ISO 4545-2:2017

Overview

ISO 4545-2:2017 - "Metallic materials - Knoop hardness test - Part 2" specifies procedures for the verification and calibration of Knoop hardness testing machines used on metallic materials. It defines both a direct method (calibration of test force, indenter geometry, and diagonal-length measuring system) and an indirect method (overall performance check using calibrated reference blocks). The standard requires traceability to national standards and documents results in a verification report or calibration certificate.

Key topics and requirements

• Scope and conditions
  • Applies to Knoop hardness testing in accordance with ISO 4545-1.
  • Verifications should normally be performed at (23 ± 5) °C and instruments must be traceable.
• Direct verification (Clause 5)
  • Test force calibration: measure each force across the machine’s force range; use an elastic proving device in accordance with ISO 376:2011 (class 1) or balanced calibrated masses (±0.2% accuracy). Specific maximum permissible relative errors are defined by force ranges.
  • Indenter verification: geometric checks (polished faces; angles and alignment). Example tolerances: angle α = 172.5° ± 0.1°, angle β = 130° ± 1.0°, indenter constant c within ±1.0% of 0.07028, axis misalignment ≤ ±0.5°, line-of-junction < 0.001 mm.
  • Diagonal measuring system: calibrate each magnification/scale with a stage micrometer. Stage micrometer uncertainty must be the greater of 0.0004 mm or 0.2%; measurement error limits are the greater of 0.0008 mm or 1.0%.
  • Testing cycle: timing verified with equipment of expanded uncertainty ≤ 1 s.
  • Uncertainty: calibration/verification uncertainties must be evaluated (Annex A gives an example).
• Indirect verification (Clause 6)
  • Uses reference blocks calibrated per ISO 4545-3 to check overall machine performance at relevant test forces and hardness levels.
• Documentation
  • A formal verification report / calibration certificate is required (Clause 8).

Applications and users

• Practical for metallurgical labs, quality control departments, calibration laboratories, hardness equipment manufacturers, and certification bodies.
• Used to ensure reliable, traceable Knoop hardness measurements for material characterization, failure analysis, production inspection, and conformity to specifications.
• Required when a machine is used for multiple hardness methods - each method must be verified independently.

Related standards

• ISO 4545-1: Knoop test method (test procedure)
• ISO 4545-3: Calibration of reference blocks (used for indirect verification)
• ISO 376:2011: Calibration of force-proving instruments (used for force calibration)

Keywords: ISO 4545-2:2017, Knoop hardness, calibration, verification, indenter, diagonal measuring system, reference blocks, metallic materials, hardness testing machines, traceability, uncertainty.