JIS SUS420J1 Stainless Steel: Martensitic Grade for Cutlery, Surgical Instruments & Wear-Resistant Components
JIS SUS420J1 (equivalent to AISI 420/ASTM 420) is a martensitic stainless steel grade renowned for its hardness, wear resistance, and moderate corrosion resistance after heat treatment. With a carbon content of 0.16-0.25% and 12-14% chromium, this grade achieves high strength (up to 55 HRC) through quenching and tempering, making it ideal for precision cutting tools, medical devices, and high-stress mechanical parts. This article explores its chemical composition, mechanical properties, heat treatment processes, and industry-specific applications.
1. Chemical Composition (JIS G4303 Standard)
| Element | Content Range | Function |
|---|---|---|
| Carbon (C) | 0.16 – 0.25% | Enhances hardness and wear resistance; higher carbon improves edge retention in cutting tools |
| Chromium (Cr) | 12.00 – 14.00% | Provides corrosion resistance via passive Cr₂O₃ film; stabilizes martensitic structure |
| Manganese (Mn) | ≤ 1.00% | Improves hardenability; aids in deoxidation during smelting |
| Silicon (Si) | ≤ 1.00% | Enhances strength and oxidation resistance at elevated temperatures |
| Phosphorus (P) | ≤ 0.040% | Controlled impurity; excess reduces toughness and corrosion resistance |
| Sulfur (S) | ≤ 0.030% | Minimized to prevent hot cracking and improve machinability |
2. Mechanical Properties (After Heat Treatment)
- Tensile Strength (σb): ≥ 585 MPa (quenched and tempered at 200-400°C)
- Yield Strength (σ0.2): ≥ 345 MPa (varies with tempering temperature)
- Elongation (δ): ≥ 12% (reduced ductility due to martensitic structure)
- Hardness (HRC): 48-55 (after oil quenching at 980-1040°C + low-temperature tempering)
- Impact Toughness (CVN): ≥ 15 J (lower than austenitic grades; avoid high-impact applications)
3. Heat Treatment Processes
- Annealing: Heat to 800-900°C, slow cool in furnace to ≤ 20°C/h to soften (≤ 22 HRC) for machining. Structure: ferrite + carbides.
- Hardening (Quenching): Austenitize at 980-1040°C for 30-60 min, oil quench to achieve martensite (50-55 HRC). Risk: distortion or cracking if cooling is uneven.
- Tempering: Reheat to 150-400°C for 1-2 hours to relieve stresses and adjust hardness:
- 150-200°C: 52-55 HRC (maximum hardness; minimal toughness)
- 200-300°C: 48-52 HRC (balanced hardness/toughness for cutlery)
- 300-400°C: 40-45 HRC (improved toughness for surgical tools)
- Stress Relieving: Optional post-machining treatment at 600-700°C to reduce residual stresses without softening.
4. Key Application Fields
Cutlery & Kitchenware
High-end chef knives, scissors, and razor blades — retains sharpness due to 50+ HRC hardness. Requires regular cleaning to prevent pitting in humid environments.
Medical & Dental Instruments
Surgical scalpels, forceps, and dental probes — corrosion-resistant when passivated; sterilizable via autoclave (≤ 250°C to avoid tempering effects).
Mechanical Components
Bearings, valves, and pump shafts for mild corrosive media (e.g., water, oils). Avoid use in chloride-rich or acidic environments without protective coatings.
Mold & Tooling
Plastic injection molds (non-abrasive polymers), food-processing dies, and forming tools — cost-effective alternative to tool steels for low-volume production.
5. Comparison with Related Grades
| Grade | Carbon (C) | Key Properties | Typical Use |
|---|---|---|---|
| SUS420J1 | 0.16-0.25% | Balanced hardness/corrosion resistance; heat-treatable to 50-55 HRC | Cutlery, surgical tools, general-purpose wear parts |
| SUS420J2 | 0.26-0.40% | Higher hardness (55-58 HRC) but reduced toughness; lower corrosion resistance | Industrial blades, shear knives, high-wear components |
| SUS440A | 0.60-0.75% | Extreme hardness (58-60 HRC) but brittle; poor weldability | High-end razor blades, bearing balls, valve seats |
| SUS410 | 0.08-0.15% | Lower hardness (40-45 HRC) but better ductility and weldability | Fasteners, turbine blades, mild corrosive environments |
6. Processing & Usage Guidelines
- Machining: Perform in annealed state (≤ 22 HRC) using carbide tools; expect tool wear due to work hardening. Use sulfurized oils for drilling/tapping.
- Welding: Preheat to 200-300°C and post-weld temper at 600-700°C to prevent martensite cracking. ER410/ER420 filler recommended.
- Corrosion Resistance: Inferior to austenitic grades (e.g., 304/316); requires passivation (nitric acid treatment) and regular maintenance to prevent rust in humid conditions.
- Surface Finishing: Polished (mirror/brush) or electropolished surfaces improve corrosion resistance. Avoid rough finishes in food/medical applications.
- Quality Certification: Verify JIS G4303 compliance via mill test reports (MTR); ensure hardness testing (Rockwell C) meets specifications post-heat treatment.
7. Request a Quote for JIS SUS420J1 Stainless Steel
Need precision-cut SUS420J1 sheets, bars, or custom heat-treated components? Contact Baoli Iron & Steel for competitive pricing, technical support, and fast lead times on martensitic stainless steel products tailored to your specifications.