Aiming at the abnormal magnetic marks found in the process of magnetic particle inspection in a certain engine combustor, the chemical composition analysis, metallographic examination, scanning electron microscopic energy spectrum examination and other physical and chemical tests were carried out on the materials used, and the causes of the magnetic marks were analyzed in detail. The results show that the existence of the metallographic structure different from the matrix is due to the obvious banded micro-segregation in the material. The composition segregation leads to the increase of Austenite Stability and the decrease of martensitic transformation starting temperature, which results in the occurrence of a certain amount of retained austenite in the structure and the appearance of magnetic particle inspection. This kind of magnetic trace does not affect the mechanical properties of the product.