The major commercial nodulizer for magnesium cast irons is a magnesium ferro silicon alloy with 5% to 7% Mg, 43-48% Si and balance iron. The magnesium is produced by the silicothermic reduction of calcined dolomite.
However, prior known magnesium ferro silicon alloys dissolve in molten iron at relatively slow rates which limit the casting parameters such as pour time and temperature of the metal being cast.
The price of Ferro Silicon Magnesium Alloy is determined by the supply and demand in the market. The prices tend to rise during a shortage, and fall during a surplus. The price is also dependent on the availability of raw materials and energy.
A magnesium ferrosilicon alloy for in-mold nodulization of ductile iron, comprising 5-15% magnesium, 60-80% silicon, 0.1-1.5 percent calcium, 0.3-1.3 percent aluminum, 0.2-2.5 percent rare earth preferably cerium, and balance iron. It is a cost-effective alternative to the use of a cerium nodulizer.
Standard 75% Ferro Silicon is used primarily as a deoxidizer and alloying component in the manufacture of steel. It can help prevent oxidation of the steel at a later stage, thereby improving its quality and production cost. It can also promote fluidity and improve the absorption rate, as well as facilitate casting. Elkem is one of the largest producers of premium-grade 75% Ferro Silicon and is ideally positioned to assist customers in finding the best product for their applications.
The nodulant/Ferro Silicon Magnesium Alloy has good spheroidizing properties and can be used in the "Sandwich" and "In Mold" processes. It has high magnesium oxide content, low levels of calcium and rare earth elements. This gives it a strong effect on deoxidization, desulfurization and recovery of chromium and vanadium.
It is an alkaline metal and reacts with water to produce hydrogen gas. It is also used to make refractory products and as a catalyst in the production of chemicals. Magnesium is produced commercially by the Pidgeon process, where it is reduced with ferrosilicon in a vacuum retort.
Secondary ion mass spectroscopy on graphite nodules of a magnesium ferrosilicon alloy containing pure cerium and pure lattice supports the hypothesis that the nucleation process is influenced by the presence of elements catalyzing or retarding this reaction. The result is a gradual enlargement of the graphite nodules. This is in contrast to the faster enlargement of nodules in an iron treated with unpurified cerium and lattice.
An improved process for preparing nodular cast iron is disclosed whereby, prior to casting, the iron melt which has been contacted with a magnesium graphite-spheroidizing agent is further contacted with an after-treating alloy containing from about 0.8 to about 1.8 weight percent magnesium. This invention permits a substantial reduction in the amount of magnesium graphite-spheroidizing agents required without adversely affecting the metallurgical and physical properties of the nodular cast iron.
The use of such an after-treating alloy significantly reduces the violence of the reaction thereby substantially decreasing smoke and flare-ups. It also allows the use of a lower concentration of graphite-spheroidizing magnesium and a higher concentration of magnesium-fluorspar and aluminum-silicon alloy. In addition, a substantial increase in the proportion of slag-forming double oxides (such as 2CaO2CaO14Al2O3) is achieved which has much lower standard free energy than single oxides. This causes a greater degree of nucleation on these double oxides, resulting in high nodule counts. This effect is further enhanced by increasing the percentage of dolomite and bauxite in the charge.
In the in-mold nodulization process used to produce spheroidal graphite iron castings, magnesium ferrosilicon alloy is introduced into an electric arc furnace as a nodulizer to accelerate solidification. The alloy is typically comprised of 5-15% by weight of magnesium, 60-80% by weight of silicon, 0.3-0.5 percent of calcium, 0.8-1.3 percent of aluminum, and 0.2-0.5 percent of rare earth (usually cerium), with the balance being iron.
During this process, the briquettes are loaded into tubular steel retorts that are surrounded by an enclosure that is evacuated to below 0.1 torr and externally heated to a temperature in the range of 1150-1200 degC. The retorts are then subjected to mechanical vibration to induce nucleation and to promote the growth of nodules within the cast metal.
Rare earth ferro silicon magnesium nodulizer has low magnesium oxide content, good chemical composition stability, stable smelting craft, no air shrinkage, and reasonable particle size distribution. It is widely used in medium frequency furnace smelting and spheroidizing treatment of low sulfur molten iron.
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