MAGNETIC-PROPERTIES OF CR-MN AUSTENITIC STAINLESS-STEELS

The magnetic susceptibility chi of three Cr-Mn austenitic stainless steels was measured as a function of temperature in the range 5-400 K. All specimens showed a characteristic susceptibility maximum. The temperature of the maximum and especially the curve shape depend strongly on specimen composition and metallurgical conditions (as-quenched, deformed). Because no significant field dependence appeared, the susceptibility maximum was identified as the antiferromagnetic Neel temperature. Chi(T) measurements above T(N) were fitted to a modified Curie-Weiss equation. Comparison between measurements and generalized-molecular-field-theory predictions allowed us to identify the magnetic structure as that of a first-type antiferromagnet with fcc crystal structure. The atomic magnetic moment and the molecular-field coefficients depend strongly not only on composition, but also on metallurgical prehistory, that is, on the degree of the applied mechanical deformation and heat treatment. Mainly, manganese affected the antiferromagnetic interactions, while chromium affected the ferromagnetic. Mn and Fe contributed the most to the effective atomic moment. Measurements on mechanically deformed specimens show a structure sensitivity of the molecular-field constants. This could be interpreted consistently in terms of lattice-parameter changes. The apparent structure sensitivity of the effective atomic moment can be attributed to changes in matrix composition caused by precipitation.