含铌钢板坯角横裂纹的控制

Control of Transverse Corner Cracking of Nb Steel Slab

采用金相显微镜和扫描电镜分析了含铌微合金化钢铸坯角部横裂纹的形成原因。发现矫直区铸坯角部温度位于该钢种第Ⅲ脆性温度区间内;拉速波动导致角部温度变化较大;二冷喷嘴状况不好导致两边角部温度相差较大。采用提高拉速、矫直区铸坯角部喷嘴遮挡等“热行”方法后,铸坯角部温度明显提高,铸坯的角横裂纹的发生率大大降低,但铸坯中心偏析恶化。采用增加角部喷嘴的“冷行”方法后,铸坯角部温度明显降低,铸坯的角横裂纹和中心偏析大大改善。

The optical microscope and SEM were applied to analyze the formation mechanism of transverse corner cracks of Nb microalloyed steel slab. It is found that the cracks occur at relatively low temperature in unbending section due to unbending strain because the corner temperatures of slab in this section is in No. 3 brittle zone of Nb steel first, then the corner temperatures of slab is changed greatly due to the casting speed fluctuation, and third the temperature difference between corners at both sides of slab is large due to misfunction of sprayers. Increasing casting speed and decreasing the cooling water flux at slab comers in the unbending section for mild cooling were performed first to control corner temperature above the upper limit in No. 3 brittle zone of Nb steel. As a result, the corner temperature of slab was increased apparantly and transverse corner cracking was minimized, but central segregation was got worsely. And then increasing the cooling water flux at corner for intensive cooling was applied to make corner temperature below the lower limit in No. 3 brittle zone. Great diminution of both transverse corner cracking and central segregation was achieved finally.