Study On The Heat-treatment Process of 20Cr Gear in The Tractor Gear-box
Abstract: The shift gear-box is the key component in a four-weel tractor. The choice for the raw materials for the gear component and determination for the heat-treatment processing paprameters have been the main subject. For the previously used 20CrMnTi materials, the heat treatment process is a gas carbonization process, the carbonizing temperature is high, and the heat-treatment time is long. This always results in grain coarsing and carbon black depostion on the surface. If the the 20Cr material is selected as the gear material instead 20CrMnTi, the heat treatment process is a direct quenching carried out via gas carbonitriding at a middle temperature. The equipment for the heat treatment is RJJ-75-9T type well furnace, the gas pressure in the furnace is controlled by instilled vapor, the permeating chemicals is the mixture of kerosene and liquid rare earths. The heat treatment temeprature is reduced to 880 degrees, and the treatment time is about 3 h. About 33.6% energy can be saved, and the repair rate of unpacked goods caused by the draw back of shrinkage hole can be reduced to 2.87%, the wear resistance, surface hardness and comprehensive mechanical properties of the core section are greatly improved.
Key Words: gear；gas carbonitriding；process parameters；wear resistance
