2002 NCSL International Workshop and Symposium August 8, 2002San Diego, CA National Institute of Standards and Technology Technology Administration, U.S. Department of Commerce Worldwide Comparisons of Rockwell Hardness Scales That Use a Diamond Indenter Sam Low Metallurgy Division NIST, Gaithersburg, Maryland John Song Precision Engineering Division NIST, Gaithersburg, Maryland HRA HRC HRD HR15N HR30N HR45N - with USA participation

Topics to be discussed National Institute of Standards and Technology Technology Administration, U.S. Department of Commerce Pre-1998: Rockwell hardness standardization in the U.S. 1990s: NIST Rockwell hardness standardization program 1983: OIML comparison 1999: EC comparison Today: CIPM Working Group on Hardness

Pre-1998: U.S. Rockwell hardness standardization National Institute of Standards and Technology Technology Administration, U.S. Department of Commerce “There are significant differences among hardness test blocks of different manufacturers for some hardness levels.” [1990 NIST Study] Prior to 1998: In the U.S., Rockwell hardness scales were defined and maintained by commercial hardness machine, test block & indenter manufacturers.

National Institute of Standards and Technology Technology Administration, U.S. Department of Commerce 3 Elements of Rockwell hardness calibration (2 are needed to obtain the third) Calibrated Test Block Calibrated Machine Calibrated Indenter Pre-1998: U.S. Rockwell hardness standardization

National Institute of Standards and Technology Technology Administration, U.S. Department of Commerce Commercial Test Block Calibration Laboratory A Commercial Test Block Calibration Laboratory B Commercial Test Block Calibration Laboratory C Test Blocks

Pre-1998: U.S. Rockwell hardness standardization National Institute of Standards and Technology Technology Administration, U.S. Department of Commerce Commercial Test Block Calibration Laboratory A Commercial Test Block Calibration Laboratory B Commercial Test Block Calibration Laboratory C Manufacturing PlantParts PurchaserLaboratory

Pre-1998: U.S. Rockwell hardness standardization National Institute of Standards and Technology Technology Administration, U.S. Department of Commerce Commercial Test Block Calibration Laboratory A Commercial Test Block Calibration Laboratory B Commercial Test Block Calibration Laboratory C Manufacturing PlantParts PurchaserLaboratory

Diamond Indenters Pre-1998: U.S. Rockwell hardness standardization Calibrated Test Block Start with nominal diamond geometry National Institute of Standards and Technology Technology Administration, U.S. Department of Commerce Performance Test Calibrated Rockwell Machine Within Tolerance: Certify Indenter

Diamond Indenters Pre-1998: U.S. Rockwell hardness standardization Calibrated Test Block Start with nominal diamond geometry National Institute of Standards and Technology Technology Administration, U.S. Department of Commerce Performance Test Calibrated Rockwell Machine Outside Tolerance: Adjust Geometry Within Tolerance: Certify Indenter

National Institute of Standards and Technology Technology Administration, U.S. Department of Commerce 1983: OIML comparison 14 countries participated Australia Austria Bulgaria Czechoslovakia Finland Federal Republic of Germany German Democratic Republic Hungary Italy Poland Romania United Kingdom United States USSR Rockwell C scale (HRC) only In 1983, NIST (NBS) did not standardize Rockwell hardness Each country was required to submit reference blocks to Československý Metrologický Ústav Prague, Czechoslovakia Hardness ranges recommended: HRC HRC HRC HRC HRC NIST chose to submit blocks from the Page-Wilson Corporation*; considered by many to be the de-facto U.S. Rockwell hardness standards at that time. *Commercial products are identified in order to adequately describe historical events. In no case does such identification imply recommendation or endorsement by the National Institute of Standards and Technology Hoped to be first step in worldwide harmonization of Rockwell hardness scales

National Institute of Standards and Technology Technology Administration, U.S. Department of Commerce 1983: OIML comparison Above 55 HRC – U.S. significantly deviated from most other countries!

