晶粒细化对奥氏体不锈钢高温力学性能的影响

摘要：对粗晶201LN奥氏体不锈钢采用60%冷变形结合700℃退火120s工艺制备超细晶奥氏体不锈钢，研究晶粒细化对奥氏体不锈钢高温力学性能的影响。利用光学显微镜、扫描电子显微镜、透射电子显微镜、电子背散射衍射技术对粗晶和超细晶奥氏体钢进行了组织表征，并使用万能试验机测试20和650℃环境下力学性能。结果显示粗晶奥氏体不锈钢经过冷变形结合退火工艺处理，平均晶粒尺寸由18μm细化为0.9μm，屈服强度由383MPa提高到704MPa，而伸长率由63.8%下降到46.3%，表明晶粒细化能有效提高奥氏体不锈钢屈服强度的同时较小损害塑性，TEM证实其形变机制均为形变诱导马氏体和孪生协同作用。当温度由20℃提高到650℃时，粗晶奥氏体不锈钢屈服强度和伸长率分别下降到180MPa和28.1%，超细晶奥氏体不锈钢屈服强度和伸长率分别为384MPa和24.2%。这表明在650℃高温环境下细晶强化作用仍然有效，粗晶和超细晶奥氏体不锈钢也有较好的塑性，其形变机制分别变为位错滑移和位错滑移+层错+孪生。

Effect of grain refinement on mechanical properties of austenitic stainless steels at high temperature

Abstract： The impact of grain refinement on mechanical properties at elevated temperature in austenitic stainless steel was investigated. The commercial 201LN austenitic stainless steel was selected as coarse grained sample, and the ultra fine grained austenitic stainless steels were obtained by cold rolled at room temperature with a thickness reduction of 60% and then annealed at 700℃ for 120s. The microstructural characteristics were identified by optical, scanning, and transmission electron microscopes together with electron backscatter diffraction. Moreover, the mechanical properties of ultrafine grained and coarse grained samples were measured though tensile test at 20 and 650℃. The results show that the average grain size is refined from 18μm in coarse grained sample to 0.9μm in ultrafine grained sample, and the yield strength is increased from 383 to 704MPa, while the elongation decreases from 638% to 46.3%. It indicates that grain refinement can effectively improve the yield strength of austenitic stainless steel without significantly impairing the plasticity. The deformation mechanisms in both samples are both deformation induced martensitic transformation and deformation twinning. When the temperature is increased from 20 to 650℃, yield strength and elongation of coarse grained sample decrease to 180MPa and 28.1% respectively, while they are 384MPa and 24.2% in ultrafine grained sample respectively. This indicates that fine grain strengthening is still effective even at 650℃. The high plasticity is confirmed to be related to the variations in microstructure dependent deformation mechanisms, varying from dislocation slip in coarse grained sample to dislocation slip + stacking faults + deformation twinning in ultrafine grained sample.