Inoculant enhancer to increase the potency of Ca-FeSi alloy in ductile cast iron

Abstract

Cast iron is at more than 70% of total world castings production, with ductile cast iron at a rate of 25% (close to aluminium and steel castings together). Rare earth elements [REE] have important contributions in ductile cast iron production, generally to neutralize tramp elements that interfere with the nodulizing effect of Mg, to assist in nodulizing by providing a supplementary boost to Mg and to assist in the inoculation effect in nucleating graphite, depending on charge materials quality and castings requirements. With less REE available, due to their world crisis, their future use in foundry alloys should be carefully thought out and other treatment methods need to be investigated. Inoculation is one of the most important metallurgical treatment applied to the molten iron immediately prior to casting, with direct effects on the primary structure. Generally, inoculation is applied to forestall solidification at excessive eutectic undercooling degree, favourable for carbides occurrence. The enhancement of the 75% Ca-FeSi alloy by the contribution of an addition of sulphur, oxygen and oxy-sulphides forming elements appears to be a better and more effective inoculation solution compared to using more expensive inoculating elements, such as the REE or Ba containing alloys. This combination alternative led to the lowest carbides amount, the highest nodule count, nodularity and graphite compactness degree. It was more effective than an equivalent addition of a REE, Ca-FeSi alloy, or compared to Ca, Ba-FeSi and Ca-FeSi variants, but with a 60% to 77% lower alloy consumption.