Research on Hole Defects of Cold Rolled Sheet and Dent Defects of Hot Rolled Thick Plate

A steel sheet has tearing hole defects and the surface of a medium steel plate presents an oxide pressing defect.Optical microscope and scanning electron microscope were used to carry out microscopic observation and micro-area composition analysis.The toughness characteristics and continuous casting protective slag elements were observed at the hole fracture of the sheet defect sample.Due to the large inclusion of continuous casting protection slag in the casting billet, the ductility of the sheet substrate of the inclusion site decreases during the rolling process, and then the hole forms.The defect of medium steel plate is pit and pressed in shape, the bottom of the defect presents oval crack, and the shape is large inside and small outside.There is a large number of high temperature iron oxide inside the crack, and a large number of high temperature oxidation points around the crack, and it has serious decarbonization phenomenon.The surface defects of the steel plate are caused by the subcutaneous bubbles in the cast billet, and the rupture in the heating furnace and are connected with the surface of the steel plate, undergo high temperature oxidation, and are deformed and extended in the rolling process.