Key microstructural changes that occur when Duplex Stainless Steels (DSS) are welded could be evaluated when bead-on-plate welding was carried out on a 2205 DSS by the GMAW process. By using numerical simulations, it was possible to calculate locally the heating and cooling rates taking place during the 2205 DSS welding and discuss its correlation to the microstructural changes experimented by the parent metal. Results showed that increasing heat input has promoted the ferritic grain growth with a slight reduction in the austenite content present at the high temperature heat affected zone (HTHAZ), whereas the cooling rates remained above from those reported as critical for sigma phase precipitation in 2205 DSS. Furthermore, nitrogen has proved to be an effective austenite former at the fusion zone (FZ), which can contributes to get a balanced microstructure in DSS welds in contrast to the effects from the elevated cooling rates.

A phenomenological model to predict the multiphase diffusional decomposition of the austenite in low-alloy hypoeutectoid steels was adapted for welding conditions. The kinetics of phase transformations coupled with the heat transfer phenomena was numerically implemented using the Finite Volume Method (FVM) in a computational code. The model was applied to simulate the welding of a commercial type of low-alloy hypoeutectoid steel, making it possible to track the phase formations and to predict the volume fractions of ferrite, pearlite and bainite at the heat-affected zone (HAZ). The volume fraction of martensite was calculated using a novel kinetic model based on the optimization of the well-known Koistinen-Marburger model. Results were confronted with the predictions provided by the continuous cooling transformation (CCT) diagram for the investigated steel, allowing the use of the proposed methodology for the microstructure and hardness predictions at the HAZ of low-alloy hypoeutectoid steels.

O presente trabalho apresenta de forma clara e concisa o modelamento e simulação de campos de deformação obtidos em treliças planas através de medidas de centralidade em refinamento de malha por nós influentes. É utilizado o método dos elementos finitos com algoritmo desenvolvido e programado em FORTRAN com representação gráfica para visualização dos resultados feita através do GNUPLOT. Comprara os resultados dos campos de deformações com os de deslocamentos nodais tradicionalmente calculados para elementos finitos de barras planas constituídos de dois nós de extremidades. Constata-se que através dos campos de deformação é possível determinar com maior acurácia os valores internos às treliças planas, possibilitando assim uma análise mais criteriosa quando ocorrem variações de materiais no mesmo componente estrutural, como é o caso do modelo de vigas de concreto armado cujo comportamento idealizado é o de uma treliça plana.