SS431 is a martensitic stainless steel with about 16% chromium and 2% nickel. It can be hardened and tempered for high strength while keeping better corrosion resistance than other hardenable stainless steels such as 410 and 420. It is a common choice for pump shafts, marine shafts and valve parts.
Quick facts
- Type
- Martensitic stainless steel (hardenable)
- Main alloys
- About 15–17% chromium, 1.25–2.5% nickel
- Hardened and tempered
- Commonly about 25–35 HRC; higher is possible
- Tensile strength
- About 850–1000 MPa in the common condition
- Magnetic
- Yes
- Also called
- 1.4057, 431S29, EN57
Equivalent grades
| Standard | Grade |
|---|---|
| AISI | 431 |
| EN | 1.4057 (X17CrNi16-2) |
| BS | 431S29 (old EN57) |
Equivalents are close, not identical. Name the grade and standard on the drawing.
Typical chemical composition
| Element | % |
|---|---|
| Carbon (C) | About 0.12–0.22 |
| Chromium (Cr) | About 15–17 |
| Nickel (Ni) | About 1.25–2.5 |
| Manganese (Mn) | Up to about 1.5 |
Values are typical. The exact limits depend on the standard and supplier; ask for the mill test certificate when it matters.
Heat treatment
- Harden from about 980–1050 °C, quench in oil or air
- Temper to the strength wanted; avoid about 400–580 °C, where toughness and corrosion resistance drop
- Often supplied already hardened and tempered for machining
Typical uses
- Pump and propeller shafts
- Valve stems, spindles and seats
- Fasteners and bolts needing strength and corrosion resistance
- Aircraft and marine fittings
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Questions
- Is SS431 better than SS410?
- For corrosion, yes: its higher chromium and added nickel resist rusting better, and it is tougher. It costs a little more.
- SS431 or 17-4 PH for shafts?
- Both are strong stainless steels. 17-4 PH is hardened by a simple low-temperature ageing with little distortion; 431 is hardened and tempered. Pick by the strength, corrosion needs and what suppliers stock.
- Is SS431 magnetic?
- Yes. Like all martensitic stainless steels it is magnetic.
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 15 October 2026.