Hardness Converter
Online Hardness Conversion Table
Which Treatment Gives the Required Hardness
Converting between scales does not answer the designer's main question: how to achieve the required hardness of a part, and to what depth. The chart below shows the ranges achieved by the main types of heat treatment and thermochemical treatment. Process names are clickable.
The ranges are approximate: the result depends on the steel grade, part cross-section and treatment parameters. The scale is common, in HV units, so that the processes can be compared.
How Hardness Scales Differ and When Each Is Used
A diamond cone or a steel ball; the tester displays the result immediately, without a microscope. That is why Rockwell hardness is the main scale on the shop floor and on drawings. HRC works reliably from about 20 to 70 units: below 20 HRC the readings become unstable, and HB or HRB is used instead. The limitation is the 150 kgf load: on a thin hardened layer the cone punches right through it.
A 10 mm ball under a 3000 kgf load; the indentation diameter is measured. The indentation is large and averages out inhomogeneities, so Brinell hardness is measured on castings, forgings, and annealed and normalized rolled stock. The upper limit is about 650 HB: on harder material the ball itself deforms and the result becomes meaningless.
A four-sided diamond pyramid and loads starting from a fraction of a kilogram. The indentation is small, so Vickers is used to measure what the other two methods cannot: nitrided and carburized layers, thin parts, and microhardness on a cross-section. The scale is continuous — one formula works both for annealed steel and for a borided layer.
Hence a typical situation: the mill certificate for rolled stock states 250 HB, while the part drawing specifies 58 HRC. There is no contradiction. The metallurgist certifies the steel in the as-delivered, that is, soft condition, while the designer specifies the hardness of the finished part after heat treatment. These are two different stages in the life of the same part, and different scales are used for them.
When a Rockwell Test Gives a Wrong Result
On nitrided, nitrocarburized and borided layers a few tenths of a millimetre thick, the Rockwell indenter punches through the hardened layer and "feels" the soft core, so the tester shows an underestimated hardness. For such surfaces, low-load Vickers testing or microhardness measurement on a cross-section is used.
Hardness of Steels After Heat Treatment
| Steel grade | Treatment | Hardness |
|---|---|---|
| 45 (C45) | Annealing, normalizing | 170–210 HB |
| 45 (C45) | Hardening + low-temperature tempering | 45–52 HRC |
| 45 (C45) | Induction hardening, surface | 50–58 HRC |
| 40Kh (41Cr4) | Quenching and tempering | 240–280 HB |
| 40Kh (41Cr4) | Hardening + low-temperature tempering | 45–52 HRC |
| 20Kh, 12KhN3A | Carburizing + hardening, surface | 58–62 HRC |
| 38Kh2MYuA (41CrAlMo7) | Nitriding, surface | 900–1100 HV |
| 40Kh13 (AISI 420) | Hardening + tempering | 48–55 HRC |
| 95Kh18 (AISI 440C) | Hardening + tempering | 56–60 HRC |
| U8, U10 (C80U, C105U) | Hardening + low-temperature tempering | 58–63 HRC |
| 65G (65Mn) | Hardening + tempering | 45–52 HRC |
| R6M5 (HS6-5-2, M2) | Hardening + triple tempering | 62–65 HRC |
Hardness Conversion: Reference Values for HRC, HV, HB, HRA
Reference values for a quick check. The full range in one-unit steps, as well as the superficial Rockwell scales (HR15N, HR30N, HR45N), HRB and HRD, is available in the converter at the top of the page.
| HRC | HV | HB | HRA |
|---|---|---|---|
| 65 | 832 | — | 84 |
| 60 | 697 | 614 | 81 |
| 58 | 653 | 587 | 80 |
| 55 | 595 | 547 | 79 |
| 52 | 544 | 509 | 77 |
| 50 | 513 | 484 | 76 |
| 48 | 484 | 460 | 75 |
| 45 | 446 | 426 | 73 |
| 42 | 412 | 393 | 72 |
| 40 | 392 | 372 | 71 |
| 35 | 345 | 322 | 68 |
| 30 | 302 | 283 | 66 |
| 25 | 266 | 255 | 63 |
| 20 | 238 | 230 | 61 |
A dash in the HB column means that the Brinell method is not applicable in this range: above about 650 HB the indenter ball itself deforms. The values are given for carbon and alloy steels — for non-ferrous alloys, cast iron and cemented carbides the relationships between the scales are different.
Need a specific hardness for your part?
Send us a drawing with the hardness requirement and the steel grade — our process engineer will select the technology, specify the actual depth of the hardened layer and calculate the cost of treating the batch.
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