Ductile iron is often chosen for large and complex cast components requiring superior impact and fatigue resistance, like housings for machine tools or oil-and-gas exporation systems. Its strength comes from a nodular graphite structure that also resists cracking.
Developer Elkem Silicon Products is introducing a new foundry inoculant that cost-effectively improves graphite structures and reduces chill, especially for ductile iron practices using cerium-free magnesium alloys or pure magnesium metal as nodularizers. Called Bisnoc, this bismuth inoculant reacts with rare earths to optimize graphite nucleation.
Foseco offers a range of premium inoculants for gray iron, ductile iron, and steel castings. These granular inoculants are available in a variety of grain sizes for metal stream, ladle, and in-mold inoculation applications.
Ductile Iron : Foundry experience has shown that a combination of Calcium and Barium inoculant produces far more potent nucleation effects than either element alone. During a two day trial at a commercial foundry, IM 75-B produced nodule counts 18% higher than standard inoculating grade ferrosilicon with the same addition rate. This reduction in chill depths is significant and translates into lower casting shrinkage.
Ductile-iron foundries often use rare earth alloys in order to neutralize the detrimental effect of tramp elements introduced through scrap. However, adding too much rare earth to the melt can cause poor graphite nodularity and chunky, inconsistent casting properties. Elkem's new Bisnoc inoculant addresses this problem with a patented coating that reacts with the rare earths to optimize graphite nucleation in molten ductile iron. This results in small, uniformly distributed spheroidal graphite nodules that maximize dendritic growth and improve cast property consistency.
Ferro silicon strontium inoculant can reduce the chill of castings,make casting dense and reduce shaped residue. The inoculant can also reduce the casting loose tendency and improve section uniformity. It is especially suitable for thin-walled or chilled sweet ash sulfur casts.
The inoculant also helps to ensure the quality balance of gray cast iron and ductile iron castings. It has good deoxidizing effects, nitrogen fixation and is highly efficient in promoting inoculation.
Elkem Silicon Products has developed a bismuth inoculant that cost-effectively improves graphite structures and reduces chill in ductile iron. The new inoculant is designed to be used with magnesium nodularizing treatments. It can be substituted for expensive cerium-based inoculants. It is an inoculant for ductile iron grades such as IM 75-B, SG 15, and SG 100-B. It can also be used with other nodularizing treatments such as LM 67, SMZ and Superseed inoculants. It produces nodule counts that are 18% higher than a regular calcium-bearing inoculant.
The process of inoculation involves the introduction of metals or alloys into the iron melt that influence its structural formation. In ductile iron, the objective is to maximize graphite nodularity and castability. The use of additives that promote nodularity can counteract the negative effects of tramp elements in scrap and/or variations in melting practices.
Inoculation helps foundries to produce quality ductile and gray iron castings by increasing the number of nucleation sites in the cast iron before or during the pouring process. It also minimizes undercooling of the melt below the metastable eutectic temperature, and favors formation of graphite rather than carbides.
Inoculants increase the nucleation potential of the molten iron to allow faster cooling, which leads to improved strength. Elkem’s SMZ inoculant contains an ideal mix of calcium, barium and rare earth elements to promote the formation of small, uniformly distributed spheroidal graphite nodules in the cast iron. Its low melting point allows it to dissolve rapidly into the molten iron and has proven very effective for a variety of cast iron grades.
Ductile iron offers better impact- and fatigue-resistance than gray or steel, making it a favorite choice for components like housings used in machine tools. It also has the advantage of a nodular graphite structure, which is less disruptive to the metal matrix than the hard cementite of gray iron.
Inoculants are added to liquid cast iron in order to control matrix structure and avoid casting defects caused by insufficient nucleation. They can be added in the furnace, ladle, in-stream or directly into the mold.
Elkem produces several premium inoculants for ductile iron foundry practices. Bisnoc inoculant uses a patented technology to coat the inoculant particles with bismuth, which interacts with rare earths in the iron to optimize graphite nodularity and density. It also eliminates hard iron carbides, or "chill," that can form in thin sections of the casting. Another Elkem inoculant is SMZ, which is a good general-purpose material suited to all cast irons and can be added in the furnace, ladle or in-stream.
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