Application of thermal analysis to monitor the quality of hypoeutectic cast irons during solidification in sand and metal moulds

Abstract

By exploring the effects of carbon equivalent (CE = 3.4–4.2%) and inoculation (Ca, Ba, Al–FeSi alloy), the thermal analysis parameters, representative temperatures and undercooling events, during solidification of cast irons are compared with chill tendency (carbides) in cast irons. Cooling curve analyses were conducted directly in the thermal centre of samples solidified in resin sand and metal moulds to explore the utility of thermal analysis in actual casting shapes. As a reference, a Quik-cup™ system was employed with the same cooling modulus (CM = 0.75 cm). The austenite formation temperature is lower at higher CE, with higher temperatures of both the start of the eutectic reaction and end of solidification. This was more pronounced for metal mould solidification and for un-inoculated irons, respectively. The transition from white iron through mottled iron up to grey iron macrostructure is illustrated by variations of eutectic undercooling compared to the metastable equilibrium temperature, as affected by increasing carbon equivalent and applied inoculation. Inoculation affected both austenite and eutectic formation, by preventing excess eutectic undercooling during solidification, even at low carbon equivalent. The differences in solidification patterns of sand and metal mould castings are discussed, for un-inoculated and inoculated irons, at different carbon equivalent values.