Overview
EN ISO 6507-3:2018 - "Metallic materials - Vickers hardness test - Part 3: Calibration of reference blocks" specifies a standardized method for calibrating hardness reference blocks used in the indirect verification of Vickers hardness testing machines (per ISO 6507-2). The procedure applies to Vickers indentations with diagonals ≥ 0.020 mm and ensures traceable, repeatable hardness reference values for quality control and machine verification.
Key Topics and Requirements
- Scope: Calibration method for reference blocks used in indirect verification of Vickers hardness machines; applicable only for indentations with diagonals ≥ 0.020 mm.
- Reference block manufacture
- Thickness: ≥ 5 mm.
- Maximum test surface area: 40 cm².
- Magnetism: Blocks shall be free of magnetism (demagnetize steel blocks after manufacture is recommended).
- Flatness/parallelism: Flatness deviation ≤ 0.005 mm; parallelism error ≤ 0.010 mm over 50 mm.
- Surface roughness: Test surface roughness R_a ≤ 0.05 µm; surface must be free of scratches that interfere with indent measurements.
- Regrind prevention: Thickness at calibration must be marked to nearest 0.01 mm or an identifying mark made on the test surface.
- Calibration machine requirements
- Must meet ISO 6507-2 general requirements plus additional clauses (5.2–5.6).
- Direct verification interval: ≤ 12 months.
- Direct verification includes: test force, indenter condition, diagonal measuring system calibration/verification, and testing cycle or force-vs-time behaviour.
- Traceability: Verification instruments must be traceable to national standards (e.g., ISO 376 for force calibration).
- Calibration procedure and quality control
- Specifies number of indentations, checks for uniformity of hardness (relative non-uniformity), and guidance on measurement uncertainty (Annex A).
- Includes practical guidance such as Köhler illumination adjustment for diagonal measurement systems (Annex B).
Applications and Users
- Calibration and metrology laboratories issuing calibrated hardness reference blocks.
- Industrial quality control and metallurgical testing labs performing Vickers hardness testing.
- Manufacturers of hardness testing machines and indenter systems.
- Accreditation bodies and conformity assessment organizations requiring traceable verification of hardness testers.
- Any organization using ISO 6507-2 verification procedures or requiring reliable indirect verification using reference blocks.
Related Standards
- ISO 6507-1: Vickers hardness test - Test method.
- ISO 6507-2: Vickers hardness test - Verification and calibration of testing machines (uses blocks calibrated under ISO 6507-3).
- ISO 376: Calibration of force-proving instruments for verification of uniaxial testing machines.
This standard supports consistent, traceable Vickers hardness verification, reducing measurement uncertainty and improving confidence in hardness testing results.
