Precipitation in Nb-Stabilized Ferritic Stainless Steel Investigated with in-situ and ex-situ Transmission Electron Microscopy

Autor: Jean Denis Mithieux, Patrick Wollants, Annelies Malfliet, Bart Blanpain, F. Mompiou, F. Chassagne
Rok vydání: 2011
Předmět:
Zdroj: Metallurgical and Materials Transactions A. 42:3333-3343
ISSN: 1543-1940
1073-5623
Popis: A Nb-stabilized Fe-15Cr-0.45Nb-0.010C-0.015N ferritic stainless steel is studied with transmission electron microscopy (TEM) to investigate the morphology and kinetics of precipitation. $$\hbox{Nb}_{x}\hbox{(C,N)}_y$$ and MnS precipitates are present in the steel in the initial condition. Ex-situ TEM analysis is performed on samples heat treated at 973 K, 1073 K, 1173 K, and 1273 K (700 °C, 800 °C, 900 °C, and 1000 °C). Within this temperature range, both $$\hbox{Fe}_2\hbox{Nb}$$ and $$\hbox{Fe}_{3}\hbox{Nb}_{3}\hbox{X}_{x}$$ (with X = C or N) precipitates form. $$\hbox{Fe}_2$$ Nb is observed at 1073 K (800 °C). $$\;\hbox{Fe}_{3}\hbox{Nb}_{3}\hbox{X}_{x}$$ precipitates form at the grain boundaries between 973 K and 1273 K (700 °C and 1000 °C). Up to at least 1173 K (900 °C) their fraction increases with time and temperature, but at 1273 K (1000 °C) they lose stability with respect to $$\hbox{Nb}_{x}\hbox{(C,N)}_{y}.$$ With in-situ TEM, no phase transition is observed between room temperature and 1243 K (970 °C). At 1243 K (970 °C) the precipitation of $$\hbox{Fe}_{3}\hbox{Nb}_{3}\hbox{X}_{x}$$ is observed in the neighborhood of a dissolving $$\hbox{Nb}_2$$ (C,N) precipitate. For sections of grain boundaries where no $$\hbox{Nb}_x\hbox{(C,N)}_y$$ precipitates are present, $$\hbox{Fe}_3\hbox{Nb}_3\hbox{X}_{x}$$ does not form. It is concluded that the precipitation of $$\hbox{Fe}_{3}\hbox{Nb}_{3}\hbox{X}_x$$ is directly related to the dissolution of $$\hbox{Nb}_2$$ (C,N) through the redistribution of C or N.
Databáze: OpenAIRE
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