Simulação numérica de ciclos térmicos decorrentes do processo de refusão do aço ASTM A743-CA6NM

Abstract

The welding process is of great industrial importance, being used in the manufacturing process of many components and structures, as well as in the recovery of damaged or worn parts. New techniques are currently the object of research to reduce the disadvantages of welding processes. One is this techniques is remelting of thermal spray coating. However, the remelting process affects the coating and the base metal, creating a heat affected zone (HAZ), as a result of the large amount of heat transfer, which may interfere with the microstructure of the material. The study of temperature distribution (thermal cycles) can be performed experimentally, by analytical models or by numerical methods. Experimental tests are not always economically viable, and, in certain situation, also provide measurement difficulties, not allowing an agile variation of study parameters. In this direction, numerical methods tend to be extremely versatile, becoming adaptable to changes of various welding parameters and allowing their rapid and detailed analysis. This study aims to perform the numerical modeling of thermal cycles resulting from the remelting process of the ASTM A743-CA6NM. The problem was solved with the commercial software ANSYS/FLUENT 14.5® for the three-dimensional case, which uses the finite volume method. The mesh used has a total of 20 492 elements, being more refined near the weld bead. To make it possible to draw graphs of thermal cycles, sensors (reading points) were created in the same location of the thermocouples used in the experiments from Oliveira (2011). To simulate the motion of the source, the line of fusion was divided into 20 areas. The boundary conditions are manually changed, so that the results of the above simulation were used as initial conditions for the next simulation. The results were analyzed for three different electrical currents: 90A, 110A and 130A. For a current of 90A, the highest rates of errors were found near the fusion line (from 13.83% to 19.45%), reaching only 0.12% in the most distant thermocouples. For current 110A, the worst rates were recorded on thermocouples that are most distant from the line of fusion (between 5.69% and 29.15%). For the current of 130A, errors ranged from 3.43% to 9.62% in the thermocouples near the fusion line, reaching 17.85% in the most distant thermocouples. In general, it was observed that, in the simulations, the test body cools faster. This can be considered as a consequence of the simplification in material properties, assumed constant with respect to temperature and of experimental errors. However, the simulation results show that, in front the adopted simplifications, the numerical model was able to satisfactorily reproduce the thermal cycles obtained experimentally.