Mn18Cr18N奧氏體不銹鋼壓拉連續(xù)加載變形行為

Mn18Cr18N奧氏體不銹鋼壓拉連續(xù)加載變形行為COMPRESSION AND TENSILE CONSECUTIVE DEFORMATION BEHAVIOR of Mn18Cr18N AUSTENITE STAINLESS STEEL

采用壓縮拉伸連續(xù)加載變形實驗方法, 即第一階段壓縮變形量 0%-40%, 第二階段拉伸至斷裂, 研究了Mn18Cr18N 奧氏體不銹鋼的室溫壓縮拉伸變形行為. 結果表明, 隨著壓縮量的增大, 后續(xù)拉伸階段的屈服應力和均勻塑性變形最大拉伸應力、斷面收縮率和延伸率均呈先增大后減小的變化規(guī)律. 臨界壓縮量 25%處, 拉伸屈服應力和最大拉伸應力達到最大值, 分別約為1039.97 和 1439.20 MPa; 試樣的斷面收縮率和延伸率也達到最大值, 分別為 68.99%和 73.80%. 微觀組織和斷口形貌的 OM 和 SEM 觀察結果表明, 當壓縮量小于臨界值時, 拉伸試樣斷口宏觀形貌呈典型的杯錐狀, 微觀形貌呈韌窩狀的韌性斷裂, 微觀組織為變形拉長的晶粒組織; 當壓縮量超過臨界值時, 拉伸試樣斷口宏觀形貌比較平齊, 微觀形貌為無韌窩狀的結晶狀特征, 微觀組織為包含大量孿晶的等軸晶粒. TEM 分析表明, 壓縮量較小時, 位錯通過滑移形成不同密度的位錯組態(tài); 反向加載拉斷后, 仍能觀察到位錯的堆積. 壓縮量較大時, 形成兩個方向交割的孿晶; 反向加載拉斷后, 孿晶呈平行排列, 且伴有高密度位錯纏結.

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 then decrease with increase of the 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.

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