Age strengthening of gray cast iron: alloying effects and kinetics study

Age strengthening of gray cast iron has become a critical issue with metal casters trying to optimize their process for the closest conformance to properties. This necessitated more robust and precise methods to predict age strengthening. Most foundries use age strengthening behavior to cast at hight carbon equivalents to facilitate smaller gating systems. Also, it is well known in the casting industry that the tool life improves with aging. Hence these foundries require a model to predict aging behavior and accelerate the mechanism from days to hours. This research focuses on the methods of composition adjustments to control aging properties, creating a model to predict the aging behavior at different temperatures and understanding the mechanism of aging --Abstract, page iii

Age Strengthening of Gray Iron - Kinetics Study

Kinetics of gray cast iron strengthening at room and elevated temperature (100°C, 182°C and 285°C) were studied using 100 specimens cast from one industrial heat of gray iron. Tensile strength and Brinell hardness was measured during age strengthening. Peak aging was observed at shorter times for higher temperatures and over-aging was observed at 182°C and 285°C. Statistically significant data was used for evaluating aging kinetics and the determination of activation energies for precipitation. Tensile strength-temperature-time curves were described using Arrhenius and Avrami-Johnson-Mehl kinetics and an attempt was made to create a predictive model for age strengthening in gray iron. Earlier literature and a current study with another foundry indicate improvement of machinability with aging. The proposed model will help in optimizing the process for maximum tool life