Estimate Rockwell C hardness from ultimate tensile strength (UTS) in ksi, MPa, or psi, or estimate UTS from HRC. This tool/alloy-steel reference correlation is approximate and limited to 109–272 ksi UTS and 20–55 HRC.
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ksi To HRC Conversion Formula
The calculator interpolates between adjacent pairs in the Diehl Tool Steel reference table. There is no universal stress-to-hardness equation; confirm the relationship for the actual alloy and heat treatment. The source values are typical estimates and must not be used for material acceptance or safety-critical design.
For the cited tool and alloy steel reference: 20–55 HRC and 109–272 ksi UTS. No extrapolation. UTS means ultimate tensile strength, not applied stress or yield strength.
Variables:
- HRC is the hardness on the Rockwell C scale
- UTS is ultimate tensile strength in ksi (1,000 pounds-force per square inch). U₁, H₁ and U₂, H₂ are the two bounding reference pairs. The reverse calculation uses UTS = U₁ + (HRC − H₁)/(H₂ − H₁) × (U₂ − U₁).
| UTS (ksi) | Rockwell C (HRC) |
|---|---|
| 45 | Outside reference range |
| 50 | Outside reference range |
| 55 | Outside reference range |
| 60 | Outside reference range |
| 70 | Outside reference range |
| 80 | Outside reference range |
| 90 | Outside reference range |
| 100 | Outside reference range |
| 110 | 20.3 |
| 120 | 24.0 |
| 130 | 27.5 |
| 140 | 30.0 |
| 150 | 33.5 |
| 160 | 35.6 |
| 170 | 37.6 |
| 180 | 39.3 |
| 200 | 43.1 |
| 220 | 46.7 |
| 240 | 49.8 |
| 260 | 52.9 |
| Rounded to one decimal. Linear interpolation between Diehl reference pairs; bounded to 109–272 ksi and 20–55 HRC. Values outside the selected range are not estimated. Typical data cannot establish properties of a particular material. | |
What is a ksi To HRC Conversion?
ksi is a stress unit; HRC is an indentation-hardness scale. They are not directly interchangeable units. A material-specific correlation can estimate Rockwell C hardness from ultimate tensile strength, or estimate UTS from measured hardness. This calculator uses typical tool/alloy-steel reference data. Composition, heat treatment and processing affect the relationship, so use testing of the actual material for acceptance and design.
How to Calculate ksi To HRC Conversion?
The following steps estimate HRC from UTS using the bounded reference table:
- First, determine ultimate tensile strength and convert it to ksi. Use the calculator unit selector for MPa or psi.
- Next, check that UTS is from 109 to 272 ksi, then find the two adjacent reference pairs.
- Then, interpolate HRC linearly between those pairs using the formula above.
- Finally, treat the result as an approximate HRC estimate and confirm it against tests of the actual material.
Example Problem:
Use the following variables as an example problem to test your knowledge:
Ultimate tensile strength = 200 ksi. Bounding pairs: 196 ksi ↔ 42 HRC and 203 ksi ↔ 44 HRC.
HRC ≈ 42 + (200 − 196)/(203 − 196) × (44 − 42) = 43.1 HRC. This is an approximate reference estimate, not a measured hardness.
