40Cr is a standard steel grade in my country's GB standard and is widely used in the machinery manufacturing industry. After quenching and tempering, 40Cr exhibits excellent overall mechanical properties, good low-temperature impact toughness, and low notch sensitivity. The steel also exhibits excellent hardenability, capable of hardening to diameters of 28 to 60 mm in water quenching and 15 to 40 mm in oil quenching.

After quenching and tempering, it is suitable for manufacturing various transmission parts that undergo carbonitriding treatment, such as gears and shafts with large diameters and good low-temperature toughness, and for manufacturing mechanical parts that withstand medium loads and medium speeds, such as steering knuckles and rear axles of automobiles, as well as gears, shafts, worms, spline shafts on machine tools, etc.