Quantitative modelling of motion, temperature gyrations, and growth of inclusions in weld pool

The velocity and temperature fields, the shape and size of the fusion zone, and the motion of the inclusions were calculated by the solution of equations of conservation of mass, momentum, and energy in three dimensions for various welding conditions. The loci and the temperature gyrations experienced by a large number of inclusions were calculated numerically to seek a statistically meaningful residence time distribution of the inclusion and the number of intensities of the temperature cycles experienced by these particles. Finally, both the growth and dissolution of the inclusions were considered to calculate their size distribution. The inclusions experienced considerable recirculatory motion and strong temperature gyrations along their paths in the weld pool. The temperature-time plots for most of the inclusion particles displayed several temperature peaks. However, about one-third of the particles experienced continuous cooling behaviour. The average number of the temperature peaks in the time-temperature plots and the average residence time of inclusions in the weld pool changed significantly with welding conditions. The calculated temperature-time-transformation diagrams of the inclusions showed that the temperature gyrations affected the growth rates and the size distributions of the inclusions. Good agreement between the calculated and measured inclusion size distributions indicates that important aspects of weld metal structure can be understood from the fundamentals of transport phenomena and kinetics.