卷曲温度对X70管线钢组织和性能的影响

采用金相显微镜、EBSD等方法,对Nb-V-Cr复合微合金生产的X70管线钢在不同卷取温度下的组织、性能进行了分析。结果表明,在相同冷却工艺条件下,随着卷曲温度的降低,管线钢组织由粒状贝氏体转变为贝氏体铁素体,M-A组元也随着卷曲温度的降低而减少。轧后弛豫条件下,组织转变为多边形铁素体及退化珠光体。卷曲温度470℃时,管线钢屈服强度最大,为680 MPa,而卷曲温度降低至380℃时,管线钢冲击功最大,为287 J。

Effect of Coiling Temperature on Microstructure and Mechanical Properties of X70 Pipeline Steel

Microstructures and mechanical properties of the X70 pipeline steel with added composite micro-alloying elements of Nb-V-Cr at different coiling temperatures are analyzed by metallurgical microscope using the electron backscatter diffraction（EBSD）.The results show that the microstructure of the X70 pipeline steel is transformed into bainitic ferrite from granular bainite with the coiling temperature decreasing under the same cooling condition and the martensite-austenite（M-A） constituent by volume also decreases as the coiling temperature goes down.However,the microstructure of the X70 pipeline steel is transformed into polygonal ferrite and degenerated pearlite at the relaxation condition after finishing rolling.So the max yield strength of the pipeline steel is up to 680 MPa when the coiling temperature is 470 ℃ while the max impact energy is 287 J as the coiling temperature goes down to 380 ℃.