SUS 420J1 Stainless Steel Chemical Composition Characteristics

The performance and application range of SUS 420J1 stainless steel are fundamentally dictated by its specific chemical composition. As a martensitic stainless steel, its elemental blueprint is precisely balanced to deliver a unique combination of hardness and corrosion resistance, setting it apart from other stainless families.
The defining components of SUS 420J1 are Chromium (Cr) and Carbon (C). The chromium content, typically ranging from **12% to 14%**, is the primary element conferring its "stainless" character. It forms a thin, passive chromium oxide layer on the surface, which provides resistance to tarnishing and corrosion in mild atmospheres, fresh water, and weak acids. The carbon content, controlled within **0.16% to 0.25%**, is the critical driver for hardness. This moderate carbon level is sufficient to allow for significant hardening through heat treatment (quenching and tempering), enabling the material to achieve high strength and excellent wear resistance, yet it remains lower than the more brittle 440C grade.
Other elements are meticulously controlled as impurities. Manganese (Mn) and Silicon (Si) are typically kept below 1.00% and 0.60% respectively, aiding in deoxidation during steelmaking and providing some solid solution strength. Phosphorus (P) and Sulfur (S) are restricted to very low levels (max 0.040% each) to minimize detrimental effects on ductility and toughness.
This specific chemistry—a careful synergy of chromium for basic corrosion protection and carbon for hardenability—makes SUS 420J1 an ideal candidate for applications like cutlery, surgical instruments, and general-purpose wear-resistant components, where a balance between performance and cost-effectiveness is essential.