Nb-V-Ti微合金低碳钢Q550D 250 mm×1820mm连铸板坯角部横裂纹的控制工艺

Control Measures of 250 mm×1820 mm Casting Slab Corner Transverse Cracks of Nb-V-Ti Micro-Alloying Low-Carbon Steel Q550D

分析了Q550D钢(/%:0.15C,0.25Si,1.40Mn,≤0.010P,≤0.002S,0.03Nb,0.06V,0.015Ti,0.020Alt)连铸板坯角部横裂纹,得出角部横裂纹产生于结晶器内,并进一步扩展于二冷区,另外,在弯曲段(Ⅲ脆性区)外弧铸坯受拉应力,也是造成外弧角部横裂纹产生的重要原因。通过降低结晶器宽面水流量200 L/min,窄面20 L/min,对弧精度从±0.5 mm提高至±0.3 mm,振幅和振频分别从4~5 mm和130~136 opm改进至3.6~4.5mm和140~146 opm,结晶器锥度从0.9%~1.0%增至1.0%~1.1%,二冷工艺由边部自然冷却改进为喷嘴冷却,钢中氮含量由≤60×10^(-6)降至≤40×10^(-6)等工艺措施,角部裂纹发生率大幅度降低。

The casting slab comer transverse cracks of steel Q550D （/% ： 0. 15C, 0. 25Si, 1.40Mn, ≤0. 010P, ≤ 0. 002S, 0. 03Nb, 0. 06V, 0. 015Ti, 0. 020Alt） have been analyzed to get the comer transverse cracks form in mold and further develop at secondary cooling area, besides at bending part （ Ⅲ brittle zone） of slab, the tensile-stress action of outer face of slab is also an important factor for comer cracking. With the process measures including decreasing water flow rate of width face of mold by 200 L/min and of narrow face by 20 L/min, improving precision of arc each other from ± 0. 5 mm to ＋0. 3 mm, improving the amplitude and vibration frequency respectively from 4 ~ 5 mm and 130 - 136 opm to 3.6 ~4. 5 mm and 140 - 146 opm, increasing the mold taper from 0. 9% ~ 1.0% to 1.0% ~ 1.1%, improving edge natural cooling at secondary section to nozzle cooling, and decreasing nitrogen content in steel from ≤ 60 × 10^-6 to ≤ 40 ×10^-6 the occurring rate of corner cracks markedly decreases.