.10

Iron bal bal

Carbon 0.03 0.0*+ Manganese .11* .0k Phosphorus .010 .00k Sulfur .006 .006 Silicon .98 • 53 Molybdenum .02 .02 Copper .0U .02

k

Each step in the preparation of the compacts is shown in a flow diagram given as Fig. 2. Initially 11

.

k kg (25 pounds) of the powders were mixed in proportions representing 15.00 percent by weight austenite

and the balance ferrite. Fifteen percent austenite by weight was determined to be equivalent

to 14.7 percent by volume. This determination was made using measurements of the densities of the starting materials. The density of

the austenite and that of the ferrite were measured picnometrically

,

after compacts of the 310 and the 430 powders were separately melted

(into buttons) and rolled. Average densities from measurements

taken on three buttons of each alloy were 7.804 g.cm-3 for the austenite and 7.643 g.cm

-3 for the ferrite. Thus, the original

blend of powder from which the compacts were taken is a blend

calculated to contain l4.7 volume percent austenite in ferrite. The mixture of 11 kg (25 lb) of the sized powders was blended

in a 4-quart "V" blender for a total of 12 hours. This total blending

time was accumulated over a much longer period, during which various

samples were taken from the blend for research purposes. The remaining

blend of 4.95 kg (10.9 lb) of powder was given a final blending for

8 minutes in a 1 1/2- quart twin- shell blender with intensifier pin

bars. This amount of powder is optimal for this size blender. This blend was placed in 12 jars. Four jars of this blend were randomly

selected for use in pressing a total of 249 compacts for use in the production of SRM 486. However, only 174 of the compacts were actually

used to produce SRM 486. The balance had been rejected (mostly for inhomogeneity or physical damage) during preparation and characterization of the compacts. The remaining blended powder, which was contained in the other eight jars, was pressed into compacts and prepared up to, but not including, the final annealing treatment. These compacts will be held in this condition until the demand for this SRM warrants the preparation of additional certified compacts.

Prior to pressing the blended metal powders into compacts, the powders in the jars were made wet with ethyl alcohol, a volatile

substance that could be baked out without leaving a residue. This was done to prevent segregation of the powders, on standing, on handling, and on sampling for pressing.

The compacts were pressed and vacuum-heat-treated. This was

done in three stages as shown in Fig. 2. Each heat treatment was conducted for 30 minutes at a temperature of 843 ±lU °C (1550 ±25 °F)

.

These vacuum-heat-treatment cycles duplicate the temperatures and hold times of hydrogen heat treatments used earlier [l] in the preparation of SRM 485. The temperatures and times used for heat treatment of compacts for SRM 486 were chosen after considerable

effort was directed towards an alternative treatment that involved

either higher temperatures, or longer times at temperature. An alternative heat treatment was sought in an attempt to enhance the bonding between the constituents, and thereby to minimize the likelihood

that the compacted particles would be removed from the surface of

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7
the compact during grinding. In the end, these alternatives vere

each found to produce levels of nickel diffusion, from the austenite

into the ferrite, that might be sufficiently high to alter the austenite content of this SRM. The alternative heat-treatment cycles were rejected after

studies conducted with the electron probe microanalyzer showed that:

(l) when the time of each of the three heat-treatment cycles was increased from 30 to 50 minutes and the temgerature of only one of these cycles was increased to 871 C (l600 F), diffusion of nickel

from the austenite was observed to occur at distances of up to 12 micrometers beyond a boundary between particles of austenite and

ferrite; and (2) when only the time of each of the three heat- treatment cycles was increased from 30 to 50 minutes, and the temperature

was maintained at that used in the earlier work (8U3 C), diffusion

of nickel was observed to occur at distances of up to 6 micrometers

into the ferrite. Thus, with these alternative heat treatments, a nickel diffusion zone of 6 to 12 micrometers could be expected.

