Cause Analysis on Crack Detection of Unqualified Steel Plate

Sampling from the crack detection of unqualified steel plate,the microstructure of defects was tested.According to the metallographic result,theoretical analysis was carried on in order to find out the primary cause which led to the disqualification.The results show that the central segregation formed in the continuous casting process is the cause of low qualification rate.Central segregation is advantageous to sulfide creating,and the bainite and martensite appears,providing conditions for crack extending,which act as two necessary factors for the cracks and lead to the hydrogen aggregation.All these defects cause the low qualification rate of ultrasonic inspection on line for steel plate.