Determination of thermal effects accompanying the austempering of copper–nickel ductile iron

Using especially designed and constructed isothermal calorimeter, the austempering of Cu–Ni ductile iron was carried out at temperatures of Tpi = 270, 350, 390 and 430 °C, simultaneously with the measurement of accompanying thermal effects. The values of enthalpy changes ΔH show the correct and expected trend, varying from 45 J/g at Tpi = 430 °C to 70 J/g at Tpi = 270 °C. The changes of enthalpy were observed to increase with decreasing temperature of the isothermal transformation during austempering. The results of the present work did not allow revealing the influence of alloying elements, i.e. Cu and Ni, on the heat of isothermal transformation. The discrepancies between the results of the actual measurements and the results quoted in other papers were discussed in terms of DSC measurements.