高速列车DZ2车轴离子渗氮工艺研究

采用N₂+H₂气氛对DZ2钢的试样及车轴进行离子渗氮工艺试验,通过温度、时间、N₂比例3种因素的正交试验以及三段式深层离子渗氮试验,结合OM、XRD、SEM等检测与分析,实现渗氮层组织结构及硬度梯度调控,得到优化工艺参数,并对渗氮后的表面粗糙度及残余应力进行表征。结果表明,气氛含N₂比例20%以下时表面可以获得γ′单相组织,厚度6~8μm,三段离子渗氮可以得到较为平缓的硬度梯度分布,表面硬度600 HV以上,离表面0.3~0.5 mm处显微硬度达400 HV以上,脆性及脉网状级别均为1级。离子渗氮后的表面粗糙度R_a有所增加,渗氮层内形成残余压应力场,最大残余压应力幅值达715 MPa,位于距表面0.51 mm深处。采取加入Ar气调整炉压等措施,实现了花键全齿廓渗氮,车轴的批量渗氮处理后,经过实体解剖检测花键齿全齿廓均达到原定技术指标。

Study on Ion Nitriding Technology of Axle of High-speed Train with DZ2 Steel

The ion nitriding process test of DZ2 steel sample and axle was carried out with N₂+H₂ gases.Through the orthogonal test of three factors of temperature,time,and N₂ ratio,as well as the three-stage deep ion nitriding test,combined with the detection and analysis of OM,XRD,SEM,the structure and hardness gradient of nitriding layer were regulated,to obtain the optimized process parameters,and to characterize the surface roughness and residual stress after nitriding.The results show that at less than 20%of N₂ content ratio,the single phaseγ′compound can be obtained on surface,with 6~8μm thickness.The three-stage ion nitriding process can deliver a relatively gentle hardness gradient distribution,with the surface hardness of above 600 HV,the microhardness of above 400 HV at 0.3~0.5 mm from the surface,and grade 1 of both brittleness and vein network grades.The surface roughness Ra increases after ion nitriding,with the residual compressive stress field formed in the nitriding layer.The amplitude of the maximum residual compressive stress can reach up to 715 MPa,which is located at a depth of 0.51 mm from the surface.By adding Ar gas and adjusting furnace pressure et al,the nitriding of the whole tooth profile was realized.After mass production of axle,the whole tooth profile of spline meets the original technical requirements through dissection inspection.