Cast Iron Explained: Definition, Properties, and Applications

What is Cast Iron?

Cast iron is a group of iron-carbon alloys with a carbon content of more than 2 to 4 percent. In addition, varying amounts of silicon from 1 to 3% by weight and manganese as well as traces of impurities such as sulfur and phosphorus. Cast iron is made by reducing Iron Ore in a Blast Furnace.

The liquid iron is poured or cast and hardened into crude ingots called pigs, and the pigs are then remelted along with scrap and alloying elements in cupola furnaces and recast into molds to produce a variety of products.

The alloying ingredients affect its color when breaks: white cast iron has carbide impurities that allow cracks to pass easily, gray cast iron has graphite flakes that deflect a passing crack and initiate countless new cracks as the material breaks, and ductile cast iron has spheroidal graphite “nodules” that stop the crack prevent further progress.

With the exception of malleable iron, cast iron tends to be brittle. With its relatively low melting point, good fluidity, castability, excellent machinability, deformation resistance, and wear resistance, cast iron has become an engineering material with a wide range of applications.

Cast iron is used in pipes, machinery, and automotive parts such as cylinder heads, cylinder blocks, and gearboxes. It is resistant to oxidation damage but difficult to weld.

what is cast iron made of?

Cast iron is made from pig iron, which is the product of melting iron ore in a blast furnace. Cast iron can be made directly from the molten pig iron or by re-melting pig iron, often along with substantial quantities of iron, steel, limestone, carbon (coke), and taking various steps to remove undesirable contaminants.

Phosphorus and sulfur may be burnt out of the molten iron, but this also burns out the carbon, which must be replaced. Depending on the application, carbon and silicon content are adjusted to the desired levels, which may be anywhere from 2–3.5% and 1–3%, respectively.

If desired, other elements are then added to the melt before the final form is produced by casting.

Cast iron is sometimes melted in a special type of blast furnace known as a cupola, but in modern applications, it is more often melted in electric induction furnaces or electric arc furnaces. After melting is complete, the molten cast iron is poured into a holding furnace or ladle.

What is the Difference Between Cast Iron & Steel?

The main difference between the two elements is that steel is produced from iron ore and scrap metals, and is called an alloy of iron, with controlled carbon. Whereas around 4% of carbon in iron makes it cast iron, and less than 2% of carbon makes it steel.

Cast iron is cheaper than most steel. Also, the cast iron melting temperature is lower than that of steel, but it has high compressive strength, high hardness, and high wear resistance. Therefore, the important difference between steel and cast iron is that steel is ductile and malleable, whereas cast iron is hardened and has high compressive strength.

As another important difference between steel and cast iron, we can say that carbon in steel is in the form of iron carbide while cast iron has carbon as graphite or iron carbide or both. In addition, cast iron has excellent fluidity, with no steel.

Properties of Cast iron

A few common mechanical properties for cast iron include:

Hardness. Cast iron is hard and it can be hardened by heating and sudden cooling. This makes it quite durable. Mild steel can be hardened and tempered by using relevant processes.
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
Melting Point. Cast iron has a lower melting point (12000C) as compared to the melting point of mild steel which lies in the range of 13000C and 14000C.
Castability. Cast iron is easier to work with when it comes to casting shapes out of the material. Due to the extra carbon present in cast iron, it’s molten form is more fluid and this makes it easier to cast the material into complex shapes.
Machinability. Cast iron are almost elastic up to ultimate tensile strength and produce discontinuous chips which break away from the sample easily. This helps to improve the cutting ability. Due to this, cast iron is the preferred material when it comes to high machinability and strength.

Composition of Cast iron

Cast iron, an alloy of iron that contains 2 to 4 percent carbon, along with varying amounts of silicon and manganese and traces of impurities such as sulfur and phosphorus. It is made by reducing iron ore in a blast furnace.

Cast iron also contains a small number of impurities such as silicon, sulfur, manganese and phosphorus, copper, nickel, chromium, which affect its properties on a small or large scale. The effect of these properties is as follows.

