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Gray Iron, Ductile Iron and Malleable Iron Castings

Iron Castings: Economical and flexible with a wide range of process options including die casting, investment casting and centrifugal casting.

Gray iron, ductile iron & malleable iron castings

Iron foundry. Image courtesy of zephylwer0 on Pixabay, published under CC0 1.0.

Iron foundry. Image courtesy of zephylwer0 on Pixabay, published under CC0 1.0.

Bunty LLC is expert at delivering quality iron castings to the automotive and other industrial sectors where the application of heavy wall components is required. Our manufacturing processes and process control protocols have been designed to enable the production of castings of consistently high quality that our customers can rely on every single day. And thanks to the relatively low cost of iron as a working material, the high quality of our heavy iron castings is complemented by comparatively low manufacturing prices.

We work with three types of iron: gray iron, ductile iron, and malleable iron. Each of these products can be identified by a characteristic micro-structure that contributes to a unique set of mechanical properties.

 

GRAY Iron Castings

Microstructure of grey cast iron. Image c/o Hb tuw on Wikimedia Commons, published under CC BY-SA 4.0.

Microstructure of grey cast iron. Image c/o Hb tuw on Wikimedia Commons, published under CC BY-SA 4.0.

Gray iron is an alloy composed of 95% of iron, with an addition of 2.1% 4% carbon and 1% 3% silicon. The name of the material is derived both from its basic composition and from the grayish hue that fractured surfaces of the metal typically possess. It can be spelt either as gray or grey, even though American usage tends to be gray.

Gray iron castings can be produced through several different metallurgical and core processes, including sand casting and die casting. Selecting your preferred casting process depends largely upon the size of the production run and the preferred characteristics of the final part.

Common applications for the use of gray iron castings in the OEM, automotive and aerospace industries include valves, forges, compressors, pumps, and more. These components exhibit the following properties:

  • excellent machinability
  • great wear resistance
  • excellent dampening capacity
  • excellent castability
  • resistance to cracking
  • low solidification shrinkage
  • significant cast-in details
  • high temperature properties.

 

Ductile Iron Castings

Microstructure of ductile cast iron. Image c/o Michelshock on Wikimedia Commons, published under CC0 1.0.

Microstructure of ductile cast iron. Image c/o Michelshock on Wikimedia Commons, published under CC0 1.0.

Ductile iron receives a treatment with magnesium before the casting process to produce a very strong, impact resistant and durable metal suitable for applications requiring both tensile strength and toughness. It typically possesses higher strength than gray iron, weighs about 10% less than steel of comparable size and weight, and displays superior corrosion resistance compared to most other cast iron products.

Ductile iron is suitable for the production of components of a very wide weight range, from several grams to hundreds of tons. It may replace aluminum or cast and forged steel in some situations, which is why it's used extensively in the automotive industry.

  • comparatively high strength-to-weight ratio;
  • excellent surface detail;
  • great surface finish;
  • great machinability ;
  • excellent wear resistance;
  • reduced weight compared to steel;
  • excellent castability.

 

Malleable Iron Castings

Pipe fitting made of black malleable cast iron. Image c/o Andreas Mühlhausen on Wikimedia Commons, published under CC BY-SA 2.5.

Pipe fitting made of black malleable cast iron. Image c/o Andreas Mühlhausen on Wikimedia Commons, published under CC BY-SA 2.5.

Malleable iron is an iron-carbon alloy that was modified by heat treatment. It is formed by heating white cast iron to around 920 °C and then allowing it to cool very slowly. This enables graphite to separate out much more slowly, so that surface tension has time to form into spheroidal particles rather than flakes, creating unique microstructure properties.

The characteristic microstructure of malleable cast iron makes it suitable for applications that require toughness and good machine workability. It is also ideal for components that need to have some ductility so that they can be flexed or bent without cracking.

Malleable iron castings exhibit the following properties:

  • higher rupture and tensile strength;
  • elongation properties;
  • great wear and shock resistance;
  • lower sensitivity to cracking;
  • excellent machine workability;
  • better strength and ductility than gray iron;
  • better shock absorption and abrasive resistance than cast steel;
  • better impact resistance than ductile iron.

 

Iron Casting Processes

Iron can be cast through several commonly used processes that include die casting, investment casting, centrifugal casting, and sand casting.

Die casting method employs finely crafted reusable dies that contain an impression of the finished product. It is a great manufacturing choice when a continuous production cycle or a fast production speed are required.


Investment casting process is used for the production of considerably more complex and detailed parts that are required to have thin walls. It is typically used to create ductile iron pieces.
 

In centrifugal casting, molten metal is introduced under controlled conditions while rotating the mold at high speeds. This complex casting process generates cylindrical parts and components.
 

Sand casting remains by far the most widely used iron casting process today. It offers numerous benefits such as low manufacturing cost, easy implementation, reduced porosity, and very few flaws in the internal structure of the finished parts.  The process involves pouring molten metal into a two-part mold cavity that is formed using a sandy mixture. The mixture is selected according to the need for accuracy and in light of the desired surface finish and may include green sand, dry sand, no bake or skin-dried materials.
 

Regardless of the casting method employed, finished parts may contain internal flaws and/or surface imperfections such as sand inclusions. These surface imperfections are removed using post-casting machining operations, while castings that exhibit any type of internal flaw are detected and discarded before the products reach the end-customer.


CONTACT BUNTY LLC

For further information about our gray iron, ductile iron, & malleable iron castings, contact us via the convenient website form or

submit a request for quote directly. We welcome your inquiries.