316L不锈钢疲劳过程微观结构演化

Microstructure evolution of 316L stainless steel during fatigue process

研究了喷丸处理后的316L不锈钢在应变控制下的低周疲劳过程中的微观结构的演化。试样先进行机械研磨和电解抛光,随后进行中断疲劳试验至裂纹萌生阶段,接下来利用电子背散射衍射技术(EBSD)、扫描电镜(SEM)、原子力显微镜(AFM)观测316L不锈钢在疲劳过程中微观组织、表面形貌、滑移带高度等的变化。结果表明:喷丸在材料表层引入了一个晶粒尺寸梯度结构,据此可将表层分为两层:强变形层和材料基体层。观测结果显示,在裂纹萌生阶段,两层的形貌更为粗糙,滑移带高度增高,晶粒平均取向差增大。进一步分析表明,由于基体层中的滑移带比强变形层中滑移带更高,因此裂纹最终更可能沿着基体层中的滑移带萌生。

In order to investigate microstructural evolution of shot peened 316 L austenitic stainless steel under strain-controlled low-cycle fatigue testing,the investigated specimen was first mechanically and electrolytically polished,then the interrupted fatigue testing was carried out until crack initiation stage.The microstructure was subsequently examined and characterized using multi-instrumental techniques such as scanning electron microscopy(SEM),electron backscatter diffraction(EBSD)and atomic force microscope(AFM).Shot peening produced a surface treated austenitic steel with gradient microstructure,and thus the surface region was divided into 2 distinct layers:highly deformed layer and bulk material.The results showed that at the crack initiation stage,the surface was roughened,the height of extrusion increased,the grain average misorientation was augmented in both the two layers.It is further revealed that the crack was more likely to occur along slip bands in the core material rather than at the near surface region as a consequence of the fact that the extrusion height measured along slip band in core material was higher than near surface region.