SUS420J1 Stainless Steel: Medium-Carbon Martensitic Grade for General Wear-Resistant Tools

SUS420J1 is a medium-carbon martensitic stainless steel (C=0.16%-0.25%, Cr=12.0%-14.0%), which is a common general-purpose grade in the 420 series. It has good hardenability, can obtain high hardness (48-53HRC) after quenching and tempering, and has moderate corrosion resistance and wear resistance. It is widely used in mass-produced hardware tools and low-cost wear-resistant components.

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/T 20Cr13

Performance Advantages: High hardness and wear resistance after heat treatment; good machinability in annealed state (hardness ≤229HB); moderate corrosion resistance in dry atmospheric environment; low cost, suitable for mass production; can be polished to medium surface finish.

Typical Applications: Household kitchen knives, scissors, fruit knives, utility knife blades, mold cores for general plastic molding, valve stems and seats for low-pressure systems, fasteners requiring high strength, mechanical seal rings, textile machine parts.

Practical Q&A

Q1: What is the optimal heat treatment process for SUS420J1 to ensure wear resistance? A1: Quench at 980-1050℃, oil cool + temper at 150-200℃, air cool. This process can stably achieve hardness of 48-53HRC, maximize wear resistance, and ensure certain toughness to avoid brittle fracture during use.

Q2: Why does SUS420J1 rust easily in humid environments? A2: Its chromium content (12-14%) is lower than that of austenitic stainless steel (such as 304's 18-20%), and there is no nickel to stabilize the passivation film. The surface oxide film is thin and easy to be damaged by moisture and chloride ions, leading to rust. Regular passivation and anti-rust treatment are required.

Q3: Can SUS420J1 be welded? A3: It can be welded, but preheating to 200-300℃ before welding is necessary to reduce welding stress and prevent cold cracking. Use ER420 welding wire, and perform tempering at 150-250℃ after welding to eliminate residual stress and restore toughness.

Q4: How to distinguish SUS420J1 from SUS420J2 in practical applications? A4: The core difference is carbon content: SUS420J1 (0.16-0.25%) < SUS420J2 (0.26-0.35%). In terms of performance, SUS420J1 has better toughness (impact toughness &ge;25J) but slightly weaker wear resistance, while SUS420J2 has higher hardness (52-57HRC) and better wear resistance but lower toughness.

Q5: Is SUS420J1 suitable for making plastic molds? A5: Yes. It is suitable for small and medium-sized plastic molds with general wear requirements. After heat treatment and polishing, it can meet the surface finish requirements of ordinary plastic products. For molds requiring high gloss or corrosion resistance (e.g., PVC molding), it is recommended to use SUS440C or austenitic stainless steel.