700 MPa级Ti-Nb-V-Mo复合微合金化高强钢的工业研制

Industrial development of 700 MPa grade high-strength steel by Ti-Nb-V-Mo micro-alloying

基于CSP工艺,采用Ti基复合微合金技术、控轧控冷及平整工艺,开发了屈服强度700 MPa级别的薄规格高强钢,借助SEM、TEM、EDS和力学性能测试等,分析了不同轧制工艺参数对高强钢性能、组织及析出物的影响。结果表明,该高强钢组织由准多边形铁素体及极少量粒状珠光体构成;薄规格强化及冷却速度控轧的细晶强化、卷取温度控制的析出强化共同决定了钢的组织和力学性能;高温大压下、头部连续冷却有利于薄规格细晶强化,高温(890±20℃)终轧、高温(620±20℃)卷取有利于析出大量尺寸20 nm以下且弥散分布细小的以含Ti为主的(Ti,Nb,Mo)C粒子,析出强化作用明显。与平整前相比,热轧带卷平整后钢屈服强度提高约30 MPa、抗拉强度提高约10 MPa、延伸率降低了7.9%~16.7%。

Based on the CSP process,the thin gauge high-strength steel with yield strength of 700 MPa has been developed by Ti-based composite micro-alloying,controlled rolling and controlled cooling and leveling process.The mechanical properties,microstructure and precipitates of the high-strength steel with different rolled parameters were analyzed by SEM,TEM,EDS and mechanical test.The results show that the microstructure of the high-strength steel is composed of quasi-polygonal ferrite and small amount of granular cementite.The microstructure and mechanical properties of the steel are affected both by fine grain strengthening caused by thinner gauge and laminar cooling rate and precipitation strengthening caused by coiling temperature;meanwhile,the heavy reduction under higher temperature and head continuous cooling are conducive to fine grain strengthening,and high temperature(890±20℃)final rolling and high temperature(620±20℃)coiling are beneficial to the precipitation of a large number of dispersed distributed fine(Ti,Nb,Mo)C particles(mainly containing Ti)with the particle size below 20 nm,and the corresponding precipitation strengthening effect is significant.Compared with the strip before flattening,the yield strength of the as-flattened strip is increased by around 30 MPa,the tensile strength is increased by around 10 MPa,and the elongation is reduced by 7.9%~16.7%.