How is alloy structural steel classified by application characteristics?

It is divided into quenched-tempered alloy structural steel and carburized alloy structural steel. Quenched-tempered grades such as 4130 and 4340 are heat-treated to obtain integrated strength and toughness for shafts, gears and pressure-bearing parts. Carburized low-carbon alloy structural steel receives surface carburizing treatment to achieve hard wear-resistant outer layers while retaining tough inner cores, perfect for transmission gears, pins and bearings suffering heavy surface friction. Each category adopts exclusive smelting and heat treatment workflows to fit distinct load and wear working conditions.