Common Hardness Conversion Table
Use this quick reference chart to compare the most common hardness scales used in the offshore and marine industries, based on ASTM A370 standards.
Standard Reference
ASTM A370 / ISO 18265
(Values are approximate conversions for non-austenitic steels)
| Rockwell C (HRC) | Brinell (HB) | Vickers (HV) |
|---|---|---|
| 20 HRC | 226 HB | 238 HV |
| 25 HRC | 253 HB | 266 HV |
| 28 HRC (NACE Limit) | 271 HB | 286 HV |
| 32 HRC | 301 HB | 318 HV |
| 40 HRC | 371 HB | 392 HV |
| 50 HRC | 481 HB | 513 HV |
Frequently Asked Questions
+ What is the difference between Brinell and Rockwell?
Brinell (HB) uses a ball indenter and is better for softer or heterogeneous materials. Rockwell C (HRC) uses a diamond cone and is standard for hard, heat-treated steels.
+ Why is maximum hardness important (NACE)?
In sour service (H2S) environments, steel that is too hard becomes brittle and susceptible to cracking (SCC). NACE MR0175 standards therefore limit hardness. For example, Duplex Stainless Steel is typically limited to max 28 HRC.
+ Can I convert Hardness to Tensile Strength?
Yes, there is a strong correlation for carbon and low-alloy steels. The rule of thumb is: Tensile Strength (MPa) ≈ 3.5 × Brinell Hardness (HB).
Note: For NACE MR0175 compliance (Sour Service), ensure hardness does not exceed the specified limits. For further questions, contact our technical team today.
