抄録
The modified austempering was applied on the ductile cast iron (DCI) to enhance its mechanical properties. This treatment named ausquenching consists of short time austempering, direct water quenching and light tempering. In this combined heat treatment, the first austempering process takes much effect on the tensile property and toughness of ausquenched DCI (AQDI). AQDI shows higher 0.2% proof stress, tensile strength and fracture toughness than the austempered DCI (ADI) at the temperature range of upper bainite. AQDI has a complex structure of bainitic-ferrite, light tempered martensite and retained austenite. For the purpose of quantitative evaluation on the compound matrix of the martensite and the bainitic-ferrite, the X-ray diffraction profiles of α-Fe were analyzed by the curve fitting technique using Pseudo-Voight function. The profile was able to separate into two parts by the difference of carbon content. From these results, it was possible to estimate appropriate each phase fraction of the complex structure.