In compacts treated using the alternative cycles, the nickel

content of the ferrite was only moderately affected over a great

majority of the diffusion zone. Nevertheless, for the preparation

of SRM h&6, it was decided to heat treat at the lower levels of these heat-treatment parameters. Thus, the treatments used are the

ones found earlier [l] to give practically no measurable diffusion

of nickel, within the limits dictated by the spacial resolution

(3 micrometers) of the x-ray signal from the microprobe. Instead,

grinding operations, which are done to render the surfaces flat,

would all be done by hand to minimize the tendency toward mechanical

pull out of particles of either constituent. This was considered to be more acceptable than the use of an alternative heat treatment. After the three cycles of compaction and heat treatment, compacts were hand ground on wet silicon carbide (SiC) papers, polished on

felt using 1-micron diamond paste and a mineral oil lubricant, and etched with Murakami's reagent, using the following technique: The compacts are pre-heated at 130 C (265 F) in an oven for 20 minutes.

Immediately upon removal from the oven, they are etched with Murakami's

reagent. Composition of the reagent is 10 grams potassium hydroxide

(K0H), 10 grams potassium ferricyanide (K 3 Fe(CN) 6 ), and 100 mL distilled water (H 2 0). The reagent is heated to a temperature in the range between 90 and 100 °C (19^ to 212 °F ) . Compacts are removed from the oven individually and swabbed for 2 minutes with

the hot etch. This procedure does not chemically remove very much metal from

the polished surface of these compacts. The purpose of the etch is to slightly darken the ferritic phase while leaving the austenitic

phase unaffected, so that the austenite particles and their distribution

in the ferrite can be inspected optically on the polished and etched

surface.

8
The inspection was performed by two observers, with the intention

of eliminating compacts that contain any gross inhomogeneities in the surfaces that were to be certified. Any compact that showed a blemish

discernible to either observer, such as a large swirl or any area richer or leaner (in austenite) than its neighborhood, was reprepared. A minimum of 0.025 mm (.001 in. ) was mechanically removed from the

surface, starting with hOO grit SiC paper. Reprepared compacts were

then reinspected. Only those that passed an inspection were further

characterized. In this way, gross inhomogeneities in the distribution

of austenite over the surface that was to be calibrated were effectively

eliminated. After three or four repetitions of this optical inspection

procedure, compacts that did not pass inspection were permanently

rejected for use as an SRM. All compacts that passed the optical inspection were polished

before being further characterized. Polishing was accomplished with

1-micron diamond on felt with a mineral oil lubricant. This polishing

treatment was established as being sufficient to remove all irregularities introduced by the Murakami's etching treatment. For example,

porosity was observed to increase slightly by this etchant , and this polishing treatment restored porosity of the surface to its original value

.

2 The appearance of the as-polished compact is shown in Fig. 3. The optical micrograph of Fig. 3a shows the porosity in a region

representative of the bulk of the compact. Porosity is greater near

the periphery of the compact. The 1-micron diamond polish leaves the

edges of the pores well delineated for QM determinations of porosity

level. In Fig. 3b, the appearance under the scanning electron microscope (.SEM) is shown for a porous region of the surface. In SEM

observations, the porosity appeared like that which would be expected

from incomplete compaction and no evidence of pull out of particles

was observed.

Weeping of this reagent Cor of reaction products) may occur, particularly if the SRM becomes wet; this will stain the certified

surface of SRM hg6. This will not affect the accuracy of the SRM. The original unmarred, polished appearance may be restored, without

adversely affecting the SRM, by wiping the surface with sterile absorbent cotton dampened with ethyl alcohol or zylene.

9
Figure 3. Appearance of as-polished compacts, a. Optical micrograph

showing porosity as it would he detected "by the QM. Magnification: hox. h. Scanning electron micrograph

showing pores, hut no evidence of powder pull out from

grinding. Magnification: 1600X.

