轧制工艺对550 MPa级桥梁钢组织和晶界特征的影响

Influence of rolling process on microstructure and grain boundary characteristics of bainitic steel

研究了桥梁用550 MPa级高强韧贝氏体钢在不同冷却速率和变形量条件下显微组织的演变。结果表明:轧制变形量由0增加到50%,显微组织由板条贝氏体转变为粒状贝氏体+针状铁素体。EBSD取向差研究表明,晶粒内相邻的贝氏体板条界、亚晶粒和基体晶粒间是小角度晶界;贝氏体板条束、多边形铁素体和针状铁素体边界是大角度晶界。在变形和无变形试样中,随着冷却速率的增加,大角度晶界的比例增加,“有效晶粒尺寸”减小。当冷却速率低于10℃/s时,变形越大,产生的大角度晶界越多。高强韧贝氏体钢获得良好强韧性匹配的冷却速率为15~25℃/s,变形量为40%以上。

The microstructure evolution of 550 MPa high strength and toughness bainitic bridge steel under different cooling rates and deformation conditions was studied.The results showed that the rolling deformation increased from 0 to 50%,and the microstructure changed from lath bainite to granular bainite+acicular ferrite.Misorientation studies showed that the adjacent bainite lath boundary,sub grain and matrix grain were small angle grain boundaries;The boundaries of bainite lath packets,polygonal ferrite and acicular ferrite were large angle grain boundaries.In deformed and undeformed specimens,with the increase of cooling rate and the ratio of large angle grain boundaries,the"effective grain size"decreased.The larger deformation produced more high angle grain boundaries when the cooling rate was lower than 10℃/s.With cooling rate of 15~25℃/s,and more than 40%deformation,high strength and toughness bainitic steel had good strength toughness matching.