Frequently Asked Questions
It is sometimes necessary to meet hardness limits for duplex and superduplex stainless steels, and it is convenient to be able to convert between the Rockwell C (HRC) and Vickers (HV) hardness scales. A conversion exists for carbon steel in ASTM E140 but there is no standard conversion for duplex and superduplex grades and the carbon steel conversion has been shown to be inappropriate for these high alloy steels. A correlation between the two hardness scales for duplex and superduplex grades has been developed at TWI from a compilation of data supplied by various organisations. There was considerable scatter in the data, indicating that the correlation between the two scales was not well defined, but the best-fit line was:
HRC = 0.091HV - 2.4
The 28HRC limit previously given in MR 0175-99 (now superseded) for wrought UNS S31803 austenitic/ferritic stainless steel is calculated to be equivalent to 334HV using this equation and the previous 32HRC limit for UNS S32750 steel (25%Cr superduplex) becomes 378HV.
NACE MR 0175/ISO 15156-3 - Petroleum and natural gas industries - Materials for use in H 2 S - 'containing environments in oil and gas production, Part 3: Cracking-resistant CRAs (corrosion-resistant alloys) and other alloys'.
ASTM E140-97 - 'Standard hardness conversion tables for metals'