Cooling Rate Dependence of STructures Characteristics in Ce-Inoculated Low-S Grey Irons

Résumé

The efficiency of Ce,Ca,Al-FeSi alloy was tested for lower addition rates (0.15-0.25wt.%), as, traditionally, high inoculant addition rates have been used in low sulphur grey cast irons, comparing to the base iron and conventional inoculated irons (Ba,Ca,Al-FeSi commercial alloy). The present work explores chill and associated structures in hypoeutectic grey iron chill wedges, with cooling modulus 0.21 cm and a large variation of the cooling rate, from the apex to the base of W₂ samples [ASTM A 367, furan resin mould]. The chill tendencies of the experimental irons correlate well with the structure characteristics, displayed as the carbides/graphite ratio of undercooled graphite morphologies. Carbide sensitivity is lower with increasing wedge width, but depends on whether the state of the iron is as base iron or inoculated with different alloys. Undercooled graphite was present for both un-inoculated irons and higher cooling rate inoculated irons. As expected, inoculation as well as an increase in wall thickness of the same wedge sample led to improved undercooled graphite control. The difference in effects of the two inoculants addition is seen as the ability to decrease the amount of carbides and undercooled graphite, with Ce-bearing FeSi alloy outperforming the conventional inoculant, especially at the low alloy addition and high cooling rate solidification.