Imao Tamura1, Hirofumi Yoshimura3, Masao Ibaraki1 and Masayoshi Tagaya2
1The Institute of Scientific and Industrial Research, Osaka University, Sakai
The effects of ausforming on the hardness and the structure of Fe-Ni and Fe-Ni-C alloys were examined. The results of micro-hardness tests showed that some amount of carbon in steel might be essential for the strengthening by ausforming. Optical micrographs showed that the martensite plate in ausformed specimen was finer than that in unausformed, and bended and kinked. Transmission electron micrographs and the electron diffraction patterns of the structures in ausformed Fe-Ni-C alloy showed as follows: (1) In thin foil for transmission electron microscopy, the martensite plates were severly distorted and bended. This means there are strong stresses in and around martensite plate in the bulk specimen. (2) The twin faults in the martensite crystal in ausformed specimen were also observed. (3) The appearance of martensitic structure in ausformed specimen was in complexion of coarseness. This shows the cloudy distribution of dislocations in the martensite plate and the carbon atoms migrate on these dislocations. The specimen is hardened by precipitation and/or dispersion hardening in such way. In unausformed specimen, carbide may precipitate mainly on twin faults even in early stage of precipitation because of relatively low dislocation density. (4) In ausformed specimen, severly kinked martensite plates were frequently observed. (5) There were tangled dislocations in the austenite of ausformed specimen. This shows the austenite is strain-hardened. (6) The lattice orientation relationship between austenite and martensite in the ausformed Fe-Ni-C alloy approximately obeys usual law, as same as in unausformed.
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