Overview
ISO 4545-3:2017 - "Metallic materials - Knoop hardness test - Part 3: Calibration of reference blocks" specifies the method for calibrating hardness reference blocks used for the indirect verification of Knoop hardness testing machines (as per ISO 4545‑2). The procedure is applicable to Knoop indentations with long diagonals ≥ 0.020 mm and defines manufacturing, measurement, environmental and documentation requirements to ensure traceability and repeatability of Knoop hardness measurements.
Key topics and technical requirements
- Scope and traceability
- Calibration method for reference blocks used in indirect verification of Knoop hardness machines.
- Verification instruments and calibration must be traceable to national standards (see ISO 376).
- Reference block manufacture
- Minimum thickness: 5 mm.
- Maximum test surface area: 40 cm².
- Blocks must be non-magnetic (steel blocks should be demagnetized).
- Flatness: max deviation 0.005 mm; parallelism: max 0.010 mm in 50 mm.
- Surface roughness: Ra ≤ 0.05 μm; no scratches that interfere with indentations.
- Thickness marked at calibration to prevent accidental regrind.
- Calibration machine and measurement systems
- Direct verification of the calibration machine at intervals ≤ 12 months (force, indenter, diagonal measuring system, testing cycle).
- Test force verification at three plunger positions, three measurements each, within ±0.5% of nominal (ISO 376 Class 0.5 or better).
- Indenter geometry and finish tightly specified (angle β = 130° ± 0.1°, face flatness and junction tolerances down to 0.0003 mm).
- Diagonal measurement resolution: estimation to 0.00015 mm or 0.25% (whichever greater); stage micrometer line interval uncertainty ≤ 0.0002 mm or 0.04%.
- Calibration procedure and environment
- Temperature (23 ± 5) °C, thermal drift ≤ 1 °C.
- Approach velocity 0.015–0.07 mm/s; time to full force ≈ 7 s; dwell time ≈ 14 s.
- Maximum vibrational acceleration
Open preview (PDF)Metallic materials — Knoop hardness test — Part 3: Calibration of reference blocks
