Causes of plasma cutting cracking of a wide and thick steel plate

In the plasma cutting process of a wide and thick plate, a central crack was generated at 1/2 thickness of the plate. The causes of cracking of the steel plate were analyzed by means of macroscopic observation, chemical composition analysis, metallographic examination, scanning electron microscope and energy spectrum analysis and hardness test. The results show that there was an obvious segregation band at 1/2 thickness of the steel plate. The microstructures of the matrix and the segregation band were tempered martensite and quenched martensite, respectively. There were long strip inclusions in the segregation band, and the cracks initiated and propagated from the inclusions. The hardened layer after plasma cutting had a large hardness and a great tendency to harden. Under the action of thermal stress and structural stress, the steel plate eventually cracked.