WELD METAL MICROSTRUCTURE CALCULATIONS FROM FUNDAMENTALS OF TRANSPORTPHENOMENA IN THE ARC-WELDING OF LOW-ALLOY STEELS

In recent years, significant progress has been made toward understandi ng the development of the weld pool shape and size from the numerical calculations of heat transfer and fluid flow in the weld pool. Althoug h such calculations have provided detailed information about the weldi ng processes, no efforts have been made to understand the development of fusion zone microstructures from the fundamentals of transport phen omena. The aim of this work is to address this. Heat transfer and flui d flow during manual metal are welding of low-alloy steels containing different concentrations of vanadium and manganese were investigated b y solving the equations of conservation of mass, momentum and energy i n three-dimensional transient form. The model incorporates fluid flow in the weld pool resulting from surface tension, electromagnetic and b uoyancy forces. The cooling rates are calculated at various locations in the weldment. The weld metal compositions are used to calculate the time-temperature-transformation (TTT) diagrams on the basis of an ava ilable phase transformation model. The calculated cooling rates and th e TTT diagrams are then coupled to determine the continuous cooling tr ansformation (CCT) behavior and volume percentages of acicular, allotr iomorphic and Widmanstatten ferrites in various low-alloy steel weldme nts. The computed microstructures are found to be in good agreement wi th the experimentally observed microstructures. The agreement indicate s significant promise for predicting weld metal microstructure from th e fundamentals of transport phenomena.