316L奥氏体不锈钢非对称载荷下的疲劳与循环塑性行为

Fatigue and Cycle Plastic Behavior of 316L Austenitic Stainless Steel Under Asymmetric Load

对316L奥氏体不锈钢非对称拉-拉疲劳载荷作用下的疲劳和循环塑性行为进行研究。通过疲劳寿命、循环应变幅、平均应变、平均应变率和失效应变的差异划分高、低应力区:在高应力区,平均应变、平均应变率和失效应变大,存在显著的循环塑性变形,疲劳寿命短;在低应力区,循环塑性变形累积有限,疲劳寿命显著增加。通过失效区域的显微组织观察和断口分析发现:在高应力区断口附近产生了大量的孔洞,断口以韧窝为主要特征;在低应力区存在疲劳裂纹,其扩展方向垂直于加载方向,断口由起裂点、疲劳裂纹扩展区、过渡区和快速断裂区组成。316L奥氏体不锈钢高应力区为循环塑性变形主导区,失效形式为循环塑性累积产生的韧性失效;低应力区为疲劳主导区,失效形式为疲劳裂纹扩展失效。

Due to excellent mechanical property and corrosion resistance of 316L austenitic stainless steel, it is widely used in chemical industry, but its fatigue behavior under asymmetric cycle load is not well understood. In this work, the fatigue and cyclic plastic deformation behavior of 316L austenitic stain less steel un der asymmetric ten sile-te nsile cycle loading are studied, focusi ng on the variations of fatigue life, cycle plastic deformation and fracture mechanism with applied cycle load. The high and low stress regions can be clearly divided based on the differences of fatigue life, cyclic strain amplitude, mean strain, mean strain rate and failure strain. In the high stress region, mean strain, mean strain rate and failure strain are large, resulting in the significant cyclic plastic deformation, and the fatigue life is short. In the low stress region, the cyclic plastic deformation accumulation is limited, and the fatigue life is significantly increased. Through microstructural observations near fracture area and fracture surface analyses, the differences between large stress region and low stress region can be found. In the high stress region, a large number of voids are generated near the fracture surface, and the fracture surface is mainly featured by dimples. In contrast, in the low stress region, the fatigue crack is found near the fracture surface, and its propagation di recti on is perpendicular to the loading di recti on. The fatigue crack initiati on site, the fatigue crack propagation zone, transition zone and rapid fracture zone are found on the fracture surface. Results of fracture mechanism analyses suggest that, the high stress region of 316L austenitic stainless steel is the cyclic plastic deformation dominant region, and the failure mechanism is the ductile failure caused by the accumulation of cyclic plastic deformation;while the low stress region is the fatigue dominant zone, and the failure mechanism is the fatigue crack propagation failure.