Analysis on Outer Surface Pit Defect of Low and Medium Carbon-manganese Steel Tube

In order to find out the causes for the outer surface pit defect of the low and medium carbon-manganese steel tube, the chemical composition, hardness and micromorphology of the steel pipe and the roll are analyzed. The analysis result shows that the said pit defective outer surface of the pipe is caused due to the facts as follows.First the hardness of the roll is rather low;and second, during the rolling process the graphite and carbide on the roll surface are broken, resulting in chipping of the roll, then during the rolling process a small part of the chips adhere to the roll surface again, and thus during high-temperature rolling, the steel pipe surface is damaged by the adhesive on the roll, and inevitably causes the pitting. It is suggested to take actions, including grinding the roll surface, and picking up and throwing the adhesive away, properly lowering the pipe rolling temperature, changing the roll material, optimizing the roll casting process to get the graphite in the roll matrix structure miniaturized, and the carbide sphericized and miniaturized so as to avoid the said in-process chipping of the roll.