Efeito do tamanho do grão austenítico na cinética e na morfologia do produto da reação bainítica de um ferro fundido nodular austemperado. / Effect of austenite grain size on the morphology and kinetics of the bainitic reaction of an austempered ductile iron.

AUTOR(ES)

Cesar Roberto de Farias Azevedo

DATA DE PUBLICAÇÃO

1991

RESUMO

The effect of austenite grain size on the kinetics and the morphology of the bainitic reaction in an austempered ductile iron (ADI) has been investigated, Three austenite grain sizes were produced: GG (coarse grain), GH (medium grain) and GR (fine grain), The GR condition was obtained by the rapid austenitization of martensitic microstructures The secondary graphite precipitation observed in GG condition strongly accelerated the rate of bainite formation and made possible the study of the effect of austenite/graphite interface on the kinetics of this reaction, The austenite grain refinement also accelerated the bainite precipitation, increased the proportion of grain boundary alotriomorphs ferrite, refined the bainitic microstructure and improved by 14% the yield stress of ADI, The predominance of grain boundary alotriomorphs in GR was associated to the structure of austenite/austenite interface formed during the rapid austenitization of the studied ductile iron at heating rates of 100oC/s. It is suggested that the dominant mechanism of austenitization in this condition is a thermally activated one (not a displacive transformation). The different morphologies of the austenite decomposition used the Duhês morphological system.

ASSUNTO(S)

bainitic reaction ferro fundido nodular austemperado cinética kinetics austenite grain size reação bainítica tamanho do grão austenítico austempered ductile iron morfologia morphology

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