纳米/超细晶奥氏体不锈钢高周疲劳性能及变形机制研究

Research on high cycle fatigue property and deformation mechanism of nano/ultrafine-grained austenitic stainless steel

随着现代工业技术的飞速发展,奥氏体不锈钢的屈服强度难以满足更高的要求,迫切需要开发出高强度的奥氏体不锈钢。近年来,纳米/超细晶材料由于其优异的力学性能,成为材料领域的研究热点之一。材料的疲劳强度与其抗拉强度密切相关,晶粒细化也是获得优异抗疲劳性能的有效手段。通过形变诱导马氏体退火逆相变的方法制备了平均晶粒尺寸分别为400 nm(纳米/超细晶)、1.4μm(细晶)和12μm(粗晶)的奥氏体不锈钢,并对其进行了轴向拉-拉高周疲劳实验,研究了不同晶粒尺寸奥氏体不锈钢的高周疲劳性能及循环变形机制。结果表明:纳米/超细晶、细晶和粗晶奥氏体不锈钢的疲劳强度分别为811、568、501 MPa。随着晶粒尺寸的减小,奥氏体不锈钢的疲劳强度得到显著提高。采用透射电镜对不同晶粒尺寸奥氏体不锈钢疲劳断口处的微观组织进行了观察,发现在粗晶钢中产生了大量的位错以及平行的变形带和层错,在循环载荷作用下,位错相互缠绕聚集形成了胞状结构。在细晶钢中,主要观察到了位错、层错以及一些细小的孪晶,位错密度明显减小。在纳米/超细晶钢中的纳米级和微米级晶粒中主要产生了位错,在冷轧过程中未发生马氏体相变的变形奥氏体晶粒中产生了位错线和变形带结构。

With the rapid development of modern industrial technology,the yield strength of austenitic stainless steel is difficult to meet higher requirements,and there is an urgent need to develop high-strength austenitic stainless steel.In recent years,nano/ultrafine-grained materials have become one of the research hotspots in the field of materials due to their excellent mechanical properties.The fatigue strength of materials is closely related to their tensile strength,and grain refinement is also an effective means to achieve excellent fatigue resistance.Austenitic stainless steels with average grain sizes of 400 nm(nano/ultrafine-grained),1.4μm(fine-grained),and 12μm(coarse-grained)were prepared by strain-induced martensite reversion process.And axial tension-tension high cycle fatigue experiments were conducted on them.The high cycle fatigue property and cyclic deformation mechanism of austenitic stainless steels with different grain sizes were studied.The result shows that the fatigue strength of nano/ultrafine-grained,fine-grained and coarse-grained austenitic stainless steels is 811 MPa,568 MPa and 501 MPa,respectively.As the grain size decreases,the fatigue strength of austenitic stainless steel is significantly improved.The microstructures of fatigue fractures of austenitic stainless steels with different grain sizes were observed using transmission electron microscopy.It was found that a large number of dislocations,parallel deformation bands and stacking faults were generated in coarse-grained steel.Under cyclic loading,dislocations intertwine and aggregate to form a cellular structure.In fine-grained steel,dislocations,stacking faults,and some fine twins were mainly observed,and the dislocation density was significantly reduced.Dislocations were mainly generated in the nanoscale and microscale grains of nano/ultrafine-grained steel.Dislocation lines and deformation band structures were generated in the deformed austenite grains that did not undergo martensitic transformation during the cold rolling process.