Modelling of the effects of strain-induced martensitic transformation on the mechanical behaviour in drawn tubes

The objective of this paper is to demonstrate the ability of a computer simulation to analyze the development of microstructure and finally to predict mechanical properties of two-phase steel after strain induced martensitic transformation. A model of a tube sinking process was coupled with closed form equations describing the mechanical properties of stainless steel. The influence of the martensitic transformation on mechanical behaviour was also noted in uniaxial tension tests and hardness measurements. First, the non-uniformity of deformation was modelled by the finite element method where the mechanical description of metal flow was based on the model of two-phase material. Secondly, a series of drawing and tension tests were carried out in order to identify the inhomogeneity of mechanical properties (yield strength, tensile strength, hardness) as a function of mechanical and thermal conditions given in each test. The investigation was focused on the case where the conical dies were used. With a combination of an amount of deformation and die geometry, based on the microstructure development the final relationships were established. Finally,it was shown that the correlation between the process parameters and the development of the resulting microstructure can be effectively described using proposed models.