管线钢连铸板坯的半宏观偏析和凝固组织

Solidification structure and semi-macro segregation of pipeline steel continuous casting slabs

研究了不同凝固组织下管线钢的中心偏析情况.低倍组织腐蚀结果表明,连铸板坯的中心偏析由相对独立的、大小不一的半宏观偏析点组成,且不同凝固组织的半宏观偏析特征有所差别.化学成分分析表明,中心等轴晶时板坯中心为负偏析,且贯穿于整个等轴晶区中,而中心为柱状晶时则表现为正偏析.通过对比化学成分和半宏观偏析面积比发现,板坯的半宏观偏析面积比随C和Mn最大偏析度的增加而增加,由于化学成分分析只能反应局部位置的偏析情况,因此半宏观偏析面积比的方法对生产实践更具有指导意义.对不同过热度下不同凝固组织的半宏观偏析面积比的统计结果显示,在合理使用轻压下技术的前提下,中心为柱状晶更有利于减轻半宏观偏析面积比,进而改善管线钢连铸板坯的中心偏析.

Center segregation with different solidification structures was investigated in pipeline steel. Macrostructure photographs show that center segregation in continuous casting slabs is composed of many semi-macro segregates, which are relatively independent and separated spot-like segregates with different sizes. The features of semi-macro segregation are different for different solidification structures. Chemical analysis shows that negative segregation is formed across the equiaxed zone in the center of the slab, while positive segregation is observed in the center of the slab surrounded by columnar crystals. It is revealed that the semi-macro segregation area in the center of the slab increases with the increase of the maximum segregation ratios of C and Mn. However, compared with the method of segregation area measurement, only local segregation could be obtained by chemical analysis, and it is obvious that the method of segregation area measurement is more helpful to industrial practice. Furthermore, the segregation area with different solidification struc-tures under different superheats was calculated. The results indicate that as the soft reduction technology is applied reasonably, colum-nar crystals in the center of the slab are more advantageous to the reduction of segregation area, and finally would be better for the im-provement of center segregation.