During the iron casting process, a manufacturer deposits molten iron and ferrous alloys into a mold. This material solidifies as it cools, ultimately hardening into a shape determined by the mold cavity. The casting process promotes important microstructural changes in cast metals.
Casting today creates many commercially important products. Three popular different cast metals frequently contribute to metal parts manufacturing and assembly operations. They include gray iron, ductile iron and malleable iron.
Gray Iron: Noted for its characteristic gray color, gray iron castings have gained wide use in numerous modern industrial applications.
Ductile Iron: Manufacturers create ductile iron by applying Magnesium to the ferrous metals used in the production of gray iron. Ductile iron castings display spheroidal carbon inclusions within the iron on a granular level, a factor which contributes to enhanced ductility.
Malleable Iron: This cast iron product contains less carbon than conventional gray iron. It offers ductility and strength, but sometimes shrinks in size during cooling.
Manufacturers produce malleable iron by first casting a brittle product known as “white iron.” Cast white iron contains carbon inclusions and offers surface hardness. The application of a special annealing heat treatment causes this metal to lose its brittleness, while also changing the internal microstructure to render it more ductile.
Manufacturers must exercise care during the annealing heat process to prevent the re-formation of brittle iron. This step sometimes involves re-heating thin sections of the cast material to ensure the carbon inclusions form irregularly shaped structures referred to as “temper graphite nodules” or “temper carbon nodules” on a microstructural level. The high temperatures during the sustained reheating operation reportedly approach 1700 degrees Fahrenheit.
In some cases, manufacturers will re-heat white iron for extended periods of time (up to 100 hours) during the production of malleable iron. They may add additional iron ore to the molten metal during this step. Since companies with both “low tech” and “high tech” foundries generate malleable iron, variations in production methods evidently exist within the commercial marketplace today.
Malleable iron demonstrates greater ductility than gray iron, and while hard, it lacks the brittleness of white iron. Although not cast as easily as gray iron or ductile iron, it will cast better than some other materials, including white iron.
Additionally, malleable iron offers excellent surface hardening. It resists scratching and abrasions. It possesses superior tensile strength compared to gray iron, although far less tensile strength than ductile iron.
Its ductility means that malleable iron permits a variety of “cold working” operations during the finishing process. Its enhanced ductility enables malleable iron to sustain machining well. Manufacturers frequently bend, straighten, or stamp this metal during the process of creating marketable components. Malleable iron will tolerate these operations.
One property of malleable iron has posed a drawback for its use in some commercial settings. It will sometimes shrink during cooling. The loss of dimensional stability makes it unsuitable for the creation of products requiring high tolerance ranges. However, many manufacturers utilize malleable iron to generate small thin castings and plates.
Malleable iron reportedly has existed for centuries. Some products using this cast metal date from ancient times. For instance, archeological digs reportedly unearthed some artifacts made from malleable iron dating from the period of the Tang Dynasty. Its use did not become widespread until after the Industrial Revolution, however.
Today, manufacturers can still employ malleable iron in a variety of products in which the generation of a high volume of uniform parts within tight tolerance ranges does not represent the paramount concern. It frequently contributes to the creation of small parts intended for extensive subsequent machining and finishing operations, for instance.
Applications for malleable iron today exist within numerous industrial sectors, including agriculture, electronics, consumer goods, and construction. Products made from malleable iron include fence hardware, pipe fittings, agricultural equipment, house wares, small machine parts, costume jewelry, electrical fittings, stamped industrial tags, and works of art. This material works well for the creation of some very thin cast components and plates, for example.
Malleable cast iron offers some advantages.
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