Let us first take a look at the different categories of cast iron. There are 3 main categories such as Gray, Ductile and Malleable Iron. In fact malleable iron is rarely specified anymore because Nodular Iron now offers better properties at comparable costs. As an obvious result nodular iron casting now stands as the most preferred choice for industrial, agricultural and even for heavy casting industry.
As a matter of fact; cast iron casting is a family of metals that are iron-carbon-silicon alloys containing more than
- 2% carbon (C)
- 1 – 3% silicon (Si)
- Few other elements for various purposes
Typically the high C and Si content in cast irons helps in the formation of lower density free graphite in the iron during solidification and makes production of more complex CI casting possible.
On the other hand; the ductile irons are represented by nodular graphite. The gray irons contain flake graphite. In fact the gray irons are generally considered lower to moderate strength. The tensile ranges in gray iron thus ranges from 20,000 psi to 60,000 psi. It needs to be mentioned here that gray irons have better damping capacity and machinability.
Nodular irons have moderate machinability and higher strength. The tensile thus ranges from 60,000 psi to over 150,000 psi. CI casting are widely used in industries like agriculture, automotive, construction, and municipal applications.
Common Gray Iron Grades –
- Class 25
- Class 30
- Class 35
- Class 40
Common nodular Iron Grades –
According to the ISO Foundry in India, an unusual combination of properties is obtained in ductile iron. This is typically because the graphite occurs as spheroids rather than as individual flakes as in gray iron.
Quite ideally therefore the nodular or ductile iron exhibits
- linear stress-strain relation
- considerable range of yield strengths
- ductility
The alloying agents thus render strength to the cast iron. The CI Casting has also stood apart as an excellent alternative to steel.
Ductile Iron Casting|Iron castings 