Investigators: Richard Ricker, Sam Low, John H. Smith, and David Pitchure

Technical Description:

In the United States and throughout the world, the Rockwell hardness test is the most often specified material property test for manufacturing process control, product quality control, and product acceptance. The NIST Metallurgy Division is working in collaboration with the Precision Engineering Division, the Standards Reference Materials program, the National Voluntary Laboratory Accreditation Program (NVLAP), the Statistical Engineering Division, ASTM and ISO to standardize Rockwell hardness measurements in the United States, to define a system for traceability of Rockwell hardness measurements to U.S. national standards, and to promote the development of uniform international Rockwell hardness standards.

Technical Objectives:

• Define the U.S. Rockwell hardness scales (e.g., HRA, HRB, HRC, Superficial N and T) based on material science and metrology.

• Develop uniform and stable hardness blocks as a means of transferring the Rockwell scales to industry.

• Provide calibrated test blocks (low, medium and high level blocks) for sale to industry as Standard Reference Materials (SRMs).

• Provide certified Rockwell indenters meeting tight geometry and performance criteria for sale to industry as Standard Reference Materials.

• Experimentally determine the effects of the variables of the Rockwell test cycle (i.e., indenter velocity and dwell times) on the hardness measurement, and understand these effects based on material science.

• Interface with the hardness standardization laboratories of other countries in an effort to unify Rockwell hardness testing worldwide.

Anticipated Outcome:

• Standard measurement methods, calibration procedures and standard reference materials that enable U.S. industry to conduct Rockwell hardness tests that are traceable to national and international standards enabling compliance with international quality standards such as ISO 9000.

• Improved national and increased international trade with U.S. manufacturers because trading partners can assure each other that they are using the same nationally and internationally accepted standard measurements to assess the quality of products for quality control and acceptance testing.

• Assurance for U.S. manufacturers that Rockwell hardness tests cannot become a technical barrier to international trade in countries which wish to inhibit the importation of U.S. manufactured goods.

• Improved national and more unified international hardness testing standards.

Accomplishments for FY 1995:

• Improved the repeatability of the NIST dead-weight standardizing hardness tester by a factor of two or three.

• Established U.S. national Rockwell hardness reference facility consisting of a computer controlled high precision dead-weight Rockwell hardness tester.

• Worked with a U.S. hardness block manufacturer to develop hardness test blocks for the Rockwell C scale which exhibit better hardness uniformity than any test block currently available. These test blocks will be used for the NIST SRM Rockwell standards.

• Acquired and characterized a group of Rockwell diamond indenters which meet the geometrical and performance criteria for NIST standardizing indenters.

• Experimentally determined the effects of indenter velocity and dwell times during the Rockwell C scale test cycle for the SRM test block material.

• Initiated and conducted hardness intercomparisons between NIST and the national hardness standardization laboratories of Japan and China.

• As chair of the Traceable Hardness Standards task group at ASTM, led the effort to develop requirements for traceability of Rockwell hardness measurements to U.S. national standards.

• Three papers on this work were prepared and submitted for publication.

Impact and Technical Highlights:

• ASTM is currently revising their Rockwell hardness testing standards to include requirements for traceability to national standards utilizing the standard reference materials to be produced by this program.

• Equipment and materials for the production of Rockwell C scale standard reference materials were obtained, tested, and evaluated. Production of the Rockwell C scale SRM will begin in the next fiscal year and these hardness calibration blocks will be available.

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Last modified: Mon Jan 06 09:46:15 1997 Metallurgy Webmeister