Primary Mechanical Properties of SUS 420J1 Stainless Steel

The mechanical properties of SUS 420J1 stainless steel are predominantly defined by its martensitic structure and, critically, by its response to heat treatment. Unlike austenitic steels, its as-rolled or annealed state is just the starting point; its true potential is unlocked through quenching and tempering, allowing for a wide range of strength and toughness combinations.

In its annealed condition, SUS 420J1 stainless steel exhibits moderate strength and good ductility, with a typical tensile strength of around 540 MPa and a Brinell hardness of approximately HB 235. This soft state is ideal for machining and forming operations. However, the material's key value lies in its hardenable nature. When subjected to an oil or air quench from a temperature between 980-1050°C, it forms a hard, metastable martensite. Subsequent tempering is then employed to tailor the final properties. By adjusting the tempering temperature and time, engineers can achieve a precise balance. Tempering at lower temperatures (150-200°C) preserves very high hardness, often reaching HRC 50-55, which is essential for cutting edges and wear resistance.

Conversely, tempering at higher temperatures (over 600°C) significantly increases toughness and ductility at the expense of some hardness, making the steel suitable for structural components requiring impact resistance. This heat-treatable versatility means a single SUS 420J1 stainless steel can be processed to meet diverse application demands, from the high wear resistance needed in bearing components to the robust strength required for valve parts and shafts, all while maintaining its fundamental stainless characteristics.