Accession Number : AD0282312

Title :   STRENGTHENING AND ANNEALING OF AUSTENITE FORMED BY THE REVERSE MARTENSITIC TRANSFORMATION

Descriptive Note : Doctoral thesis.

Corporate Author : MASSACHUSETTS INST OF TECH CAMBRIDGE

Personal Author(s) : Krauss,George , Jr. ; Cohen,Morris

Report Date : 01 DEC 1961

Pagination or Media Count : 52

Abstract : The reverse martensitic transformation (i.e., the conversion of martensite to austenite on heating) was investigated in Fe-Ni alloys containing 30.5 - 33.5 w/o Ni. The reversed austenite was found to be sufficiently distorted to exhibit marked differences in mechanical properties and to undergo recovery and recrystallization on further heating. In particular, the yield strength of the reversed austenite was as much as 2.5 times higher than that of the virgin austenite; with five cycles of the direct and reverse martensitic transformation, the yield strength was 2.8 times higher. There was an accompanying decrease in strain-hardening capacity and in stable ductility or uniform elongation. The recrystallization was observed to follow sigmoidal kinetics, but was characterized by an abnormally large temperature dependence which was evidently due to carbon segregation at the migrating grain boundaries. Upon recrystallization, the strength properties reverted to those of the virgin austenite, but the ductility did not fully recover until the annealing temperature was raised. Transformation of reversed austenite to produce second-generation martensite resulted in an imperfect structure, leading to additional strengthening. (Author)

Descriptors :   *ALLOYS, *AUSTENITE, *MARTENSITE, *TRANSFORMATIONS, CARBON, CRYSTALLIZATION, DEFORMATION, FERRITES, GRAIN STRUCTURES (METALLURGY), HARDNESS, HEAT TREATMENT, IRON ALLOYS, MECHANICAL PROPERTIES, MICROSTRUCTURE

Distribution Statement : APPROVED FOR PUBLIC RELEASE