Convert Rockwell C hardness to Brinell HBW, estimate tensile strength, or reverse HBW to HRC for steel hardness values within ASTM E140.
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HRC to HBW Formula
The calculator uses the ASTM E140 polynomial relating Brinell hardness (HBW) to Rockwell C (HRC) for non-austenitic steels:
To go from HRC to HBW, the equation is solved numerically. Tensile strength is estimated from Brinell using:
- HRC — Rockwell C hardness, 150 kgf load, diamond cone indenter
- HBW — Brinell hardness, 3000 kgf load, 10 mm tungsten carbide ball
- UTS — ultimate tensile strength in MPa
Valid range: HRC 20 to 68, HBW 145 to 627. The conversion applies to non-austenitic carbon and alloy steels. It does not apply reliably to stainless, cast iron, aluminum, or hardened tool steels above 68 HRC. Treat all converted values as approximate; direct measurement on the scale you need is always preferred over conversion.
Reference Tables
Approximate equivalents per ASTM E140, rounded for quick lookup.
| HRC | HBW | HV | UTS (MPa) | UTS (ksi) |
|---|---|---|---|---|
| 20 | 226 | 238 | 780 | 113 |
| 25 | 253 | 266 | 873 | 127 |
| 30 | 286 | 301 | 987 | 143 |
| 35 | 327 | 344 | 1128 | 164 |
| 40 | 371 | 392 | 1280 | 186 |
| 45 | 421 | 446 | 1452 | 211 |
| 50 | 481 | 513 | 1660 | 241 |
| 55 | 551 | 595 | 1900 | 276 |
| 60 | 618 | 697 | 2130 | 309 |
Typical hardness ranges by steel condition:
| Condition | HRC | HBW |
|---|---|---|
| Annealed mild steel | < 20 | 120–200 |
| Normalized medium-carbon | 20–28 | 220–280 |
| Quenched and tempered alloy | 30–45 | 285–420 |
| Case-hardened / induction | 50–60 | 480–620 |
| Tool steel, fully hardened | 58–66 | 600+ |
Worked Example
A shaft is specified at 45 HRC. Find the equivalent Brinell and approximate tensile strength.
- Solve the polynomial for HBW where HRC = 45. Result: HBW ≈ 421.
- Estimate UTS: 3.45 × 421 ≈ 1452 MPa (about 211 ksi).
Why the result may differ from a published table. Conversion tables round to integers and assume non-austenitic steel. Stainless, work-hardened, or anisotropic material can deviate by 2 to 5 HRC points from the calculated value. Use a direct test when the specification calls for it.
Why HBW is preferred for soft material. Below 20 HRC the diamond cone produces shallow indents with poor repeatability. Switch to the Rockwell B scale (HRB) or use Brinell directly.
