NIST recommended practice guide : Rockwell hardness measurement of metallic materials

124 Pages·2001·8.2 MB·English

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Rockwell Hardness
Measurement
of
Metallic Materials
Samuel Low
R.
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ational Instituteof
andardsandTechnology
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NIST Recommended Practice Guide
Special Publication 960-5
Rockwell Hardness
Measurement
of
Metallic Materials
Samuel Low
R.
Materials Science and
Engineering Laboratory
January 2001
U.S. Department of Commerce
Donald L. Evans, Secretary
Technology Administration
Karen H. Brown, Acting Under Secretary of
Commerce for Technology
National Institute of Standards and Technology
Karen H. Brown, Acting Director
Certaincommercial entities, equipment, ormaterialsmaybe identifiedin
this document in order to describe an experimental procedure or concept
adequately. Suchidentificationisnotintendedto implyrecommendationor
endorsementbytheNational Institute ofStandards andTechnology, noris it
intendedto implythatthe entities, materials, orequipmentare necessarilythe
best available forthe purpose.
National Institute ofStandards andTechnology
SpecialPublication960-5
Natl. Inst. Stand. Technol.
Spec. Publ. 960-5
116 pages (January 2001)
CODEN: NSPUE2
U.S. GOVERNMENT PRINTING OFFICE
WASHINGTON: 2000
For sale by the Superintendent ofDocuments
U.S. GovernmentPrinting Office
Internet: bookstore.gpo.gov Phone: [phone] Fax: [phone]
Mail: Stop SSOP, Washington,DC 20402-0001
FOREWORD
The Rockwell hardness test continues to be applied as a tool for assessing
the properties ofa product while the tolerances on the acceptable material
hardness have become tighter and tighter. Adhering to "good practice"
procedures when performing Rockwell hardness measurements and
calibrations is a beneficial step to reducing measurement errors. The purpose
ofthis Guide is to explainthe causes ofvariability inRockwellhardness test
results andto supplementthe information givenintestmethod standards with
goodpractice recommendations. Although this Guide is directed more towards
the users ofRockwell hardness having the greatest concern for accuracy in
their measurements, much ofthe information given is also applicable forusers
that only require test results to be within wide tolerance bands, where high
accuracy is not as critical.
More information on the SP 960 series canbe found on the internet at
http;//www.nist.gov/practiceguides. This web site includes a complete
list ofNIST Pratice Guides and ordering information.
iii

ACKNOWLEDGMENTS
The authorwouldliketothankthe followingpersons forsharingtheir
experience andprovidinginformationforthis Guide. Theirinputandreview
has provided a linkto the practical world ofRockwell hardness testing.*
T.RobertShives, Consultant
RichardAntonik, SUN-TEC Corporation
RobertA. Ellis andRichard'A. Ellis, DavidL. EllisCo., Inc.
ThomasP.Farrell,MitutoyoAmericaCorporation
Giancarlo Mazzoleni andDouglas B. McGhee, Newage Testing
Instruments,Inc.
MichaelL. MilalecandRichardJ. Snow, GilmoreDiamondTools, Inc.
PaulM. Mumford,UnitedCalibrationCorporation
EdwardL. Tobolski,WilsonDivisionofInstronCorporation
The author would also like to thank present and formerNIST co-workers
James L. Fink, Carole D. Flanigan, Robert J. Gettings, Walter S. Liggett, Jr.,
DavidJ. Pitchure, John H. Smith, and John Song fortheir contributions towards
the Rockwell hardness standardization program atNIST.
*The acknowledgements ofthe persons and companies listed above should
notbe interpreted as an endorsement byNIST oftheir products or services.
v

Table of Contents
List ofFigures ix
List ofTables xii
1. Introduction 1
2. Rockwell Hardness Test 2
2.1 Significance ofthe test 2
2.2 Rockwellindentation testprinciple 2
2.3 Rockwell hardness scales 4
2.4 Rockwell hardness number 4
2.5 Test method standards 6
3. Test Procedure 9
3.1 Choosing the appropriate Rockwell scale 9
3.2 Test surface preparation 13
3.3 Rockwell hardness testing machine 13
3.4 Hardness measurement 26
4. Reference Test Block Standards 37
4.1 Primary reference test blocks 37
4.2 Secondary reference test blocks 40
4.3 Use ofreference test block standards 41
5. Verifications ofRockwell Hardness Machines 44
5.1 Direct verification 44
5.2 Indirect verification 47
5.3 Correcting measurement biases 49
6. Monitoring Test Machine Performance 51
6.1 Reproducibility 51
6.2 Daily verification 52
vii
Table of Contents
7. Reducing Measurement Differences and Errors 53
7. 1 Reduce machine component operating errors 53
7.2 Verify machine measurement performance 53
7.3 Measurement locations 55
8. Traceability, Error, and Uncertainty 56
8.1 Traceability 56
8.2 Measurement error 58
8.3 Uncertainty 58
9. Status ofRockwell Hardness Standardization
in the Year2000 63
9.1 United States 63
9.2 International 65
10. Bibliography 69
AnnexA: Applied Force Effect 71
Annex B: Rockwell Hardness Testing Cycle Effect 73
B. 1 Effect offorce application rate 74
B.2 Effect ofdwell times 78
Annex C: Use ofNISTRockwell C Scale SRM Test Blocks 84
C. 1 Recommendations for use 84
C.2 Calculation ofcertified values forarbitrary locations 86
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