Engenharia de Materiais
URI permanente desta comunidadehttps://repositorio.fei.edu.br/handle/FEI/17
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2 resultados
Resultados da Pesquisa
- Kinetic Study to Predict Sigma Phase Formation in Duplex Stainless Steels(2016) dos Santos D.C.; Magnabosco R.© 2016, The Minerals, Metals & Materials Society and ASM International.This work presents an improved kinetic study of sigma phase formation during isothermal aging between 973 K and 1223 K (700 °C and 950 °C), based on Kolmogorov-Johnson-Mehl-Avrami (K-J-M-A) model, established from volume fraction of sigma phase determined in backscattered electron images over polished surfaces of aged samples. The kinetic study shows a change in the main mechanism of sigma formation between 973 K and 1173 K (700 °C and 900 °C), from a nucleation-governed stage to a diffusion-controlled growth-coarsening stage, confirmed by a double inclination in K-J-M-A plots and microstructural observations. A single inclination in K-J-M-A plots was observed for the 1223 K (950 °C) aging temperature, showing that kinetic behavior in this temperature is only related to diffusion-controlled growth of sigma phase. The estimated activation energies for the nucleation of sigma phase are close to the molybdenum diffusion in ferrite, probably the controlling mechanism of sigma phase nucleation. The proposed time-temperature-transformation (TTT) diagram shows a “double c curve” configuration, probably associated to the presence of chi-phase formed between 973 K and 1073 K (700 °C and 800 °C), which acts as heterogeneous nuclei for sigma phase formation in low aging temperatures.
- Intermetallic phases formation during short aging between 850 °c and 950 °c of a superduplex stainless steel(2012) Magnabosco R.; Dos Santos D.C.This paper is based on the study of intermetallic phase formation during aging between 850 C and 950 C, for periods up to 5 min; those treatments were conducted in liquid aluminum bath, allowing fast heating of the small sized specimens. It was found that backscattered electron images could be used in the automatized routines of quantitative stereology of intermetallic phases and nitrides found in duplex and superduplex stainless steels. A measurable intermetallic phase fraction was observed just after 1 min aging in the studied temperatures, but it was not possible to distinguish sigma and chi phases from the observed intermetallic phases. Nitrides were also observed, but they were probably formed in steel manufacturing, since there was no significant influence of aging on its volume fraction. © 2012 Elsevier Editora Ltda. and Brazilian Metallurgical, Materials and Mining Association.