控轧控冷工艺对海洋高应变管线钢性能和组织的影响

Effect of thermo-mechanical control process on properties and microstructure of high strain submarine pipeline steel

采用工业试验、性能检测、显微组织分析及原位拉伸等研究了控轧控冷工艺对海洋高应变管线钢力学性能、微观组织、析出相和塑性断裂的影响。结果表明,海洋高应变管线钢的微观组织主要是多边形铁素体和贝氏体。当精轧终止温度从780℃下降至750℃时,多边形铁素体体积分数增加约20%,析出相的数量明显增加,屈服强度降低,应变硬化指数和均匀伸长率升高。当轧后弛豫时间从30 s增加至60 s时,多边形铁素体体积分数增加约25%,10 nm以下析出相明显增多,其对性能的影响与精轧终止温度下降时类似。终冷温度的降低使硬相组织从粒状贝氏体向板条贝氏体转变,抗拉强度升高,屈强比降低,而应变硬化指数和均匀伸长率变化不大。

The effects of thermo-mechanical control process on properties,microstructure,precipitations and plastic fracture of high strain submarine pipeline steel were studied by industrial test and inspections including mechanical properties detection,microstructure analysis,situ tension,etc.The results show that the microstructure of high strain submarine pipeline steel is mainly polygonal ferrite and bainite.The volume fraction of polygonal ferrite increases by about 20%and the amount of precipitation increases significantly when the final rolling temperature decreases from 780℃to 750℃.That leads the yield strength reduce while the strain hardening index and uniform elongation rise.When the relaxation time after rolling increases from 30s to 60s,the volume fraction of polygonal ferrite increases by about 25%,the precipitation with size below 10 nm increases significantly too.And the effect on properties is similar to that decreasing the end finishing rolling temperature.When the final cooling temperature reduces,the hardness structure changes from granular bainite to lath bainite with higher tensile strength and lower yield ratio,while the strain hardening index and the uniform elongation have a tiny change.