The 42SiMn (GB/T 3077-1988) alloy steel, a kind of medium carbon low alloy structural steel, is mainly used in the manufacture of tempered type parts with medium and high strength grade stress and complex shape, such as shafts, gears, connecting rods, and carburising parts. With superior bending and formation processability, it is widely used in medium and heavy load vehicles, boilers, construction machinery and agricultural tools.
At room temperature, the hardness range of 42SiMn is about 250HBS to 300HBS, and the yield strength is about 930Mpa. The sensitivity to quenching temperature is low. The comsumption of 42SiMn alloy steel is less than other carbon and alloy steels. It is much easier to process with machining and heat treatment, and can improve machining quality and reduce tool wear with appropriate cutting conditions. The 42SiMn alloy steel can be stable in air, gas, water and organic electrolyte solution. The microstructure of the heat-treated parts of 42SiMn steel is mainly tempered sorbite, and the hardenability is low. The maximum hardening depth of some steels is not more than 5mm.
The carburizing treatment of the 42SiMn alloy steel generally needs preheating, carburizing and quenching. The pre-heat temperature is 300-370 C, the carburizing temperature is 850-900 C, and the furnace cooling time should be controlled adequately when carburizing and cooling. The quenching medium is usually oil, and the oil temperature is about 820-860 C. After carburizing and quenching, tempering should be carried out, and tempering temperature should be high enough to provide requirements for strength and toughness.
Common heat treatment methods of 42 SiMn steels are tempering, nitriding, quenching and tempering, and carburizing quenching. Tempering is usually performed after quenching to adjust hardness and plasticity. Nitriding can not only improve the wear resistance and fatigue strength, but also obtain the surface with nitriding layer which a kind of corrosion resistance. Quenching and tempering can also improve the strength, but also make the parts have good comprehensive performance of comprehensive properties including improved toughness and plasticity. Carburizing and quenching can improve the wear resistance and fatigue resistance of parts.
42 SiMn alloy steel has good mechanical properties, excellent hardenability, limited welding performance and easy to handle. In vehicle and construction machinery manufacturing, 42SiMn is used to make parts with medium and high strength, such as shafts, gears, connecting rods, and high-hardness components with good wear resistance and fatigue strength after carburizing quenching treatment. So it is widely used in field of medium and heavy load vehicle, boiler, construction machinery and agricultural tools.
