Z3CN20—09M铸造奥氏体不锈钢的低周疲劳行为

采用径向应变控制研究了Z3CN20-09M奥氏体不锈钢在室温和350℃高温下的低周疲劳行为.Z3CN20-09M不锈钢表现为先硬化后软化的循环特性,但硬化的程度取决于温度和应变幅.随着应变幅的增加,Z3CN20-09M钢的低周疲劳循环寿命逐渐减短,而相同循环次数下应力幅也随之提高.温度对Z3CN20-09M钢的低周疲劳行为影响较大,与室温相比高温下的循环硬化程度更高,相同应变幅下高温的低周疲劳寿命也高于常温下的寿命.通过疲劳实验的原位观察发现,奥氏体内的滑移面、夹杂物及奥氏体和铁素体两相的界面是疲劳裂纹可能的形核位置,奥氏体和铁素体两相的不协调变形使相界处产生应力集中,导致疲劳裂纹容易沿两相界面扩展. 

Low cycle fatigue behaviors of Z3CN20-09M cast austenitic stainless steel

The low cycle fatigue (LCF) behaviors of Z3CN20- 09M austenitic stainless steel were tested by the method of radial strain control at room temperature and 350℃. The steel presents cyclic hardening followed by cyclic softening, and the degree of cyclic hardening depends on temperature and strain amplitude. With the increase of strain amplitude, the LCF life of the steel decreases, but the stress amplitude for the same cycles increases. Temperature has great effect on the LCF behaviors of the steel, the degree of cyclic hardening at 350℃ is higher than that at room temperature, and the LCF life at 350℃ is also higher than that at room temperature for the same strain amplitude. Through in-situ observations in fatigue testing, slip planes within austenite, inclusions, and austenite/ferrite phase boundaries are considered to be the possible nucleation sites of fatigue cracks. The incongruous deformation abilities of austenite and ferrite cause stress concentration in the phase boundaries and become the preferential propagating paths of fatigue cracks.