10
PREFERRED ORIENTATION

In a material to be used as a reference standard for measurements

of retained austenite in steels, it is desirable to have reasonably good

homogeneity and a minimum of metallurgical confoundments , such as residual stress, large grain size, twinning, and preferred orientation. Each of these factors was considered in the selection of materials and methods of preparation for this SRM. Six specimen compacts taken from

the lot were used to determine whether the thermal and mechanical

treatments that were used to prepare the compacts had resulted in an undesirable texture. X-ray diffraction measurements were made using

filtered iron radiation. The 110 peak of the alpha phase was monitored

during the angular change. In addition, specimen oscillations of 5 mm

in its plane (at 67.5 cycles per minute) were used to average grain size

effects. These measurements indicated that for five of the six specimens,

the observed variations in intensity were consistent with that expected

from graininess and not from preferred orientation of cryst allograph!

c

planes. For the sixth specimen, the observed variations were slightly

greater than those for the other five, but here too the level of variation

was considered to be within acceptable limits for purposes of this SRM. Further, the results of measurements (discussed later) of the austenite

content from integrated intensities of diffraction lines indicated no significant texture. The austenite content, as measured from various

pairs of lines, varied within expected limits. Somehow for the sixth specimen mentioned above, this variation was smaller than that observed

for any of the other five specimens. It is concluded that any preferred

orientation that may exist in these compacts is not sufficient to significantly affect the austenite content as measured using the recom- mended procedures.

11
CHARACTERIZATION OF SRM 486 The austenite content of this SRM can be related directly to the nickel content, because the nickel content of the austenite (20.9% Ni by wt.) is many times that of the ferrite (0.10$ Ni by wt.). As very

precise measurements of the nickel-K count rate in x-ray fluorescence

(XRF) analyses are possible, this count rate was used to establish

the percentage austenite in this SRM. A calibration curve that relates the volume percentage austenite to the nickel-K count rate

was developed. The percentage austenite was determinedaoptically

,

using quantitative (television) microscopy (QM), for 12 specially

prepared specimens that were statistically selected from the lot of compacts produced for this SRM. The special (etch/stain) preparations

used to obtain the QM percentage austenite on these 12 specimens

substantially increases the nickel count rate of x-ray fluorescence

measurements. Therefore, the calibration curve was established for specimens in the unetched condition, and this SRM is issued in the unetched condition.

The increase in the count rate that occurs on etching can be explained as follows: The etchant reacts with the ferrite at a much

greater rate than with the austenite. Hence, the austenite particles

stand slightly in relief of the ferrite on the etched surface. This relief interferes with the normal x-ray absorption processes. Those

parts of the austenite particles that stand in relief are in the paths of incident, diffracted, and fluorescent radiation to and from

the ferrite crystals, and those parts of the ferrite particles that have been etched away no longer occupy positions at which they would

have absorbed the radiation to and from the austenite crystals that

stand in relief. As a result, the measured diffracted energy from

the austenite is intensified. The measured fluorescent radiation

from nickel is also intensified, as the nickel content of the austenite

is many times greater than that of the ferrite.

The optical percentage of austenite on this same surface is not significantly affected by this etching procedure. As the ferrite is attacked, a thin layer of dark brown reaction products forms wherever

the ferrite had been. On the surface of the compact, these products

surround the austenite particles and have a detectably different gray

level when compared with that of the austenite. The gray level difference is sufficient so that CM procedures can be used to distinguish the austenite from the ferrite. In the relatively unaffected,

nearly white austenite, some pitting occurs, but pits that are contained

totally within an austenite particle are counted by the CM procedures

as though they were "white" austenite. Thus, the etchant increases

the x-ray responses of the austenite, but the optical QM response is not significantly affected by the etchant. Procedures used to certify the percentage austenite in each of l62 compacts are outlined in a flow diagram given as Fig. k. Each of 17U compacts that passed the optical inspection described earlier were

12
FABRICATION AND

INSPECTION OF COMPACTS

PRELIMINARY X-RAY FLUORESCENCE ANALYSIS

174 COMPACTS RANKED BY

NiKa COUNTS

12 SPECIMENS 162 COMPACTS

ASSESS TEXTURE BY X-RAY DIFFRACTION TECHNIQUES

(6 SPECIMENS ).

X-RAY FLUORESCENCE

ANALYSES

MEASURE % AUSTENITE

BY X-RAY DIFFRACTION METHODS (6 SPECIMENS). MEASURE POROSITY

BY QM METHODS.

