ISO 6507-3:2018

Overview

ISO 6507-3:2018 - "Metallic materials - Vickers hardness test - Part 3: Calibration of reference blocks" specifies a calibrated method for producing and certifying hardness reference blocks used for the indirect verification of Vickers hardness testing machines (as per ISO 6507-2). The standard applies only to indentations with diagonals ≥ 0.020 mm and defines manufacturing, dimensional, surface and calibration requirements to ensure traceable, repeatable hardness reference values.

Key topics and technical requirements

• Scope and applicability: Calibration method for reference blocks used in indirect verification of Vickers testers; applicable for indentation diagonals ≥ 0.020 mm.
• Reference block manufacture:
  • Minimum thickness: ≥ 5 mm
  • Maximum test surface area: ≤ 40 cm²
  • Magnetism: blocks should be demagnetized (if steel)
  • Flatness ≤ 0.005 mm; parallelism error ≤ 0.010 mm in 50 mm
  • Surface roughness Ra ≤ 0.05 µm; no scratches interfering with indentations
  • Block thickness or identifying mark recorded to detect regrind
• Calibration machine requirements:
  • Direct verification at intervals ≤ 12 months
  • Verification of test force, indenter, diagonal measuring system and testing cycle
  • Test-force verification tolerances: typically ±0.2% (normal hardness), ±0.3% (low-force), ±0.5% (microhardness) using ISO 376 traceable proving devices
• Indenter specifications:
  • Square-based diamond pyramid with face flatness ~ 0.0003 mm
  • Pyramid angle 136° ± 0.1°; axis misalignment < 0.3°
  • Geometrical deviations must be certified
• Diagonal measuring system:
  • Resolution and maximum permissible errors provided by diagonal length ranges (see standard Table 2)
  • Stage micrometer verification across magnifications; max expanded uncertainty of line intervals 0.0002 mm or 0.04%
• Calibration procedure and sampling:
  • Calibration at (23 ± 5) °C, thermal drift ≤ 1 °C
  • Test force application timing and approach velocity specified; force hold 14 s
  • Minimum 5 indentations per block (recommend 10–25 for microhardness / reduced uncertainty)
• Uncertainty & uniformity: Methods for evaluating block uniformity and uncertainty of mean hardness (Annex A).

Applications and users

• Calibration laboratories and national metrology institutes performing traceable calibration of hardness reference blocks.
• Materials testing and quality control labs in metallurgy, aerospace, automotive and manufacturing that perform Vickers hardness testing.
• Manufacturers of Vickers hardness testers and accreditation bodies ensuring measurement traceability, reproducibility and compliance with ISO 6507 series.

Related standards

• ISO 6507-1: Vickers hardness test - Test method
• ISO 6507-2: Verification and calibration of Vickers testing machines
• ISO 376: Calibration of force-proving instruments

Keywords: ISO 6507-3:2018, Vickers hardness test, calibration of reference blocks, hardness reference block, diagonal measuring system, indenter specification, test force verification, traceability.