喷丸强度对不同粗糙度表面超高强度钢疲劳性能的影响

Effect of Shot Peening Intensity on Fatigue Behavior of Ultrahigh Strength Steel with Different Surface Roughness

不同方式加工的高强度钢零件具有不同的表面状态,对其采用相同的喷丸工艺是否合理尚不明确。对不同表面粗糙度23Co14Ni12Cr3Mo E超高强度钢作不同强度的喷丸强化。采用扫描电镜及白光干涉仪观察了喷丸试样的表面形貌,采用金相显微镜观察喷丸试样的表面组织,采用旋弯疲劳试验机测试了喷丸试样的疲劳性能,采用X射线衍射残余应力测试仪测试喷丸试样的残余应力。研究了喷丸强度对不同表面粗糙度超高强度钢的表面组织、形貌、残余应力场及疲劳性能的影响。结果表明:喷丸过程可以细化表面组织,引入残余压应力场,改变表面形貌特征,从而引起表面应力集中状况的改变,其改善效果与原始表面状态有关;对于初始表面粗糙度Ra≤0.4μm的表面,喷丸强化过程能有效提高材料的疲劳寿命,促使疲劳裂纹源内移;随表面粗糙度的提高,当应力集中状况过于严重时,表面组织细化和残余压应力对疲劳性能的提升作用会被抑制,喷丸工艺对疲劳寿命的提升效果大幅下降,疲劳裂纹源均位于表面。

23Col4Nil2Cr3 MoE ultrahigh strength steel with different surface roughness was shot peened under different intensities.The surface morphology of the shot-peened steel was observed with a scanning electron microscope and a white light interferometer,and the surface structure of the shot- peened steel samples was analyzed with a metal lorgraphic microscope.Moreover,the fatigue behavior of the shot- peened steel samples was evaluated with a rotary bending fatigue test rig,and the residual stress of the shot-peened steel samples was determined by X-ray diffraction.Furthermore,the effect of shot peening intensity on the surface structure and morphology as well as residual stress field and fatigue behavior of the ultrahigh strength steel was discussed.Results indicated that shot peening helped to refine the surface structure of the steel,generated residual compressive stress field,and changed the surface morphology,thereby causing changes in the surface stress concentration state;and the improvement in the surface stress concentration state was related to the initial surface roughness of the steel.Namely,for the ultrahigh strength steel with an initial surface roughness of R,≤0.4μm,shot peening helped to considerably prolong the fatigue life and confine the initiation of fatigue crack far beneath the surface.With the increase in the surface roughness of the steel,the stress concentration was enhanced,and the improvement in the fatigue behavior of the steel associated with the refinement of the surface structure and residual compressive stress was limited under a too severe stress concentration.In this case,shot peening was less effective in extending the fatigue life of the steel,and the fatigue cracks tended to be initiated on the steel surface.