Mechanical Performance of Nodular Cast Irons After Prolonged High-Temperature Exposure

Ductile cast irons (DIs) are widely used in industrial applications. Their use is, however, often limited to components working at room temperature, since prolonged exposure at high temperature can lead to decomposition of both ausferrite and pearlite, with a consequent strength reduction. The present paper evaluated the effects of prolonged high-temperature exposure on microstructure and residual strength of DIs with different matrices, after an isothermal soaking at temperatures between 200 and 600 °C. Microstructural analyses highlighted that long-term exposure at temperatures higher than 500 °C leads to the complete decomposition of ausferritic and pearlitic matrix microstructures, while hardness tests showed that the hardness is stable up to 500 °C for the pearlitic ductile iron (PDI), up to 450-500 °C for the ausferritic ductile iron (ADI) and up to 400-450 °C for the perferritic isothermed ductile iron (IDI). Exposure at 500 °C for 240 h induces a reduction in tensile strength of IDI and ADI, respectively, of 10 and 25% (for both room temperature and 500 °C tensile testing), while it has no significant effects on PDI.