Ductile Iron (also known as spheroidal graphite iron or nodular iron) is the result of casting liquid iron that has been treated with magnesium to promote the formation of graphite spheroids, instead of interconnected flakes. This form of ductile iron is used for a variety of applications, including automotive components and structural parts.
The addition of a treatment alloy that is capable of completely dissolving in the reaction chamber prior to pouring of the iron into the mold can be very helpful for producing ductile iron. This is especially true in cases where the casting chamber has a size and configuration that is intended for this purpose. In addition, this alloy should have a dissolution rate that is such that it completely dissolves in the molten iron during the entire casting process.
Hickman, Williams & Company offers several different varieties of Magnesium Ferrosilicon Treatment Alloys for ductile iron. These include a 3 to 4 percent magnesium alloy for minimal reactivity and high magnesium recovery, as well as the standard 5 to 6 percent magnesium alloy for normal practices.
These alloys can be used in most common magnesium treatments for ductile iron, including the open ladle, sandwich, tundish, pocket and in-mold processes. They also can be used as recarburizers, adjusting carbon levels in the melt and/or just before tapping from the furnace.
Using a magnesium ferrosilicon treatment alloy with a small percentage of rare earth elements (RE) is an excellent way to improve the microstructure and strength of cast iron. This alloy is also a good choice for enhancing nodule count and reducing the fading effect in the cast iron.
Alloys with REs have a low carbon content that is important for controlling the melting point of the metal. They also enhance a variety of other properties, such as thermal shock resistance, tensile strength, flexural strength, toughness and fracture toughness.
In addition to REs, other important ingredients for enhancing microstructure and strength are magnesium, titanium, and silicon. The magnesium and titanium are used in a specified proportion to each other and are preferably accompanied by other additives, such as calcium and aluminum. The alloy may also contain small amounts of lanthanides and cerium sulfides to counteract the deleterious effects of certain trace elements in the cast iron, notably Pb, Sb, and Bi.
This alloy can be used in a wide range of magnesium treatments for ductile iron, and is especially effective in the in-mold process. Its ability to completely dissolve in the reaction chamber during the casting process, coupled with its low reactivity and high magnesium recovery make it a desirable alloy for use in a wide range of ductile iron casting processes.
In order to minimize the loss of nucleation, a nodularizer must be carefully chosen for each treatment process. This can be done by examining the production capacity of the foundry, as well as by understanding the type and amount of the nodularizer that will be needed to achieve the desired results.
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