Hardness conversion chart — steel
Rockwell C, Vickers, Brinell and approximate tensile strength from the published ASTM E140 anchors — including, unlike most charts, where the standards say a scale stops being valid.
| Rockwell C | Vickers HV | Brinell HBW | Approx. tensile (MPa) | Relative | Typical material |
|---|---|---|---|---|---|
| 20 | 238 | 226 | 750 | Mild steel, annealed | |
| 25 | 266 | 253 | 855 | Normalised EN8 | |
| 30 | 302 | 286 | 965 | EN8 / EN3 heat treated | |
| 35 | 345 | 327 | 1105 | EN19 quenched & tempered | |
| 40 | 392 | 371 | 1255 | EN24 Q&T, 17-4 PH H1025 | |
| 45 | 446 | 421 | 1420 | Hardened alloy steel, 17-4 PH H900 | |
| 50 | 513 | 481 | 1605 | Tool steel, 440C hardened | |
| 55 | 595 | 560 | 1890 | D2 / H13 hardened | |
| 60 | 697 | beyond range | 2205 | M2 HSS | |
| 65 | 832 | beyond range | none published | File-hard, nitrided case |
These are correlations, not conversions
Each scale uses a different indenter and load, so a converted value is roughly ±5–10%. Where a specification names a scale, test in that scale — do not test in another and convert.
Do not use this table for non-steel
Austenitic stainless, aluminium, copper alloys and cast iron all behave differently. ASTM E140 publishes separate tables for each. Using the steel table on them returns a plausible-looking wrong answer.
Why the gaps are blank
Brinell stops being valid above about 650 HBW (ASTM E10) because the ball itself deforms, and no tensile correlation is published at HRC 65. Most charts print numbers there anyway. We would rather leave it empty and say why.
Case depth is not bulk hardness
A nitrided or carburised part can read file-hard at the surface and be soft half a millimetre down. If the drawing calls a case depth, a surface hardness reading does not prove it — that needs a sectioned micro-hardness traverse.
Hardness decides how it gets made
Most alloy steels still turn and mill with carbide in the mid-40s HRC. Above that you move toward ceramics, CBN or grinding — which is precisely why so many parts are machined soft, heat treated, then finish-ground to size.
Test in the scale the drawing names
Drawings tend to call HRC for through-hardened steel, HV for thin cases, coatings and small features, and HB for castings and soft stock. Matching the called scale removes the conversion argument entirely — and the inspection report is then directly comparable to the spec.
How the part is presented changes the reading
Rockwell needs a clean, flat, properly supported surface. A curved surface reads low and needs the correction factors in ASTM E18; a part that flexes on the anvil reads low too. Test thin work on Vickers or a superficial Rockwell scale instead of forcing HRC.
Convert any value properly
This sheet lists the published anchors only. Interpolate between them, and see the validity limits enforced rather than ignored, with the hardness conversion calculator at dalloways.com/tools.
Typical reference values: the governing standard or your material certificate takes precedence.
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