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采用压缩拉伸连续加载变形实验方法, 即第一阶段压缩变形量0%~40%, 第二阶段拉伸至断裂, 研究了Mn18Cr18N奥氏体不锈钢的室温压缩拉伸变形行为. 结果表明, 随着压缩量的增大, 后续拉伸阶段的屈服应力和均匀塑性变形最大拉伸应力、断面收缩率和延伸率均呈先增大后减小的变化规律. 临界压缩量25%处, 拉伸屈服应力和最大拉伸应力达到最大值, 分别约为1039.97和1439.20 MPa; 试样的断面收缩率和延伸率也达到最大值, 分别为68.99%和73.80%. 微观组织和断口形貌的OM和SEM观察结果表明, 当压缩量小于临界值时, 拉伸试样断口宏观形貌呈典型的杯锥状, 微观形貌呈韧窝状的韧性断裂, 微观组织为变形拉长的晶粒组织; 当压缩量超过临界值时, 拉伸试样断口宏观形貌比较平齐, 微观形貌为无韧窝状的结晶状特征, 微观组织为包含大量孪晶的等轴晶粒. TEM分析表明, 压缩量较小时, 位错通过滑移形成不同密度的位错组态; 反向加载拉断后, 仍能观察到位错的堆积. 压缩量较大时, 形成2个方向交割的孪晶; 反向加载拉断后, 孪晶呈平行排列, 且伴有高密度位错缠结.

The higher strength requirement of heavy generator retaining rings made of Mn18Cr18N austenitic stainless steel can be obtained by cold deformation strengthening. However, the yield ratio of Mn18Cr18N austenitic stainless steel is close to 1 gradually during the unidirectional tensile deformation, which will limit the unidirectional tensile deformation of cold deformation strengthening. In order to investigate the cold deformation strengthening by complex loading paths of Mn18Cr18N austenitic stainless steel, compression-tensile deformation behavior of Mn18Cr18N austenite stainless steel at room temperature was investigated by compression and tensile consecutive loading deformation experiments with the first compressive reduction range of 0%~40% and the second tensile range to fracture. Microstructure evolution, deformation dislocations, fracture behavior and mechanisms have been analyzed by OM, SEM and TEM. The results indicate that the subsequent tensile yield stress and the maximum tensile stress at the uniform plastic deformation stage, the reduction of cross sectional area and elongation increase at first and then decrease with the increase of compressive deformation. When the compressive deformation increases up to the critical reduction of 25%, the subsequent tensile yield stress and the maximum tensile stress reach up to the maximum values of 1039.97 and 1439.20 MPa respectively, and the reduction of cross sectional area and the elongation also reach up to the maximum values of 68.99% and 73.80% respectively. When the compressive deformation is less than the critical reduction, appearance of fractures shows the cup-cone shaped macroscopic fracture profiles, the dimpled microscopic fracture surfaces and the elongated grains. When the compressive deformation is greater than the critical reduction, fractures morphology is distinguished by the flat macroscopic fracture profiles, the crystalline microscopic fracture surfaces and the equiaxed grains with a lot twin structures. Several dislocation configurations with different density forms by dislocation slip when the compressive reduction is lower. Dislocation pile-up can be observed in the subsequent broken tensile specimen. Cross twins emerge in the specimen compressed up to 35% reduction. Twins with high density dislocation tangles arrange in parallel in the subsequent broken tensile specimen.