ISO 6508-2:2023

Overview - ISO 6508-2:2023 (Rockwell hardness test - verification & calibration)

ISO 6508-2:2023 specifies procedures for the verification and calibration of Rockwell hardness testing machines and indenters. It defines two complementary verification routes - direct and indirect - and gives requirements for calibrating test forces, depth-measuring systems, testing cycles, machine hysteresis and Rockwell indenters (diamond and ball). The standard applies to both stationary and portable hardness testing machines and identifies tungsten‑carbide composite ball indenters as the standard ball type.

Key topics and technical requirements

• Direct verification: calibration/verification of main machine parameters:
  • Test forces - each preliminary force and total force measured (traceable force‑proving devices or calibrated masses). Permissible relative errors given (preliminary ±2.0%, total ±1.0%) and acceptable ranges for repeated readings.
  • Depth‑measuring system - calibrated by known incremental movements; gauge blocks used must have max expanded uncertainty of 0.0003 mm. Depth indication tolerances: ±0.001 mm (scales A–K) and ±0.0005 mm (scales N and T).
  • Testing cycle - timing and sequence checks in line with ISO 6508-1; manufacturer responsibility for full cycle calibration after repairs.
  • Machine hysteresis and repeatability - tests to ensure consistent load/unload behaviour.
• Indirect verification: uses calibrated reference hardness blocks to assess bias, repeatability and measurement uncertainty of the complete measurement process.
• Indenter verification: separate procedures for diamond and ball indenters, including direct calibration and indirect verification of ball‑holder assemblies and marking requirements.
• Environmental & traceability: direct verification recommended at (23 ± 5) °C; all calibration instruments must be traceable to national standards.
• Documentation: required verification reports and specified intervals between calibrations.

Practical applications and users

ISO 6508-2 is essential for:

• Calibration laboratories performing Rockwell hardness machine certification
• Manufacturers of hardness testers (development, factory calibration, post-repair checks)
• Quality and metrology departments in metalworking, heat‑treating and inspection labs
• Third‑party inspection and accreditation bodies ensuring compliant hardness measurement Using ISO 6508-2 ensures reliable Rockwell hardness results, demonstrable traceability, and compliance with supplier/customer quality agreements.

Related standards

• ISO 6508-1 - Rockwell hardness test: test method
• ISO 6508-3 - Calibration of reference hardness blocks
• ISO 376 - Calibration of force‑proving instruments
• ISO 6507-1 - Vickers hardness test: test method

Keywords: ISO 6508-2:2023, Rockwell hardness test, calibration, verification, hardness testing machines, indenters, tungsten carbide, depth measurement, force-proving device, reference hardness blocks, uncertainty of measurement.