“两次造渣法”冶炼不锈钢超薄带理论和工业应用

 精密压延不锈钢冷轧超薄板带(<0.3 mm)要求具有良好的洁净度和夹杂物塑性化以获得良好的表面质量和力学性能,但钢水的洁净化和夹杂物塑性化在冶炼上是相互矛盾的,这增加了精密压延不锈钢板带的冶炼难度。为解决不锈钢超薄带夹杂物塑性化和钢水洁净化的矛盾问题,通过热力学理论分析和实验室渣-金平衡试验研究了精密压延不锈钢冶炼的关键问题并得出相应应对策略,炉渣碱度降低,对脱氧和脱硫不利,钢水洁净度变差,高碱度渣的使用是获得较高洁净度钢水的必要条件;随着炉炉渣碱度降低,夹杂物由CaO-SiO₂-Al₂O₃系演变为良好塑性的SiO₂-Al₂O₃-MnO系,低碱度炉渣是夹杂物塑性化必需条件; 钢中Al_s含量降低,夹杂物中Al₂O₃含量明显减小,塑性变好; 通过在渣中配加适量的MgO,可以有效抑止低碱度渣对炉衬的侵蚀。并在此基础上开发出新的“两次造渣法”冶炼工艺,在AOD脱硫期造高碱度渣脱硫和脱氧,在LF精炼造低碱度渣塑性化钢中夹杂物,实现不锈钢优异的钢水洁净度和夹杂物塑性化。工业试验结果表明, w(TO])小于0.002 5%, w(S])小于0.001 0%,夹杂物成分为以SiO₂-Al₂O₃-MnO系为主的硅锰铝榴石类夹杂物,Al₂O₃平均质量分数小于20%,具有良好的塑性,满足生产不锈钢超薄板带的要求。

Theory and industrial applications for improvement of ultra-thin stainless steel strip purity and inclusion plasticity by development of "two step slagging strategy"

Precision calendered ultra-thin stainless steel strip (<0.3 mm) is required with sound steel cleanness and non-inclusion plasticity to obtain high comprehensive properties and surface quality while the two aspects are in contradiction. In order to solve the conflicts between steel cleanness improvement and non-inclusion plasticity,thermodynamic analysis and laboratory-scale slag-metal equilibrium experiments were carried out for achievement of high purity for stainless steel and admirable inclusion plasticity. The results show that with the slag basicity decrease, the desulfurization and deoxidation are depressed, as well as the molten steel purity, the use of high basicity slag is a necessary condition for obtaining high purity of molten steel. The inclusion composition evolves from CaO-SiO₂-Al₂O₃ based system to plasticized SiO₂-Al₂O₃-MnO based system with the decrease of slag basicity. The content of Al_s in the steel decreases, and the content of Al₂O₃ in inclusions also decreases obviously, while the plasticity becomes better. Proper MgO content addition into the slag can restrain the corrosion of lining refractory effective. It proposes a new "two step slagging strategy" based on the thermodynamic analysis, in which high basicity slag is applied in AOD to desulfurization and deoxidation, low basicity slag is employed in LF refining process to plasticized inclusions in the steel. The industrial trial results verify that the new strategy can achieve high steel cleanness and inclusion plasticity. w(TO]) is less than 0.002 5%,w(S]) is less than 0.001 0% and inclusion is SiO₂-Al₂O₃-MnO dominated silicon-manganese aluminum-garnet inclusions with an average mass percent of Al₂O₃ lower than 20%, the plasticity is outstanding, which meets the requirement of ultra-thin stainless steel trip.