Short answer: Alloy steel bars are supplied soft so they can be machined, and only reach working hardness after heat treatment. Annealed EN24 and EN47 are at most 248 HB (about 24 HRC). Hardened and tempered EN24 is about 22–43 HRC depending on bar size (EN24T is about 25–32 HRC), EN47 springs are about 43–50 HRC, and case-hardening grades such as SAE 8620, EN353 and EN36C reach 58–63 HRC on the surface with a tougher 30–45 HRC core.
In this guide: Hardness chart by grade · HB, HRC and HRB · EN24 hardness by bar size · HB to HRC conversion · Through vs case hardening · Specifying hardness · FAQ
Alloy steel hardness chart: as supplied vs after heat treatment
| Grade | As supplied annealed, max. | After heat treatment | Treatment |
|---|---|---|---|
| EN24 817M40 | 248 HB ≈ 24 HRC | 22–43 HRC EN24T: 25–32 HRC | Through-hardened |
| EN47 51CrV4 | 248 HB ≈ 24 HRC | 43–50 HRC spring temper | Through-hardened |
| SAE 8620 805M20 | 197 HB ≈ 92 HRB | Case 58–63 HRC core 30–45 HRC | Case-hardened |
| EN353 815M17 | 217 HB ≈ 96 HRB | Case 58–62 HRC core 30–42 HRC | Case-hardened |
| EN36C 832M13 | 255 HB ≈ 25 HRC | Case 60–62 HRC core 30–45 HRC | Case-hardened |
Values are typical ranges. The hardness you actually get depends on bar size, heat treatment and tempering temperature. HRC and HRB figures for annealed bars are approximate conversions from HB. Our EN36C stock is as-rolled, which can be harder than the annealed figure; annealed EN36C is supplied against orders.
HB, HRC and HRB: what the numbers mean
- Brinell (HB or HBW) presses a 10 mm ball into the steel and measures the dent. It averages over a large area, so it is the usual scale for annealed, as-rolled and hardened-and-tempered bars.
- Rockwell C (HRC) uses a diamond cone and measures how deep it goes. It is the normal scale for hardened parts and is only reliable from about 20 HRC upward.
- Rockwell B (HRB) uses a small ball and is used for softer steels, below about 100 HRB (roughly 240 HB).
- Vickers (HV) uses a small diamond pyramid and is used to measure case depth on carburised parts.
Because the scales measure different things, conversions between them are approximate. When hardness matters, specify the scale you will actually test with.
EN24 hardness by bar size
EN24 is a through-hardening steel, but even it cannot harden a thick bar as much as a thin one: the centre of a large bar cools more slowly during quenching. That is why the hardness you can expect after hardening and tempering falls as the bar size rises:
| Bar size (hardened and tempered) | Brinell | Rockwell C |
|---|---|---|
| Ø up to 16 mm | 359–404 HB | about 38–43 HRC |
| Ø 16–40 mm | 331–380 HB | about 36–41 HRC |
| Ø 40–100 mm | 298–359 HB | about 32–38 HRC |
| Ø 100–160 mm | 271–331 HB | about 28–35 HRC |
| Ø 160–250 mm | 240–286 HB | about 22–30 HRC |
| Annealed (as supplied, Ø16–100 mm) | max. 248 HB | about 24 HRC max. |
If your drawing asks for, say, 35–40 HRC on a Ø150 mm part, check with your heat treater whether EN24 can reach it at that size, or whether the part should be rough-machined before hardening so the section is smaller. Our EN24 vs EN24T guide explains the standard hardened conditions.
HB to HRC conversion chart
Approximate values for steel, based on ASTM E140. Tensile strength is a rough guide only (about 3.4 × HB).
| HRC | HB (approx.) | Tensile, MPa (approx.) |
|---|---|---|
| 20 | 226 | 770 |
| 22 | 237 | 810 |
| 24 | 247 | 840 |
| 25 | 253 | 860 |
| 26 | 258 | 880 |
| 28 | 271 | 920 |
| 30 | 286 | 970 |
| 32 | 301 | 1020 |
| 34 | 319 | 1080 |
| 35 | 327 | 1110 |
| 36 | 336 | 1140 |
| 38 | 353 | 1200 |
| 40 | 371 | 1260 |
| 42 | 390 | 1330 |
| 44 | 409 | 1390 |
| 45 | 421 | 1430 |
| 46 | 433 | 1470 |
| 48 | 456 | 1550 |
| 50 | 481 | 1640 |
Above about 50 HRC, Brinell is no longer used and hardness is quoted in HRC or HV. Case-hardened surfaces at 58–63 HRC are measured this way.
