Analysis on Causes of Surface Cracks of Q345GJC Steel Plate Used for High-rise Buildings

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.