Everything You Need To Know About Cast Iron: Types, Properties, and Applications

Metals are integral raw materials in the manufacturing industry. One example, iron, is second in abundance to aluminum and makes up about 5% of the Earth’s crust. It is rare to find pure metal occurring naturally, resulting in numerous iron alloys. 

This gives rise to cast iron, a versatile metal with numerous unique uses in the industrial and commercial sectors. Here, we answer “What is cast iron?” and outline its main and specialty types. We also explore cast iron: 

• Composition
• Properties
• Pros and cons
• Uses across different sectors
• Future trends

What Is Cast Iron?

Cast iron, which has existed since the 5th century B.C., is one of the oldest iron alloys. It was first used to make weapons and agricultural tools. Cast iron contains between 2% and 5% carbon, which may be higher depending on the type of alloy. It’s created by smelting iron ore and mixing it with different alloys and scrap metals.

Cast iron variants with a high carbon content offer exceptional strength and wear resistance. In addition to carbon, cast iron contains 1-3% silicon, which enhances its casting performance. Trace amounts of phosphorus, manganese, and sulfur also exist. These impurities give cast iron a unique toughness and ductility.  

The Four Main Types of Cast Iron Explained

There are four main cast-iron variants. They arise from differences in heat treatments and processing techniques. 

These cast iron types are:

1. Grey Cast Iron: The Affordable and Versatile Option

Grey cast iron is the most common variant, featuring a graphite microstructure comprising numerous small flakes. The grey appearance that gives the alloy its color comes from the presence of these small flake-shaped fractures. Under immense stress, the metal can fracture along these graphite flakes, revealing the grey-colored graphite underneath. 

You can control the matrix structure and size of the graphite flakes by adjusting the cooling rate during production. Grey iron has a lower tensile strength than other cast iron metal types and isn’t as ductile. However, it offers higher vibration damping and better thermal conduction. 

This cast iron type is also easier to machine, and its wear resistance characteristics make it one of the highest-volume cast iron products. These properties make grey cast iron ideal for machining:

• Tool bodies
• Industrial compressors
• Pipe and pipe fittings
• Household and agricultural tools
• Hydraulic components.

2. White Cast Iron: Hard and Abrasion-Resistant

This cast iron type derives its name from its silvery or white appearance. Under a high cooling rate and with the proper carbon content, iron combines with carbon atoms to form iron carbide. Once the alloy solidifies, there is no room for the graphite molecules, resulting in the white color.

White cast iron has a brittle and hard cementite microcrystalline structure. It offers excellent wear resistance and high compressive strength. Ni-Hard Iron is one of the most popular grades of white cast iron. It contains nickel and chromium additives that are ideal for low-impact, sliding abrasion uses. 

These applications include:

• Malleable rolls
• Pump linings
• Wear plates
• Inferior castings
• Applications that require a hard exterior coating, such as industrial rollers or crushing equipment components.

3. Ductile Cast Iron (Nodular Iron): Combining Strength and Flexibility

The graphite molecules in ductile or nodular cast iron have a unique spheroidal shape, unlike the flakes of graphite present in grey iron. This particular feature arises from the presence of magnesium in the alloy that reacts with other impurities like oxygen and sulfur. 

Manipulating the microcrystalline framework around the graphite spheroid can yield different ductile iron grades. This is achievable through heat treatment or the casting process. 

Ductile cast iron deforms on impact instead of shattering into shards. This impact profile makes it an excellent material for creating cast iron bollards. 

Other uses include making:

• Pump bodies
• Valves
• Pinions
• Pipe fittings
• Gear housings
• Flanges
• Non-destructive testing
• Earthmoving machinery

4. Malleable Cast Iron: The Ductility Champion

This cast iron type results from extensive heating and cooling, which breaks down the iron carbide molecules. The heat treatment process releases free graphite molecules, creating a malleable crystalline structure. This process makes the material less brittle and more ductile, which is ideal for uses that require machinability and toughness. 

