Question 1

Why can't hardness values be converted with a simple formula?

Accepted Answer

Hardness tests measure different indentation geometries and material responses. HRC measures a depth differential, HB measures a diameter, and HV measures a diagonal length. The relationships between these measurements change with material modulus, yield strength, and work-hardening behavior, making universal conversion formulas inaccurate.

Question 2

What hardness conversion is most accurate for tool steels?

Accepted Answer

For tool steels (A2, D2, H13, O1), the Rockwell C scale is the standard. Conversion to HB using ASTM E140 provides accuracy within ±15 HB for most tool steels. For critical specifications, use direct measurement on the required scale rather than conversion.

Question 3

Can hardness predict tensile strength?

Accepted Answer

Yes, with reasonable accuracy for carbon and alloy steels. A general rule of thumb: tensile strength (ksi) ≈ 500 × HRC for steels below 40 HRC. Above 40 HRC, the relationship becomes non-linear. ASTM A370 provides standardized tensile-strength-to-hardness correlations for carbon and alloy steels.
⚡ Calculated for Carbide-Tooling.com High-Performance Series. View Catalog →

HRC	HB	HV	MPa	Application
20	225	230	770	Mild steel
30	285	290	980	Tough alloy
40	370	380	1250	Tool steel
45	420	440	1400	Die steel
50	480	500	1620	Hardened
55	545	570	1850	Bearing
60	615	650	2100	Carbide

Hardness Converter

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Reference Chart (Common Ranges)

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