超声表面冲击强化对316L不锈钢疲劳性能的影响

EFFECT OF ULTRASONIC SRUFACE IMPACT MODIFICATION ON THE FATIGUE PROPERTIES OF 316L STAINLESS STEEL

用超声冲击方法对试件表面进行改性,可以提高316L不锈钢性能。结合拉伸试验、高周疲劳试验、扫描电子显微镜(Scanning Electron Microscope,SEM)、X射线衍射(X⁃Ray Diffraction,XRD)及能量色散谱仪(Energy Dispersive Spectrometer,EDS),测试了316及316L不锈钢的疲劳性能和断裂特性。结果表明,含碳量稍低的316L不锈钢拉伸强度及疲劳强度也略低;表面超声冲击强化可提高该奥氏体不锈钢抗拉强度约19.7%,但韧性会有所降低。316、316L、冲击处理后316L三组材料的疲劳极限分别为209 MPa、204 MPa、254 MPa,均为本身抗拉极限的35%左右,拟合公式S=-64+0.45σb;含碳量高的316,其S⁃N曲线数据归一性更好,试样无侧边裂缝。疲劳断面显示,裂纹源萌生于异质相或非金属夹杂,裂纹沿晶扩展,裂纹扩展区的速度波动也归因异质相。超声冲击后316L的裂纹扩展速度明显降低,断面的起伏更大,瞬断速度更快。

The properties of 316L stainless steel can be improved by using ultrasonic impact method to modify the specimen surface.The fatigue properties and fracture properties of 316 and 316L stainless steel were treated by tensile test,high⁃cycle fatigue test,SEM,XRD and EDS.The results show that both the tensile strength and the fatigue strength of 316L stainless steel with lower carbon content are lower.The tensile strength of this austenitic stainless steel can be increased by 19.7%,but the toughness decreased.The fatigue limits of 316,316L and 316L after impact treatment are 209 MPa,204 MPa and 254 MPa,respectively.Both of them are about 35%of their tensile strength.The fitting formula of S⁃N curve is S=-64+0.45σb.The fatigue data of 316 with higher carbon content has better normalization,and no side⁃crack is observed.The fracture surface shows that the cracks initiate from the heterogeneous phase or the non⁃metallic inclusion.Cracks usually propagate along the grain boundary.The velocity fluctuation of crack propagation zone is also attributed to the heterogeneous phases.After the ultrasonic impact,the crack growth of 316L is obviously reduced,the section fluctuation is larger,and the transient fracture speed is faster.