Malleable iron
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Malleable iron is cast as
Three basic types of malleable iron are recognized within the casting industry: blackheart, whiteheart, and pearlitic.[1]
History
Malleable iron was used as early as the 4th century
Castability, heat treating and post-casting operations
Like similar irons with the carbon formed into spherical or nodular shapes, malleable iron exhibits good ductility. Incorrectly considered by some to be an "old" or "dead" material, malleable iron still has a legitimate place in the design engineer's toolbox. Malleable iron is a good choice for small castings or castings with thin cross sections (less than 0.25-inch, 6.35 mm). Other nodular irons produced with graphite in the spherical shape can be difficult to produce in these applications, due to the formation of carbides from the rapid cooling.
Malleable iron also exhibits better fracture toughness properties in low temperature environments than other nodular irons, due to its lower silicon content. The ductile to brittle transition temperature is lower than many other ductile iron alloys.
In order to properly form the spherical-shaped nodules of graphite (called temper graphite nodules or temper carbon nodules) in the annealing process, care must be taken to ensure that the iron casting will solidify with an entirely white iron cross section. Thicker sections of a casting will cool slowly, allowing some primary graphite to form. This graphite forms random flake-like structures and will not transform to carbide during heat treatment. When stress is applied to such a casting in application, the fracture strength will be lower than expected for white iron. Such iron is said to have a 'mottled' appearance. Some countermeasures can be applied to enhance the formation of the all-white structure, but malleable iron foundries often avoid producing heavy sections.
After the casting and heat treatment processes, malleable iron can be shaped through cold working, such as stamping for straightening, bending or coining operations. This is possible due to malleable iron's desirable property of being less strain rate sensitive than other materials.
Applications
It is often used for small castings requiring good tensile strength and the ability to flex without breaking (ductility). Uses include electrical fittings, hand tools, pipe fittings, washers, brackets, fence fittings, power line hardware, farm equipment, mining hardware, and machine parts.[5]
See also
References
- ISBN 0-7506-4284-X.
- ^ ISBN 978-90-04-09632-5.
- ISBN 978-90-04-09632-5.
- ^ Journal and Proceedings of the Hamilton Scientific Association. 1927.
{{cite journal}}: Missing or empty|title=(help) - ^ Harvey E Steinhoff; Gordon B Mannweiler (1960). Malleable Iron Castings. Malleable Founders Society.