AISI 410 and AISI 420 are the two basic grades of martensitic stainless steel. Unlike the austenitic 304/316 family, these steels are hardenable and magnetic. Both contain roughly 12–14% chromium; the difference between them is in carbon.
The carbon content sets the hardness that can be reached
In martensitic stainless steels, hardness comes directly from carbon. In AISI 410 carbon is max 0.15%, in AISI 420 0.16 – 0.25%. Chromium is also slightly higher in 420 (12–14% against 11.5–13.5%).
That difference is reflected in the values reached after hardening. It can even be seen in the annealed-condition figures on our datasheets: for 410 the tensile strength is 480 MPa and the yield 275 MPa, while for 420 they are 655 MPa and 345 MPa.
In return, 410 is a tougher steel and easier to weld. As carbon rises, weldability falls and the cracking risk increases — 420 is generally used for parts that are not welded.
Comparison in numbers
| PROPERTY | AISI 410 | AISI 420 |
|---|---|---|
| Carbon (C) | max 0.15% | 0.16 – 0.25% |
| Chromium (Cr) | 11.5 – 13.5% | 12 – 14% |
| Nickel (Ni) | max 0.75% | — |
| Manganese (Mn) | max 1.00% | max 1.00% |
| Tensile strength Rm | 480 MPa | 655 MPa |
| Yield strength Rp0.2 | 275 MPa | 345 MPa |
| Elongation A50 | 16% | 25% |
| Hardness | — | max 196 HB (annealed) |
| Density | 7.80 g/cm³ | 7.80 g/cm³ |
| Thermal conductivity | 24.9 W/m·K | 24.9 W/m·K |
| Melting range | 1480 – 1530 °C | 1454 – 1510 °C |
| UNS | S41000 | S42000 |
| W.Nr (DIN/EN) | 1.4006 | 1.4021 |
| AMS | 5504 · 5505 · 5591 · 5609 · 5611 · 5612 · 5613 · 5614 | 5506 · 5620 · 5621 |
| ASTM | A240 · A276 · A479 · A493 · A580 · F899 | A276 · A314 · A484 · A580 |
Values are taken from our product datasheets; section thickness and the applied heat treatment regime change the result.
Which one, and when?
AISI 410 is preferred — valve components, pump shafts, turbine blades, steam line fittings, parts that need moderate hardness and have to be welded. If the specification calls out AMS 5504 or AMS 5505, the grade being asked for is 410.
AISI 420 is required — knives and cutting tools, surgical instruments, plastic injection moulds, shafts and pins, parts exposed to wear. Where higher hardness is needed, the 420B and 420C versions are used.
The top of the family
For much higher hardness and wear resistance there is AISI 440C; we covered the difference in our AISI 420 – AISI 440C comparison. For the intermediate grades see our AISI 420B, AISI 420C and AISI 431 pages.
Technical datasheets
AISI 410 — chemical composition, mechanical values, standard equivalents
AISI 420 — chemical composition, mechanical values, standard equivalents
Both grades are supplied to order in round bar, flat bar, plate, sheet, pipe and forged forms. Contact us for a quotation.