SS440C is a high-carbon martensitic stainless steel that can be hardened to about 58–60 HRC, the hardest of the common stainless grades. It combines high wear resistance with moderate corrosion resistance, so it is used for stainless bearings, valve balls and seats, nozzles, knife blades and wear parts. It is machined annealed and hardened afterwards.
Quick facts
- Type
- Martensitic stainless steel
- Carbon
- About 0.95–1.2%
- Chromium
- About 16–18%
- Hardness
- About 58–60 HRC hardened and tempered
- Corrosion
- Moderate; best when hardened and polished
- Magnetic
- Yes
Equivalent grades
| Standard | Grade |
|---|---|
| AISI / ASTM | 440C |
| EN | 1.4125 (X105CrMo17) |
| UNS | S44004 |
| JIS | SUS440C |
Equivalents are close, not identical. Name the grade and standard on the drawing.
Typical chemical composition
| Element | % |
|---|---|
| Carbon (C) | About 0.95–1.2 |
| Chromium (Cr) | About 16–18 |
| Molybdenum (Mo) | Up to 0.75 |
| Manganese (Mn) | Up to 1 |
| Silicon (Si) | Up to 1 |
Values are typical. The exact limits depend on the standard and supplier; ask for the mill test certificate when it matters.
Heat treatment
- Supplied annealed (about 25 HRC or lower) for machining
- Hardened from about 1,010–1,065 °C, oil or gas quenched
- Sub-zero treatment helps reach full hardness
- Tempered at about 150–370 °C to suit the hardness needed
- Vacuum hardening keeps finished parts clean and true
Typical uses
- Stainless ball and roller bearings
- Valve balls, seats and stems
- Nozzles and pump wear parts
- Knife and cutting blades
- Gauges and measuring tools
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Questions
- How hard can SS440C get?
- About 58–60 HRC after hardening and low tempering, the highest of the common stainless steels.
- Is SS440C as corrosion resistant as SS304?
- No. It resists rust in mild conditions, especially when hardened and polished, but SS304 and SS316 are much better in wet and chemical service.
- SS440C or EN31 for bearings?
- EN31 is the usual bearing steel and is cheaper. SS440C is chosen where bearings must resist water or mild chemicals.
The figures on this page are typical values for guidance, written by Diemeco from standard engineering practice. They are not a specification: confirm grades and properties with the relevant standard or the supplier's mill test certificate, and tolerances with your workshop. Last checked 22 October 2026.