MICRO-SEGREGATION OF CHROMIUM IN Fe-Cr ALLOY

L'objectif de cette investigation est le comportement des atomes de Chrome dans un alliage de fer avec 5at.%Cr.Après une trempe solubilisante a 1150°C pendant une heure (les spécimens 'étant trempés dans l'eau), l'image FIM ne montrait qu'une région claire , mais après détrempe entre 450 à 650°C on pouvait observer des régions claires et sombres.Dans ces spécimens trempés il y avait de la microségrégation des atomes de Chromé : Dans les régions claires la concentration de Chrome était moins grande que la moyenne, tandis que dans les régions sombres elle était plus grande que la moyenne.La différence des concentrations de Chrome augmentait avec la température du recuit .Cependant il n'y a pas de microségrégation d'atomes de Chrome dans des spécimens de ferrite en solution solide refroidis lentement.Le rôle des dislocations dans la microségrégation d'atomes de Chrome est discutée enfin.Abstract -The objective of this investigation is to clarify the behavior of chromium atoms in iron-5at.%chromiurnalloy.When the specimens were quenched after solution annealing at 1150°C for Ihr, FIM image was only a bright area, but when they were tempered from 450°C to 650 C, both bright areas and dark areas were observed in the FIM image.In these quenched specimens there was microsegregation of chromium atoms: In bright areas the chromium concentration was lower, and in dark areas it was higher than the average concentration.The difference of chromium concentrations became larger with increasing tempering temperature.However, there is no microsegregation of chromi-um atoms in slowly cooled solid slolution ferrite specimen.The role of dislocations in the microsegregation of chromium atoms was discussed then. -INTRODUCTIONThe mechanical properties of alloy steels are very sensitive to the alloying elements in steels, among which chromium is a fundamentel element.And therefore it is one of the most important problems to clarify the behavior of chromium atoms in steels.In this investigation, the objective is to study on microsegregation in Fe -Cr alloy system for the fundamental understanding of chromium steels.Hitherto, in Fe -Cr system, 14-75at.%Cralloys have been investigated and spinodal decomposition was observed[l-3], but in this study 0-10at.%Cralloys are of main interest because the phase diagram is still not clear.The alloy was treat treated and observed by the atom-probe (AP). -EXPERIMENTAL PROCEDUREThe material_ used is iron-chromium alloy which was prepared from high purity materials by an arc-melting of constituents in a purified Ar atomosphere.The chemical composition is 5.59at.%Cr,0.014at.%0,0.028at.%Cand iron is balanced.