MATERIALS · September 2, 2026 · 6 MIN READ

Hardness Conversion HB, HRC, HV and HS: Where the Tables Are Valid and Where They Are Not

HB 226, HRC 20 and HV 240 describe the same hardness in a medium-carbon steel, and conversion tables let you move between them — but only within a defined material group. ASTM E140 limits conversion to non-austenitic steels in the 200–650 HB range; apply the same table to a 304 stainless forging or to a carburised case and the number you get can be wrong by 30 %.

WHERE THIS APPLIES AT FORGEPRESS CHINA

ForgePress China reports hardness on the scale that matches the part — HB for large sections, HV for cases, HRC for production screening — and states the scale on the certificate. Capacity: HKM3 hot-die forging line 1,000–5,000 t, part weight 0.1–500 kg, maximum envelope 1,200 × 800 mm, as-forged to ISO 8062 class C with critical dimensions machined to ±0.2 mm, process control to ISO 9001, first article 4–8 weeks from die design release.

KEY NUMBERS

HB 226 ≈ HRC 20 ≈ HV 240; HB 371 ≈ HRC 40 ≈ HV 392; HB 481 ≈ HRC 50 ≈ HV 513.
ASTM E140 conversion applies to non-austenitic (ferritic, pearlitic, martensitic) steels only.
HRC is unreliable below about 20 HRC; use HB or HV instead.
HS (Shore) is a rebound method — do not convert it by formula, use the instrument's own table.

What each scale physically measures

Brinell (HB) presses a 10 mm hardened ball into the surface under a defined load and measures the diameter of the impression; the result is an average over a relatively large area, which is why it is used on castings and forgings with coarse structure. Vickers (HV) uses a pyramidal diamond and measures diagonals, giving a much smaller indentation and a scale that runs continuously from soft to very hard.

Rockwell C (HRC) uses a 120° diamond cone under a 150 kg major load and reads depth of penetration directly. It is fast and is the shop-floor default, but the indentation is small, so it is sensitive to surface condition and to coarse microstructures, and it loses resolution below about 20 HRC.

Conversion table for non-austenitic steel

HB (10/3000)	HRC	HV	Approx. UTS (MPa)
226	20	240	760
248	23	260	825
286	30	302	960
331	35	345	1,110
371	40	392	1,245
429	45	446	1,440
481	50	513	1,615
560	55	595	1,880
654	60	697	2,195

Approximate values for non-austenitic steels per ASTM E140. UTS column uses UTS ≈ 3.35 × HB. Do not use this table for stainless, cast iron, or case-hardened surfaces.

Four cases where conversion is simply wrong

Austenitic stainless (304, 316): work-hardens, and the HB/HRC relationship is completely different. Report HV or convert with a stainless-specific table.
Carburised or nitrided case: the case is a few tenths of a millimetre thick, so a 10 mm ball Brinell test measures the soft core, not the case. Use HV 0.3 or HR15N.
Cast iron and powder-metallurgy parts: graphite and porosity change the indentation response; conversion tables do not apply.
Below 20 HRC: the Rockwell C scale is not reliable at the soft end. Report HB or HV.

The practical rule for inspection

Pick the scale that matches the part, not the scale that is on the drawing. A large forged block with a coarse structure needs Brinell for a representative average; a thin case needs micro-Vickers; a production line checking 500 parts an hour needs Rockwell C on a prepared surface.

Then convert once, at the end, and record both the measured value and the scale it was measured on. A certificate that says only "HRC 45" on a nitrided part is not evidence of anything.

Frequently asked questions

What is HB 200 in HRC?

Approximately 13 HRC for non-austenitic steel, but that is below the reliable range of the Rockwell C scale, which is why the conversion should not be used there. Report the Brinell value directly instead.

Can I convert HV to HRC for stainless steel?

Not with the standard carbon-steel table. Austenitic stainless work-hardens differently and the standard ASTM E140 conversion does not cover it. Use a stainless-specific conversion or simply report HV.

Why does my hardness reading vary across the forging?

Decarburisation at the surface, segregation at the centreline, and uneven cooling during quenching all produce real variation. A 30 HB spread across a large section is normal for a forged and normalized part; a 30 HB spread on a small part usually means a heat treatment problem.