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从化学成分、热轧工艺、冷却工艺等方面对大壁厚海底管线钢X70进行了研制,并且研究了工艺制度对大壁厚海底管线用钢的组织和性能的影响。结果表明:采用轧后弛豫+控制冷却的工艺可以获得铁素体+贝氏体双相组织,弛豫终止温度是影响铁素体体积含量和晶粒大小的决定因素。弛豫终止温度越低,铁素体体积含量越高,晶粒尺寸越大,屈强比越低,塑性指标越好。随弛豫终止温度的降低,先共析铁素体含量逐渐增加,贝氏体组织含量逐渐降低,当弛豫终止温度为710～780℃时,实验钢的强度和塑性达到了较好的匹配。
From the aspects of chemical composition, hot rolling technology, cooling technology and so on, a large wall thickness submarine pipeline steel X70 was developed, and the influence of technology system on the microstructure and properties of large wall thickness steel pipelines was studied. The results show that the duplex structure of ferrite and bainite can be obtained by the post-rolling relaxation + controlled cooling process, and the relaxation termination temperature is the determinant of the ferrite volume fraction and grain size. The lower the relaxation relaxation temperature, the higher the volume fraction of ferrite, the larger the grain size and the lower the yield ratio, the better the plasticity index. The content of pro-eutectoid ferrite increased gradually and the content of bainite decreased with the decrease of relaxation temperature. When the relaxation temperature was between 710 and 780 ℃, the strength and ductility of experimental steel reached a good match .