40Cr steel is a medium hardenability quenched and tempered steel, one of the widely used alloy structural steel grades in mechanical manufacturing. It boasts good hardenability, capable of being quenched through a diameter of 28~60mm in water quenching and 15~40mm in oil quenching. After heat treatment, 40Cr steel exhibits excellent comprehensive mechanical properties, along with good notch sensitivity and low-temperature impact toughness. After heat treatment, it is often subjected to surface high-frequency quenching or nitriding. When the hardness is between 174~229HBS, it has good machinability, with a relative machinability of 60%. The tensile strength, yield strength, and hardenability of 40Cr steel are higher than those of 40 steel, but its weldability is limited and prone to cracking. To save on Cr, under certain conditions, steel grades such as 40MnB, 45MnB, 35SiMn, 42SiMn, 40MnVB, 42MnV, 40MnMoB, and 40MnWB can be used to manufacture corresponding components instead of 40Cr steel.