DIN 1.4125 Stainless Steel: Martensitic Stainless Steel for High-Strength & Corrosion-Resistant Applications
DIN 1.4125 (AISI 440A) is a high-carbon martensitic stainless steel known for its exceptional hardness, wear resistance, and moderate corrosion resistance. With a chromium content of 16-18% and carbon content of 0.60-0.75%, this grade achieves a Rockwell hardness of up to 58 HRC after heat treatment, making it ideal for precision components, surgical instruments, and high-stress mechanical parts. This article covers its chemical composition, mechanical properties, heat treatment processes, and key industrial applications.
1. Chemical Composition (DIN EN 10088-3 Standard)
| Element | Content Range | Function |
|---|---|---|
| Carbon (C) | 0.60 – 0.75% | Enhances hardness and wear resistance; critical for martensitic transformation |
| Chromium (Cr) | 16.00 – 18.00% | Provides corrosion resistance via Cr₂O₃ passive film formation |
| Manganese (Mn) | ≤ 1.00% | Improves hardenability and deoxidation during smelting |
| Silicon (Si) | ≤ 1.00% | Enhances high-temperature oxidation resistance |
| Phosphorus (P) | ≤ 0.040% | Minimized to prevent embrittlement |
| Sulfur (S) | ≤ 0.030% | Controlled to avoid hot cracking and reduce machinability issues |
| Molybdenum (Mo) | ≤ 0.75% | Optional addition to improve pitting resistance in chloride environments |
2. Mechanical Properties (After Heat Treatment)
- Tensile Strength (Rm): ≥ 700 MPa (annealed), ≥ 1900 MPa (quenched & tempered)
- Yield Strength (Rp0.2): ≥ 450 MPa (annealed), ≥ 1700 MPa (quenched & tempered)
- Elongation (A5): ≥ 12% (annealed), ≥ 2% (hardened)
- Hardness: ≤ 255 HB (annealed), 55-58 HRC (quenched & tempered)
- Impact Toughness (KV): ≥ 20 J (tempered at 200-300°C)
3. Heat Treatment Processes
- Annealing: Heat to 800-900°C, slow furnace cooling to ≤ 600°C (10-20°C/h) to soften for machining (hardness ≤ 255 HB).
- Hardening: Austenitize at 1010-1070°C, oil or air quench to achieve martensitic structure (hardness 55-58 HRC).
- Tempering: Reheat to 150-370°C (low-temp) for secondary hardening or 400-700°C (high-temp) to improve toughness (trade-off with hardness).
- Stress Relieving: Heat to 600-650°C for 1-2 hours to reduce residual stresses post-machining/welding.
4. Key Application Fields
Precision Instruments
Surgical blades, dental tools, and scalpel handles — combines sharpness retention with sterilization compatibility (autoclave-safe).
Mechanical Components
Bearings, valves, pump shafts, and gears in corrosive environments (e.g., marine, chemical processing).
Cutting Tools
Knife blades, shear blades, and industrial cutters where edge retention and corrosion resistance are critical.
Aerospace & Defense
Fasteners, landing gear components, and missile parts requiring high strength-to-weight ratio and temperature stability.
5. Comparison with Similar Martensitic Grades
| Grade | Carbon Content | Hardness (HRC) | Key Application |
|---|---|---|---|
| DIN 1.4125 (440A) | 0.60-0.75% | 55-58 | Precision tools, surgical instruments |
| DIN 1.4112 (440B) | 0.75-0.95% | 58-60 | High-wear cutlery, industrial blades |
| DIN 1.4120 (440C) | 0.95-1.20% | 58-62 | Bearings, valve seats (highest wear resistance) |
| AISI 420 | 0.15-0.40% | 50-55 | General-purpose cutlery, turbine blades |
6. Selection & Processing Guidelines
- Machinability: Best in annealed condition (≤ 255 HB); use carbide tools and slow speeds for hardened states to avoid work hardening.
- Welding: Preheat to 200-300°C and post-weld temper at 600-700°C to prevent cracking; avoid in highly stressed weldments.
- Corrosion Resistance: Inferior to austenitic grades (e.g., 304/316) in chloride environments; passivate with nitric acid after machining.
- Surface Finishes: Polished (Ra ≤ 0.4 μm) for medical applications; shot peened for fatigue resistance in mechanical parts.
7. Request a DIN 1.4125 Stainless Steel Quote
For customized DIN 1.4125 stainless steel products (bars, sheets, or precision-machined components), contact our team with your specifications. We provide mill-certified materials with full traceability and technical support for heat treatment optimization.