Ferromagnetic properties of cold rolled AISI 304L steel

Abstract

The ferromagnetic properties (coercive force, residual and saturation magnetisation) of a cold rolled AISI 304L stainless steel were measured as function of the applied deformation, using a vibrating sample magnetometer. The martensite volume fraction produced by deformation was calculated through the magnetisation saturation ( σ s) value. A maximum amount of martensite (81%) was obtained by applying a true deformation ε=2.41 and a heat treatment at 400°C after rolling. The residual induction ( B r) and the squareness (=ratio between residual ( B r) and saturation ( B s) inductions) increased, while the coercive field ( H c) decreased with the amount of deformation. The heat treatment at 400°C promotes as well the increase of both B r and B r/ B s and the decrease of H c. The magnetic properties obtained in the most severely deformed samples ( H c=23.08–23.63 kJ/m 3, B r=1.01–1.20 T and B s=1.12–1.28 T) are comparable to that of some hard and semi-hard alloys used as magnets. The stability of the ferromagnetic martensite ( α′) was investigated by thermomagnetic analysis. The starting ( A s) and final ( A f) temperatures of the martensite phase ( α′) transformation into austenite during heating were determined to A s=430–440°C and A f=610–616°C.