Hardenability is one of the important performance indexes of gear steel. It is mainly to ensure the central hardness of different sized gears, and is conducive to controlling gear heat treatment deformation. The control of hardenability and hardenability bandwidth of gear steel mainly depends on chemical composition and its homogeneity. That is to control the elements that have a great influence on the hardenability, such as carbon, manganese, etc. According to the influence of carbon and alloy elements in the steel on the hardness values of each point of the hardenability, determine the internal control composition range of the steel.
The oxide and sulfide inclusions and harmful elements such as nitrogen, hydrogen and oxygen in steel will reduce the mechanical properties of steel, deteriorate the technological properties of steel, and thus affect the service life of automobile carburized gears.
Grain size is an important index of gear steel. Fine and uniform austenite grains in gear steel can obtain fine martensite structure after quenching, which can obviously improve the fatigue performance of gears and reduce the deformation of gears after heat treatment. The grain size of gear steel is required to be ≥ 6, which is usually achieved by controlling the residual aluminum content in the steel to refine the grain during smelting.
