石油钻杆钢冶炼过程中夹杂物的析出和衍变

系统分析了国内某钢厂复合脱氧工艺下Cr Mo石油钻杆钢夹杂物在EAF-LF-VD-CC流程中的析晶和衍变规律.由于铝酸盐的上浮，LF冶炼前钢中TO]含量较低，冶炼过程中氮含量逐渐升高.电镜下钢中大尺寸夹杂物（50μm左右）只出现在LF-VD阶段，主要为低熔点的硅锰酸盐、包含Na₂O的混合物和含有少量CaO的镁铝尖晶石，中间包阶段大尺寸夹杂物完全消失.小尺寸夹杂物（<10μm）出现在精炼全过程中，主要成分是Mg、Al、Si和Ca的复合氧化物、CaS以及二者的复合物，LF冶炼前到中间包阶段小尺寸夹杂物粒径相似，铸坯中其粒径稍微增加.随着精炼过程的进行，钢中小尺寸夹杂物的成分逐渐向复合氧化物的低熔点区域转移，夹杂物中CaO和MgO含量存在竞争关系.铸坯中大型夹杂物（>100μm）包括卷渣引起的复合夹杂，耐材剥落产生的MgO-CaO夹杂和钢液内生的铝酸盐夹杂.内生铝酸盐与精炼过程中小尺寸夹杂物成分相似，外层包覆Ca S，轧制过程中容易破碎成链状引发钻杆钢裂纹.建议适当延长VD处理后钢液的镇静时间，以去除钢中大型铝酸盐夹杂，提高钻杆钢质量. 

Inclusion formation and evolution in steelmaking process for drill pipes

The crystallization and evolution of non-metallic inclusions in CrMo drill pipe steel refined with a complex deoxidizer were investigated for the EAF-LF-VD-CC process flow of a domestic steel plant. As a result of aluminates floating, lower TO] content in the steel before the LF refining was shown, while nitrogen content in the steel gradually increased during the whole flow. Large size inclusions (about 50 μm), namely, silicic manganates with low melting point, complexes with Na₂O and magnesium aluminate spinels with a little CaO, appeared at the LF-VD stage and disappeared completely after the tundish process. Small size inclusions (< 10 μm) could be found during the whole refining flow. Their size at different refining stages was similar to each other, while smaller than that of the casting blank. The small size inclusions were complex oxides which consist of Mg, Al, Si, Ca and CaS respectively. The composition of the small size inclusions gradually moved to the liquid phase region during the smelting flow, and competition existed between CaO and MgO contents in these inclusions. Macro inclusions (> 100 μm) in the casting blank included complex inclusions caused by entrapped slag, MgO-CaO inclusions from refractories and endogenous aluminate inclusions coated by a CaS layer, whose composition was similar to small size inclusions in the smelting processes. The macro aluminate inclusions were easily broken into chain and further resulted in cracks in the steel during the rolling process. Hence, it is suggested to prolong the steel standing time after the VD operation to remove detrimental aluminate inclusions.