The solidification modes of two new classes of austenitic stainless steels with a low content of Ni are shown. Their chemical composition is similar to that of the standard AISI 304 and AISI 316, except for the content of nickel, manganese and nitrogen. It is found that standard formulas for predicting the residual ferrite can be fairly well used in the prediction of the solidification mode while they do not work in predicting the residual ferrite content. In particular, it is found that ferrite is the first phase to solidify for values of the equivalent ratio (calculated according to the formulas developed by Hammar and Svensson) greater than 1.50, otherwise austenite is the first phase to solidify. A new set of equations for predicting the residual delta-ferrite in these new classes of materials is determined via multivariable linear regression. The influence of the steel solidification mode on the material structural transformations during heat treatment is also shown.