A steel mill smelted 20 t steel ingots of 20Mn5,and found intensive defects after flaw detection for hammer cogging.After chemical composition analysis,low magnification inspection,metallographic microanalysis,energy spectrum analysis and numerical simulation by THERCAST software,the defects were studied and preventive measures were proposed.The results show that the gray matters near the crack are MnS inclusions.Qualified ingots were obtained after the smelting process was optimized and the process control was improved.
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