Influence of nitriding on magnetic properties of steel ball samples

The nitriding is a thermo-chemical treatment of the steel which can improve its wear resistance, corrosion resistance and hardness. At a constant temperature, depending on the value of the nitriding potential, the subsurface iron nitride layer, known as "white layer", formed may consist of only the Gamma'-Fe4N phase or a mixture of phases Gamma'-Fe4N, and -Fe2-3N. A diffusion zone is formed under the iron nitride layer, in which nitrogen is dissolved interstitially in a ferritic matrix and carbo-nitrides of iron and alloying elements occur. The thickness and phase composition of the layers of iron nitrides are decisive on the resistance to corrosion and the abrasive wear of steel after nitriding. The diffusion zone, in the case of alloy steels, increases the fatigue strength of steel. Several AISI steel balls with different diameters and thermal treatments were investigated using FMR and SQUID techniques. Magnetization measurements have shown the non-uniform behavior of the investigated samples with temperature variation. For most of them, having carbon content higher than 0.13 wt. %, the rise of magnetization with increasing temperature was observed, which strongly depended on the field.