Abstract
Austenite and martensite lattice parameters of Fe-8.7∼4.1%Mn-0.57∼1.25%C alloys have been measured in detail as a function of temperature, by means of X-ray diffractometer with a cooling stage. The austenite lattice parameters during martensitic transformatins are smaller than the extrapolated ones from high temperature values before the martensitic transformations occur. The amount of the reduction is nearly the same for all the alloys when the amount of martensites is less than about 50%, but it becomes larger with decreasing carbon content when the amount of martensites is over 50%. The a parameters of martensites upon cooling decrease with decreasing temperature and/or increasing amount of martensite, and those upon heating first increase and then linearly decrease with temperature showing a critical transition point at about 160 K . On the other hand, the c parameters of martensites are nearly the same upon cooling and heating. It is also confirmed that the martensites at liquid nitrogen temperature have an anomalously small c⁄a ratio and change to normal upon heating to room temperature. The c parameters and c⁄a ratios of martensites are changed upon ageing at room temperature. The origins of the anomalous changes in austenite and martensite lattice parameters are discussed.