Through-hardening vs case-hardening steels
- Through-hardening steels such as EN24, EN19 and EN47 have enough carbon (about 0.4–0.55%) to harden right through when quenched. They are tempered to the hardness and toughness the part needs: shafts, axles, high-tensile bolts and springs.
- Case-hardening steels such as SAE 8620, EN353 and EN36C have low carbon (about 0.13–0.2%). Carbon is added to the surface by carburising, so after hardening the outside becomes very hard (58–63 HRC) to resist wear, while the core stays tough to take shock loads: gears, pinions, cams and crankshafts. The nickel in EN353 and EN36C gives a tougher core in heavier sections. See our EN36 guide and equivalent grades chart.
How to specify hardness when you order
- Say which condition you need from the supplier. Most buyers want annealed or as-rolled bar to machine, then harden the finished part themselves. If you need bar that is already hardened and tempered (for example EN24T), say so.
- Give a range, not a single number, and name the scale: "28–32 HRC" or "248–302 HB".
- For case-hardened parts, specify both the case hardness and the effective case depth (for example "58–62 HRC, 0.8–1.2 mm"), plus a core hardness if it matters.
- Check the mill test certificate for chemistry. The right chemistry is what makes the final hardness achievable.
Stock in Mumbai
Sai International stocks EN24 (Ø16–205 mm; annealed up to Ø100 mm, as-rolled from Ø105 mm), EN47 (annealed, round, square and flat), SAE 8620 (Ø14–315 mm), EN353 (Ø16–205 mm) and EN36C (Ø14–205 mm, as-rolled; annealed against orders) at Darukhana, Mumbai. EN24T is supplied against orders of 3–5 tons. Minimum order is 100 kg, and every dispatch comes with a mill test certificate. Use our round bar weight calculator to work out weights before you order.
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Alloy steel hardness: frequently asked questions
What is the hardness of EN24 in HRC?
Annealed EN24 is soft, at most 248 HB (about 24 HRC), so it can be machined. Hardened and tempered, it is about 22–43 HRC depending on bar size and tempering, with large bars at the lower end. EN24T, the most common hardened condition, is 248–302 HB, or about 25–32 HRC.
What is the hardness of EN47 spring steel?
EN47 is supplied annealed at a maximum of 248 HB. After hardening and tempering for spring use (1350–1650 MPa tensile), it is roughly 43–50 HRC.
What hardness does SAE 8620 reach after case hardening?
After carburising and hardening, the surface of SAE 8620 typically reaches 58–63 HRC, while the core stays tougher at about 30–45 HRC, depending on section size.
Why is annealed steel quoted in HB and not HRC?
The Rockwell C scale is only reliable from about 20 HRC upward, and annealed bars sit at or below the bottom of that range. Brinell (HB) is more accurate for soft and medium-hard bars, so annealed and as-rolled hardness is usually quoted in HB, or for very soft steel in Rockwell B (HRB).
How do I convert HB to HRC?
Use a standard conversion table such as ASTM E140 or ISO 18265. For example, 250 HB is about 24–25 HRC, 300 HB is about 32 HRC, 350 HB is about 38 HRC and 400 HB is about 43 HRC. Conversions are approximate, so specify the scale you will actually test with.
Can EN24 be hardened to 50 HRC?
EN24 can reach around 50 HRC or more when hardened and tempered at low temperature, especially in smaller sections, but toughness drops sharply. Most engineering parts in EN24 are used between about 25 and 45 HRC.
Do you supply hardened bars?
We stock bars in the annealed or as-rolled condition so they can be machined. EN24T (hardened and tempered EN24) is supplied against orders of 3–5 tons.