420 Stainless Steel
A 13% chromium martensitic stainless with carbon for high hardness
Typical values for the temper in the title
420 contains more carbon than 410 (at least 0.15%, in practice usually 0.2–0.4%). The carbon allows higher hardness after hardening, so it is used for knives, surgical instruments and plastic molds.
When hardened with a low-temperature temper, and especially with a polished surface, it reaches its best corrosion resistance. Annealed, resistance is lower.
Mechanical and physical properties
| Property | Value | Note |
|---|---|---|
| Tensile strength Rm | 586–1900 MPa | |
| Yield strength Rp0.2 | 414–1650 MPa | |
| Elongation A | 25–8% | |
| Hardness | 195 → HRC 50-56 | |
| Modulus of elasticity E | 200 GPa | |
| Density ρ | 7.73 g/cm³ | |
| Machinability | 65% | relative rating in the site database |
Chemical composition (wt %)
| Element | Range | Role |
|---|---|---|
| Cr chromium | 12.0–14.0 | corrosion resistance |
| C carbon | min 0.15 (0.15–0.40 in producer data) | hardness |
| Mn manganese | max 1.00 | |
| Si silicon | max 1.00 | |
| Fe iron | balance |
Ranges per ASTM A276 and A240, and producer data (ATI). For purchasing, rely on the standard in the order.
Conditions and heat treatment
Martensitic stainless is hardened like steel: heating to the austenite range (usually 925–1070 °C), rapid cooling, then tempering. The tempering temperature sets the balance between hardness and toughness.
| Condition | Properties | When to choose it |
|---|---|---|
| Annealed | soft, for machining | the common delivery condition |
| Hardened, low-temperature temper | high hardness and best corrosion resistance | knives, tools and molds |
| Tempering in the intermediate range | tempering around 400–580 °C lowers toughness and corrosion resistance, so it is avoided |
Applications
- Knives and cutlery
- Surgical and dental instruments
- Plastic injection molds
- Wear-resistant shafts and valves
- Measuring instruments
Fabrication
Heat treatment
Hardened in oil or air, and tempered low for maximum hardness.
Polishing
Takes an excellent polish, so it is common in plastic molds.
Welding
Difficult: the higher carbon produces a hard, brittle zone. Preheat and post-weld treatment are needed.
Compared with similar materials
| Material | Rm / Rp0.2 | Welding | When it is the better choice |
|---|---|---|---|
| 410 | 480–830 / 275–620 MPa | Medium — Preheat | less carbon: more weldable and less hard · material page |
| 440C | 760–1900 / 450–1860 MPa | Not recommended | harder, for bearings and tools · material page |
| 431 | 860–1035 / 655–760 MPa | Difficult — Preheat 150-260°C | more corrosion resistant · material page |
Common mistakes
Leaving the part annealed
In that condition corrosion resistance is also low. 420 works best hardened.
Ordering "420" without stating carbon
The carbon range is wide, and the achievable hardness changes with it. State the version or the required hardness.
Welding without proper treatment
High risk of cracking.
Equivalents, standards and supply
| EN | 1.4021 (also 1.4028 / 1.4034, depending on carbon) |
|---|---|
| DIN | X20Cr13 |
| JIS | SUS420J1 |
| Standards | ASTM A240 / EN 10088-2 |
| Forms | plate · rod |
| Producers | Outokumpu · Aperam · Valbruna |
Learn more
Values are typical and for comparison only. For design, rely on the standard and on the mill certificate. Sources: ASTM A240, ASTM A276 and EN 10088 (composition), producer data sheets, and the METAL HUB materials database.
Updated: October 31, 2026