Regulating Non-metallic Inclusions with Pulsed Electric Current in Ultra-Low Carbon Steel and Industrial Practice
摘要
Non-metallic inclusions in steel can significantly impact material properties, leading to stress concentration and cracking. Pulsed electric current (PEC) treatment offers a novel approach to molten steel purification and continuous casting optimization by precisely regulating inclusion size, number density, and types, making it promising for high-grade steel production. This study applies the intrinsic positive charge characteristic of Al2O3 inclusions to break the limitations of traditional density difference theory, successfully applying it to nozzle anti-clogging technology. Industrial practice confirms the feasibility of PEC in efficiently migrating and removing inclusions. PEC inhibits inclusion collision and aggregation inside nozzles, reducing the inner wall adhering layer thickness by 30–40 pct and avoiding large inclusions formed by detachment from refractory materials. Notably, PEC enables 7-heat continuous casting of ultra-low carbon steel with a single nozzle handling over 1000 tons. In PEC-treated strands, inclusion number density decreases from 0.73 to 0.57 per mm2 with Al2O3 inclusions dropping from 13.7 to 2.6 pct and Al2O3-TiOx from 22.6 to 10.4 pct. It significantly suppresses > 5 μm Al2O3 inclusions (33→12 pct), eliminates > 20 μm ones, and increases ≤ 5 μm inclusions (70.3→89 pct). Mold-level stability improves, with ± 3 and ± 5 mm fluctuation qualification rates rising to 81 and 94 pct, respectively. Cold rolling defects are reduced, with inclusion defect rate from 1.21 to 0.75 pct and slag entrapment from 2.15 to 1.53 pct. Overall, PEC regulation improves steel cleanliness, inclusion size distribution, mold-level stability, and reduces defects, providing technical support for high-quality ultra-low carbon steel production.