Abstract: Elaborated here in the paper are the main aspects of the inner projection defects staying with pierced shell end that are named in jargon as“iron fin”（the strip type）and“iron ring”（the circular type），covering distribution，harmfulness and generating mechanism.Also discussed is a new process to eliminate the said defects，i.e.，bloom end hot-centering.Result of trial implement of the new process shows that the said defects can be remarkably eliminated，which is helpful for improving the shell end geometric shape to have easy mandrel insertion for rolling operation，and thus enhance both productivity and yield.