Case-hardening steel grades
4 case-hardening steel grades from 2 designation systems, each with a full data sheet. Sorted by system; the yield and tensile values are the first line of each grade's mechanical table.
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EN (European)
| Grade | No. | Type | C % | Yield MPa | Tensile MPa | Equivalents |
|---|---|---|---|---|---|---|
| 16MnCr5 | 1.7131 | Alloy case-hardening steel | 0.14 – 0.19 | ≥ 590 | 780–1080 | 5115, SCr415 / SCr420, 16CrMn / 20CrMn |
| C10 | 1.0301 | Unalloyed low-carbon case-hardening steel | 0.07 – 0.13 | ≥ 295 | 490–690 | 1010, 1008, S10C / S09CK |
| C15 | 1.0401 | Unalloyed case-hardening steel | 0.12 – 0.18 | ≥ 355 | 590–780 | 1015, 1018, S15C / S15CK |
AISI / SAE
| Grade | No. | Type | C % | Yield MPa | Tensile MPa | Equivalents |
|---|---|---|---|---|---|---|
| 8620 | G86200 | Nickel-chromium-molybdenum case-hardening steel | 0.18 – 0.23 | ≈ 385 | ≈ 540 | 20NiCrMo2-2, SNCM220, 20CrNiMo |
Hard skin, tough core, one component
Case-hardening steels are low-carbon grades — typically 0.10 to 0.25 % — designed to have carbon diffused into the surface and then be quenched. The result is a part with a 58 to 62 HRC wear-resistant case over a core that stays tough and ductile at 30 to 40 HRC.
No single homogeneous steel can do this. A through-hardened part at 60 HRC is brittle; one tough enough to take impact is too soft to resist wear. Gears, shafts, pins and cams need both, and carburising is how they get it.
Case depth is the specification
The grade tells you the core strength; the case depth tells you whether the part will survive. Deeper cases carry higher contact loads but take longer to produce — carburising time goes roughly with the square of depth, so doubling the case quadruples the furnace hours.
Case depth is specified as effective depth to 550 HV, and it should appear on the drawing alongside the surface hardness. A gear ordered as 16MnCr5 without a case depth is not fully specified.
Distortion is designed around, not eliminated
Quenching a carburised part moves it. The response is to machine before heat treatment with a grinding allowance, then grind the critical surfaces afterwards — which is why gear teeth are ground and why the grinding allowance must be bigger than the case is deep is a common and expensive mistake.
Grinding through the case leaves soft steel exactly where the contact stress is highest.
faq.h
What is case-hardening steel?
A low-carbon grade, typically 0.10 to 0.25 % carbon, intended to have carbon diffused into the surface and then quenched. This gives a hard wear-resistant case over a tough ductile core — the combination gears and shafts need.
What is 16MnCr5 used for?
Gears, shafts, pins and cams of moderate size. It is the general-purpose European case-hardening grade; 20MnCr5 is used where higher core strength or a larger section is involved.
What case depth should I specify?
It depends on contact load and tooth or journal size, typically 0.6 to 1.5 mm effective depth to 550 HV for medium gears. It must appear on the drawing with the surface hardness — a grade name alone does not specify the part.
Why do carburised parts need grinding afterwards?
Quenching distorts the part. Critical surfaces are machined with an allowance before heat treatment and ground after it. The allowance must be well within the case depth, or grinding cuts through to soft steel.
What is the AISI equivalent of 16MnCr5?
AISI 5115 is the nearest, and 8620 is often used for the same applications although its chemistry differs — it carries nickel and molybdenum where 16MnCr5 relies on manganese and chromium.