Analysis on Spot Defects of E355 Steel Cold Drawing Cylinder Tube

The inner surface of a cold drawing cylinder tube of E355 steel had dense spot defects. The causes of spot defects on the surface of cylinder tube were analyzed by means of macroscopic observation, chemical composition analysis, non-metallic inclusion analysis, metallographic examination, scanning electron microscope and energy spectrum analysis. The results show that the improper smelting process control of E355 steel resulted in the high sulfur content, which resulted in the formation of more sulfur-containing A-type non-metallic inclusions, the destruction of the passivation film on the surface of the cold drawn cylinder tube, the formation of cavities around the A-type non-metallic inclusions, and the improper pickling process resulted in the formation of pitting corrosion due to over pickling, which eventually led to the formation of pitting defects on the inner surface of the cold drawn cylinder tube.