Simple Solutions That Work! Issue 8

For many decades ferrosilicon producers have sought to make improvements in gray and ductile iron inoculants. This developmental work was the result of changes in the primary iron melting method. Medium frequency coreless induction melting rapidly replaced cupola melting due to environmental requirements. More steel and purchased scrap were being used in the charges to replace some or all of the pig iron previously used, and a general increase in the average melting temperature resulted in greater metal oxidation state. Further, cupola melted irons typically responded far better to inoculation than irons melted in coreless induction furnaces. Ferrosilicon-based inoculants are made using quartzite, coal, wood chips and steel scrap in large submerged arc furnaces (see Figure 1). Mineral oxides rich in elements from Group IIA, IIIB and IVB in the Periodic Table of Elements, such as strontium, barium, calcium, titanium, cerium and magnesium are often added to the smelting furnace or to the pouring ladle to achieve the desired inoculant chemistry. However, there is a finite limit to the amount of these elements that can be added to or else the smelting and reduction reactions will be negatively impacted. Other important inoculating elements that have been shown to be critical for improving inoculation and that cannot be added to the smelting furnace, are sulphur and oxygen. If the sulphur and oxygen content of the molten iron that is to be treated with an inoculant is insufficient, an abundance of carbides and chill may result. Thus, the only feasible way to insure that the molten iron has sufficient levels of oxygen and sulfur is to mechanically blend sulfur and oxide rich elements into the inoculant additive. Group IIA, IIIB and IVB in the Periodic Table of Elements react with dissolved oxygen and sulfur to varying degrees to form atomic clusters of oxy-sulphide particles that have a similar crystalline structure to graphite. These surfaces greatly assist in graphite nucleation and prevent “undercooling” during solidification process. Undercooling can lead to carbides, poor graphite shape, low nodule quantity in ductile (S.G.) irons and have an adverse effect on mechanical properties and machining characteristics. DR. R.L. (ROD) NARO & D.C. WILLIAMS ASI INTERNATIONAL, Inc. ARTICLE TAKEAWAYS: 1. Blended inoculants outperform smelted inoculants 2. The importance of Sulphur during inoculation 3. Calcium, Rare Earth, Sulphur containing inoculants WHY CUSTOM BLENDED GRAY AND DUCTILE IRON ADDITIVES OUTPERFORM TRADITIONAL INOCULANTS 32 Figure 1. Ingredients used to make Ferrosilicon