X-RAY FLUORESCENCE

ANALYSIS

ETCH: MODIFIED GROSBECK'S REAGENT MEASURE OPTICAL PERCENT AUSTENITE

BY QM METHODS.

CORRECT FOR POROSITY .

FURNISH CALIBRATION

CURVE: NICKELKa COUNTS VS. PERCENT AUSTENITE.

ASSIGN COMPUTED

PERCENT AUSTENITE TO 162 COMPACTS.

147 COMPACTS

15 COMPACTS

FOR USE IN RESEARCH ATNBS

CERTIFIED STANDARD REFERENCE MATERIALS

COMPARE X-RAY

DIFFRACTION RESULTS WITH CERTIFIED PERCENT AUSTENITE.

12 SPECIMENS

RETAINED AT NBS

Figure 4. Characterization procedures for SRM-486.

13
ranked by nickel content using a preliminary XRF analysis of significantly lower precision than that which was used in final analyses. From this ranked set of unetched compacts, a group of 12 specimens

were statistically selected for use in the establishment of a calibration curve that relates nickel-K count rate to austenite content for specimens in the unetched condition.

Six of 12 specimens were examined for preferred orientation and austenite content, using x-ray diffraction (XRD) methods. Then, for all 12 specimens 3

, duplicate porosity measurements were made using QM

methods, and additional XRF measurements of nickel count rate were

taken. The additional XRF measurements were used to more precisely

characterize the nickel content of the 12 specimens before they were

etched for use in establishing a calibration curve. The QM porosity

content of each sample was used to individually correct the QM

determination of austenite content, as discussed later. The XRD determinations of austenite content are compared later with their

certified austenite contents, as determined by XRF measurements. The certified content is obtained from a relationship between unetched

nickel-K counts and QM austenite content. This relationship is referred to as the calibration curve. The calibration curve was established using the results of the quantitative microscopy (QM) measurements of austenite content and porosity content. Duplicate QM determinations were made, with the second set of measurements being taken after a 90 rotation in the plane of the specimen. The QM techniques were specifically perfected

for the characterization of this SRM, with considerable research

efforts being directed at the problem. As a result, these QM measurements are believed to be very precise and highly accurate. The precision is reflected by the relative standard deviation, as pooled

for duplicate measurements. Based on duplicate measurements of porosity on 12 specimens, this pooled value is 15- T percent relative

(or 0.U6 percent absolute). Based on duplicate measurements of the austenite content on 12 specimens, this pooled value is O.i+5 percent

relative (0.067 percent austenite). The accuracy of these measurements

For 2 of these 12 compacts, the percent porosity could not be determined by the QM method. This method rejects a specimen if the "threshold," which is determined for various randomly chosen sites

on the specimen, varies beyond prescribed limits. When this rejection occurred, two additional samples were taken from the remainder of the ranked set of 17*+ compacts (see Fig. h) . These two

compacts were used to complete the set of 12 specimens to be etched

for use in the establishment of a calibration curve. The two rejected compacts are two on which preferred orientation and austenite content measurements had been performed by XRD methods and they are 2 of 15 compacts retained for use in research at NBS

(Fig. k) . This substitution is a detail, which (for simplicity of presentation) is not given in the flow diagram of Fig. h. Ik
has been verified in several ways. The most cogent verification is the agreement between the mean of the austenite content (l^.T percent

by volume) of the l62 certified compacts and the computed nominal

austenite content of 1^.7 percent by volume of the original blend of powders from which these compacts were taken. The results of porosity measurements made on the 12 specimens used to establish the calibration curve can be considered to typify

the porosity of the lot of certified compacts because the specimens were statistically selected to represent the entire lot. These

results indicate that the porosity for these 12 specimens is 2.93 ±0.98 percent. A single QM determination is a result of measurements taken over

