利用SEM和TEM原位拉伸方法研究了轧后冷却制度对X80级抗大变形管线钢组织的影响及低屈强比的微观机理. 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. 当弛豫终止温度区间为690-705 ℃时, 试样的强度和塑性达到了较好的匹配, 满足X80级抗大变形管线钢的性能要求. 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. 对拉伸过程进行动态原位观察的结果表明, 铁素体(软相)和贝氏体(硬相)的协调变形机制是屈强比降低的原因.
The influence of cooling process on microstructure of high-strain pipeline steel X80 with its low yield ratio has been examined by SEM and in situ TEM. The results illustrate that ferrite+bainite dual phase structure is obtained after proper relaxation and chilling down process, while the terminate temperature of relaxation is the decisive factor. When the stop temperature for relaxation ranges from 690 to 705 ℃, the combination of strength and ductility reaches the need for the use of X80 pipeline steel. The reduction of relaxation stop temperature results in increases of the volume of ferrite phase and grain size, which leads to lower yield ratio. Tensile test shows that the lower yield ratio mainly attributes to the cooperative deformation mechanism between soft ferrite and hard bainite.
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