钒含量对X80管线钢显微结构及强塑性影响研究

Effect of vanadium content on microstructure and strength plasticity of X80 pipeline steel

借助高分辨透射电镜、扫描电镜、电子背散射衍射技术等手段分析了四种不同钒含量(0.036%,0.075%,0.110%,0.150%)X80管线钢中析出相和显微组织结构特征及对钢强塑性等性能的影响。结果表明,随着钒含量的升高,钢中纳米级析出相的数量和体积分数均呈增高趋势,四种试验钢中析出相尺寸主要集中在0~20 nm,且随着钢中钒含量的升高,尺寸小于10 nm的析出相数量增多,无论是晶内还是晶界附近析出的纳米级第二相颗粒均多为含钒的碳化物。四种不同钒含量试验钢的显微组织均由块状铁素体及粒状贝氏体组成,内部大角度晶界比例分别为23.27%、20.69%、23.13%和16.24%,钒含量最高的4#钢中的大角度晶界最少。随着钒含量由0.036%增加到0.075%,试验钢的抗拉强度和屈服强度均有明显的提高,然而钒含量进一步升高对试验钢的强度影响较小,甚至屈服强度还有一定的下降。试验钢强度的增加主要是纳米级析出相沉淀强化和细晶强化的共同作用,试验钢的塑性受钒含量变化的影响不大。

In this work,the precipitates and microstructure characteristics in four X80 pipeline steels with different vanadium contents(0.036%,0.075%,0.110%and 0.150%)and their effects on the strength and plasticity of the steels were investigated by means of high-resolution transmission electron microscope,scanning electron microscope and electron backscatter diffraction.The results show that with increase of the vanadium content,the number and volume fraction of nano-sized precipitates in the steel increase.The size of precipitates in four experimental steels is mainly in the range of 0~20 nm.The number of precipitates with size less than 10 nm in the steel increases with increasing the vanadium content.The nano-sized second phase particles precipitated in or near the grain boundary are mostly vanadium containing carbides.The microstructure of four experimental steels with different vanadium contents is composed of massive ferrite and granular bainite.The proportions of large angle grain boundaries in steels are 23.27%,20.69%,23.13%and 16.24%,respectively,and the 4#steel with the highest vanadium content has the least large angle grain boundaries.With increase of the vanadium content from 0.036%to 0.075%,the tensile strength and yield strength of the experimental steel are significantly improved.However,further increase of the vanadium content has little effect on the strength of the experimental steel,and even the yield strength has a certain decrease.The increasing strength of the experimental steel is mainly due to the combination of precipitation strengthening and fine grain strengthening of nano-sized precipitates,and the plasticity of the experimental steel is almost not affected by change of the vanadium content.