The knowledge of steel sheet mechanical properties is a very significant aim in the manufacturing of industrial components based on cold-drawing machining, where large strains are involved (e.g. in the production of metallic crown caps). In the strain range that covers the region of the stress-strain plot over the necking point, the mechanical behaviour of steel sheets can be described by the Yun Ling constitutive equation, obtained by FEM (Finite Element Method) models calibrated by means of tensile tests on steel sheet samples. The present work describes the experimental activity and the FEM modelling performed at the ENEA Research Laboratories of Faenza to determine the true curve of two different types of steel sheets. The described method can so be applied to different types of steel sheets used in cold-drawing machining processes, allowing to estimate their full true curves: this type of result can then be inserted in FEM simulations of particular industrial applications.