500 fields that represent the central 90 percent of the area of the surface of the specimen. Other measurements taken on fields near the periphery of the specimen (the outer 10 percent of the surface area) could not be used in the determination because their proximity to the periphery of the specimen confounded the measured value. This unavoidable selectivity, in the fields that are counted, results in a determination that is characteristic of the central 90 percent of the specimen surface. For measurements of the austenite content, the number obtained by this procedure adequately represents the entire

specimen because the austenite distribution over the entire surface

is relatively uniform, with no systematic bias being observed from

the center to the periphery of the specimen surface. For measurements

of the porosity content, the number is biased on the low side because the outer parts of these compacts are more porous than the central parts, due to the method of compaction. Even this biased

measurement of porosity is considered to be an adequate estimate of the porosity of the specimen because only 10 percent of the surface

is unexamined and because a large bias would be needed to significantly

affect the final result—porosity is used in a correction factor, which

is explained later. For example, a very large error of 1 percent

absolute in the porosity estimate of a specimen would yield an error of

less than 0.2 percent absolute in the determination of the final

austenite content of that specimen.

The results of XRF analyses were based on a minimum of six determinations of nickel-K count rate for each of the 12 specimens used for the calibration curve. A minimum of three determinations

were analyzed for the other l62 compacts. Standards were rerun after

5 to 20 determinations, depending upon the rate of drift of the XRF

unit. Drift corrections were made whenever the count rate exceeded predetermined drift limits. In addition, in a computer analysis of the data, the raw data for each set of measurements was drift corrected

and normalized, using an internal standard having a predetermined mean

value (107,U50 counts). The operating conditions were:

15
X-ray tube Platinum

LiF . 39 kV

3^ ma

Pulse height discriminator at 165O volts

Fine Coarse l/k, fine 1 30 s in air.

Crystal

Voltage

Current Detector Collimator

Gain

Count While the compact was spinning, the primary x-ray beam irradiated

nearly the entire face of the compact, except for a narrow band (near the circumference) that was blocked out by the holder (fixture). The average of three or more determinations of nickel-K counts computed for every compact in the certified lot is within the range 0.87 x 10 5 to 1.1 x 10 5 counts. The standard deviation among these normalized

determinations for a given compact is always less than 7^0 counts and

is typically hOO nickel-K^ counts (0.07 percent austenite).

The 12 specimens selected for use in the calibration curve were

etched with a modification of Grosbeck's reagent, which was used to prepare the surfaces of these specimens for QM measurements of the austenite content. The composition of the reagent is 150 grams potassium permanganate, 150 grams sodium hydroxide, and 500 mL

distilled water. The reagent is brought to a boil, and specimens are immersed in the boiling reagent. The number of specimens immersed at one time is held constant, at five, so that the potency of the solution

is uniformly high for every specimen. Previously rejected compacts were used to maintain five compacts in the bath, as needed to meet

this requirement. The total time of immersion for each compact is 20 minutes. To maintain potency throughout the etching period, a fresh

solution is prepared after it has been in use for only 15 minutes.

Therefore, two solutions are prepared for each set of five specimens.

The appearance of the etched specimen is shown in Fig. 5, which

presents two micrographs. The optical micrograph of Fig. 5a shows the austenite as a nearly white phase surrounded by a matrix of dark gray—actually a deep reddish brown—ferrite. The sharp difference

in contrast between the two phases in this etched condition permits

accurate QM determinations of the optical percent austenite. The scanning electron micrograph (Fig. 5b) shows that sharp delineation

exists between the large austenite particles and the ferrite matrix

of smaller ferrite particles.

The degree of uniformity in the distribution of austenite is shown in Fig. 6. Two compacts in the etched condition are shown at about three times actual size. While small local areas may appear

sparse or rich in austenite content, the distribution of austenite

over an entire surface is relatively uniform.

16
Figure 5- Structure of etched compacts. a. Optical micrographs

showing austenite (.white) and ferrite (black). Magnification: hOX. b. Scanning electron micrograph showing sharp

delineation between large austenite particles and ferritic

matrix. Magnification: 800X.

IT
Figure 6. Two compacts, as etched with modified

Grosheck's reagent.

