大壁厚31.8 mm海底管线用钢X70的研制
Development of Submerged Pipeline Steel X70 with Thickness of 31.8 mm
陈奇明, 李中平
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作者单位：湖南华菱湘潭钢铁有限公司, 湖南 湘潭 411101
中文关键字：海底管线； 弛豫终止温度； 铁素体； 显微组织
英文关键字：submerged pipeline; terminate relaxation temperature; ferrite; microstructure
中文摘要：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。
英文摘要：Submerged pipeline steel X70 with larger thickness was researched at aspects of chemical component, the technique of hot rolled and cooling, and the effects of the processes on microstructure and mechanical properties of the steel were investigated. The results show that the dual phase microstructure comprising ferrite and bainite can be obtained after proper relaxation and controlled cooling, the terminate temperature of relaxation is the most important factor to influence the volume percentage of ferrite and grain size. The lower the terminate temperature, the higher the volume fraction of ferrite, the larger the size of grain, the lower the yield ratio, the better the ductility. With the decrease of terminate relaxation temperature, the volume fraction of pro-eutectoid ferrite increases and the volume fraction of bainite decreases generally. In order to obtain a good combination of strength and ductility, the terminate relaxation temperature should be retained at 710～780 ℃.