Certification Report for SRM 2810a, 2811a, and 2812a: Rockwell C Scale Hardness – Low, Medium, and High Ranges

Published

August 5, 2026

Author(s)

Louise Ahure Powell, Carlos Beauchamp, Renato Machado, Antonio Possolo

Abstract

The procedures used by the National Institute of Standards and Technology (NIST) to establish certified Rockwell C hardness values for three Standard Reference Materials (SRMs): SRM 2810a (low range, nominal 25 HRC), SRM 2811a (medium range, nominal 45 HRC), and SRM 2812a (high range, nominal 63 HRC) are documented. These materials serve as the primary transfer standards of NIST's Rockwell C Hardness Scale realization. These standards are used for the calibration and verification of Rockwell C hardness testing machines and provide a direct link in the traceability chain through SI-traceable force and displacement measurements. Certified values were obtained using the NIST Primary Hardness Standard Machine (PHSM) under conditions consistent with ASTM E18-25 (2025), ISO 6508-1 to -3 (2023), and the CCM Working Group on Hardness (WGH) definition of the Rockwell C hardness scale. The certification process included the direct verification of the test forces using force measuring instruments (load cells) and the calibration of the depth-measuring system using laser interferometry with gauge block stacks, both traceable to the SI. It also incorporated a statistical evaluation of hardness measurements across multiple blocks spanning the low, medium, and high hardness ranges. Comparisons with historical NIST certifications and international key comparison results confirmed continuity of traceability. The resulting certified values and expanded uncertainties provide industry and the hardness metrology community with reliable reference standards that ensure accuracy and global comparability of Rockwell C scale hardness measurements.

Citation

Special Publication (NIST SP) - 260-269

Report Number

260-269

NIST Pub Series

Special Publication (NIST SP)

Pub Type

NIST Pubs

Download Paper

https://doi.org/10.6028/NIST.SP.260-269

Local Download

Keywords

Hardness testing, Rockwell C hardness (HRC), Standard Reference Material (SRM), Primary Hardness Standardizing Machine (PHSM), Traceability, Uncertainty.

Citation

Ahure Powell, L. , Beauchamp, C. , Machado, R. and Possolo, A. (2026), Certification Report for SRM 2810a, 2811a, and 2812a: Rockwell C Scale Hardness – Low, Medium, and High Ranges, Special Publication (NIST SP), National Institute of Standards and Technology, Gaithersburg, MD, [online], https://doi.org/10.6028/NIST.SP.260-269, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=962145 (Accessed August 9, 2026)

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