The three-dimensional morphology, size, content and composition of large-size inclusions extracted by large sample electrolysis from RH refining to hot rolling were investigated during the tinplate steel industrial test without calcium treatment. The results showed that the large-size inclusions in the RH refining process are Al₂O₃ inclusions and incompletely modified CaO·2Al₂O₃ inclusions, while those in tundish are Al₂O₃, CaO–Al₂O₃, CaO–SiO₂–Al₂O₃ and CaO–SiO₂–Al₂O₃–MgO. The typical types of large-size inclusion in slab and hot rolling plates are Al₂O₃, CaO–Al₂O₃, SiO₂–Al₂O₃, CaO–SiO₂–Al₂O₃, CaO–SiO₂–Al₂O₃–MgO and CaO–SiO₂–Al₂O₃–TiO₂. Secondary oxidation was found to occur in molten steel during the pouring process and protective casting should be improved. Large-size inclusions in hot rolling plates are Al₂O₃ with a mass fraction of 19.8% and incompletely modified CaO·2Al₂O₃ inclusions with a mass fraction of 45.9% those have not been completely modified, which have high hardness and are difficult to deform. Therefore, it is recommended that calcium treatment should be carried out at the end of RH refining to reduce the Al₂O₃ and CaO·2Al₂O₃ contents. And the effect of calcium addition on the inclusion evolution has been studied by a thermodynamic analysis at 1873 K. With the increase of calcium addition in molten steel, the evolution route of equilibrium precipitations is Al₂O₃ → CaO·6Al₂O₃ → CaO·2Al₂O₃ → CaO·Al₂O₃ → 3CaO·Al₂O₃ → 12CaO·7Al₂O₃ → CaO. The critical calcium content for CaS and CaO formation increases with increasing oxygen content. To avoid the precipitation reaction between [Ca] and [S], the mass fraction of calcium addition needs to be controlled below 0.0040%.

在未经钙处理的马口铁钢工业试验中，研究了从RH精炼到热轧大样品电解提取的大尺寸夹杂物的三维形貌、尺寸、含量和成分。结果表明，RH精炼过程中大尺寸夹杂物为Al ₂ O ₃夹杂物和未完全改性CaO·2Al ₂ O ₃夹杂物，中间包夹杂物为Al ₂ O ₃、CaO-Al ₂ O ₃、CaO- SiO ₂ –Al ₂ O ₃和 CaO-SiO ₂ –Al ₂ O ₃-氧化镁。板坯和热轧板中大尺寸夹杂物的典型类型有Al ₂ O ₃、CaO-Al ₂ O ₃、SiO ₂ -Al ₂ O ₃、CaO-SiO ₂ -Al ₂ O ₃、CaO-SiO ₂ - Al ₂ O ₃ -MgO 和 CaO-SiO ₂ -Al ₂ O ₃ -TiO ₂。在浇注过程中发现钢水发生二次氧化，应改进保护铸造。热轧板中大尺寸夹杂物为Al ₂ O ₃质量分数为19.8%的CaO·2Al ₂ O ₃夹杂物的质量分数为45.9%，未完全变质的夹杂物硬度高，不易变形。因此，建议在RH精炼结束时进行钙处理，以降低Al ₂ O ₃和CaO·2Al ₂ O _{3 的}含量。并通过1873 K热力学分析研究了钙添加对夹杂物演化的影响。随着钢水中钙添加量的增加，平衡析出的演化路线为Al ₂ O ₃ → CaO·6Al ₂ O ₃→ CaO·2Al ₂ O ₃ → CaO·Al ₂ O ₃ → 3CaO·Al ₂ O ₃ → 12CaO·7Al ₂ O ₃ → CaO。CaS 和 CaO 形成的临界钙含量随着氧含量的增加而增加。为避免[Ca]和[S]之间发生沉淀反应，需要将钙加入的质量分数控制在0.0040%以下。