含Nb管线钢针状铁素体相变动力学研究

采用Gleeble 3500热模拟试验机,研究含Nb管线钢连续冷却过程中的针状铁素体转变行为。将试样加热到1 050℃奥氏体化,冷却至850℃并分别保温0,300,600,1 200 s后冷却到室温。根据热膨胀曲线,采用杠杆定律绘制了相转变量-温度曲线,建立含Nb针状铁素体相变Jeziorny动力学方程。结果表明:随保温时间的增加,由于Nb(C,N)的析出,Nb(C,N)颗粒为针状铁素体提供更多形核位置,提高相变温度,促进针状铁素体转变,抑制贝氏体转变,最终由贝氏体、针状铁素体的混合组织转变为针状铁素体组织;相变开始时间减少,同时相变完成时间缩短,针状铁素体体积分数增加。

Study on Phase-transformation Kinetics of Acicular Ferrite in Nb Micro-alloyed Pipeline-purposed Steel

With Gleeble 3500 thermal simulator,the transformation behavior of the acicular ferrite of the Nb microalloyed pipeline-purposed steel during continuously cooling process is studied.The specimen is heated up to 1050℃ to get austenitized,and then cooled down to 850 Xl,and isothermally held on for 0 s,300 s,600 s and 1200 s,and then cooled to the room temperature.The Jeziomy kinetics formula of the acicular ferrite of the Nb micro-alloyed steel is established through phase transition volume-temperature curve as calculated by the lever law according to the thermal expansion curve.The results indicate that along with increase of the thermal holding duration,precipitation of the Nb(C,N)particle is promoted,which provides nucleation sites for acicular ferrite transformation,so as the phase transformation temperature is increased,and accordingly the acicular ferrite transformation is promoted,whereas the bainite transformation is restrained;and finally the bainite-acicular ferrite mixed microstructure is transformed into the pure acicular ferrite microstructure;and the phase transformation starting time is reduced,and the phase transformation ending time is accordingly shortened,while the volume fraction of the acicular ferrite increases.