连铸板坯角横裂纹的形成机理及控制措施

Formation mechanism and control measures of corner transverse cracks in continuous casting slab

板坯角横裂纹是在钢的第Ⅲ脆性区产生的一种沿晶开裂。在第Ⅲ脆性区温度范围内,在奥氏体晶界铁素体薄膜的析出(晶界析出)弱化了晶界,或由于碳氮化物等的析出,在奥氏体晶界附近形成无析出区(晶界滑移)导致的晶界脆性,当铸坯在该温度区间受到弯曲、矫直或0号段错位等拉应力作用后产生的裂纹。奥氏体晶粒越粗大和奥氏体晶界越弥散细小的析出,越容易产生裂纹。保证连铸机设备精度和制定合适的连铸生产工艺参数是消除铸坯角横裂纹的根本方法。

Slab corner transverse cracks are intergranular cracking at the Ⅲ brittle zone in steel. In the Ⅲ brittle zone temperature range, the precipitation of ferrite films in austenite grain boundaries weakens the grain boundaries, or due to the precipitation of carbon- nitrides, no precipitation area（grain boundary sliding） in the vicinity of the austenite grain boundaries forms, causing grain boundary embitterment. When the slab is subjected to tensile stress of bending, straightening or number zero dislocation segments at the temperature range, the cracks generate. The austenite grains are more coarse, the austenite grain boundary are more dispersed and fine, the more prone to cracking. The guarantee of continuous casting machine equipment precision and formulation of appropriate continuous casting process parameters are the most effective measures to eliminate the corner transverse cracks in continuous casting slab.