SS 420 is a martensitic stainless steel with about 12–14% chromium and more carbon than SS 410. It can be hardened by heat treatment (roughly 45–52 HRC), so it is used where stainless parts must also be hard: knives, surgical tools, valve parts and plastic moulds.
Quick facts
- Type
- Martensitic (hardenable) stainless steel
- Chromium
- About 12–14%
- Hardness
- About 45–52 HRC hardened, depending on carbon
- Corrosion resistance
- Moderate; lower than SS 304
- Magnetic
- Yes
- As supplied
- Annealed, for machining
Equivalent grades
| Standard | Grade |
|---|---|
| AISI | 420 |
| EN / W.Nr. | X20Cr13 (1.4021), X30Cr13 (1.4028), X39Cr13 (1.4031) |
| JIS | SUS420J1, SUS420J2 |
420 covers a range of carbon levels; the higher-carbon versions get harder. Name the exact grade on the drawing.
Typical chemical composition
| Element | % |
|---|---|
| Carbon (C) | About 0.15–0.40 |
| Chromium (Cr) | About 12.0–14.0 |
| Manganese (Mn) | Up to about 1.0 |
| Silicon (Si) | Up to about 1.0 |
Values are typical. The exact limits depend on the standard and supplier; ask for the mill test certificate when it matters.
Typical uses
- Knives, blades and scissors
- Surgical and dental instruments
- Valve parts, pump shafts and bushes
- Plastic mould plates (mould-quality 420)
- Measuring tools
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Questions
- Is SS 420 magnetic?
- Yes. Martensitic stainless steels such as 410 and 420 are magnetic, unlike 304 and 316.
- SS 420 or SS 304?
- 304 resists corrosion better and cannot be hardened by heat treatment. 420 can be hardened, so it is chosen where hardness or a cutting edge matters more than maximum corrosion resistance.
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 9 October 2026.