Development of prediction model for precipitates kinetics and austenite grain growth in the weld heat affected zone

Abstract

During welding process, austenite grain growth in the weld heat affected zone occurs and this austenite grain growth is important factor for the mechanical properties and safety of welded steel structures. Therefore, many researches have been performed to control austenite grain growth by using the precipitates of micro alloying elements such as niobium and/or titanium or vanadium. The austenite grain growth pinning effect by precipitates is affected by size and fraction of precipitates. Therefore, the behaviors of precipitates during welding thermal process have been focused. Most previous researches on the particle behavior treated only continuous growth of mean sized particles at a temperature below the dissolution temperature. But, in the view point of Ostwald ripening by Gibbs-Thomson effect, coarsening kinetic of particle occurs simultaneously with dissolution of small particles. Then, it is expected that there is a critical size which does not shrink and grow. In this study, an isothermal kinetic model of TiN considering critical particle size was developed and it was transformed as a general kinetic model by using the additivity rule. Finally, from combining austenite grain growth model and particle kinetic model, generalized austenite grain growth model was established in Ti added low alloyed steel HAZ .