高强度油井套管钢偏析与含Nb析出相研究

点状偏析是连铸坯中的常见半宏观缺陷之一,严重影响后续产品的加工性能和服役性能。点状偏析的形成与枝晶形貌以及凝固末期钢液流动有关,经热轧会遗留至管材中变成带状偏析,两者在成分和位置上存在一致性。热力学计算分析表明,该钢种圆坯点状偏析内存在富Nb碳化物,该析出相是凝固过程中分散型剩余液相溶质偏析的产物。通过SEM观察到,在常规加热过程中该富Nb碳化物并不能完全回溶,在管材带状偏析处仍然可以发现未溶碳化物的存在。

Study on segregation and Nb bearing precipitates of high strength oil well casing steel

One of the common defects during the continuous casting is the spot like semi macrosegregation, which seriously impacts the processing and service performance of subsequent products. The analysis shows that the formation of spot segregation is related to dendrite morphology and the liquid steel flow at the end of solidification. After hot rolling, the retained spot segregation in the casing could form banded segregation, whose composition and location are consistent with those of spot segregation. The thermodynamic calculation results show that Nb rich carbides exist in the spot segregation of the round billet. The carbide precipitates generate solute segregation in dispersed residual liquid during solidification. As is observed through SEM, during the conventional hot rolling process, Nb rich carbides cannot be re dissolved completely, which could be still found in the banded segregation.