Mo和Cr对X80管线钢相变行为的影响

Effect of Mo and Cr on Phase Transformation Behavior of X80 Pipeline Steel

分别测定了低碳高铌含Mo、Cr两种成分体系X80管线钢的CCT曲线,研究了在连续冷却条件下过冷奥氏体的转变规律,通过光学显微镜观察了两种钢的显微组织。结果表明,随冷速的提高,两种钢的显微组织均经历了由准/多边形铁素体PF/QF＋珠光体P类型向粒状贝氏体GB＋针状铁素体AF的变化,晶粒不断细化,相变点随着冷速的增加略有下降。Mo使CCT曲线中珠光体转变线右移,扩大形成针状铁素体的冷速范围;而Cr有利于在低冷速下获得贝氏体组织。热力学计算表明,随着Mo、Cr含量的增加,珠光体的形核驱动力降低,相同含量的Cr对珠光体形核驱动力的影响明显小于Mo。

The CCT curves of X80 pipeline steels with low content of C and high content of Nb and Mo or Cr were tested, respectively. The transformation behavior of undercooled austenite under continuous cooling condition was investigated, as well as the microstructure of the two steels was observed by OM. The results show that with the increase of cooling rate, the microstructure of the steels changes from polygonal/quasi-polygonal ferrite ＋perlite to granular bainite ＋acicular ferrite, and the grain is refined continuously. The phase transformation point decreases with the increase of cooling rate. Mo plays an important role in moving the perlite transformation line to the right, which can expand the cooling rate region of acicular ferrite, while Cr helps to obtain bainite under lower cooling rate. The thermodynamic calculation results show that with the increase of Mo and Cr contents, the nucleation driving force of perlite decreases, and the influence of Cr on the nucleation driving force of perlite is obviously smaller than that of Mo with the same addition.