EN ISO 6508-3:2023

Overview

EN ISO 6508-3:2023 - Metallic materials - Rockwell hardness test - Part 3: Calibration of reference blocks specifies a method for calibrating Rockwell hardness reference blocks used for the indirect and daily verification of Rockwell hardness testing machines and indenters (see ISO 6508-2). It also defines requirements and verification/calibration methods for the Rockwell calibration machines and calibration indenters. The document is intended for laboratories, manufacturers and quality teams involved in hardness testing and calibration.

Key topics and technical requirements

• Purpose: Calibration of hardness-reference blocks for use in routine verification and traceability of Rockwell hardness testing.
• Reference indenters: Notes that hard-metal ball indenters are considered the standard ball type; includes requirements for calibration diamond and ball indenters.
• Environmental condition: Calibrations and verifications at (23 ± 5) °C.
• Reference block manufacture:
  • Minimum thickness: 6 mm (thicker preferred to reduce indent effect).
  • Flatness deviation: ≤ 0.01 mm; parallelism: ≤ 0.02 mm per 50 mm.
  • Surface roughness: Ra ≤ 0.3 µm (test surface), Ra ≤ 0.8 µm (bottom).
  • Blocks must be free from magnetism and surface damage; thickness should be marked at calibration.
• Calibration-machine & indenter requirements:
  • Direct verification annually (not exceeding 13 months): test force, measuring system, testing cycle, machine hysteresis.
  • Test force measurement: use ISO 376 traceable force-proving device class 0.5 or better.
  • Force tolerances: preliminary test force within ±0.2%, total test force within ±0.1% of nominal.
  • Measuring system: resolution ±0.0001 mm, maximum expanded uncertainty 0.0002 mm (95% confidence).
  • Testing cycle timing uncertainty: **