In this article, you’ll learn the definition, applications, properties, composition, and types of cast iron. You’ll also get to know the advantages and disadvantages of cast iron.
What is Cast iron?
Cast iron is a group of carbon alloys that contains 2 to 4% of carbon and a varying amount of silica and manganese. It also contains impurities such as phosphorus and sulfur. It is produced by reducing iron ore in a blast furnace and its primary material is pig iron produced from smelted iron ore in a furnace. This iron is made directly from molten pig iron or by remelting pig iron, often along with substantial quantities of iron, limestone, steel, or coke.
It can be melted on a special type of blast furnace called Cupola but it is more often melted in electric induction furnaces or electric arc furnaces.
Read more: Properties and Composition of Pig Iron
As mentioned earlier, cast iron is produced from pig iron, limestone, and coke. It manufacturing process takes place in a cupola furnace by remelting those three materials. The cupola furnace is more or less the same as the blast furnace. It is cylindrical in shape and has a diameter of about 1m and a height of about 5m. The materials are poured from the top of the furnace and then heated. At this point impurities of pig iron are removed to some extent by oxidation which forms the molten iron. The slag is then removed from the top of the molten iron at regular intervals. The molten iron is then poured into a mold to form the required shapes.
Applications of Cast Iron
The applications of cast iron are common in the engineering world such as mechanical engineering, construction site, wood workshop, etc. The following explained below are applications of cast iron.
One of its applications is for ornamental casting such as gates, lamppost, bracket, an iron column for small coverage.
It is used for compression member
Its applications o include the production of cisterns, water pipes, gas pipes, sewers, sanitary fittings, and manhole cover. and
cast iron is used for making rail chains, carriage wheels, etc.
Read more: Understanding wrought iron
Common applications of types of cast iron include:
- Grey iron is capable of resisting wear, which is why it’s used for producing engine blocks and cylinder heads, manifolds, gas burner gear blanks, enclosures, and housings.
- white cast iron is a brittle material because of the chilling process used in its production. This is why white cast iron is used on applications that require wear-resistant and abrasions such as shot-blasting nozzles, mill lining, railroad brake shoes, rolling mill rolls, slurry pump housings, and crushers.
- The applications of ductile iron are so vast because they can be broken down into different grades. The material can be easily machined, has good fatigue, and yield strength, and also good wear resistance. it is used for making steering knuckles, crankshafts, heavy-duty gears automotive suspension components, hydraulic components, and automobile door hinges.
- Finally, malleable iron is also of different grades. it has the ability to retain and store lubricants, non-abrasive wear particles, and the porous surface which traps other abrasive debris. Because of this, malleable iron is used for heavy-duty bearing surfaces, chains, sprockets, connecting rods, drive train and axle components, and railroad rolling stock.
Mechanical properties of cast iron
Below are the mechanical properties of cast iron:
Hardness – material’s resistance to abrasion and indentation
Toughness – material’s ability to absorb energy
Ductility – material’s ability to deform without fracture
Elasticity – material’s ability to return to its original dimensions after it has been deformed
Malleability – material’s ability to deform under compression without rupturing
Tensile strength – the greatest longitudinal stress a material can bear without tearing apart
Fatigue strength – the highest stress that a material can withstand for a given number of cycles without breaking.
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Other alloying elements are added to produce:
- Manganese: Increases resistance to wear and abrasions
- Chromium: Increases hardenability, wear resistance, corrosion, and oxidation resistance
- Nickle: Increases tensile strength
- Tungsten: It increases hot hardness and hot strength
- Molybdenum: Increases hardenability
- Vanadium: Increases hardenability and hot hardness
- Silicon: Increases hardenability and electrical resistivity
- Aluminum: Works as deoxidizer in steel
- Titanium: Works as deoxidizer in steel
- Niobium: It reduces hardenability and increases ductility, which results in increased impact strength
- Cobalt: It reduces hardenability and resists softening at elevated temperatures
Read more: Raw materials used in making iron and steel
Types of cast iron
Below are the various types of cast iron:
These types of cast iron are grayish in appearance, caused by their graphitic microstructure which leads to the fractures of the color. It has less tensile strength and resistance than steel and its compressive strength is comparable to low and medium carbon steel. These are based on the size and shape of the graphite flakes present in the microstructure in the cast iron.
white iron shows white fractioned surfaces because it contains an iron carbide which is called “cementite”. Due to low silicon content and faster cooling rate. Carbon in white cast iron precipitates out and allows it to melt as metastable phase cementite, fe3c, rather than graphite. The cementite precipitates from the melt as relatively large particles. As the iron carbide precipitates out, it withdraws carbon from the original melt, moving the mixture toward one that is closer to eutectic, and the remaining phase is the lower iron-carbon austenite (which one cooling might transform to martensite).
Read more: Various methods of the steelmaking process
The malleable iron process begins being white casting which is heated at about 950°c (1,740°f) and then cooled for a day or two the carbon in iron carbide then changes to graphite and ferrite plus carbon (austenite). The slow process allows the surface tension to form the graphite into spheroidal particles rather than flakes.
These types of cast iron are also known as nodular or ductile iron. It was developed in 1948. Ductile types of cast iron have graphite in form of very tiny nodulus with the graphite in form of concentric layers forming the nodulus. The properties of ductile these irons are that spongy steel with the stress concentration effect that flakes of graphite would produce – tiny amounts of 0.02 to 0.1% magnesium, and only 0.02 to 0.4% cerium added to these alloys slow the growth of graphite precipitates by bonding to the edges of the graphite planes.
Read more: Different types of chips in metal cutting
Advantages and disadvantages of cast iron
Below are the benefits of cast iron in its various applications:
- good casting properties.
- available in large quantities.
- low cost to the material
- good machinability for grey cast iron.
- good sensibility.
- excellent resistance to wear.
- constant Mechanical properties between 20 to 350 degrees Celsius.
- high durability.
- resistance to deformation.
despite the good advantages of this material, some limitations still occur. Below are the disadvantages of cast iron in its various applications:
- poor tensile strength.
- prone to rusting.
- the materials are section sensitive, due to the slow cooling of thick sections.
- high brittleness
- white cast iron cannot be machined.
- no exhibition of yield point.
That is all for this article, where the definition, applications, properties, composition, and types of cast iron are discussed. You also learned the advantages and disadvantages of cast iron. I hope you get enough from this post, if so, kindly share with other students. Thanks for reading, see you next time!