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通过力学性能测试和微观组织分析,研究了回火温度对低碳贝氏体X80管线钢组织及低温冲击韧性的影响。结果表明,低碳贝氏体X80管线钢在300℃回火2 h后达到最佳强韧性匹配,屈服强度在625 MPa,-40℃夏比冲击功为315 J,冲击断口呈现明显的韧性断裂形貌,-60℃夏比冲击功也达到了268 J。低碳贝氏体管线钢轧态组织以粒状贝氏体为主,经过300℃回火2 h后,组织与TMCP状态基本相似,仍保持粒状贝氏体组织,但是MA组元略细小;经过600℃回火2 h后,贝氏体出现粗化,并且出现多边形铁素体组织。低温韧性的改善是由于回火处理过程中富碳残留奥氏体发生转变,M/A组元由岛状转变为点状及细条状,粒状贝氏体晶间细化的M/A组元更好的阻碍了裂纹的扩展。
The effects of tempering temperature on microstructure and low temperature impact toughness of low carbon bainite X80 pipeline steel were studied by mechanical properties test and microstructure analysis. The results show that the low carbon bainite X80 steel has the best ductility matching after being tempered at 300 ℃ for 2 h, the yield strength is 625 MPa, the Charpy impact energy at -40 ℃ is 315 J, and the ductile fracture shows obvious ductile fracture Morphology, -60 ℃ Charpy impact energy has also reached 268 J. The microstructure of the low-carbon bainitic pipeline steel was mainly granular granular bainite. After being tempered at 300 ℃ for 2 h, the microstructure of the low-carbon bainitic steel was similar to that of the TMCP. The granular bainite retained the microstructure but the MA components were slightly smaller. After tempering at 600 ℃ for 2 h, bainite appeared coarsened and polygonal ferrite structure appeared. The improvement of low temperature toughness is due to the transformation of carbon-rich retained austenite during the tempering process. The M / A component changes from islands to dots and strips. The M / A component of granular bainite refinement Good hinder the expansion of the crack.