Abstract: The linear indications was detected on the bore surface of adjusting washer (9Cr18 stainless) while performing magnetic particle inspection. The linear indication was analyzed by fluorescent penetrant inspection and metallographic examination. The results showed that the indication was caused by carbide segregation. The MPI technology was analyzed and special test piece was fabricated. The results show that the magnetic current determined by experience formula is too high for the adjusting washer. Carbide segregation linear indication can be recognized by controlling the tangential magnetic field of part surface.