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通过金相组织观察和室温横向拉伸、-20℃横向冲击及-15℃落锤撕裂性能测试,研究了不同高温回火温度对X70管线钢组织性能的影响。结果表明,500~650℃回火时,X70管线钢的组织主要为针状铁素体,屈服强度在500 MPa以上,抗拉强度在600 MPa以上,完全能满足X70管线钢对强度的要求。而回火温度超过750℃时,X70管线钢含有大量的多边形铁素体,-20℃横向冲击功降到193J,-15℃落锤剪切面积百分数只有82%,850℃回火时,屈服强度只有340 MPa。综合比较,X70管线钢在500~650℃回火、保温25 min的条件下综合性能较好。
The effects of different high temperature tempering temperatures on the microstructure and properties of X70 pipeline steel were studied by observing the microstructure and transverse stretching at room temperature, transverse impact at -20 ℃ and drop weight tear at -15 ℃. The results show that the microstructure of X70 pipeline steel is mainly acicular ferrite when the temperature is 500-650 ℃. The yield strength of the X70 pipeline steel is above 500 MPa and the tensile strength is above 600 MPa, which can fully meet the strength requirements of X70 pipeline steel. However, when the tempering temperature exceeds 750 ℃, the X70 pipeline steel contains a large amount of polygonal ferrite. The transverse impact energy at -20 ℃ is reduced to 193J, and the percentage of drop shear area at -15 ℃ is only 82%. When tempered at 850 ℃, The strength is only 340 MPa. Comprehensive comparison, X70 pipeline steel tempering at 500 ~ 650 ℃, 25min insulation conditions under good overall performance.