Abstract: In according with issue of central segregation of 250 mm x 2 000 mm slab of steel Q345 (/% : 0.14-0.18C, 0.20-0.50Si, 1.30-1.50Mn, ≤ 0.025P, ≤ 0.025S, 0.015-0.060A), a solidification heat transfer mathematical model is established, and verified and modified by nail shooting test to study the effect of secondary cooling intensity (light, middle and strong) and casting speed (0.80-1.10 m/min) on casting slab temperature field and shell thickness, and optimize the soft reduction process and correspondent casting parameters. Results show that with typical casting speed 0. 95 m/min and light cooling scheduling, the final solidification point of slab is 23.43 m, the length of mushy (liquid-solidified phase) zone is 7.22 m； with decreasing the secondary cooling intensity, the final solidifying point extends 0.56-0.67 m and the length of mushy zone increases by 0.25-0.29 m； with increasing casting speed by 0.15 m/min, the final. solidifying point extends 3. 45 ~3. 90 m while the length of mushy zone increases by 0.94-1.22 m； with optimized light cooling schedule, casting speed 0. 95 m/min, solidified fraction, 0.4-0.9 at soft reduction zone, and total reduction amount 6mm, the qualified percentage for ≤ I ratting central segregation of slab of steel Q345 increases to 98.0% from original 83.1%.

Key words: Steel Q345, 250 mm x 2 000 mm Slab, Casting, Mathematical Model, Final Solidifying Point, Central Segregation

摘要： 针对Q345钢(/%:0.14～0.18C、0.20～0.50Si、1.30～1.50Mn、≤0.025P、≤0.025S、0.015～0.060Al)250 mm×2 000 mm板坯中心偏析质量问题,建立凝固传热数学模型,并经射钉试验验证及修正,研究二冷强度(弱冷、中冷、强冷)、连铸速度(0.80～1.10 m/s)对铸坯温度场和坯壳厚度的影响,同时优化轻压下工艺和相应的连铸参数。结果表明,在典型拉速0.95 m/min及弱冷制度下,板坯凝固末端23.43 m,两相区长度7.22 m;减弱冷却强度,凝固末端后移0.56～0.67 m,两相区长度变长0.25～0.29 m;拉速增大0.15 m/min,凝固末端后移3.45～3.90 m,两相区长度变长0.94～1.22 m;优化采用弱冷冷却制度,拉速为0.95 m/min,轻压下位置对应固相率fs=0.4～0.9,总压下量达6 mm时,Q345钢板坯中心偏析Ⅰ级内平均合格率由83.1%提高到98.0%。

关键词: Q345钢, 250 mm x 2 000 mm板坯, 连铸, 数学模型, 凝固末端, 中心偏析