Silicon: In cast iron, silicon particles have up to 4 percent presence. It promotes graphite formation which makes it soft and easily machinable and Increases hardenability and electrical resistivity.
Sulfur: It is present up to 0.1 percent. It makes cast iron hard and brittle.
Manganese: It promotes carbide formation of cast iron which makes it elite, hard and increases resistance to wear and abrasions. It is present up to 0.75 percent.
Chromium: It also promotes carbide formation which 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.
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.

Types of Cast Iron

The four basic types of cast iron – are white iron, gray iron, ductile iron, and malleable iron.

White iron.
Gray iron.
Ductile iron.
Malleable iron.

1. Gray Cast Iron

The most common type, gray iron, has a graphite microstructure made up of many small fractures. It is called “grey iron” because the presence of these small cracks creates the appearance of a gray color.

During the production of gray iron, the cracks open up and reveal the grey-colored graphite beneath the surface. Gray iron is not as strong as steel, nor can it absorb the same amount of impact as steel. Gray cast iron offers a similar compressive strength as steel. As a result, it has become a popular metal choice for applications where compressive strength is important.

Characterized with graphite in the microstructure, giving:

Good machinability
Good resistance to wear and galling

2. White Cast Iron

White iron, while not as common as gray iron, is another type worth mentioning. It gets its namesake from its off-white color, which is the result of iron compounds known as cementite. Like gray cast iron, white cast iron has many small cracks.

The difference is that white cast iron has features cementite below its surface, while gray cast iron has graphite below its surface. The graphite produces a gray color appearance while the cementite produces a white color appearance. White cast iron is hard and offers excellent abrasion resistance.

Characterized by the prevalence of carbides, impacting:

High compressive strength
Hardness
Good resistance to wear

3. Ductile Cast Iron

Ductile iron, also known as nodular iron, is a type of soft, ductile, high-carbon iron alloy. It is typically made with traces of other compounds, including magnesium and cerium.

When these trace compounds are added, they inhibit the rate at which graphite grows, keeping the metal soft and ductile. The ductile iron was invented in the early to mid-1940s.

Gray iron with small amounts of magnesium and cesium nodules the graphite, resulting

High Strength
High Ductility

4. Malleable Cast Iron

Finally, a malleable iron that is easy to “work on”. It is typically made by heat treatment processes on white cast iron. The white cast iron is heated for up to two days and then cooled. Once completed, malleable iron can be bent and manipulated to achieve unique shapes and sizes.

White cast iron heat-treated to improve

Higher Ductility

5. Mottled Cast Iron

Cast iron has an equal amount of free carbon and carbide known as mottled cast iron. It has intermediate property and color of Gray cast iron and white cast iron.

6. Chilled Cast Iron

If the white cast iron quickly cooled from the molten stage, the iron produced is known as chilled cast iron.

7. Alloy Cast Iron

Alloy cast iron is produced by adding some alloying elements in cast iron like nickel, chromium, copper, etc. It has increased properties according to the alloying element. This cast iron is produced to get the desired properties of cast iron.

Use of Cast Iron

Cast iron can be used for many types of materials and making different tools etc.

Grey cast iron: Engine cylinder blocks, flywheels, gearbox cases, machine-tool bases.
White cast iron: Bearing surfaces.
Ductile cast iron: Gears, camshafts, crankshafts, piston ring.
Many types of sanitary fittings like sewer pipes, manholes, water pipes, cisterns are manufacturing using cast iron.
Column base and metal columns can be made using cast iron
Casting mold used for making lamp posts, metal staircases, gates,s, etc.
Carriage wheels and rail chairs are made from cast iron.
Various types of agriculture equipment and implements can be made from it.
Various machinery parts can be made from cast iron
It is used in making automotive parts
It is used in making pots pans and utensils
It is used in making anchors for ships

