Abstract The formation and evolution of nonmetallic inclusions in pipeline steel were investigated by SEM, EDS and INCA Feature Analysis System, with the industrial process of electric arc furnace → ladle furnace (LF) refining → vacuum degassing → continuous casting. The composition, size and amount of inclusions during refining process were discussed systematically. The results show that inclusions at each refining step are mainly small-particle inclusions (below 5 µm), and the total number of inclusions has been reduced significantly due to the refining effect of slag during LF refining. The calcium (Ca) treatment increases the amount of small inclusions. The types of inclusion are mainly Al2O3 and MnO–SiO2–Al2O3 before LF, and they are transformed into CaO–Al2O3, MgO–Al2O3 and CaO–MgO–Al2O3 during LF process. After Ca treatment, inclusions are changed to CaO–Al2O3–(CaS) and CaO–MgO–Al2O3–(CaS). Typical inclusions are still mainly CaO–Al2O3 and CaO–MgO–Al2O3 in tundish, but the composition of those inclusions has been changed and located to the low melting point region in ternary phase diagram. Such inclusions will further be removed as continuous casting approaches.

中文翻译：

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LF和VD精炼过程中管线钢非金属夹杂物的演变

摘要 通过电弧炉→钢包炉（LF）精炼→真空脱气→连铸的工业过程，采用SEM、EDS和INCA特征分析系统，对管线钢中非金属夹杂物的形成和演化进行了研究。系统地讨论了精炼过程中夹杂物的成分、大小和数量。结果表明，各精炼步骤的夹杂物主要为小颗粒夹杂物（5 µm以下），由于LF精炼过程中炉渣的细化作用，夹杂物总数已显着减少。钙 (Ca) 处理增加了小夹杂物的数量。夹杂物类型主要是 LF 前的 Al2O3 和 MnO-SiO2-Al2O3，它们在 LF 过程中转化为 CaO-Al2O3、MgO-Al2O3 和 CaO-MgO-Al2O3。Ca处理后，夹杂物变为 CaO–Al2O3–(CaS) 和 CaO–MgO–Al2O3–(CaS)。典型夹杂物仍以中间包中的CaO-Al2O3和CaO-MgO-Al2O3为主，但这些夹杂物的成分发生了变化，在三元相图中位于低熔点区域。随着连续铸造方法的进行，这些夹杂物将被进一步去除。