In addition to the general requirements of strength, plasticity and toughness of engineering materials, the performance requirements of automobile gear steel also require three basic characteristics, namely specific hardenability, narrow hardenability bandwidth, high purity and fine grain size. In addition, good machinability is also an important index concerned by the gear industry, mainly including cold and hot machinability and free cutting. Putting forward the performance requirements of gear steel is very important for the R & D and production of gear steel.
The hardenability of automobile gear steel determines the core strength of gear carburizing and quenching, which is one of the important performance indexes of automobile gear steel. According to the working conditions and effective section of the gear, it is very necessary to select the hardenability material to meet the service performance and reduce the heat treatment deformation.
The control of hardenability and hardenability bandwidth of automobile gear steel mainly depends on the uniformity of chemical composition and chemical composition, that is to control the elements with great influence on hardenability, such as C, Cr, Mn, Mo and so on. After the hardenability is determined, the hardenability bandwidth greatly affects the deformation of gears after carburizing and quenching. Therefore, in the past, in order to reduce heat treatment deformation, gear manufacturers chose different alloy series or the same alloy series to change the carbon content for gears with different effective sections to ensure different requirements for hardenability of gears with different effective sections.
In recent years, using the secondary refining and continuous casting technology outside the furnace, based on the perfect hardenability database, through computer pre furnace analysis and calculation, the hardenability of steel can be accurately predicted, and all mechanical properties of steel can also be predicted.