热处理冷却速率对热轧316L不锈钢显微组织演变的影响

Effect of Cooling Rate of Heat Treatment on Microstructure Evolution of Hot Rolled 316L Stainless Steel

采用高温激光共聚焦显微镜、纳米压痕和EBSD,研究热处理冷却速率对热轧316L不锈钢显微组织演变的影响。结果表明:316L热轧板组织为带状组织,奥氏体晶粒拉长变形,长条状第二相由奥氏体、铁素体和Sigma(σ)相混合组成,硬度为奥氏体的2倍,达到13.48 GPa。原位观察发现温度达到1065.4℃时第二相中的铁素体和σ相开始向奥氏体转变;1200℃保温10 min后,原第二相区域奥氏体晶粒仍富集Cr、Mo元素,降温后奥氏体转变为铁素体/σ相。不同冷却速率冷却后,初始形变织构弱化,转变为随机织构。冷却速度越慢,合金均匀化程度越高,奥氏体含量越高。原第二相长条位置的奥氏体晶粒,500℃/min时全转变为铁素体,100℃/min时出现少量σ相,12℃/min冷速时,大部分铁素体转变成σ相。

The effect of cooling rate of heat treatment on microstructure evolution of hot rolled 316L stainless steel was studied by high temperature laser confocal microscopy,nano-indentation and EBSD.The results show that the microstructure of 316L hot-rolled plate is banded structure,the austenite grains are elongated.The hardness of long second phase is 13.48 GPa,which is twice of austenite.Its internal phase structure is complex,which is composed of austenite,ferrite and Sigma(σ)phase.In-situ observation shows that the ferrite andσphase in the second phase begin to transform to austenite when the temperature reaches 1065.4℃.After holding at 1200℃for 10min,the austenite grains in the original second phase region are still rich in Cr and Mo elements.After cooling,the austenite therefore transforms to ferrite/σphase.The initial deformation texture weakens and transforms into random texture at different cooling rates.The homogenization degree and the content of austenite increase with the reducing of cooling rate.The austenite grains all transform from the second phase into ferrite at 500℃/min,a small amount ofσphase appears at 100℃/min,and most of ferrite transforms intoσphase at 12℃/min.