440A Stainless Steel
A 17% chromium martensitic stainless steel with high carbon
Typical values for the temper in the title
440A contains about 17% chromium and 0.60–0.75% carbon. The high carbon forms hard martensite and carbides after hardening, so it reaches a hardness of up to about 56 HRC.
Of the three versions (A, B, C) it has the least carbon, so it is the toughest and most corrosion resistant of them, with slightly lower hardness than 440C.
Mechanical and physical properties
| Property | Value | Note |
|---|---|---|
| Tensile strength Rm | 725–1790 MPa | |
| Yield strength Rp0.2 | 415–1650 MPa | |
| Elongation A | 20% | |
| Hardness | 220 → HRC 55-57 | |
| Modulus of elasticity E | 200 GPa | |
| Density ρ | 7.68 g/cm³ | |
| Machinability | 55% | relative rating in the site database |
Chemical composition (wt %)
| Element | Range | Role |
|---|---|---|
| Cr chromium | 16.0–18.0 | corrosion resistance |
| C carbon | 0.60–0.75 | hardness and carbides |
| Mo molybdenum | max 0.75 | |
| 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 | delivery condition |
| Hardened, tempered at 150–370 °C | up to about 56 HRC | bearings, knives, wear parts |
Applications
- Knives and cutting tools
- Surgical instruments
- Lightly loaded bearings
- Valve parts
- Tools
Fabrication
Heat treatment
Hardened in oil or air, and tempered low (150–370 °C). Temper immediately after hardening.
Machining
Machine annealed, and grind after hardening.
Welding
Not suited to welding.
Compared with similar materials
| Material | Rm / Rp0.2 | Welding | When it is the better choice |
|---|---|---|---|
| 440C | 760–1900 / 450–1860 MPa | Not recommended | more carbon: harder · material page |
| 420 | 586–1900 / 414–1650 MPa | Difficult — Preheat 200C | cheaper, lower hardness · material page |
| 431 | 860–1035 / 655–760 MPa | Difficult — Preheat 150-260°C | more corrosion resistant, less hard · material page |
Common mistakes
Choosing 440A for a shock-loaded part
Toughness is low. For such a part, 431 or 17-4PH.
Leaving time between hardening and tempering
The part may crack. Temper immediately.
Welding
The high carbon causes cracking.
Equivalents, standards and supply
| EN | 1.4109 |
|---|---|
| JIS | SUS440A |
| Standards | ASTM A240 |
| Forms | plate · rod |
| Producers | Carpenter · Böhler · 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