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

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.