In a classic paper presented at the “1979 AFS-CMI Conference on Modern Inoculating Practices for Gray and Ductile Iron” Professor J.F. Wallace proposed that the major nucleation mechanism in cast iron inoculation is perhaps the formation of certain sulfides upon the addition of strong sulfide formers such as Calcium, Barium, Cerium, or Strontium. These sulfides, with lattice parameters very similar to the graphite crystal structure, serve as substrates to begin the graphite nucleation and growth mechanism.
Of all the reactive elements currently used in commercial inoculants, Strontium forms the sulfide with the least lattice disregistry as compared to graphite and would thus be expected to provide the most potent nucleating effect. Such in fact is the case.
Strontium bearing ferrosilicons have been recognized in the foundry industry for many years as the alloys providing the greatest chill reduction per pound of alloy added.
All inoculants perform better in iron containing 0.06% sulfur or greater, adding further credibility to the sulfide substrate theory. Commercial experience has shown over and over that to obtain equivalent chill depths, about 60% less of a Strontium-bearing inoculant can be used when compared to all regular inoculating grades of ferrosilicon. In situations where there is a tendency to casting shrinkage problems, reduced inoculant additions can be very advantageous. Reduced ferrosilicon alloy additions mean less cell refinement, and less tendency to shrinkage.
Calcium in IM SR must be kept to very low levels of less than 0.10% because of an interference phenomenon between Strontium and Calcium. Because of this low Calcium level, and the accompanying low Aluminum level, IM SR goes into the solution with a minimum of dross formation when compared to most other complex inoculants. The alloy is based on 75% ferrosilicon and its reaction with liquid iron is exothermic, thus ensuring excellent dissolution and consistency of results.
IM SR is produced in state-of-the-art submerged arc furnaces in one of the newest ferrosilicon plants in the world, completed in 1980. By using charcoal and iron ore in place of metallurgical coke and steel scrap as reducing agent and iron unit source, respectively, residual levels of harmful tramp elements are controlled to extremely low levels. The manufacturing operation is supported by an in depth quality program devoted to problem prevention through the application of statistical control techniques. This is a unique combination of modern facility and quality attitude aiming to provide products that consistently conform to specific customer requirements.
|Size||Si %||St %||Ca %||Al %|
|74-79%||0.80-1.20%||0.10% max.||0.50% max.|
|20Mx80M||70-75%||0.80-1.20%||0.10% max.||0.50% max.|
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