Estudio cinetico y microestructural de la transformacion austenitica durante el austemperizado de hierros nodulares

The transformation kinetics of austenite to ausferrite for five ductile cast irons during the austemperign between 280 and 420 °C has been studied. Using dilatometry data, the kinetic parameters n and k of the Johnson-Mehl model, were determined. The activation energy was determined using the Arrhenius equation. The microstructure of samples austempered at 370 and 315 °C was observed by transmission electronic microscopy. It was found that the k constant decreased when copper and molybdenum were added and the temperature was decreased. At 370 °C and short austempering time, precipitation of carbides did not occur, while at 315 °C hexagonal carbides e appeared. The behavior of the activation energy, which increases with temperature, and the slower transformation kinetics at low temperatures seem to be related to the presence of carbides.