Abstract
Surface defects of large castings of plain carbon steel and alloyed steel which being detected by magnaflux can be roughly classified into hot tear, cold crack, sulfide inclusion and creasy surface. The characteristic of each defect is summarized as follows; 1. Hot tear can be further divided into three types, namely open crack, hair crack and internal crack. All of them have the dense part of sulfur print, sulfide inclusions of type II being found in hot tear. In case of the open crack the fracture is dendritic and oxidized, its microstructure being quite abnormal as compared with the sound part, while in case of the internal crack it looks like microshrinkage. 2. Cold crack is a stress cracking which being mainly caused by improper cooling or heating and has a linear form. It can not be distinguished by sulfur print. 3. As cast surface is sensitive to sulfur print and sulfide inclusions of type II exist throughout in the depth of 0.5mm. 4. Sulfide inclusions do not always accompany with cracking. It forms networks in sulfur print when it presents much. 5. Creasy surfaces are of 100 to 150mm length and found on drag surface. They are caused due to improper pouring. The depth of surface folding is approximately 1 to 2mm. There exist many globular oxide inclusions around the defect but it has no relation with the density of sulfur print. Sulfide inclusions and creasy surfaces are not harmful and so it need not repair by welding.
