铌对高钢级管线钢中第二相析出与奥氏体晶粒长大行为的影响

基于双亚点阵模型,计算了两种不同铌含量的高钢级管线钢在不同温度下Nb、Ti和Al的析出量,测定了不同加热温度和保温时间下奥氏体晶粒尺寸,建立两种钢奥氏体晶粒长大模型.发现Nb含量增加提高了其全固溶温度,并且温降过程中Nb析出量显著增多,在晶界两边析出的细小碳氮化物对奥氏体晶粒长大有显著的阴碍作用.高铌钢加热温度为1250℃时奥氏体晶粒显著粗化,预测模型也不同于1050~1200℃的模型,但相同保温温度下晶粒尺寸明显小于低铌实验钢.通过数据拟合计算出高铌钢的长大激活能远远高于低铌钢,再次证明高Nb的管线钢在1200℃以下能够有效地细化奥氏体晶粒,预测模型与实验值吻合较好. 

Effect of niobium on second phase precipitation and austenite grain growth behavior in high-grade pipeline steel

Based on the double-sublattice model,the mass fractions of Nb,Ti and Al precipitates in two high-grade pipeline steels were calculated at different temperatures.The sizes of austenite grains in the two steels were determined at different heating temperatures after different soaking time.Two models were built to describe the austenite grain growth.It is found that the complete-solution temperature increases with the addition of Nb.The amount of small carbonitrides at the sides of grain boundaries,which hinder the austenite grain growth,also increases due to the drop of temperature.Austenite grains in the high-Nb steel remarkably coarsen when the soaking temperature is 1250℃,the prediction model is different from those used between 1050 and 1200℃,but the austenite grain size is obviously smaller than that of the low-Nb steel at the same soaking temperature.Based on the data-fit method,the austenite-growth activation energy of the high-Nb steel is calculated,which is much larger than that of the low-Nb steel.It is again proved that austenite grains are greatly refined in the high-Nb pipeline steel soaked at temperatures no more than 1200℃.The prediction models show good agreement with experimental data.