A study of the effect of the thermomechanical history on the mechanical properties of a high niobium steel

A methodology for including the thermomechanical history in hot forming analyses is presented. A finite element formulation is employed for analysis of the inhomogeneous microstructural development. An earlier model, describing the development of the microstructure in niobium steels, is expanded to predict the final properties of the product and is integrated into the complete model of the hot compression process. Mechanical properties are obtained from a macroscopic description based on the Hall-Petch formulae. The results show that the model calculates correctly the influence of microstructure on the mechanical inhomogeneity. The analyses indicate that when all of the strengthening mechanisms are employed, the root of the sum of the squares summation method gives better agreement with experimental data than linear summation, of importance especially when the last deformation occurs in the two-phase or ferrite region. The proposed model can be used to investigate the complex behavior of a large range of microalloyed steels in hot rolling or forging processes.