Overview
EN ISO 3738-2:2006 - Hardmetals: Rockwell hardness test (scale A) - Part 2 specifies the preparation and calibration of standard test blocks used to verify Rockwell hardness testing machines and indenters for hardmetals. Adopted by CEN from ISO 3738-2:1988, the standard defines master, primary, secondary and working standard blocks, their dimensions, surface quality and the calibration workflow to establish traceable hardness values on the HRA (scale A) Rockwell scale.
Key topics and technical requirements
- Scope: Calibration hierarchy - master → primary → secondary → working standard test blocks for Rockwell hardness (scale A) verification.
- Block geometry and finish:
- Nominal diameter: 45 mm; nominal thickness: 8 mm; bottom chamfer 0.8 mm × 45°.
- Test face ground both sides; test surface Ra < 0.2 µm (may be polished).
- Maximum flatness deviation 0.010 mm; parallelism max 0.020 mm per 50 mm; bottom face must not be convex.
- Nominal hardness values for primary sets: 93, 92, 91, 88.5 and 85.5 HRA (sets of five blocks).
- Marking conventions:
- Primary blocks: marked with CCPA and designated numbers/series.
- Secondary: letter S + serial number.
- Working: letter W + serial number.
- Calibration procedures and acceptance criteria:
- Master sets are retained by the Cemented Carbide Producers Association (CCPA) and ISO/TC 119 secretariat.
- Calibration involves controlled indentations, calculation of arithmetic mean and standard deviation, and corrections for machine/indenter error.
- Example acceptance limits: standard deviation thresholds and correction limits (e.g., corrections >0.20 HRA require machine/indenter investigation; secondary blocks rejected if SD >0.10 HRA).
- Documentation: Each block requires a test report/certificate including reference to this part of ISO 3738, identification, hardness, standard deviation, thickness and calibration date, serial number and issuing laboratory.
Applications and practical value
- Ensures traceable, repeatable Rockwell A hardness measurements for cemented carbides and other hardmetals.
- Used for periodic verification and calibration of Rockwell hardness testing machines and indenters in:
- Calibration and metrology laboratories
- Hardmetal (cemented carbide) manufacturers and suppliers
- Quality control and R&D in powder metallurgy and tooling industries
- Supports inter-laboratory consistency and compliance with quality systems (e.g., ISO/IEC 17025).
Related standards
- EN ISO 3738-1 / ISO 3738-1 - Hardmetals - Rockwell hardness test (scale A): Test method. EN ISO 3738-2 is intended to be read in conjunction with ISO 3738-1 for complete test and verification practice.
Keywords: EN ISO 3738-2:2006, hardmetals, Rockwell hardness test scale A, standard test blocks, calibration, primary standard, secondary standard, working standard, indenter verification, CEN.
