采用宏观分析、化学成分分析、金相检验、扫描电镜观察和能谱分析等方法对某批轧制后表面存在纵向裂纹的高层建筑用Q345GJC钢板的裂纹形成原因进行了分析。结果表明：钢板表面裂纹在连铸板坯上就已经存在，裂纹产生的主要原因是在连铸过程中结晶器涂层严重磨损致使铜板外露，从而使铜元素渗入到连铸板坯中，降低了钢的热塑性，导致了裂纹的产生;在随后的轧制过程中,裂纹沿轧制方向进一步扩展形成纵向裂纹。

The formation causes of longitudinal surface cracks of Q345GJC steel plate used for high-rise building after being rolled was analyzed by means of macro observation, chemical compositions analysis, metallographic examination, scanning electronic microscope testing and energy spectrum analysis. The results show that the surface cracks on the rolled steel plate had existed on the continuous cast slab. During the continuous cast process there was Cu element penetrating into continuous cast slab because the crystallizer was seriously worn and Cu board was exposed to the cast slab. Cu element penetrating reduced the thermal plasticity of the steel plate and caused cracks. In the following rolling process, the had existed cracks were further expanded along the rolling direction and formed longitudinal cracks.