Revision of E140-12B(2019)e1 Standard Hardness Conversion Tables for Metals Relationship Among Brinell Hardness, Vickers Hardness, Rockwell Hardness, Superficial Hardness, Knoop Hardness, Scleroscope Hardness, and Leeb Hardness
Rationale
Members of API and E28 identified some shortcomings in E140 when looking to convert hardness numbers for martensitic stainless steels. Specifically, Table 1 for non-austenitic steels is not appropriate for martensitic stainless steels such as those included in NACE MR0175 / ISO 15156, and Table 3 for nickel-aluminum-silicon alloys is not appropriate for nickel-chromium–iron-molybdenum precipitation hardened (PH) nickel alloys, such as those included in API Standard 6ACRA and NACE MR0175/ISO 15156.
A round robin test was conducted jointly by members of ASTM E28.06.02 task group and API subcommittee 21 to establish conversion tables in E140 for the above mentioned materials. The results of the round robin testing are published as API TR 21B.
The data for the martensitic stainless steels confirmed that the conversions in E140 Table 1 are not appropriate for martensitic stainless steels and exhibited excellent lab-to-lab correlation which makes the results suitable for inclusion in E140 as a new conversion table. However, the data for the PH nickel alloys was inconclusive due to a high dispersion and consequent low correlation between labs. This information for the PH nickel alloys will be added as a footnote to E140 Table 3.
Work Item Status
Date Initiated: 01-16-2026
Technical Contact: Tom Ott