Hardness and Structure of Ausformed Fe-Ni and Fe-Ni-C Alloys

The effects of ausforming on the hardness and structure of Fe-Ni and Fe-Ni-C alloys were examined. The results of microhardness tests showed that some amount of the carbon content might be essential for the strengthening of steel by ausforming. Optical micrographs showed that a martensite plate in the ausformed specimen was finer than that in the unausformed, and was bent and kinked. Transmission electron micrographs and electron diffraction patterns of ausformed Fe-Ni-C alloy showed that: (1) There were strong stresses within and around the martensite plate. (2) The twin faults in the martensite crystal were also recognized. (3) A cloudy distribution of dislocations was observed in the martensite plate, and the carbon atoms might migrate on these dislocations. The ausformed specimen was hardened mainly by precipitation and/or dispersion of carbides. (4) Severely kinked martensite plates were frequently observed. (5) The lattice orientation relationship between austenite and martensite in the ausformed Fe-Ni-C alloy approximately obeyed the usual law in the same way as in the unausformed.