Alloy structural steel
Alloy structural steel is generally divided into tempered structural steel and surface hardened structural steel.
① Tempered structural steel The carbon content of this type of steel is generally about 0.25%~0.55%, for the structural parts of the given cross-section size, in the tempered treatment (quenching and tempering), if the quenching along the cros...
Alloy structural steel is generally divided into tempered structural steel and surface hardened structural steel.
① Tempered structural steel The carbon content of this type of steel is generally about 0.25%~0.55%, for the structural parts of the given cross-section size, in the tempered treatment (quenching and tempering), if the quenching along the cross-section, then the mechanical properties are good, if the quenching is not permeable, there is free ferrite in the microstructure, then the toughness is reduced. For steels with tempering brittleness tendency such as manganese steel, chromium steel, nickel-chromium steel, etc., they should be cooled quickly after tempering. The quenching critical diameter of this kind of steel increases with the increase of grain size and alloying element content, for example, 40Cr and 35SiMn steel is about 30~40mm, and 40CrNiMo and 30CrNi2MoV steel is about 60~100mm, which is often used to manufacture shafts, connecting rods and other structural parts that bear large loads.
② Surface hardened structural steel is used to manufacture parts with hard, wear-resistant surface and flexible heart, such as gears, shafts, etc. In order to make the core toughness of the parts high, the carbon content in the steel should be low, generally 0.12~0.25%, and there is an appropriate amount of alloying elements to ensure appropriate hardenability. Nitriding steel also needs to add alloying elements that are easy to form nitrides (such as Al, Cr, Mo, etc.). Carburized or carbonitriding steel, after carburizing or carbonitriding at 850~950 ° C, quenching and tempering at low temperature (about 200 ° C). Nitriding steel after nitriding treatment (480~580℃), direct use, no longer by quenching and tempering treatment.
