Abstract: In the installed operation of vehicle transmission gears after being normalized, machined and carbonized, noise is produced and it will have adverse effects on the service life of gears. In view of this problem, different microstructures obtained by using two different normalizing processes are studied, and tests are carried out on the surface micro-deformation after machining and surface polishing under the same condition, so as to analyze the cause of difference of micro-deformation. The test results show that the noise produced in the early operation stage of vehicle transmission gears is mainly caused by the deformation that is initiated by the internal stress produced in the machining process of steel gear parts after normalization. Therefore, it is suggested that the vehicle gear blanks should adopt isothermal normalizing process by utilizing the residual forging heat, so as to reduce the friction caused by the deformation in the work pieces operation.

Key words: Isothermal normalizing, Micro-distortion, Microstructure, Surface profile