控轧控冷工艺对X70级抗大变形管线钢组织与性能的影响

Effect of controlled rolling and controlled cooling process on microstructure and mechanical properties of X70 pipeline steel

采用光学显微镜、扫描电镜及力学性能实验等研究了控轧控冷工艺对X70级管线钢的组织与力学性能的影响。结果表明:不同终轧温度下X70管线钢的显微组织主要由多边形铁素体、贝氏体和少量的珠光体组成,且随着终轧温度的升高,抗拉强度与屈服强度降低,硬度下降,冲击韧性提高,但屈强比变化不大,并且落锤性能较差;随着终轧温度的升高,晶粒尺寸逐渐增大,铁素体体积含量增多。在不同的终冷温度下,X70管线钢的显微组织主要由多边形铁素体和贝氏体组成,并且随着终冷温度的升高,抗拉强度大幅度降低,屈服强度则呈M形波动,硬度呈线性降低,冲击吸收能量大幅度升高且落锤性能较好,屈强比缓慢升高;随着终冷温度的升高,晶粒度等级基本保持稳定,铁素体含量呈线性增加。该大变形管线钢最优的轧制工艺为控制终轧温度为840℃,终冷温度为450℃。

Effects of controlled rolling and controlled cooling process on microstructure and mechanical properties of X70 grade pipeline steel were studied by means of optical microscope,scanning electron microscopy and mechanical properties test.The results show that the microstructure of the X70 pipeline steel is mainly composed of polygonal ferrite,bainite and a small amount of pearlite at different finish rolling temperatures,and with the increase of finish rolling temperature,the tensile strength and yield strength of the steel decrease,hardness decreases,impact toughness increases,but the ratio of yield strength to tensile strength does not change much,and the DWTT(drop weight tear test)performance is lower.With the increase of finish rolling temperature,the grain size of the steel decreases and the content of the ferrite increases.At different finish cooling temperatures,the microstructure of the X70 pipeline steel is mainly composed of polygonal ferrite and bainite,and with the increase of finish cooling temperature,the tensile strength of the steel decreases greatly,the yield strength fluctuates in M shape,the hardness decreases linearly,the impact absorbed energy increases greatly and the DWTT performance is better,and the ratio of yield strength to tensile strength increases slowly.With the increase of the finish cooling temperature,the grain size of the steel keeps basically stable and the content of the ferrite increases linearly.The optimum rolling process of the X70 pipeline steel is as follows:the finish rolling temperature is 840℃and the finish cooling temperature is 450℃.