Modelling the microstructural changes in steels due to fusion welding

Abstract: Theoretical, physically-based models of fusion welding are developed, and calibrated using experimental data from practical welds. The following heat-affected zone phenomena are investigated: grain growth, precipitate dissolution and coarsening, martensite formation and hardness. A model is also developed to describe the effects of the welding arc and their dependence on welding conditions. All calculations are carried out using a microcomputer which readily allows the influence of a large number of material and welding variables to be taken into account. The results are presented as read-outs in the form of various types of Welding Process Diagrams, these providing information on weld geometry, H.A.Z. microstructure and hardness in a form understandable to the welding metallurgist and engineer alike. In addition, Implant Testing Diagrams are developed, based on similar modelling, which help to exactly locate the notch with respect to the grain growth zone and weld process. Diagrams can be constructed showing microstructural variation over a wide range of energy inputs corresponding to different welding processes, or for a particular process showing weld geometry and providing a physical picture of the weld. The programs are written such as to allow easy interaction between the operator and computer concerning choice of welding parameters, steel composition etc., and the storage of material data which can be readily called up by the operator. It is thus shown that the diagrams can be used to help optimize welding conditions, as well as supply information on the H.A.Z. microstructure and hardness.