Reason Analysis of Machining Defects in 304 Stainless Steel Cooling Coil

The reason which caused the defects in 304 stainless steel pipe in cooling coil making process was analyzed by means of chemical component analysis, metallographic examination and fracture analysis. The results showed that the main defects were pit and crack after welding; there were such harmful elements as O and Sn etc, and unequally-distributed element Cu and Se etc in the steel that led to those defects. When the steel was welded with TIG, oxides in welding pool formed slag particles and some of which remained on the surface of weld metal, and the pit came into being after cleaning the weld joint; when the welded pipe was bended, copper brittleness caused by Cu-Sn eutectic alloy resulted to the local crack in the tension stress side of steel pipe. Therefore, these defects resulted from impurity of steel.