TWI Frequently asked questions
by Joanna Nicholas
There is no direct, universally used correlation between the different hardness scales. However, a few national standards do list hardness conversion tables, and related equations. These have arisen from many hardness readings, thevalues have been plotted and a conversion established. Two such standards are BS EN ISO 18265:2003 [1] , and ASTM E140: 2007 [2] . The conversions for these standards are not exactly the same, but are similar, incorporating Vickers, Brinell, Rockwell B, and Rockwell C hardness scales, and conversions for a limited number of material types. Some otherhardness scales are included in the standards, but these are used less often.
An earlier standard, BS 860:1967 [3] , which has been superseded by BS EN ISO 18265:2003 gives the following equation for hardness conversion between Brinell and Vickers scales.
HB = 0.95 HV
As with all conversions, it must be appreciated that the conversion between hardness scales is approximate, not absolute.
References
- BS EN ISO 18265:2003 'Metallic materials - Conversion of hardness values'. BSI, London.
- ASTM E140: 2007 'Standard hardness conversion tables for metals relationship among Brinell hardness, Vickers hardness, Rockwell hardness, Superficial hardness, Knoop hardness and Scleroscope hardness'. ASTM International, West Conshohocken, PA, www.astm.org.
- BS 860:1967 'Tables for comparison of hardness scales' BSI, London.
