SUS 420J1 Stainless Steel Heat Treatment Process and Application

The utility of SUS 420J1 stainless steel is fundamentally defined by its heat treatment process. Unlike austenitic grades, its mechanical properties are not fixed; they are developed and tailored through precise thermal cycles, transforming its inherent potential into high performance for demanding applications. The process is a critical sequence of hardening and tempering, each stage meticulously controlled to achieve the desired balance of hardness, strength, and toughness.
The first essential stage is austenitizing, or hardening, where the material is heated to a temperature between approximately 980°C and 1050°C. This soaks the carbon into a solid solution within the austenite phase. The SUS 420J1 stainless steel is then rapidly cooled, or quenched, typically in oil or air, to transform the austenite into a very hard and brittle microstructure known as martensite. While this state provides extreme hardness, it lacks the necessary toughness for most practical uses.
The subsequent and equally vital stage is tempering. The quenched steel is reheated to a specific temperature, typically ranging from 150°C to 600°C or higher, and held for a predetermined time. This process relieves internal stresses, improves toughness, and adjusts the final hardness. A low tempering temperature (150-300°C) preserves most of the quenched hardness, ideal for cutting edges and wear-resistant parts. Conversely, a higher tempering temperature (400-600°C) significantly increases ductility and impact resistance, making the steel suitable for structural components like shafts and valve parts.
Therefore, the application dictates the heat treatment recipe. For surgical instruments, knives, and bearing components, a low-temperature temper achieves maximum hardness and wear resistance. For engineering components requiring a blend of strength and toughness, a higher temper is applied. This customizable nature makes heat-treated SUS 420J1 stainless steel a versatile material, its properties precisely engineered from the mill to meet specific operational challenges.