亚包晶钢Q235D连铸大方坯的质量控制

Quality Control for Casting Bloom of Hypo-Peritectic Steel Q235D

莱钢特钢厂50 t UHP-EAF(热装铁水比≥50%)+LF(VD)冶炼的Q235D钢(0.10%～0.17%C)260mm×300 mm的连铸坯轧制成直径Φ150 mm圆钢后,钢材表面出现裂纹。分析表明,钢的包晶点的碳当量[C_1]与钢中实际碳含量[C]之间的差别△C越大,亚包晶钢Q235D钢材废品率越高。实践表明,控制0.15%～0.17%[C]使△C<0.015%,钢液过热度20～30℃,结合降低结晶器冷却水流量和二冷区冷却强度,低拉速,使成品材表面质量合格率在99.3%以上。

The cracks at surface of 150 mm round bar occur after rolled from 260 mm × 300 mm continuous casting bloom of steel Q235D （0. 10%×0. 17% C） melted by 50 t UHP EAF （hot metal charging ratio more than 50% ） ＋ LF （VD） process at Special Steel Works, Laiwu Steel. Analysis indicated that the larger the AC-difference between carbon e- quivalent [ Cj ] at peritectic point of steel and real carbon content in steel ~ C J, the higher the crack rejection rate of hypo- peritectic steel Q235D products. Practice show that with controlling 0.15% -0.17% [ C ] for AC 〈 0. 015%, overheating extent of liquid steel 20 - 30 ℃, combined with decreasing mold cooling water rate, decreasing cooling water intensity in sec- ondary zone and with low casting speed, the qualified rate for surface quality of finished products is more than 99.3%.