Magnification: 3X

18
The volume percent austenite was determined from the results of QM measurements of the area fraction of "white" austenite on the surface of each of the etched calibration specimens. To obtain the area (volume) percent austenite for each of the specimens, the optical

percentage of the white area is divided "by a porosity correction factor,

which was determined separately for each of the 12 calibration specimens.

The correction factor represents the area fraction of pore-free surface,

i.e. (100 -percent porosity ) /100

.

In earlier research [l] conducted to establish a calibration curve

for the certification of SRM U85, it was found that the relationship

between nickel-K count rate and the percent austenite over the range of from 0 to 30 percent is of the second order, and over the range of from

10 to 30 percent, it is nearly linear. Preliminary analyses of data for the 12 calibration specimens for SRM hQ6 suggested that the data are linear and extend over a relatively narrow range of 13 A to l6.9 percent

austenite. Therefore, a linear fit was used to describe the portion of the calibration curve that is represented by the compacts certified for SRM h86. The results of a linear regression analysis of the data for

12 calibration compacts are presented as Fig. 7. The QM measurements of volume percent austenite are fitted to the XRF measurements of nickel-K

counts. The equation of the least-squares-fitted line is: Vol. % Austenite = 1.755 x

10~ 4 C - 1.976 where C represents nickel-K counts taken under conditions stated

, . a earlier. Using this relationship and the normalized results of nickel-K^

counts taken on l62 unetched compacts, the certified percentage

austenite was computed for each compact. The distribution of the austenite contents for the l62 compacts is given in a histogram

presented as Fig. 8, which shows the frequency of occurrence for 20 austenite-content cells. The certified values (percent) vary from

13. h to 16.9, with a mean of ih.J and a sample standard deviation of 0.60 for the 162 observations. The standard error of the mean is 0.05 percent austenite. A total of 15 of these 162 compacts are being retained at the NBS for the development of additional reference materials

.

It is recognized that a significant random error in the certified

austenite content of any given sample is introduced due to variability of porosity in the 162 certified samples. Because

this error is believed to be within ±0.2 percent austenite, the porosity level was not measured on each of the l62 certified

SRM's.

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21
COMPARISON OF DIFFRACTION AND FLUORESCENCE RESULTS

Results of x-ray diffraction measurements of the percentage austenite are shown here to he in generally good agreement with the certified

values. The six specimens used in the XRD measurements for preferred

orientation, described earlier, are also used here. For this comparison,

XRD and XRF measurements were conducted with the specimens in the as- polished condition, i.e. before the modified Grosbeck's reagent was applied for QM measurements.

The XRD measurements of austenite content were conducted using

methods and recommendations described in NBS TN 709 12], which recommends

that the surface to be analyzed shall be rotated in its plane. The operating conditions were X-ray tube - chromium

Voltage - kO kV

Current - 30 mA

Scan rate, 20 - 1/8 degree/minute

Monochromator - curved oriented graphite

Counting interval - 20 s Divergence slit - 1 or k degrees.

The percentage austenite was computed for each specimen, using measurements taken on three planes (111, 200 and 220) for both the alpha

(ferrite) phase and the gamma (austenite) phase. In Table 2, a summary

of these results is given under the heading XRD. Under the heading CV are results of XRF measurements. These values were computed from the regression result of the calibration curve using

the normalized nickel-K counts taken on each specimen in the unetched

condition. The abbreviation CV for certified value is used to represent

these results. This is done to acknowledge that the indicated value is the certified value that could have been assigned to the specimen had it not been altered by the etchant used to prepare it for QM measurements.

The table shows that the differences (XRD-CV) range from +0.k to

-1.3 percent austenite (+3 to -8 percent relative), with a mean of -0.21 percent austenite, and the data suggest that systematic bias might

exist. At larger values of CV, the difference tends to be more negative.

Although it is not shown in the table, the standard deviation for an XRD measurement is of the order of 0.5 percent austenite. Further, it is noted that the austenite (certified) content from fluorescence measurements

(CV) is believed to be accurate within ±0.5 percent. Thus, the differences in the table all appear to be within expected limits, except for the specimen with a difference of -1.3 percent austenite.

