4340 steel is nickel-chromium-molybdenum alloy steel . It will get high strength after the heat treat. And it has good toughness, fatigue resistance, impact toughness and etc. 4340 steel round bar sheet plate will get high tensile strength, hardness and toughness after heat treatment. It is used widely in the transmission components of heavy chemical machinery. Different sections of each part of the casting which cause the temperature difference stress and phase transformation stress.
Its equivalent grade is JIS SNCM439 and DIN 1.6563. The properties and composition of 4340 steel round bar sheet plate as below.