抄録
The X-ray diffraction method can be applied to the measurement of the carbon concentration of retained austenite in austempered ductile iron (ADI). The diffraction line profile is fitted by the Pseudo-Voigt function using a nonlinear least squares method, and is separated into the lower and the higher carbon containing part. At the early stage of the isothermal transformation, there was a region where low and high carbon austenite were mixed. The result suggests that the first stage of the transformation can be divided into two steps ; one is where the ferrite supersaturated with carbon forms from the parent austenite, and the other the low-carbon austenite is changed into the high-carbon or stable austenite by the carbon diffusion from the ferrite. This first stage finishes when all the austenite becomes the stable austenite, and the volume depends on the austempering temperature.
