The purpose of this paper is to show a modelling scheme to predict rapidly three dimensionnal grain structure. The modelling is based on a plane thermal finite element for the process coupled with a monte carlo simulation for grain structure. To demonstrate the interest of this type of modelling the simulations are done for a squared pulse mode and results are compared with experimental results (EBSD) done during the work of A.Chiocca. The originality of the paper is that predictions of grain structure are investigated with current and arc voltage evolving with time. Results show the interest of using monte carlo simulation.