Characterization of the isothermal phases transformations and the respectives products in three eutectoid steels for railroad application.

Artigos recentemente publicados v?m destacando a import?ncia do conhecimento sobre a cin?tica de transforma??o de fases em a?os eutet?ides aplicados em ferrovias, visando o aprimoramento de processos de fabrica??o e de soldagem. Nesse sentido, o presente trabalho apresenta um estudo de caracteriza??o da cin?tica de decomposi??o isot?rmica da austenita em tr?s a?os atualmente utilizados no mundo para a fabrica??o de trilhos ferrovi?rios, sendo dois de classifica??o premium e um de classifica??o standard. Os a?os estudados foram caracterizados em seu estado de entrega e, por meio de ensaios de dilatometria, as temperaturas cr?ticas de austenitiza??o e os intervalos de tempo de decomposi??o da austenita foram medidos. Diagramas tempo-temperatura-transforma??o (TTT) foram determinados. A influ?ncia de alguns par?metros como o espa?amento interlamelar perl?tico original e o tamanho de gr?o austen?tico pr?vio sobre as transforma??es de fases e sobre as microestruturas resultantes, foram discutidos. Mostrou-se ainda que, a partir de tratamentos isot?rmicos bem planejados, ? poss?vel a obten??o de uma microestrutura majoritariamente bain?tica em a?os eutetoides com composi??es qu?micas relativamente simples.Recently published papers have been enhancing the importance of understanding about the kinetics of phase transformation in eutectoid steels applied to railways, aiming the improvement of the manufacturing and the welding processes. In this sense, this work presents a characterization study on the austenite?s isothermal decomposition kinetics in three steels currently used worldwide in the manufacturing of railway tracks, being two of then premium and the other standard. The steels studied were characterized at initial state and, through dilatometry, the austenitization critical temperatures and the austenite decomposition?s time intervals were measured. Time-temperature-transformation (TTT) diagrams were determined. The influence of some parameters such as the original pearlite interlamellar spacing and the prior austenitic grain?s size on the phase transformations and the resulting microstructures, was discussed. The study also showed that stemming from well-planned isothermal treatments, it is possible to obtain a mostly-bainitic microstructure in eutectoid steels of fairly simple chemical compositions