高强度油井管钢中的Nb偏析及形成机制分析

研究了含Nb高强度油井管钢连铸坯和管材的Nb偏析行为。利用OM、SEM、EDS、EMPA等手段,揭示了含Nb高强度油井管钢连铸圆坯中存在的富Nb、富C点状缺陷及其与管材内壁出现的条带组织中大尺寸NbC的对应关系。从Nb、C元素含量与其固溶度积间的关系分析了Nb的偏析机制。分析认为,大尺寸NbC是由于Nb的分配系数小,在连铸坯凝固后期枝晶间大量富集所形成。经固溶度积计算,富集的Nb含量可高于基体的5.4倍。

Segregation of Nb and its formation mechanism of high strength casing steel

The Nb segregation behavior of Nb bearing high strength oil well casing steel with as cast and as roll state was studied. With aids of OM, SEM, EDS and EMPA observation and analysis, the corresponding relationship between the as cast spot segregation and the following as rolled banded structure was revealed. The segregation mechanism of Nb was analyzed from the relationship between the Nb, C contents and their solid solubility product. It was analyzed that large size NbC is formed by the accumulation of large amount of Nb between dendrites in the late solidification stage of continuous casting billet due to the small distribution coefficient of Nb. The enriched Nb content can be 5.4 times higher than that of the matrix by solid solubility product calculation.