Tecnologia em Metalurgia, Materiais e Mineração
https://tecnologiammm.com.br/article/doi/10.4322/2176-1523.20191992
Tecnologia em Metalurgia, Materiais e Mineração
Artigo Original

CARACTERIZAÇÃO DAS TRANSFORMAÇÕES DE FASES ISOTÉRMICAS E DOS SEUS RESPECTIVOS PRODUTOS EM TRES AÇOS EUTETÓIDES DE APLICAÇÃO FERROVIÁRIA

CHARACTERIZATION OF THE ISOTHERMAL PHASES TRANSFORMATIONS AND THE RESPECTIVES PRODUCTS IN THREE EUTECTOID STEELS FOR RAILROAD APPLICATION

Karine Fernandes Rodrigues, Gabriel Marques Magalhães Mourão, Geraldo Lúcio de Faria

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Resumo

Artigos recentemente publicados vêm destacando a importância do conhecimento sobre a cinética de transformação de fases em aços eutetóides aplicados em ferrovias, visando o aprimoramento de processos de fabricação e de soldagem. Nesse sentido, o presente trabalho apresenta um estudo de caracterização da cinética de decomposição isotérmica da austenita em três aços atualmente utilizados no mundo para a fabricação de trilhos ferroviários, sendo dois de classificação premium e um de classificação standard. Os aços estudados foram caracterizados em seu estado de entrega e, por meio de ensaios de dilatometria, as temperaturas críticas de austenitização e os intervalos de tempo de decomposição da austenita foram medidos. Diagramas tempo-temperatura-transformação (TTT) foram determinados. A influência de alguns parâmetros como o espaçamento interlamelar perlítico original e o tamanho de grão austenítico prévio sobre as transformações de fases e sobre as microestruturas resultantes, foram discutidos. Mostrou-se ainda que, a partir de tratamentos isotérmicos bem planejados, é possível a obtenção de uma microestrutura majoritariamente bainítica em aços eutetoides com composições químicas relativamente simples.

Palavras-chave

Aço eutetóide; Trilhos ferroviários; Transformação de fases; Diagrama TTT.

Abstract

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.

Keywords

Eutectoid steel; Railway tracks; Phase transformation; TTT diagram

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