Causes and improvement measures of delamination of tensile fracture of Q355B steel plate

By means of macroscopic observation,chemical composition analysis,tensile test,thermal acid etching inspection,metallographic inspection,scanning electron microscope and energy spectrum analysis,the reasons for the delamination of tensile fracture of Q355B steel plate were analyzed.The results showed that the main reason for the delamination of tensile fracture of Q355B steel plate was that there were shrinkage holes,porosity,segregation and inclusion defects in the center continuously cast product thickness,which led to the central micro crack in the steel plate.During the tensile test process,stress concentration occurred at the crack,as the amount of deformation continued to increase,the micro cracks continued to expand,and finally the fracture delamination was occurred.In the appropriate adjustment of continuously cast products casting and steel plate rolling process parameters (such as superheat degree,secondary cooling rate,billet drawing speed,pass reduction rate,rolling temperature),electromagnetic stirring and light reduction technology,and slow cooling measures after rolling were adopted,the failure rate of Q355B steel plate tensile fracture was reduced from 6.82% to 0.84%,and stabilized below 1%.