60Mn3Al3Ni2CrVNb调质型低密度钢奥氏体晶粒长大行为

Austenite grain growth behavior of 60Mn3Al3Ni2CrVNb quenched and tempered low density steel

研究了60Mn3Al3Ni2CrVNb调质型低密度钢的奥氏体晶粒长大行为,并分析了析出相对奥氏体晶粒长大行为的影响机理。结果表明,在不同加热温度下(950~1250℃),随加热温度升高,实验钢的奥氏体晶粒逐渐增大,其中,1100℃以下加热时晶粒生长缓慢,1100℃及以上加热时,晶粒粗化明显,其晶粒粗化温度约为1100℃,此外存在1250℃加热时晶粒再次显著粗化现象。显微组织分析表明碳化铌是影响实验钢奥氏体晶粒长大行为的关键因素,且碳化铌的尺寸具有重要影响,实验钢中存在3种尺寸的碳化铌析出相,分别为小于50 nm、0.2~0.35μm、大于1μm。1100℃及以上加热时,尺寸小于50 nm的微小碳化铌析出相固溶,对奥氏体晶界的钉扎作用减弱,是1100℃及以上加热时晶粒粗化的主要原因;1250℃加热时,0.2~0.35μm的碳化铌析出相固溶,导致1250℃加热时晶粒显著粗化;尺寸大于1μm的碳化铌析出相即使在1250℃保温12 h也难以溶解。

The austenite grain growth behavior of 60Mn3Al3Ni2CrVNb quenched and tempered low density steel was studied,and the influence mechanism of precipitates on austenite grain growth behavior was analyzed.The results show that at different heating temperatures(950-1250℃),with the increase of heating temperature,the austenite grain of the experimental steel increases gradually.The grain growth is slow when the heating temperature is below 1100℃,and the grain coarsening is obvious when the heating temperature is above 1100℃.The grain coarsening temperature is about 1100℃.In addition,the grain coarsening phenomenon occurs again when the heating temperature is 1250℃.Microstructure analysis shows that the NbC is the key factor affecting austenite grain growth behavior of the experimental steel,and the size of the NbC has an important influence.There are three kinds of NbC precipitates in the experimental steel,which are less than 50 nm,0.2-0.35μm and more than 1μm,respectively.When the heating temperature is or above 1100℃,the solid solution of NbC with size less than 50 nm weakens the pinning effect on austenite grain boundary,which is the main reason for grain coarsening.When the heating temperature is 1250℃,the solid solution of NbC with size of 0.2-0.35μm leads to significant grain coarsening.The niobium carbide precipitates with size larger than 1μm are difficult to dissolve even when heated at 1250℃ for 12 h.