Overview - ISO 18265:2013 (Metallic materials - Conversion of hardness values)
ISO 18265:2013 defines principles and practical guidance for the conversion of hardness values between different hardness scales (e.g., Vickers, Brinell, Rockwell) and for converting hardness to estimates of tensile strength. The standard provides informative conversion tables (Annexes A–G) for specific material groups and discusses the effects of changed test procedures (Annex H). It emphasizes that converted values are informative indicators only - they are directly applicable to the exact material tested and are not a substitute for measurements obtained by the correct standardized test method.
Key technical topics and requirements
- Scope of conversion tables: Annexes A–G cover unalloyed and low-alloy steels, cast steel, quenching-and-tempering steels, cold-working steels, high-speed steels, tool steels, hardmetals, and non‑ferrous metals/alloys.
- Principles of conversion: Conversions are empirical and, where possible, derived by regression analysis. Users must account for statistical uncertainty and material-specific behaviour; tensile strength estimates are the least reliable results of conversion.
- Use and limitations: Converted values are intended only when the prescribed test cannot be performed (e.g., machine or sample constraints). Conversions must be declared (including the original hardness method used, e.g., ISO 6506-1, ISO 6507-1, ISO 6508-1).
- Measurement best practice: Basis of conversion should be the mean of at least three individual hardness values (or five if a stricter uncertainty is agreed). Surface preparation, machine repeatability and local hardness variation affect uncertainty and must be controlled.
- Annex H & test procedure effects: Provides guidance on how changes in test conditions influence conversion accuracy.
Practical applications and typical users
- Materials and metallurgical engineers estimating tensile properties from hardness testing when destructive tensile tests are impractical.
- Quality control and inspection teams who need to compare hardness results reported in different scales.
- Testing laboratories and third-party inspectors applying hardness-to-hardness conversions for internal checks.
- Manufacturers selecting alternative hardness methods due to part geometry, coatings, or limited sample size.
Note: Converted values should not be used as sole evidence of contractual compliance without explicit agreement.
Related standards and references
- ISO 6506‑1 (Brinell), ISO 6507‑1 (Vickers), ISO 6508‑1 (Rockwell) - referenced hardness test methods.
- Portions reprinted from ASTM E140 (hardness conversion tables) are included as informative material.
- Developed by ISO/TC 164/SC 3 (Mechanical testing of metals - Hardness testing).
Keywords: ISO 18265, hardness conversion, metallic materials, hardness scales, tensile strength estimates, conversion tables, Vickers, Brinell, Rockwell, hardness testing, material testing.
