中文摘要：

利用热模拟、力学性能测试和材料显微分析等试验技术，研究了X70管线钢在延迟加速冷却条件下的组织与性能的变化规律。研究表明，通过延迟加速冷却，X70管线铜可获得贝氏体＋铁素体（B＋F）双相组织。随着始冷温度的上升，试验钢的贝氏体含量增加，铁素体含量降低，导致材料屈服强度上升，塑性下降。当始冷温度为530℃时，X70管线钢有较低的屈强比，较大的均匀伸长率和较大的形变强化指数，符合大变形管线钢的技术要求。

英文摘要：

The change rule of microslrueture and properties after delaying accelerated cooling（DAC） for X70 pipeline steel was in- vestigated through thermal simulation, mechanical property test and microscopic analysis method. The results showed that bainite ＋ ferrite （B＋F） duaL-phases microstrueture can be obtained by DAC. With the increasing of starting cooling temperature, the content of bainite increases and content of ferrite decreases, which lead to increase of yield strength and reduce of plasticity. When starting cooling temperature is 530 ~C, lower yield ratio, higher uniform elongation and strain hardening index can be obtained, which accord with the technical requirements of high deformation pipeline steel.