Abstract： A hot-rolled steel plate was purchased by a company and used as the bottom plater for artillery. After flame cutting using the numerically-controlled machine tool， the cracks were observed at the transition arc. The causes of crack formation were analyzed by chemical composition analysis， mechanical properties test， metallographic examination and scanning electron microscopy （SEM）. The experimental results showed that the chemical composition and main mechanical properties of the bottom plate were normal. The cooarse original structure decreased the material perpormance. After the flame cutting， the microstructure of bottom had great changes. The undesirable structures including coarse bainite and martensite were generated. The comprehensive analysis indicated that the major reason for the cracking of the bottom plate was the excessive stress of structure after NC flame cutting and the stress concentration at the transition arc angle. The material performance could be enhanced by the normalizing treatment of bottom plate before flame cutting， thus effectively avoiding the cracking failure of bottom plate.
2020, Vol. 38 