National Institute of Standards and Technology Technology Administration, U.S. Department of Commerce 1990s: NIST Rockwell hardness standardization program Rockwell Diamond Indenter Measurement Facility Change in HRC scale Rockwell Hardness Standard Reference Materials 1998 Rockwell Hardness Standardizing Machine

National Institute of Standards and Technology Technology Administration, U.S. Department of Commerce 1990s: NIST Rockwell hardness standardization program Commercial Test Block Calibration Laboratory A Commercial Test Block Calibration Laboratory B Commercial Test Block Calibration Laboratory C Manufacturing PlantParts PurchaserLaboratory Other NMIs Standard Reference Test Blocks & Standard Force, Length, and Time ACCREDITATION

National Institute of Standards and Technology Technology Administration, U.S. Department of Commerce 1999: EC comparison 1995: ISO TC 164/SC 3 resolution – need for worldwide unified Rockwell hardness scales 1996: European Community (EC) funded an intercomparison Limited to Rockwell hardness scales that use a diamond indenter. HRA, HRC, HRD, HR15N, HR30N, HR45N 11 Rockwell standardization facilities participated, including non-EC countries. Laboratory data would NOT be identified. Coordinated by MPA-NRW, Germany. In future, to be accepted as a CIPM Supplementary comparison. NIM - China Force Institute – Denmark PTB – Germany IMGC – Italy NRLM – Japan KRISS – Korea Central Office of Measures – Poland OFMET – Switzerland CMI – Czech Republic NIST – USA MPA-NRW - Germany

National Institute of Standards and Technology Technology Administration, U.S. Department of Commerce 1999: EC comparison Three test parameters to be investigated: *Same reference blocks used by all laboratories. Test Variables Test Matrix HRC HRA, HRD, HR15N, HR30N, HR45N INDENTERDWELL TIMEREFERENCE BLOCKS* Laboratory’s ownShort (5.5 s)114 Common #1Short (5.5 s)114 Common #2Long (15 s)44 1. Effect of each NMI’s standardizing machine 2. Effect of each NMI’s standardizing indenter 3. Effect of the total force dwell time

HRC National Institute of Standards and Technology Technology Administration, U.S. Department of Commerce 1999: EC comparison Test variables: own standardizing indenter short dwell time

National Institute of Standards and Technology Technology Administration, U.S. Department of Commerce 1999: EC comparison Examines indenter effectExamines machine effect Test variables: own standardizing indenter short dwell time HRC Conclusion: Standardizing indenters play significant role in measurement differences. HRC Test variables: common indenter #1 short dwell time

National Institute of Standards and Technology Technology Administration, U.S. Department of Commerce 1999: EC comparison Long dwell time effect Short dwell time effect Test variables: common indenter #1 short dwell time HRC Test variables: common indenter #2 long dwell time Conclusion: Increased dwell times did not reduce measurement differences.

National Institute of Standards and Technology Technology Administration, U.S. Department of Commerce 1999: EC comparison HRAHRD Test variables: own standardizing indenter short dwell time Other Rockwell scales

National Institute of Standards and Technology Technology Administration, U.S. Department of Commerce 1999: EC comparison HR30N HR15N HR45N Test variables: own standardizing indenter short dwell time

National Institute of Standards and Technology Technology Administration, U.S. Department of Commerce Today: CIPM Working Group on Hardness Since the 1983 OIML comparison, Measurement agreement has improved, BUT still significant differences 1999: New Working Group on Hardness under the CCM of the CIPM Barriers to world Rockwell hardness harmonization: ¤ Test procedure / machine ¤ Indenter performance

National Institute of Standards and Technology Technology Administration, U.S. Department of Commerce Today: CIPM Working Group on Hardness Indenter performance: Common inventory or New evaluation methods? ¤ Evaluation methods / tests ¤ Improved geometries Developing a better definition for Rockwell hardness procedure for NMIs ¤ Consequence: NIST scale may shift Comparison is planned for the systems and techniques used by NMIs to measure the geometrical parametersof the Rockwell diamond indenter. Current WGH activities Participating laboratories: IMGC, Italy NIST, USA MPA-NRW, Germany PTB, Germany NMIJ, Japan NPL, U.K. KRISS, Korea CENAM, Mexico OFMET, Switzerland

National Institute of Standards and Technology Technology Administration, U.S. Department of Commerce Summary 1983 OIML comparison - Helped initiate NIST Rockwell hardness standardization program World comparison demonstrated that - Advanced from “measurement tool” to “metrological measurement.” Improvements are still needed before harmonization can be achieved. WGH is currently working towards harmonization. 1. Diamond indenter - significant source of measurement bias. 2. Standardizing machine & testing procedure – significant sources of measurement bias. 3. Total force dwell time: need not be increased.

2002 NCSL International Workshop and Symposium August 8, 2002San Diego, CA National Institute of Standards and Technology Technology Administration, U.S. Department of Commerce THE END THANK YOU FOR YOUR ATTENTION