22
Table 2 - Comparison of X-Ray Diffraction and X-Ray Fluorescence

Measurements of Austenite Content for Six Specimens

Austenite Content

(volume percent) CV XRD

Difference Absolute Relative

XRD-CV XRD-CV

CV

13.68

lU.62

lU.89

lh.96

15.92

16.38

Ik. 00 15.03 lh.96

ih.kQ

15.62 15.12

0.32

a. hi 0.07

o.i+8 -0.30 1.26

0.023

0.028

0.005 -0.032

-0.019

-0.0TT

Average 15. Std. Dev. —

1^.87 0.21

-.62

-0.012 +0.039

CV = certified value

For this specimen, the XRD measurement appears to he unexpectedly

low. Of course, this was not known at the time that the XRD measurements were taken, as the austenite (certified) contents of these samples were not known until after they had been etched and the calibration

curve had been established. Further, the XRD measurements were made

without a Standard Reference Material for use in the optimization of experimental and computational techniques used in these determinations.

With these considerations in mind, the agreement between the XRF and XRD measurements is believed to be generally good. It is also noted that without the value (XRD-CV) of -1.3, the data set would have an average difference of nearly zero, instead of the suggested biased average of -0.21 percent austenite (-1.2 percent relative).

23
On the question of the accuracy of the certified value, several

factors are considered here on the precision and possible sources of bias in measurements for the certification of this SRM. The CV for each compact is obtained from the calibration curve (which has a residual

standard deviation of s =0.35) using XRF measurements; a minimum

of three determinations^of the nickel-K count rate is taken. Typically, the standard deviation among these determinations is ±^00 counts or 0.07 percent austenite. These XRF measurements are considered to be without significant bias, and their precision is sufficiently high so that the total precision of the certified value

is due almost entirely to the precision of the quantitative microscope

measurements of austenite content. The precision with which a future data point can be added to this curve is ±0.87% austenite, at the 95% confidence level. Some possible sources of bias were found not to be significant. These include bias in the QM determinations themselves, which would

tend to make the mean for all calibrated compacts different from, the

l4.7 percent austenite that was actually computed; this number exactly

equals the value expected from the weights of the powders that were blended to make this standard. Further, the available data indicates

no bias due to the use of etched specimens for calibration of unetched

specimens. In addition, it is noted that the porosity of the calibrated surface is different for each compact. By our choice of specimens for the calibration curve, this introduces an error that is considered to be unbiased and random^; in essence, the mean porosity of the 12 calibration specimens is the assumed porosity for each compact.

Thus, in the absence of known bias, the accuracy of the certified

value is estimated 5 from the precision with which the mean value of a point on the calibration curve is known, at the 95 percent confidence

level. These uncertainties are larger near the extremes of the curve than near the mean value of ih.'J percent austenite, but should not exceed ±0.5 percent austenite.

5 This accuracy is computed from data for the 12 calibration-curve

specimens using the expressions [3j

(t ) s [- +

a y n

2

(x 1/2 W

o

•1

(2.18) (0.35) [ri 1/2 ¥ +

E (C.-C)

2

2h
CONCLUSIONS

SRM hS6 is satisfactory for issuance as a Standard Reference

Material for x-ray diffraction determinations of retained austenite.

The percent austenite for the l62 certified compacts is within the range

of 13.^ to l6.9 percent by volume. The mean austenite content for the

l62 certified compacts is Ik. 7 volume percent, a value that exactly

equals the computed volume percent of the blend from which powders were

taken to produce this SRM. In special cases, SRM kti6 also may be useful

as an x-ray fluorescence standard for determining the nickel content in nickel-iron or nickel-iron-chromium alloys. In using SRM U86, care must

be taken not to alter the certified face, and rotation of the SRM is highly recommended to minimize the effects of inhomogeneities in the distribution of austenite on the certified face of the SRM.

