Abstract: There appears the magnetic mark line during magnetic particle inspection of the batch atresias used by rockets. It was suspected that there might be cracks in the products. It is whereas concluded that the magnetic mark lines are caused by segregation and there are no cracks in the material following a careful analysis by macroscopic examination, scanning electronic microscope and metallographic microscope. The magnetic mark lines can be avoided by choosing the appropriate electromagnetic stirring intensity and stirring time during continuous casting.