Hardness Conversion Chart — HRC, HRB, HB & HV

What it is

Hardness is measured by pressing an indenter into the material. Each scale uses a different indenter and load, so results are not directly the same. ASTM E140 gives approximate conversions between scales, based on test data, for specific material groups. The values below are for non-austenitic steels (carbon and alloy steels, not 300-series stainless).

• HRC (Rockwell C): diamond cone, 150 kgf. For hardened steel.
• HRB (Rockwell B): 1/16 in ball, 100 kgf. For soft steel, brass and aluminum.
• HB (Brinell): 10 mm ball, 3000 kgf for steel. Large indent; good for castings and forgings.
• HV (Vickers): diamond pyramid. Works across the full range and for thin sections.

How to read it

Find the measured value on its scale and read across. Treat results as estimates. When a specification calls for a scale, test on that scale.

Approximate conversions for steel

Below about 20 HRC, steel is tested on the Rockwell B scale. In ASTM E140, HRB 100 is roughly 240 HB, and HRB 90 roughly 185 HB.

Key points

• Conversions are approximate and material-specific. Do not use a steel conversion for aluminum, copper alloys or austenitic stainless.
• Rockwell C below 20 and Rockwell B above 100 are outside their useful ranges.
• Surface hardness on case-hardened parts differs from core hardness. A deep-reading scale can pass through the case.
• File-hard checks only show that a part is harder than the file, not a value.

Common mistakes

• Treating a converted value as if it were measured, for acceptance.
• Testing on scale, paint or a curved surface without correction.
• Using a chart for one material group on another.

Governing standards: ASTM E140 (standard hardness conversion tables for metals). ASTM E18 (Rockwell), ASTM E10 (Brinell) and ASTM E384 or E92 (Vickers) for test methods.

Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.