Advantages of cast iron

It has good casting properties
It has good Sensibility
It has excellent resistance to wear
It has good machinability.
It has very low notch sensitivity
It has a Low-stress concentration
It bears Low cost
It has Durability
It has Resistance to deformation
It has three to five times higher compression strength than steel.
It has excellent anti-vibration (or damping) properties so it is used to make machine frames.
It has constant mechanical properties between 20 and 350 ° C.
It is available in large quantities, hence produced on a mass scale. Tools required for the casting process are relatively cheap and inexpensive. This results in a low cost of its products.
It can be given any complex shape and size without using costly machining operations

Disadvantages of cast iron

It is Prone to rust
It has a poor tensile strength
It has a high weight to strength ratio
It has High brittleness
It has poor impact resistance
Compared to steel it has poor machinability
Its parts are section sensitive; this is due to the slow cooling of thick sections.
The failure of its parts is sudden and in total, it does not reflect the yield point.
It is Nonmachinable (white cast iron).

FAQs.

What is Cast Iron?

What is the composition of cast iron?

What are the types of cast iron?

There are four basic types of cast iron – white iron, gray iron, ductile iron, and malleable iron

White iron.
Gray iron.
Ductile iron.
Malleable iron.

What are the uses of cast iron?

As a result of its good tensile strength and ductility, malleable cast iron is used for electrical fittings and equipment, hand tools, pipe fittings, washers, brackets, farm equipment, mining hardware, and machine parts. A common classification for malleable cast iron is ASTM A47.

Is it healthy to cook in cast iron?

Cast iron isn’t all about frying. True, a cast-iron skillet is an excellent vehicle for frying. But its ability to retain heat also lends itself to healthy cooking, says Kerri-Ann Jennings, a Vermont-based registered dietitian and nutrition coach.

What are the benefits of cast iron?

Cast Iron Maintains Heat. Stainless steel cookware can heat evenly, quickly, but cast iron can hang onto that heat throughout the entire pan for much longer. This makes for a more even and desirable result for foods like meats and steaks.

What are the disadvantages of cast iron?

Disadvantages of cast iron:

It is Prone to rusting.
It has poor tensile strength.
Its parts are section sensitive, this is due to slow cooling of thick sections.
failure of Its parts is sudden and total; it does not exhibit yield point.
It has poor impact resistance.
Compared to steel it has poor machinability.

Is cast iron better than steel?

Cast iron typically has better resistance to mechanical wear than steel, especially in friction-wearing situations.

Which is better iron or cast iron?

Cast iron is harder, more brittle, and less malleable than wrought iron. It cannot be bent, stretched, or hammered into shape, since its weak tensile strength means that it will fracture before it bends or distorts. It does, however, feature good compression strength.

Is cast iron strong?

Cast iron, again like masonry, is very strong in compression. Wrought iron, like most other kinds of iron and indeed like most metals in general, is strong in tension, and also tough – resistant to fracturing.

Is cast iron cheap?

Retailers will always charge the highest amount they can for any given product. Cast iron pans are cheap to make and they do not have the advantage of branding like La Creuset. Which makes fine enameled cast iron cook ware. Cooking in cast iron is in a way a niche market and they can be passed down from generations.

Why does cast iron not rust?

Cast iron is an alloy with a high carbon content (at least 1.7% and usually 3.0–3.7%), making it relatively resistant to corrosion.

Is black iron the same as cast iron?

Despite its name, black iron pipe is actually made of a low-grade “mild steel” compound. This gives it much better corrosion resistance than traditional cast iron piping.

Who invented cast iron?

Englishman Abraham Darby is credited with revolutionizing cast iron cookware; in 1707, he patented a method for casting iron into relatively thin pots and kettles, a process that made them cheaper to produce.

Why is cast iron so heavy?

Cast iron has a higher heat capacity than copper, so it takes more energy to heat a pound of cast iron to a given temperature than a pound of copper. More energy is stored in each pound of the cast iron. Â Aluminum has a higher heat capacity than iron (it stores more heat per pound) but is much less dense than iron.

Is cast iron stronger than aluminum?

Cast iron and cast aluminum look and feel the same, but cast aluminum is lighter and stronger. Due to the heavier mass of iron, it holds heat longer, but it takes a bit longer to get hot. Cast iron has a longer lifespan and is more expensive.

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