SUS420J1 Stainless Steel: Medium-Carbon Martensitic Grade For General Cutting Tools

SUS420J1 is a medium-carbon martensitic stainless steel (C=0.16%-0.25%, Cr=12.0%-14.0%) with good hardenability. It can obtain high hardness (48-53HRC) after quenching and tempering, and has moderate corrosion resistance and wear resistance, making it a common material for general cutting tools and hardware.

Core Parameters

Chemical Composition (wt%): C=0.16-0.25, 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 ≥520MPa, Elongation ≥15%, Hardness 48-53HRC

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

Equivalent Grades: EN 1.4021, UNS S42000, GB 20Cr13

Performance Advantages: High hardness and wear resistance after heat treatment; good machinability in the annealed state; moderate corrosion resistance in dry atmospheric environments; low cost, suitable for mass-produced tools.

Typical Applications: Household kitchen knives, scissors, fruit knives, utility knives, mold cores, valve stems, fasteners requiring high strength, mechanical seals.

Practical Q&A

Q1: What is the optimal heat treatment process for SUS420J1? A1: Quenching at 980-1050℃, oil cooling + tempering at 150-200℃, air cooling. This process can achieve hardness of 48-53HRC, balancing wear resistance and toughness, and avoiding excessive brittleness.

Q2: Is SUS420J1 suitable for making high-quality knives? A2: It is suitable for household and general-purpose knives, but not for high-end professional knives. Its hardness (48-53HRC) is lower than that of high-carbon tool steel (58-62HRC), and edge retention is relatively poor.

Q3: Why does SUS420J1 rust easily? A3: Its chromium content (12-14%) is lower than that of 304 (18-20%), and there is no nickel to stabilize the passivation film. The oxide film is thin and easy to be damaged by chloride ions or acidic media, leading to rust.

Q4: Can SUS420J1 be welded? A4: It can be welded, but preheating to 200-300℃ before welding is required to prevent cold cracking; use ER420 welding wire; perform tempering at 150-250℃ after welding to eliminate welding stress and restore toughness.

Q5: How to distinguish SUS420J1 from SUS420J2? A5: The key difference is carbon content: SUS420J1 (0.16-0.25%) vs. SUS420J2 (0.26-0.35%). SUS420J2 has higher hardness (52-57HRC) after heat treatment, better wear resistance, but lower toughness.