Study on Cleanliness of Q235B Steel under the Conditions of Substituting Iron Ore for Partial Scarp in Converter

Oxygen and nitrogen analyzer,metallographic examination,SLIME,SEM and EDS techniques had been used to study the cleanliness of plain carbon structural steel Q235B produced via KR-BOF-ArCC process under the conditions of substituting iron ore for partial scarp in converter. The results show that the total amount of microscopic inclusions decreases from argon refining inlet to casting process. After argon refining,average number of microscopic inclusions decreases by 26.63%,indicating a significant effect from argon refining. Major microscopic inclusions at various steps are Al₂O₃ and Mn S as well as small amount of CaO-MgO-Al₂O₃,CaO-Al₂O₃ and MgO-Al₂O₃ composite inclusions. In the process of argon refining,TO content decreases by 19.60×10^-6 while casting step makes TO content increase by 10.55 × 10^-6 which is due to molten steel secondary oxidation or slag entrapment. From the converter to the casting process,the average nitrogen content gradually increases and maximum nitrogen increasing takes place during the convertor to argon refining process. The large inclusions are dominant SiO₂ and small amount of MgO-Al₂O₃-SiO₂.