开冷温度对厚壁管线钢组织和低温力学性能的影响

Effect of start cooling temperature on microstructure and low temperature mechanical properties of thick-walled pipeline steel

采用3种不同开冷温度(720,740和760℃)制备厚度为31.75 mm的管线钢,结合微观组织观察和低温力学性能测试,研究3种开冷温度对管线钢微观组织和低温断裂行为的影响。研究结果表明:当开冷温度为760℃时,转变产物为准多边形铁素体(QF)+多边形铁素体(PF)+粒状贝氏体(GB)+细粒状马氏体-奥氏体(M/A),有效晶粒粒径为4.6μm;当开冷温度为740℃时,转变产物为多边形铁素体+粒状贝氏体+贝氏体铁素体(BF)+块状M/A,有效晶粒粒径为3.9μm;当开冷温度为720℃时,转变产物为多边形铁素体+贝氏体铁素体+长条状M/A,有效晶粒粒径为4.1μm;随着开冷温度降低,实验钢中马氏体变体的体积分数增大,C和Mn等合金元素在M/A组元处偏聚程度增大;当力学性能测试温度在-60~-10℃范围内时,开冷温度为740℃的实验钢能够兼顾较好的低温强度和韧性,屈服强度不低于526 MPa,抗拉强度不低于700 MPa,断后伸长率高于24.6%,低温冲击吸收功高于273 J。

Three different start cooling temperatures(720,740 and 760℃)were used to prepare pipeline steel with the thickness of 31.75 mm.Combined with the observation of the microstructure and the low-temperature mechanical property test,the influence of the three start cooling temperatures on the microstructure and low temperature fracture behavior of pipeline steel was analyzed.The results show that when the start cooling temperature is 760℃,the transformation products are quasi-polygonal ferrite(QF)+polygonal ferrite(PF)+granular bainite(GB)+fine granular martensite-austenite(M/A),and the effective grain size is 4.6μm.When the start cooling temperature is 740℃,the transformation products are polygonal ferrite+granular bainite+bainitic ferrite(BF)+massive M/A,and the effective grain size is 3.9μm.When the start cooling temperature is 720℃,the transformation products are polygonal ferrite+bainitic ferrite+elongated M/A,and the effective grain size is 4.1μm.With the decrease of the start cooling temperature,the volume fraction of martensite variants in experimental steel increases,and the degree of segregation of C,Mn and other alloying elements in M/A component increases.When the start cooling temperature is 740℃and the mechanical performance test temperature is within the range of−60-−10℃,the experimental steel has excellent low-temperature strength and low-temperature toughness at the same time.The yield strength of the test steel is not less than 526 MPa;the tensile strength is not less than 700 MPa,the percentage elongation after fracture is higher than 24.6%,and the low-temperature impact absorption energy is higher than 273 J.