等温温度对X90管线钢组织性能的影响

Effect of the isothermal temperature on the microstructure and mechanical properties of X90 pipeline steel

对等温处理后X90管线钢显微组织和力学性能进行分析,讨论了等温处理对其组织性能的影响。结果表明:X90管线钢在等温处理后,组织由多边形铁素体、贝氏体铁素体和粒状贝氏体组成,随着温度的降低铁素体体积分数增加,铁素体的晶粒尺寸减小,粒状贝氏体减少,贝氏体铁素体增多。在550℃等温,硬度值最低(Hv 177.4)。在650℃等温,其强塑积和硬度值都达到最高值(16 675 MPa%和Hv 200.6)。在750℃等温,抗拉强度最低(631 MPa)。650℃等温时,碳氮化物析出量多,其产生析出强化贡献最大,因此得到最佳的力学性能。当750℃等温时,碳氮化物粒子长大,强化作用减弱,性能降低。

Effect of the isothermal temperature on the microstructure and mechanical properties of X90 pipe line steel was investigated. The results show that X90 pipeline steel consists of polygonal ferrite, bainitic ferrite and granular bainite after isothermal treatment. The volume fraction of the ferrite and bainitic ferrite increased, and the grain size of the ferrite and the amount of granular bainite decreased when isothermal tem- perature decreased. Hardness value was the lowest（Hv177.4） when isothermal temperature was 550 ℃. The maximal tensile strength, total elongation（ 16675 MPa% ）and hardness value （Hv200. 6 ）were obtained when isothermal temperature was 650℃. Tensile strength was the lowest（ 631 MPa）when isothermal temperature was 750 ℃. The reason for the highest mechanical properties when isothermal temperature was 650 ℃ is attributed to maximizing precipitation strengthening of the most carbonitride precipitates. The mechanical properties decreased and the precipitation strength weakened because of coarse carbonitride precipitates when isothermal temperature was 750℃.