【摘要】 针对断面尺寸为350 mm×430 mm的55SiCrA弹簧钢大方坯连铸时存在的碳偏析问题，本研究建立了考虑连铸机弧度、两孔水口以及二冷区不均匀冷却的多物理场耦合模型，系统探究了过热度和结晶器电磁搅拌（mold electromagnetic stirring,M-EMS）对钢液流动、传热、凝固与传质的影响规律，并通过工业试验对优化方案进行验证。结果表明，无M-EMS时，钢液射流持续冲刷铸坯窄面凝固坯壳，致使坯壳生长停滞并形成显著负偏析，碳偏析度最低降至0.899 1，钢液溶质富集于弯月面、宽面中心及弯月面下0.4 m处；当过热度由15℃升高至30℃后，结晶器出口处铸坯窄面坯壳厚度由25.3 mm降低至20.8 mm，窄面皮下5 mm处的偏析度由0.969 8降低至0.910 3，宽面坯壳中的碳偏析度基本不变，距结晶器弯月面2.5 m处铸坯中心的碳偏析度由1.012 1升高至1.013 3。施加MEMS能够降低钢液射流冲刷强度，改善偏析，当电磁搅拌参数为200 A/2.5 Hz时，铸坯窄面皮下5 mm处的偏析度升高了0.061 2，宽面内外弧坯壳中最低偏析度的差值降低了64%，距结晶器弯月面2.5 m处铸坯中心的碳偏析度升高了0.002 8。增大M-EMS强度会增强结晶器中溶质冲刷效应，坯壳生长速率降低，坯壳中碳的负偏析程度加剧，距结晶器弯月面2.5 m处铸坯中心的碳偏析度呈现先升高后降低的趋势。工业试验结果表明，在240 A/2.5 Hz的电磁搅拌参数下，过热度由30℃降低至20℃时，铸坯碳偏析度极差由0.131降低至0.045，等轴晶率由25.17%提高至29.41%；在20℃的过热度下，电磁搅拌参数由200 A/2.5 Hz调整为240 A/2.5 Hz和300 A/2.5 Hz时，初轧坯碳偏析度极差由0.070分别变化至0.021和0.074。基于模拟与工业试验结果可知，降低过热度或适当增大电磁搅拌强度能够有效控制55SiCrA弹簧钢大方坯偏析缺陷，提升连铸坯凝固组织的均匀性。更多还原

【Abstract】 To address the carbon segregation problem in the continuous casting of 55 SiCrA spring steel blooms with a cross-section of 350 mm×430 mm, a multi-physics field coupling model incorporating caster curvature, two-port submerged entry nozzle, and non-uniform secondary cooling was developed.The influences of superheat and mold electromagnetic stirring(M-EMS) on molten steel flow, heat transfer, solidification, and solute transport were systematically analyzed, and the optimized process parameters were further verified via industrial trials.The results show that without M-EMS, jet impingement on the narrow-face solidification front causes shell growth stagnation and pronounced negative segregation, resulting in a minimum segregation index to 0.899 1.Solute enrichment occurs near the meniscus, at the center of wide face, and approximately 0.4 m below the meniscus.Increasing the superheat from 15 ℃ to 30 ℃ reduces the narrow-face shell thickness at the mold exit from 25.3 mm to 20.8 mm and decreases the segregation index 5 mm below the narrow-face from 0.969 8 to 0.910 3, while the segregation level in the wide-face shell remains essentially unchanged.Meanwhile, the carbon segregation index at the bloom center 2.5 m below the meniscus rises slightly from 1.012 1 to 1.013 3.Applying M-EMS weakens jet impingement and improves segregation uniformity.Under stirring parameters of 200 A/2.5 Hz, the segregation index at a depth of 5 mm below the narrow face increases by 0.061 2, whereas the difference between the minimum segregation indices at the inner and outer arcs of the wide face decreases by 64%.The carbon segregation index at the bloom center 2.5 m below the meniscus increases by only 0.002 8.Increasing the M-EMS current enhances solute washout in the mold, reduces shell growth rate, and intensifies negative segregation in the shell.However, the central segregation index at the bloom center 2.5 m below the meniscus first increases and then decreases with further increases in current.Industrial trials indicate that, under stirring parameters of 240 A/2.5 Hz, reducing the superheat from 30 ℃ to 20 ℃ decreases the maximum segregation index difference from 0.131 to 0.045 and increases the equiaxed crystal ratio from 25.17% to 29.41%.At a superheat of 20 ℃, when the M-EMS parameters are adjusted from 200 A/2.5 Hz to 240 A/2.5 Hz and 300 A/2.5 Hz, the segregation index difference of the intermediate bloom changes from 0.070 to 0.021 and to 0.074, respectively.Based on simulation and industrial results, reducing the superheat or appropriately increasing the M-EMS intensity can effectively control segregation defects in 55 SiCrA spring steel blooms and improve the uniformity of solidification structure.更多还原