960-5Rockwell HardnessMeasurement ofMetallic MaterialsSamuel R. LowNIST recommendedpractice guideSpecialPublication960-5iRockwell HardnessMeasurement ofMetallic MaterialsSamuel R. LowMaterials Science and Engineering LaboratoryJanuary 2001U.S. Department of CommerceDonald L. Evans, SecretaryTechnology AdministrationKaren H. Brown, Acting Under Secretary of Commerce for TechnologyNational Institute of Standards and TechnologyKaren H. Brown, Acting DirectorUNITED STATES OF AMERICADEPARTMENT OF COMMERCENIST Recommended Practice GuideSpecial Publication 960-5Certain commercial entities, equipment, or materials may be identified inthis document in order to describe an experimental procedure or conceptadequately. Such identification is not intended to imply recommendation orendorsement by the National Institute of Standards and Technology, nor is itintended to imply that the entities, materials, or equipment are necessarily thebest available for the purpose.National Institute of Standards and TechnologySpecial Publication 960-5Natl. Inst. Stand. Technol.Spec. Publ. 960-5116 pages (January 2001)CODEN: NSPUE2U.S. GOVERNMENT PRINTING OFFICEWASHINGTON: 2000For sale by the Superintendent of DocumentsU.S. Government Printing OfficeInternet: bookstore.gpo.gov Phone: (202) 512–1800 Fax: (202) 512–2250Mail: Stop SSOP, Washington, DC 20402-0001◆FOREWORDThe Rockwell hardness test continues to be applied as a tool for assessingthe properties of a product while the tolerances on the acceptable materialhardness have become tighter and tighter. Adhering to “good practice”procedures when performing Rockwell hardness measurements andcalibrations is a beneficial step to reducing measurement errors. The purposeof this Guide is to explain the causes of variability in Rockwell hardness testresults and to supplement the information given in test method standards withgood practice recommendations. Although this Guide is directed more towardsthe users of Rockwell hardness having the greatest concern for accuracy intheir measurements, much of the information given is also applicable for usersthat only require test results to be within wide tolerance bands, where highaccuracy is not as critical.................................iiiACKNOWLEDGMENTSThe author would like to thank the following persons for sharing theirexperience and providing information for this Guide. Their input and reviewhas provided a link to the practical world of Rockwell hardness testing.*T. Robert Shives, ConsultantRichard Antonik, SUN-TEC CorporationRobert A. Ellis and Richard A. Ellis, David L. Ellis Co., Inc.Thomas P. Farrell, Mitutoyo America CorporationGiancarlo Mazzoleni and Douglas B. McGhee, Newage TestingInstruments, Inc.Michael L. Milalec and Richard J. Snow, Gilmore Diamond Tools, Inc.Paul M. Mumford, United Calibration CorporationEdward L. Tobolski, Wilson Division of Instron CorporationThe author would also like to thank present and former NIST co-workersJames L. Fink, Carole D. Flanigan, Robert J. Gettings, Walter S. Liggett, Jr.,David J. Pitchure, John H. Smith, and John Song for their contributions towardsthe Rockwell hardness standardization program at NIST.◆*The acknowledgements of the persons and companies listed above shouldnot be interpreted as an endorsement by NIST of their products or services............................................................vTable of Contents ◆List of FiguresList of FiguresList of FiguresList of FiguresList of Figures.........................................................................................................................................................................................................................................................................................................................................................................................................................................ixixixixixList of TList of TList of TList of TList of Tablesablesablesablesables..............................................................................................................................................................................................................................................................................................................................................................................................................................................xiixiixiixiixii1.1.1.1.1.IntroductionIntroductionIntroductionIntroductionIntroduction....................................................................................................................................................................................................................................................................................................................................................................................................................................111112.2.2.2.2.Rockwell Hardness TRockwell Hardness TRockwell Hardness TRockwell Hardness TRockwell Hardness Testestestestest................................................................................................................................................................................................................................................................................................................................222222.1 Significance of the test .............................................................22.2 Rockwell indentation test principle ............................................22.3 Rockwell hardness scales ........................................................ 42.4 Rockwell hardness number ......................................................42.5 Test method standards ............................................................. 63.3.3.3.3.TTTTTest Procedureest Procedureest Procedureest Procedureest Procedure...........................................................................................................................................................................................................................................................................................................................................................................................................999993.1 Choosing the appropriate Rockwell scale ................................93.2 Test surface preparation ......................................................... 133.3 Rockwell hardness testing