440C / X105CrMo17
1.4125Highest-hardness standard martensitic stainless steel. Achieves 57-60 HRC — the hardest commonly available stainless grade. Excellent wear resistance from chromium carbides. Used for bearings, races, valve components, surgical instruments, high-end cutlery, and precision molds.
International equivalents
| Flag | Standard | Country | Grade | Number | Match |
|---|---|---|---|---|---|
| 🇺🇸 | AISI | USA | AISI 440C | S44004 | REF |
| 🇪🇺 | EN | Europe | X105CrMo17 | 1.4125 | 100% |
| 🇯🇵 | JIS | Japan | SUS440C | — | 97% |
| 🇨🇳 | GB | China | 9Cr18Mo | — | 93% |
Sources: ASTM A276, EN 10088-3, JIS G4303, GB/T 1220
Chemical composition comparison (wt%)
Side-by-side: 440C / X105CrMo17 (EN) (EN 10088-3) vs SUS440C (JIS)
| Element | 440C / X105CrMo17 (EN) | SUS440C (JIS) | Overlap |
|---|---|---|---|
| C | 0.95–1.2% | — | — |
| Si | 0–1% | — | — |
| Mn | 0–1% | — | — |
| P | 0–0.04% | — | — |
| S | 0–0.03% | — | — |
| Cr | 16–18% | — | — |
| Mo | 0.4–0.8% | — | — |
Mechanical properties
Hardened Tempered
| Property | Value | Unit |
|---|---|---|
| Hardness HRC | 57–60 | HRC |
| Tensile Strength | ≥ 690 | MPa |
| Yield Strength | ≥ 440 | MPa |
| Elastic Modulus | ≥ 215 | GPa |
| Density | ≥ 7.8 | g/cm3 |
Annealed
| Property | Value | Unit |
|---|---|---|
| Hardness HB | ≤ 285 | HB |
Heat treatment
| Process | Temperature | Medium | Holding Time | Notes |
|---|---|---|---|---|
| quenching | 1010–1065 °C | oil | 30-60 min | Higher temp = more Cr in solution = better corrosion resistance, but coarser grain |
| tempering | 150–300 °C | air | min 2 hours | Low temper for max hardness (57-60 HRC). Do not temper 400-550°C. |
| annealing | 840–900 °C | furnace | 2-4 hours | Slow furnace cool to 600°C, then air |
Compatibility verdict
440C / X105CrMo17 and SUS440C: 97% composition match
Close equivalents but NOT identical.
Related materials
304 Stainless Steel
1.4301The most widely used austenitic stainless steel. Excellent corrosion resistance, good formability and weldability. Standard choice for food processing, chemical, and architectural applications.
316L
1.4404Low-carbon austenitic stainless steel with molybdenum addition. Superior corrosion resistance to 304, especially against chlorides and pitting. Standard choice for chemical processing, marine, medical implants, and pharmaceutical equipment.
430 Stainless Steel
1.4016Ferritic chromium stainless steel with good corrosion resistance and formability. Lower cost than austenitic grades. Used for automotive trim, kitchen sinks, architectural panels, and appliance components.
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