Prediction of the residual state of stress in a superduplex stainless steel produced by sand casting (using a coupled thermo-mechanical approach)

The present work aims at investigating the effect, in terms of residual stress prediction, determined by the adoption of different material constitutive models in the Finite Element simulation of the casting process of a superduplex stainless steel benchmark, from the cooling after the pouring phase to the subsequent heat treatment (heating and water quenching). A 3D thermo-mechanical Finite Element (FE) model was created with the commercial code Abaqus: the preliminary thermal problem, i.e. the determination of the heat transfer coefficients during both the mould cooling and the quenching, was solved by means of an inverse analysis approach by minimizing the difference between the numerical evolution of temperature and the experimental acquisition coming from real casting test. Two separate routes were followed according to the adopted constitutive equations: modelling the material as (i) elasto-plastic or (ii) elasto-viscoplastic. The numerical prediction of the residual state of stress in terms of casting relaxation was compared with the experimental data after the cut of the casting using an electro-discharge machine. The analysis revealed that when the elasto-viscoplastic modelling was adopted, the simulations underestimated the relaxation with an error larger than 50%; on the other hand, the elasto-plastic model leads to an overestimation with an error of about 30%.