Abstract: Aiming at the sags and longitudinal cracks of 15CrMoG rectangular billet， the melting temperature， alkalinity， viscosity and other technical parameters of protective slag were designed. By adjusting the alkalinity of the protective slag from 0.85 to 1.15， the melting point from 1 132 ℃ to 1 200 ℃， and the viscosity from 0.67 Pa·s to 1.4 Pa·s， the crystallization rate of the protective slag was increased， the thickness of solid-state slag film was increased， the thermal resistance was improved， and the heat transfer was uniformly stabilized. At the same time， the melting rate of the slag was optimized from 70 s to 32 s， vibration parameters were controlled， non-sinusoidal vibration bias slope was increased， slag consumption was increased， and lubrication was improved. The surface sags and longitudinal cracks of the billet were eliminated by optimizing the physicochemical parameters and vibration parameters of the slag. The proportion of defective casting billet finishing treatment was greatly reduced， which reduced the grinding work of casting billet and improved the metal recovery rate.

Key words: 15CrMoG Steel, Sags, Longitudinal Cracks, Protective Slag

摘要： 针对15CrMoG矩形坯出现的凹陷与纵向裂纹，设计了保护渣熔化温度、碱度、粘度等技术参数。将保护渣碱度由0.85调整到1.15，熔点由1 132 ℃调整到1 200 ℃，粘度由0.67 Pa·s调整到1.4 Pa·s，提高保护渣的析晶率，增大固态渣膜厚度，提高热阻，均匀稳定了传热；同时将保护渣熔速由70 s优化到32 s，控制振动参数，提高非正弦振动偏斜率，增大保护渣消耗量，改善润滑。通过保护渣理化指标和振动参数的优化，消除了铸坯表面凹陷与纵向裂纹。不良铸坯的精整处理比例大幅降低，减少了铸坯修磨工作量，提高了金属收得率。

关键词: 15CrMoG钢, 凹陷, 纵裂, 保护渣