Abstract: The causes of delayed cracks forming in 80 mm-thick abrasion-resistant steel plates NM400 after cutting were investigated by analyzing macrostructures and microstructures of the plates,and countermeasures to avoid such kind of cracks were considered. The result shows that there are several center contraction cavities and segregations in the mid-depth of the plate,and microstructures there are coarse; the impact of various residual stresses generating during heat treatment and the flame cutting process on this area is the main reason for the formation of the delayed crack. The delayed cracks can be effectively avoided by reducing defects in continuously cast blooms and improving heat treatment and cutting process.