Analysis of decomposition processes of ausferrite in copper-nickel austempered ductile iron

Analysis of thermal decomposition processes of the ausferrite obtained during simulation of austempering heat treatment was performed on austempered ductile iron (ADI). The analysis method consisting in investigation of inverse phase transformations was applied. The material with specified phase composition and well-defined thermophysical properties, both resulting from the conducted heat treatment cycle, was heated under controlled conditions and the thermal effects-enthalpy change and volume change were recorded by means of differential scanning calorimetry (DSC) and differential dilatometry. The process of ausferrite decomposition in the range of 100-800 A degrees C was discussed; the identification scheme and temperature sequence of phase transformations accompanying the ausferrite decomposition were established. The elaborated decomposition scheme allows selection of the ADI heat treatment and its optimization by means of the non-isothermal thermal analysis methods.