ISO 6506-3:2014

Overview

ISO 6506-3:2014 - "Metallic materials - Brinell hardness test - Part 3: Calibration of reference blocks" defines a standardized method for calibrating Brinell hardness reference blocks used in the indirect verification of Brinell testing machines (per ISO 6506-2). The standard also specifies procedures to ensure metrological traceability of the calibration machine and provides guidance on measurement uncertainty (Annex A).

Key topics and requirements

• Scope & references
  • Applies to calibration of specially manufactured hardness reference blocks for Brinell testing.
  • Normative references include ISO 6506-1, ISO 6506-2 and ISO 376.
• Manufacture and physical requirements
  • Block thickness minimums: 16 mm (10 mm ball), 12 mm (5 mm ball), 6 mm (smaller balls); exceptions noted.
  • Blocks must be demagnetized, have controlled surface roughness and parallel flatness (specified tolerances), and be free of scratches.
• Calibration machine and verification
  • Calibration machine must meet ISO 6506-2 general requirements plus: direct verification at intervals ≤ 12 months; measurement of test forces, indenter properties (diameter, hardness, density), and calibration of the indentation diameter measuring system.
  • Force measurements: minimum three measurements per test force using an ISO 376 class 0.5 (or better) proving device; mean must be within ±0.1% of nominal.
  • Indentation diameter measuring system resolution and performance limits are specified (e.g., read to 0.002 mm for 5–10 mm balls).
• Calibration procedure
  • Performed at (23 ± 5) °C; thermal drift ≤ 1 °C.
  • Indenter approach velocities, force application timing (time to full force (7 ± 1) s), and dwell (14 ± 1) s) are defined.
• Measurements and acceptance
  • Minimum of five indentations per block, uniformly distributed; at least one reference indentation identified.
  • Non‑uniformity R is calculated from ordered mean diameters; maximum permissible R values depend on indentation diameter/hardness.
• Marking and validity
  • Blocks must be marked with mean hardness (e.g., “348 HBW 5/750”), supplier, serial number, calibration agency, thickness/identifying mark and year.
  • Calibration validity: up to 5 years (reduced to 2–3 years for aluminium and copper alloys).

Applications and who uses it

• Calibration and accreditation laboratories performing Brinell hardness scale dissemination.
• Manufacturers of hardness reference blocks and Brinell hardness testing machines.
• Quality managers and NDT/metallurgical labs needing traceable hardness verifications.
• Certification bodies and procurement/specification engineers ensuring compliance with hardness testing metrology.

Related standards

• ISO 6506-1: Brinell test method
• ISO 6506-2: Verification and calibration of testing machines
• ISO 376: Calibration of force-proving instruments

Keywords: ISO 6506-3, Brinell hardness, calibration of reference blocks, metrological traceability, hardness reference block, Brinell hardness test, calibration machine, indirect verification.