420 Stainless Steel: Versatile Martensitic Stainless Steel For Medium-Hardness Applications

420 stainless steel is a classic martensitic stainless steel primarily composed of 12%-14% chromium, with no nickel added. It achieves high hardness and strength through heat treatment (quenching and tempering), while maintaining basic corrosion resistance. Unlike austenitic stainless steels, it is magnetic at room temperature and exhibits good machinability after annealing. Its cost-effectiveness and adjustable mechanical properties make it widely used in mechanical manufacturing and precision components.

Core Parameters

Chemical Composition (wt%): C=0.15-0.25, Si≤1.00, Mn≤1.00, P≤0.040, S≤0.030, Cr=12.00-14.00, Fe=Balance

Mechanical Properties (Quenched & Tempered): Tensile Strength ≥725MPa, Yield Strength ≥515MPa, Elongation ≥15%, Hardness ≥217HB (annealed) / ≥50HRC (quenched & tempered)

Service Temperature: -20℃ to 300℃ (continuous service)

Equivalent Grades: SUS420J1 (JIS), EN 1.4021 (EN), UNS S42000 (ASTM)

Performance Advantages: High hardness and wear resistance after heat treatment; good corrosion resistance in atmospheric, fresh water and mild acid-alkali environments; excellent machinability and grindability; low cost due to no nickel addition; magnetic, suitable for magnetic separation scenarios.

Typical Applications: Knife blades, scissors, surgical instruments, mold parts, valve cores, pump shafts, precision bearings, mechanical seals, fasteners requiring high strength.

Practical Q&A

Q1: What heat treatment process is suitable for 420 stainless steel? A1: The standard process is quenching (980-1050℃, oil cooling) + tempering (150-200℃, air cooling). This achieves hardness of 50-55HRC, balancing strength and toughness. For parts requiring higher toughness, tempering at 300-400℃ can be used, but hardness will decrease to 35-40HRC.

Q2: Is 420 stainless steel suitable for food contact applications? A2: Yes, but only for non-acidic food contact scenarios (such as stainless steel scissors for food packaging). It is not recommended for long-term contact with acidic foods (e.g., citrus, vinegar) as it may corrode and release chromium ions. Food processing equipment requiring high corrosion resistance should use 304 stainless steel.

Q3: Why does 420 stainless steel rust more easily than 304? A3: Its chromium content (12%-14%) is lower than 304 (18%-20%), and there is no nickel to stabilize the passivation film. The oxide film is relatively thin and easily damaged. Regular cleaning and oiling can improve its corrosion resistance.

Q4: Can 420 stainless steel be welded? A4: It can be welded, but preheating (200-300℃) is required before welding to prevent cold cracking, and post-weld tempering (150-250℃) should be performed immediately. Use ER420 welding wire, and avoid large heat input to prevent grain coarsening.

Q5: What is the difference between 420 and 420J2 stainless steel? A5: 420J2 (UNS S42020) has a higher carbon content (0.20-0.30%) than 420 (0.15-0.25%), so its hardness after heat treatment is higher (up to 58HRC) and wear resistance is better, but toughness is slightly lower. It is more suitable for wear-resistant components such as high-hardness knife blades.