Hardness Conversion
Pick the chart for the material: hardened steel on the Rockwell C chart, unhardened steel, cast iron and most non-ferrous metals on the Rockwell B chart. Read across a row for the approximate equivalent on another scale. Conversions are approximate, not a substitute for testing on the scale a drawing or specification calls for.
Hardness conversion chart
Method & sources
Basis: the hardness conversion chart in the U.S. Air Force / Navy / Army technical manual T.O. 1-1A-9, Aerospace Metals – General Data and Usage Factors (Table 8-1), shown as printed. Blank cells are blank in the original.
Hardness conversion is empirical: there is no exact relationship between scales, and alloy, cold work, heat treatment and grain structure all move it. Treat every converted value as approximate. Where a drawing or specification names a hardness test, test by that method. Do not read these values as tensile strength for anything but steel.
The Rockwell B chart is a general chart for soft metals. It is less reliable on annealed austenitic stainless, nickel and high-nickel alloys, and on cold-worked aluminum and the softer alloys.