ACKNOWLEDGMENTS

Over a period of 8 years, the authors conducted research to develop the method that was used to produce this SRM. In that span of

time, many have contributed to this work. Messrs. D. E. Harne and

C. H. Brady have diligently applied their skills as technician and metallographer, respectively. Messrs. R. Frace, R. Dotter and R. Heid

of the Patterson-Kelley Company, Inc. did the final blending of the powders in their laboratory in East Stroudsburg, PA. Dr. J. J. Filliben

has spent many hours developing computer routines and counseling the authors on statistical problems. Mr. C. J. Bechtold and Dr. W. Ruff

have assisted greatly through their measurements and counsel on x-ray diffraction measurements. Dr. George A. Moore assisted in development

of methods used for the quantitative television microscopy measurements.

Dr. P. A. Pella, Dr. K. F. Heinrich, and Ms. M. Darr conducted the x-ray

fluorescence measurements. Mr. S. R. Low handled some of the computational tasks. Finally, Dr. E. Passaglia, over many years, was patient

as a Division Chief, offered astute technical advice, and frequently

gave his time to problem solving. REFERENCES

[l] Hicho, G.E.; Yakowitz, H. ; Rasberry, S.D.; and Michaelis, R.E.; A standard reference material containing nominally four percent

austenite. Spec. Publ. 260-25; 1971 February, Ih p.

[2] Bechtold, C.J., An x-ray diffraction method for determining the amount of austenite in an austenite-ferrite mixture. Tech. Note 709; 1972 February, lk p. [3] Walpole, R.E. ; Myers, R.H. Probability and statistics for engineers

and scientists (2 ed) MacMillan Publishing Co., Inc.; 1978. p. 292.

25
NBS-114A (REV. 2-8C

U.S. DEPT. OF COMM. 1. PUBLICATION OR 2. Performing Organ. Report No. 3. Publication Date BIBLIOGRAPHIC DATA REPORT NO. January 1982 SHEET (See instructions) NBS SP 260-73

4. TITLE AND SUBTITLE Standard Reference Materials: A Standard Reference Material Containing Nominally Fifteen Percent Austenite (SRM 486)

5. AUTHOR(S)

C. G. Interrante and G. E. Hicho

6. PERFORMING ORGANIZATION (If joint or other than NBS. see instructions) NATIONAL BUREAU OF STANDARDS DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

7. Contract/Grant No..

8. Type of Report & Period Covered Final

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

10. SUPPLEMENTARY NOTES Library of Congress Catalog Card Number: 81-600173

Document 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 si gnificant bibliography or literature survey, mention it here) This Standard Reference Material, SRM-486, is intended for the calibration of x-ray diffraction equipment used in determining the amount of retained austenite in ferrous materials. It was produced using powder metallurgical techniques and known

amounts of type 310 stainless steel powder (austenitic) and type 430 stainless steel powder (ferritic) to make a blend of 15 percent by weight (14.7 percent by volume) austenite in ferrite. From a larger blend of these powders, powder for 174 compacts

was taken. Using 12 of these compacts, a calibration curve was established for the certification of the remaining compacts. The curve relates the nickel x-ray count rate

of x-ray fluorescence measurements to the volume percentage of austenite as determined

by quantitative microscopy measurements of area percentage. The austenite content of this SRM can be related directly to the nickel count rate, because the nickel content

of the austenitic powder (20.9 weight percent) is many times that of the ferritic

powder (0.10 weight percent). The mean percentage austenite for 162 certified

standards is 14.7 volume percent; this value exactly equals the volume percentage of austenite powder in the original blend. X-ray diffraction determinations of the austenite content are in good agreement with the certified content of austenite. The

SRM may be used as an x-ray diffraction standard for austenite or, in special cases, as an x-ray fluorescence standard for nickel content.

12. KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolon s) Austenite in ferrite; austenite standard; electron microprobe; powder metallurgy;

quantitative microscopy; Standard Reference Material; x-ray diffraction; x-ray fluorescence analysis.

13. AVAILABILITY

[X] Unlimited

f~J For Official Distribution. j&Order From Superintendent 20402.

Do Not Release to NTIS

of Documents, U.S. Gove Printing Office, Washington, D C

Order From National Technical Information Service (NTIS), Springfield, VA 2216 1

14. NO. OF PRINTED PAGES

34

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