Application of thermal analysis in solidification pattern control of La-inoculated grey cast irons

Abstract

The new generation of acid-lined medium-frequency coreless induction furnaces revolutionized the iron foundries, resulting higher overheating and lower S and Al content iron melt, characterized by higher eutectic undercooling solidification and consequently high chill [carbides] and unfavourable undercooled graphite morphologies sensitiveness. Having established that Al, Zr, Ti, Ca, Ba and La appear to have a key role in graphite nucleation in grey cast iron, thermal [cooling curves] investigations are undertaken to explore their effects on solidification parameters. The experimental heats are obtained in acid-lined coreless induction melting. Some important active elements are added to FeSi-based alloy, usually used as conventional inoculant in cast iron foundry industry, resulting complex inoculating systems [Al, Ca–La; Al, Ca–La, Zr; Al, Ca–La, Ba; Al, Ca–La, Zr, Ba; Al, Ca–La, Zr, Ti and Al, Ca–La, Zr, Ba, Ti]. In-mould [ceramic cup, cooling modulus of approximately 0.75 cm] inoculation is applied directly in the Quik-cup™ cooling curve analysis equipment, for the same alloy addition rate. The La effects are evaluated in low S and Al, high overheated electric grey iron solidification pattern with and without any other oxide-sulphides forming elements contribution. Study is focused on the representative temperatures during eutectic reaction and at the end of solidification, and it results in an undercooling referring to equilibrium eutectic temperature in the stable and metastable solidification system. As primary evaluation for general application, La, Ca, Al–FeSi alloy have a high efficiency in low S and Al and higher carbon equivalent grey cast irons, electrically melting, without any other active elements contribution. For specific applications, more complex La-bearing alloys are recommended, such as for higher dendritic austenite amount promotion [LaBaZrTi–FeSi alloy] or for lower eutectic recalescence [LaBaZr–FeSi alloy].