The best way to avoid metallurgical defects such as chill, dross formation and iron carbides is by using an effective inoculant. Our specialists will help you select the right inoculant for your needs.
The inoculant according to the invention contains between 0J and 10% strontium, less than 0.35% calcium, between 0.1 and 15% zirconium or a combination thereof and between 0J and 5% aluminium.
The high nucleation rate of the inoculant is due to the presence of strontium, a strong graphite promoter. Unlike most other inoculants that contain calcium, strontium does not suppress the formation of iron carbide and is therefore much more effective in promoting the growth of graphite.
The inoculant consists of a low calcium/high strontium ferrosilicon alloy. Its reaction with the liquid iron is exothermic, resulting in minimal dross formation compared to other complex inoculants. This low dross formation results in a high level of inoculation and good casting consistency.
The exact chemistry of the inoculant’s mechanism of action is not fully understood, but it is believed that the strontium is involved in the formation of clusters of icosahedral silicon crystals around which aggregations of individual silicon atoms form. Thermal analysis, scanning electron microscopy and (high-resolution) transmission electron microscopy support the proposed cluster-assisted nucleation mechanism. The effect of the inoculant is enhanced by the participation of these icosahedral precursors and a high level of divorced eutectic cells is observed in Sr-modified samples.
The exact chemistry of how inoculants work is not fully understood, but it is believed that the addition of calcium suppresses iron carbide formation and promotes graphite nucleation. Strontium forms sulfides with lattice parameters very similar to those of graphite and is believed to serve as an excellent substrate for the nucleation process.
Resulf 30 IEP Plus is a unique inoculant additive that allows for controlled amounts of oxygen and sulfur to be added to molten gray or ductile iron. This results in lower chill, reduced carbide formation, increased nodule count and improved machinability.
Sphere-O-Dox G is a high performance, patented inoculant which represents the latest advances in contemporary inoculation concepts. Using just fractional amounts of Sphere-O-Dox, typically 1/4 to 1/2 that of traditional ferrosilicon based inoculants, will provide exceptional chill reduction, nodule count and mechanical properties increases. Sphere-O-Dox can be used as a ladle inoculant, in-stream inoculant or cast and sintered insert. It is also available in the form of tablet and pressed briquette (InocuBloc). Sphere-O-Dox is available in both low and high silicon versions.
The inoculants used by foundries promote nucleation of graphite particles during solidification, which minimizes undercooling below the metastable eutectic temperature and helps to prevent the formation of iron carbide (cementite). This helps to avoid casting defects such as dross and shrinkage. The inoculants can be added to the melt directly or as blocks which can be injected into the ladle or in-stream.
Strontium-bearing ferrosilicon inoculants have been recognized by the industry as being those that give the best chill reduction and the highest nodule count of all commercial iron inoculants available. The inoculants according to the present invention perform even better, especially in ductile iron.
In addition, the inoculants of the present invention can be combined with a variety of other elements to improve their performance, particularly when used for nickel ductile irons. This allows a higher number of nodules to be formed and, at the same time, results in good sulphide suppression and high corrosion resistance.
Inoculants that contain strontium have the additional advantage of being more consistent in their performance than the calcium-only types. This is because the reaction between Strontium and Liquid Iron occurs with a lower temperature than that of Calcium, and consequently dross formation is less pronounced.
The inoculant according to the present invention contains between 0.1 and 10% by weight of strontium, less than 0.35% by weight of calcium, 0 to 5 % by weight of aluminium, 0.5 and 10 % by weight of zirconium, 0.1 and 20 % by weight of titanium, and the balance being iron.
The resulting inoculant G-K gives a very high nodule count when tested in ductile cast iron with lamellar, compacted or spheroidal graphite and performs appreciably better than the commercial barium-containing inoculants. This supports the theory that the primary nucleation mechanism in casting is the formation of sulfide substrates by elements such as calcium, barium, cerium and strontium, whose lattice parameters are very similar to graphite.
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