ISO 4545-1:2023

Overview

ISO 4545-1:2023 - "Metallic materials - Knoop hardness test - Part 1: Test method" - defines the standardized procedure for performing the Knoop microhardness test on metallic materials and selected inorganic coatings. The third edition (2023) covers test forces from 0.009807 N to 19.613 N and specifies minimum indentation size (long diagonal ≥ 0.020 mm). The standard also includes user-level periodic verification guidance and expanded applicability to metallic and other inorganic coatings.

Key technical topics and requirements

• Test force range: 0.009807 N to 19.613 N (micro- to low macro-range).
• Indentation size limit: long diagonal d ≥ 0.020 mm; smaller indentations are outside scope (use ISO 14577-1 for instrumented nano/micro-indentation).
• Indenter geometry: rhombic-based diamond pyramid with nominal angles α = 172.5° and β = 130°; indenter constant c ≈ 0.07028 (used in hardness calculation).
• Hardness calculation: Knoop hardness (HK) is calculated from test force and projected indentation area; standard provides the conversion relationships and notes for reducing uncertainty (use actual indenter angles where possible).
• Diagonal measurement: optical or camera-based measuring systems with specified resolution (e.g., for 0.020 mm ≤ d < 0.080 mm resolution 0.0004 mm; for d ≥ 0.080 mm resolution 0.5% of d).
• Test piece preparation: polished, smooth, oxide- and contaminant-free surface; avoid preparation methods that alter surface hardness (recommend adapted polishing/electropolishing).
• Thickness/support rules: test piece or layer thickness ≥ 1/3 of long diagonal; coating thickness minimums - not applicable when testing normal to surface if coating < 0.007 mm, nor for cross-section if coating < 0.020 mm.
• Machine verification: references to ISO 4545-2 and ISO 4545-3 for calibration and verification; Annex A provides a periodic verification procedure for routine checks.
• Measurement orientation: applicable to measurements normal to coated surfaces and to cross-sections when surface characteristics permit accurate diagonal readings.

Practical applications and users

ISO 4545-1:2023 is used where reliable microhardness data are required:

• Quality control and acceptance testing in metallurgy and heat-treatment shops
• Failure analysis and materials research labs (metallurgists, materials scientists)
• Coatings evaluation (electrodeposited, autocatalytic, sprayed, anodic coatings)
• Manufacturing QA for components with thin hard layers (bearing surfaces, coatings)
• Hardness testing instrument manufacturers and calibration laboratories Users benefit from standardized procedures to ensure repeatable Knoop hardness values and traceability.

Related standards

• ISO 4545-2:2017 - Verification and calibration of Knoop testing machines
• ISO 4545-3 - Calibration of reference blocks
• ISO 6507-1:2023 - Vickers hardness test (related macro/microhardness context)
• ISO 14577-1 - Instrumented indentation testing (for smaller indentations)

Keywords: ISO 4545-1, Knoop hardness test, metallic materials, microhardness, coatings, hardness testing, diagonal measurement, indenter geometry, test force, calibration.