What Is HRC? Metal Hardness HRC, HV, HB with Conversion Table

A technician in a V.S. Heat Treatment polo shirt seated at a bench-top micro-Vickers hardness tester, the monitor beside it showing a magnified indentation, with a results logbook open on the desk. — Micro-Vickers hardness testing in our laboratory. Each reading is logged alongside the image of its indentation, not as a bare number.

Answer read from our own grade table

What is HRC, and how does it convert to HV and HB?

Attainable hardness depends on grade and section size. S45C is the most economical carbon steel for small parts; SCM435 and SCM440 add chromium and molybdenum, so they harden further through a thick section and hold it more uniformly. The figures below separate the as-quenched ceiling from the hardness actually specified in service after tempering — two different numbers.

S45C: As-quenched ceiling 50–58 HRC · Specified in service 40–55 HRC
SCM435: As-quenched ceiling 48–55 HRC · Specified in service 33–44 HRC
SCM440: As-quenched ceiling 50–58 HRC · Specified in service 28–48 HRC
SWCH10B21: As-quenched ceiling 40–48 HRC · Specified in service 28–40 HRC

The hardness specified in service after tempering is always below the as-quenched ceiling — specify the service range on the order, not the ceiling.

What is HRC?

HRC stands for Rockwell Hardness scale C, the most widely used hardness unit for hardened steel. A 120° diamond cone is pressed into the surface at 150 kgf and the depth of the indent is measured — the shallower the indent, the higher the HRC and the harder the material.

The usable window is roughly 20–65 HRC. Below that the indent is too shallow to read reliably and you should switch to the HRB or HB scale.

Reference values you will meet on screws, nuts and bolts: property class 8.8 sits around 23–34 HRC, class 10.9 around 32–39 HRC and class 12.9 around 39–44 HRC. Wear parts such as small bearings or spring washers run much higher, at 58–64 HRC.

HV (Vickers) and HB (Brinell) measure the same property but with a different indenter and load, so they produce a different set of numbers. They convert approximately — see the table below.

Hardness correlates with wear resistance and tensile strength, which is why it is the number customers use to accept hardened parts. But harder also means more brittle, so real drawings specify a *range*, never "as hard as possible".

Quick HRC ↔ HV ↔ HB conversion

Per ASTM E140 / ISO 18265 for non-austenitic steel. The last column is approximate tensile strength.

20 HRC = 238 HV = 226 HB ≈ 760 MPa
25 HRC = 266 HV = 253 HB ≈ 850 MPa
30 HRC = 302 HV = 286 HB ≈ 965 MPa
35 HRC = 345 HV = 327 HB ≈ 1,125 MPa
40 HRC = 392 HV = 371 HB ≈ 1,290 MPa
45 HRC = 446 HV = 421 HB ≈ 1,455 MPa
50 HRC = 513 HV = 481 HB ≈ 1,630 MPa
55 HRC = 595 HV = 560 HB ≈ 1,810 MPa
60 HRC = 697 HV = 654 HB — above the range where the standards still correlate tensile strength
64 HRC = 800 HV = 722 HB — the top of the table

Two cautions: these hold for non-austenitic steel only (they do not apply to SUS304), and they are estimates that should not replace a real measurement on precision work.

For values between these rows, our hardness conversion calculator carries the full 63-row table.

Common scales

HRC (Rockwell C) — the most common for hardened steel; fast and easy over 20–65 HRC; used on screws, nuts and bolts.
HV (Vickers) — a diamond pyramid indenter measures from very thin surfaces to very hard parts; ideal for case-depth profiling.
HB (Brinell) — a hard ball on softer/medium material leaves a large mark; suited to castings and raw steel.

Conversion and cautions

Approximate conversion tables exist (e.g. ASTM E140), but they are estimates and should not replace real measurement on precision work.

Watch out: plated surfaces, decarburized skins or parts that are too thin can skew readings. Prepare the surface and pick the right scale.

Hardness certificates

Good hardening comes with a test report stating actual hardness, number of points measured and accepted limits.

The V.S. Heat Treatment lab uses a Vickers Hardness Test (HV) — a diamond pyramid indenter read under a microscope for high precision — plus an X-ray coating-thickness gauge resolving down to 0.3 mm per point, and issues a report with every lot under ISO 9001:2015.

FAQ

What does HRC stand for?+

Rockwell Hardness scale C — the most common hardness unit for hardened steel. A 120° diamond cone is pressed in at 150 kgf and the indent depth is read. It is usable from roughly 20 to 65 HRC.

How many HRC counts as hard?+

It depends on the job. A class 10.9 bolt at 32–39 HRC is already on spec, while a wear part such as a small bearing needs 58–64 HRC. Specifying more hardness than the part needs simply makes it brittle.

How do I convert 1 HRC to HV?+

There is no fixed ratio — the scales diverge as they rise. 40 HRC is 392 HV but 50 HRC is 513 HV, so the gap widens at the top. Use the table above or a converter rather than multiplying.

How hard is grade 10.9?+

Typically around 32–39 HRC, with the real spec set by ISO 898-1 for that grade.

HRC vs HV?+

HRC is fast for general work; HV is finer and better for thin surfaces and case depth, because its much lighter load does not punch through the hardened case.

Why do repeat readings on the same spot disagree?+

The usual causes are a surface that is not flat enough, a part thin enough for the anvil to matter, a plated or decarburized skin, and measuring too close to an edge. Surface preparation and scale choice matter as much as the tester itself.