Abstract: Hot compression test for gear steel FAS3420H was conducted by Gleeble-1500 thermomechanical simulator, and the effects of hot deformation parameters such as deformation amount and deformation temperature on size and relative plasticity of MnS were studied. The results show that during the deformation process, the fragmentation and growth of sulfide occur alternately, and the deformation temperature and deformation amount have a significant impact on the size of MnS inclusions. The change rule is related to the degree of recrystallization of the gear steel matrix. When the deformation temperature is low (900 ℃), with the increase of deformation amount, the amount of sulfides with small aspect ratio first decreases and then increases, and the relative plasticity presents a downward trend, while the dynamic recrystallization fraction gradually increases. When the deformation temperature is high (1200 ℃), with the increase of deformation amount, the amount of sulfides with small aspect ratio first increases and then decreases, and the relative plasticity shows an increasing trend, however, it is generally lower than when rolling at low temperature, and at this time, sufficient dynamic recrystallization occurs at a lower deformation amount. It can be seen that in the actual rolling process, when a higher temperature is selected, the matrix is prone to dynamic recrystallization. Under the interaction of matrix deformation and grain boundary movement during the recrystallization process, smaller and more MnS inclusions can be obtained.

Key words: gear steel FAS3420H, MnS inclusion, hot deformation parameter, dynamic recrystallization