Abstract: The production flowsheet of steel 25MnCrNiMoA (/%: 0.25~0.26C, 0.22~0.25Si, 1.25~1.30Mn, 0.008~0.011P, 0.002~0.004S, 0.45~0.50Cr, 0.36~0. 38Ni, 0.24~0.26Mo, 0.04~0.08Cu, 0.025~0.031Alt) is 100t UHP EAF-LF-VD-Φ650mm bloom casting-rolling to Φ120mm products. By observing and analysis on structure at crack area, it is found that there is obvious decarburization and inclusions in structure near the cracks, and multi-ferrite strips exist at end of cracks, it shows that the quality defects of casting bloom are main reason to form surface cracks of round bar of steel 25MnCrNiMoA. With the process measures including controlling [S]≤0.003% , liquid surface fluctuation ≤2mm during casting, casting speed 0.26m/min, overheating extent of liquid 20~30°C，decreasing secondary water rate, straightening temperature of bloom ≥950°C and optimizing ingredient of shielding slag, the surface cracks of hot-rolled products of steel 25MnCrNiMoA are avoided.

摘要： 25MnCrNiMoA 钢(/%：0.25~0.26C,0.22~0.25Si,1.25~1.30Mn,0.008~0.011P,0.002~0.004S,0.45~0.50Cr,0.36~0.38Ni,0.24~0.26Mo,0.04~0.08Cu,0.025~0.031Alt)的生产流程为100t UHP EAF-LF-VD-Φ650mm坯连铸-轧制Φ120mm材。试制过程热轧材出现批量表面裂纹。通过对轧材表面裂纹缺陷部位组织观察和分析，发现裂纹附近组织存在明显的脱碳及夹杂物,并且裂纹末端存在多条铁素体条带，表明连铸坯质量缺陷是25MnCrNiMoA圆钢产生表面裂纹的主要原因。通过控制[S]≤0.003% ,连铸时液面波动≤2mm,拉速0.26 m/min,过热度20~30℃ ,降低二冷水量，矫直温度≥950°C，优化保护渣组成等工艺措施，避免了25MnCrNiMoA钢热轧材表面裂纹的形成。

关键词: 25MnCrNiMoA钢, Φ120mm轧材, 表面裂纹, 脱碳, 夹杂物