Hardness conversion

Austenitic stainless steel work-hardens during the test, so a Rockwell C indenter produces a meaningless reading. The standard scale for these grades is Rockwell B or Vickers, and ISO 18265 explicitly marks the conversion as not applicable. Specifying HRC for 304 or 316L usually means the supplier has to reject the requirement or ask for clarification.

Pick the scale that the material is normally reported in. Low-carbon and low-alloy steel is usually reported as Brinell or Rockwell B when it is soft and Rockwell C when it is hardened. Austenitic stainless steel, most aluminium alloys, copper alloys and every plastic use Brinell, Rockwell B, Vickers or their own scale.

No. The tables are empirical averages, and the same material can read differently on a different machine or with a different indenter. Always convert on the same specimen and compare like with like. Treat the converted value as an estimate and confirm the real requirement on the drawing.

Give the material grade, the condition and the scale, for example 1.7225 (42CrMo4) +QT, 32 to 38 HRC. A hardness range without a scale is not a usable requirement, and a hardness range without a material grade cannot be checked at all.

A great deal. The same grade in the annealed, quenched and tempered, or cold-worked condition has completely different hardness and strength. Precipitation-hardening alloys add the ageing condition, for example 17-4 PH H900 or H1150, because the same alloy at a different ageing level is a different part.

Yes. For austenitic stainless steel, nickel alloys and titanium, the hardness reference temperature is usually defined at 20 °C, and readings taken at a different temperature need a correction. Always state the test temperature when the material is temperature sensitive.