We have investigated the magnetic properties of four model alloys (18Cr8Ni0.5Si, 16Cr10Ni1Si, 13Cr20Ni2Si, and 10Cr30Ni3Si) for simulating radiation induced segregation in SUS304 austenitic stainless steels. All alloys are paramagnetic at room temperature. With reduction of temperature, a structural transition was occurred for alloys with lower Ni content (18Cr8Ni0.5Si and 16Cr10Ni1Si), which produced ferromagnetic martensite. Alloys with higher Ni content (13Cr20Ni2Si, and 10Cr30Ni3Si) became ferromagnetic at low temperature without martensitic transformation. Different effects of stress on the structure and magnetism were found also. Martensitic transformations and magnetic properties of austenitic stainless steels depend strongly on its chemical composition and can be classified by the value of Ni equivalent. This study suggests the possibility of applying magnetic methods to the nondestructive detection of radiation induced segregation.