激光冲击强化前处理对 AISI9310 齿轮钢低温渗碳的影响

AISI 9310 steel is a kind of high-strength carburized steel with good toughness. Owing to its material properties, this steel is usually used to fabricate gear parts. Gear tooth surface is prone to wear and contact fatigue damage during service processing. Therefore, to effectively resolve the resistance properties and for the synergistic strengthening of the wear and contact fatigue properties, the AISI 9310 steel sample was processed by laser shock peening (LSP) and then treated by low temperature gaseous carburization (LC). The carburized layer and cross-sectional crystallographic characteristics were imaged using optical microscopy (OM), scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD); subsequently, the cross-sectional hardness was measured. The following results were obtained. After LC treatment, a white carburized layer, which was approximately 14-μm thick and uneven, was induced on the 9310 steel matrix surface. The maximum hardness achieved for the carburized layer of 9310 steel was about 305.67 HV with the depth of work hardening being 300 μm. The maximum hardness of the LCed sample was enhanced by 27.56% compared to the as-received sample. However, with pre-LSP treatment, the thickness of the carburized layer of 9310 steel was improved to approximately 23 μm and the maximum hardness to approximately 328.87 HV with the depth of work hardening being 700 μm. The maximum hardness of the LSP-LCed sample was enhanced by 5.46 % compared to the LCed sample. However, in comparison, the pre-LSP treatment improves the thickness of the carburized layer by 64.3%, the maximum hardness by 23.17 HV, and the depth of work hardening by 133%. The underlying reasons for these enhancements are as follows. Generally, LSP treatment induces plastic deformation and improves the proportion of low angle grain boundary (LGB); this enhances the diffusion behavior of the carbon atoms, and consequently improves the hardness of the LCed layer and the depth of work hardening. After pre-LSP treatment, the carbon diffusion behavior and hardness of LC were enhanced. Specifically, combining pre-LSP and LC processing results in cross-sectional work hardening because LC alone can hardly influence the Kernel average misorientation (KAM) and proportion of LGB of as-received 9310 steel. In other words, pre-LSP improves the KAM of the LCed sample by 15.38% (from 0.52° to 0.60°), and the depth from 0-100 μm. Moreover, pre-LSP enhances the KAM of the LCed sample by 15.79 % (to 0.66°) and the depth from 100-200 μm. Finally, the low angle grain boundary was measured. Notably, LC does not affect the proportion of the low angle grain boundary and the cross-sectional distribution for 9310 steel. On the contrary, pre-LSP processing evidently enhances the proportion of the low angle grain boundary. At the depth of 0-100 μm, pre-LSP enhances the total proportion of the LGB of the LCed sample by 13.04% (from 36.8% to 41.6%). Moreover, the total proportions of the LGB of the LCed sample were enhanced from 36.8% to 55.8% and from 38% to 46.2% for the depth ranging from 100-200 μm and 200-300 μm, respectively. Based on the above results, the main conclusions to enhance the carbon atoms diffusion behavior are as follows. Pre-LSP enhances the carbon diffusion behavior of LC by inducing plastic deformation via increased KAM and increasing the proportion of low-angle grain boundary. Consequently, the easier carbon diffusion behavior of LC could induce the thicker carburized layer, the harder work hardening level, and even improves the thickness of work hardening layer. The problem of carbon diffusion enhanced by microstructure defects induced by LSP pretreatment is preliminarily solved. This resolution would provide technical support for LSP compound strengthening to extend the service life of key components of aviation gear.