轧制工艺对460 MPa级低屈强比耐火耐候钢组织性能的影响

利用热模拟方法测定低屈强比耐火耐候钢不同速率冷却后的组织。对比轧后弛豫工艺与未弛豫工艺以及终冷温度对试验钢性能的影响,利用光学显微镜、扫描电镜、透射电镜分析不同工艺对钢轧后显微组织的影响。结果表明,随冷却速度的增加,钢板组织由多边形铁素体变为针状铁素体+粒状贝氏体复相组织;由于弛豫处理过程中过冷奥氏体部分转变为多边形铁素体,钢板屈服强度和屈强比均下降;随着终冷温度的降低,钢板的屈服强度和屈强比上升,与钢中针状铁素体的细化与M/A组元的弥散强化有关;轧后直接水冷,并控制终冷温度至500~560 ℃,可获得高强度与低屈强比的良好匹配。

Effect of rolling parameters on microstructure and mechanical properties of 460 MPa grade low yield ratio fire-resistant weathering steel

Microstructure of low yield ratio fire-resistant weathering steel after cooling at different rates was determined by thermal simulation method.By comparing the effects of post-rolling relaxing process or not and final cooling temperature after hot rolling on mechanical properties of the steel,the effect of different processes on microstructure was investigated by using OM,SEM and TEM.The results show that with cooling rate increasing,the microstructure of the steel plates changes from polygonal ferrite to (acicular ferrite+granular bainite) duplex microstructure.Due to the transformation of undercooled austenite into polygonal ferrite during relaxation treatment,the yield strength and yield ratio of the steel plates decrease.With the decrease of final cooling temperature,the yield strength and yield ratio of the steel plates increase,which is due to the refinement of acicular ferrite and the dispersion strengthening of M/A constituent.Good match of high strength and low yield ratio of the steel plates are successfully achieved by the combination of direct water-cooling after hot rolling and controlled final cooling temperature between 500 ℃ to 560 ℃.