Application of cooling curve analysis in solidification pattern and structure control of grey cast irons

Abstract

Commercial cast iron is a typical multi-phase, natural metal matrix composite, including a ferrous matrix at different alloying grade and several phases, each having varying levels of carbon and other elements present, such as carbide, graphite and nitride. It was found that some active elements, such as S, O, Al, Ca, Ba and RE (rare earth), are important to control carbide/graphite phase formation. A major purpose of the present paper was to investigate the solidification pattern and structure of un-inoculated and inoculated cast irons, with intentionally critical conditions for graphite nucleation, typical for electric melted iron, by thermal (cooling curve) analysis technique; this is especially pertinent to the production of thin section iron castings. Increased chill (carbides formation), undercooled graphite amount, eutectic cells count and relative density correlate well with the degree of eutectic undercooling, at the beginning of eutectic reaction and at the end of solidification. Inoculation application led to decrease of ∆Tm and increase of ∆T1 (it became positive) and ∆T3 (less negative) parameters, at higher influencing power on ∆T1 parameter (narrow variation range). Higher inoculant addition rate gives better cooling curve analysis parameters. ∆T1 appears to be the recommended cooling curve analysis parameter to characterize the specifics of solidification pattern and structure formation on the entire solidification range.