What is 1.4125 Stainless Steel?
Jan 14, 2026
Leave a message
1.4125 stainless steel, commonly known as 440C or UNS S44004, is a high-carbon, high-chromium martensitic stainless steel renowned for achieving the highest hardness and wear resistance among standard stainless steel grades. It is widely used for applications requiring extreme hardness and moderate corrosion resistance, such as high-end bearings, precision knives, surgical instruments, and valve components.
This premium high-hardness martensitic grade is standardized under key international systems.
| Standard | Equivalent Grade |
|---|---|
| EN (Europe) | 1.4125 |
| ASTM/AISI (USA) | 440C, UNS S44004 |
| JIS (Japan) | SUS440C |
| KS (Korea) | STS440C |
Its high carbon and chromium content are key to its extreme hardness and wear resistance.
| Element | C | Si | Mn | P | S | Cr | Mo |
|---|---|---|---|---|---|---|---|
| Content (%) | 0.95 - 1.20 | ≤ 1.0 | ≤ 1.0 | ≤ 0.04 | ≤ 0.03 | 16.0 - 18.0 | 0.4 - 0.8 |
It achieves very high hardness but with reduced toughness compared to lower-carbon martensitic grades.
| Condition | Yield Strength (Rp0.2) | Tensile Strength (Rm) | Elongation (A) | Hardness (HRC) |
|---|---|---|---|---|
| Annealed | ~ 450 MPa | ~ 740 MPa | ~ 12% | ~ 25 HRC |
| Hardened & Tempered | ≥ 700 MPa | ≥ 850 MPa | ≥ 2% | 58 - 62 HRC |
Key Characteristics and Applications of 1.4125 / 440C
Extreme Hardness and Wear Resistance: Capable of reaching hardness levels up to 62 HRC, providing outstanding abrasion resistance and edge retention.
Moderate Corrosion Resistance: Offers better corrosion resistance than many tool steels due to its high chromium content, but is not suitable for severe corrosive environments like marine or chemical exposure.
Magnetic and Brittle: Strongly magnetic and can be brittle in the fully hardened state, requiring careful tempering to balance hardness and toughness.
Primary Applications:
Bearings: Ball and roller bearings for precision instruments, aerospace, and medical devices.
Cutlery and Blades: High-end knives, surgical scalpels, and industrial blades.
Valve Components: Seats, balls, and stems in high-wear applications.
Nozzles and Wear Parts: Components subjected to abrasive conditions in manufacturing and processing.
What is the key difference between 440C (1.4125) and 440B (1.4112)?
The main difference is carbon content: 440C contains 0.95–1.20% C, while 440B contains 0.75–0.95% C. This higher carbon allows 440C to achieve greater maximum hardness (up to 62 HRC vs. ~58 HRC for 440B) and superior wear resistance, but at the cost of reduced toughness and increased brittleness. 440C is chosen for applications where maximum hardness is critical, while 440B offers a better balance of hardness and toughness.
What are the heat treatment guidelines for 440C stainless steel?
To achieve maximum hardness, 440C is typically austenitized at 1010–1065°C, followed by oil quenching. It is then tempered at temperatures between 150–370°C, often with multiple tempering cycles to ensure stress relief and dimensional stability. Lower tempering temperatures yield higher hardness; higher temperatures improve toughness but reduce hardness. Preheating is recommended to prevent cracking during hardening, especially for complex or thick sections.
Looking for a Reliable Supplier of 1.4125 / 440C Stainless Steel?
GNEE Steel supplies premium high-hardness 440C (1.4125) stainless steel in bar, wire, and precision ground stock, available in annealed or heat-treated conditions for demanding wear-resistant applications. We provide full material certification and processing support. If you have any requirements, please feel free to contact us.
Send Inquiry