Abstract: The steelmaking flowsheet of tested casting bloom of steel Q420C (/%: 0.18C, 0.34Si, 1.40Mn, 0.013P, 0.011S, 0. 066V, 0.018Als, 0.0110N) is 80t BOF-LF-CC process. The hot ductility of casting bloom of steel Q420C at 600~1400°C is tested by using Gleeble-1500D thermal simulator and the morphology of fracture and structure of steel is analyzed by optical, scanning- and transmission-electron microscope to study effect of the solidification segregation and precipitates on hot ductility of casting bloom. Results show that of steel Q420C the I brittle zone is >1250~1350°C and the Ⅲ brittle zone is 700~1050 °C , and at 1050~1250℃ the steel has better ductility with reduction of area more than 60%, Commercial pilot production results show that with controlling Als content in steel 0.015%~0.020% , properly decreasing ratio of secondary cooling water to 7~8t/h at feet roller zone, 5.5~6.5t/h at Ⅰ zone and 14±1t/h at support roller zone, and controlling straightening temperature of casting bloom ≥1050℃ , the cracking ratio of rolled products decreasing from original 45.3% to 4.6%.

摘要： 试验用Q420C钢（/%:0.18C,0.34Si,1.40Mn,0.013P,0.011S,0.066V,0.018Als,0.0110N）铸坯的冶炼工艺为80t BOF-LF-CC。采用Gleeble-1500D热模拟试验机测试Q420C钢连铸坯的600~1400℃热塑性,并利用金相显微镜、扫描电镜以及透射电子显微镜分析断口形貌及金相组织和研究凝固偏析和析出物粒子对铸坯热塑性的影响。结果表明,Q420C钢第Ⅰ脆性区为>1250~1350℃;第Ⅲ脆性区为700~1050℃;在1050~1250℃,断面收缩率大于60%。工业试验结果表明,通过控制Als含量0.015%~0.020%,适当降低二冷比水量（足辊段7~8t/h,Ⅰ段5.56.5t/h,托辊段14±1t/h), 铸坯矫直温度≥1050℃,轧材开裂率由原45.3%降至4.6%。

关键词: V-微合金化钢Q420C, 热塑性, 析出物, 断口形貌