0Cr19Ni15Mn5Mo2NbN铸钢晶界高温相析出及对力学性能的影响

利用光学显微镜、扫描电镜及透射电镜,结合Thermo-Calc热力学分析,研究了铌稳定化0Cr19Ni15Mn5Mo2NbN奥氏体不锈钢铸钢晶界处高温相析出行为及其对力学性能的影响。结果表明,0Cr19Ni15Mn5Mo2NbN钢晶界处存在Nb Cr(CN)、Nb(CN)2种大尺寸高温析出相,均为凝固末期液析形成。在铌含量确定条件下,这2种大尺寸晶界析出相在凝固末期的竞争析出行为受碳含量的影响。碳含量存在临界成分,碳含量低于临界成分时,Nb Cr(CN)首先液析形成;碳含量高于临界成分时,Nb(CN)首先液析形成。液析形成的NbCr(CN)热稳定性较高,1 050℃固溶处理无法使之完全溶入奥氏体。沿晶界分布的大尺寸析出相,对0Cr19Ni15Mn5Mo2NbN铸钢固溶热处理后的塑性及冲击韧性损害较大。

High temperature precipitation of 0Cr19Ni15Mn5Mo2NbN cast steel at grain boundary and its effect on mechanical properties

High temperature precipitations of Nb-stabilized 0Cr19Ni15Mn5Mo2NbN austenitic stainless steel at grain boundary and their effect on mechanical properties were investigated through optical microscope,SEM,TEM analysis and Thermo-Calc thermodynamic calculation.The results show that two types of large-sized NbCr (CN) and Nb(CN) precipitations formed from liquid at the final stage of solidification are found at grain boundary in as-cast 0Cr19Ni15Mn5Mo2NbN steel.When the content of niobium is fixed,these two types of precipitations compete to precipitate from liquid at the final stage of solidification and are influenced by the carbon content.There is a critical value of carbon content.When carbon is lower than the critical value,NbCr(CN) precipitates first from liquid;and when carbon is higher than the value,Nb(CN) forms first from liquid.The NbCr(CN) precipitated from liquid is thermodynamically stable and can not dissolve in austenite by solution treatment at 1050 ℃.The ductility and toughness of 0Cr19Ni15Mn5Mo2NbN steel after solution are severely deteriorated by the precipitations in big size at grain boundary.