Some of these applications include the production of:

• Gearbox housings
• Electrical fittings
• Industrial brake systems
• Wheel hubs
• Connecting rods
• Door hinges
• Mechanical linkages
• Connecting rods
• Railroad rolling stock 

Beyond the Basics: Specialty Types of Cast Iron You Should Know

In addition to the four main cast iron types, other unique alloys have special cast iron properties. These specialty cast iron types include:

Chilled Cast Iron: The High-Wear Solution

This cast iron variant has a tough, wear-resistant surface. A metal chiller can quickly cool molten metal to create chilled cast iron. The cooling process is faster when the molten metal is in contact with the wall and decreases as you approach the center. The rapid cooling process produces white cast iron on the surface, while the slower cooling below the surface creates a grey iron core.

Increasing the carbon content can improve the hardness of the chilled zone while decreasing the depth of the chill. Adding about 1-4% of chromium further helps control the chill depth and improve abrasion resistance. This enhanced toughness makes chilled cast iron an excellent material for creating machinery, dies, and tools exposed to heavy wear. 

Alloyed Cast Irons: Enhanced for Specific Needs

Adding elements like nickel and chromium to cast iron improves its properties. This alloying process produces corrosion-resistant and elevated-temperature cast iron types. The corrosion-resistant variant can help create engineering parts that operate in a harsh environment with seawater, alkalis, and acids.

This elevated-temperature alloyed cast iron can resist buckling under:

• Oxidation by the ambient atmosphere
• Service loads
• Instability and growth in structure up to 1,100°F 

Cast Iron in Action: Applications Across Industries

Cast iron is quite versatile. Its numerous variations have indispensable uses across several industries, such as: 

Construction and Infrastructure: Pipes, Fittings, and Support Systems

Cast iron is a popular architectural raw material used to construct pipes, buildings, and bridges. It offers excellent strength and deformation resistance, improving its longevity and durability. 

The extended lifespan reduces the frequency of repairs and replacement, minimizing waste generation. In addition, cast iron pipes and fittings have smooth inner surfaces that lower flow resistance while promoting the efficiency of transporting water. 

Household Goods: Cookware and Decorative Items

Cast iron has extensive household uses. It offers exceptional heat retention when used as cookware, helping your food stay warm and cook evenly, whether you’re simmering soup or searing steak. Cast iron features a healthy nonstick surface, Unlike the harmful chemicals in other nonstick cookware containing Teflon or PFOA (forever chemicals). 

Cast iron can also be used to make remarkable furniture with unique ornamental designs. Melting and pouring the molten iron into molds can form intricate patterns that are tricky to achieve with other materials. The result is robust cast iron furniture and decorative items that offer timeless elegance for patios, gardens, and terraces.

Energy Sector: Cast Iron Components for Power Generation

Power production involves high-heat procedures that benefit significantly from the durability of cast iron valves and pipes. These components manage flow in boilers and power facilities under extreme heat and pressure conditions. By regulating steam flow through turbines and facilitating water circulation to cooling systems, these cast iron parts help prevent safety risks. 

Cast Iron Properties vs. Other Metals: What Sets It Apart?

Cast iron metal composition has several unique features in its microstructure that distinguish it from other non-ferrous metals. Some of these differing mechanical properties include

Comparing Cast Iron With Steel, Aluminum, and Bronze

Steel and cast iron may appear similar, but they have different properties. Steel has less than 2% carbon content but a higher melting point at 2,500-2,800 degrees Fahrenheit. Stainless steel also offers more corrosion and impact resistance while being more expensive than cast iron. Steel is ideal for making construction beams, heavy machinery, or industrial equipment. 

Aluminum is a strong yet lightweight alternative to steel. However, it has lower heat retention and conductivity and is generally more expensive than cast iron. Aluminum‘s unique properties make it well-suited for applications requiring a balance of strength and reduced weight.

Bronze and cast iron are both durable materials with excellent thermal conductivity and retention. However, bronze is denser, making it more durable and impact-resistant. It is a fantastic alternative to cast iron for making cookware and for use in high-pressure scenarios, such as those in the oil, gas, and marine sectors.  

Strengths and Weaknesses: When To Choose Cast Iron

Cast iron offers excellent castability and fluidity after melting, allowing you to create complex parts with intricate designs. Its high wear resistance and compression strength are ideal for structures and buildings taking up compressive loads. 

However, it is relatively brittle and may fracture under pressure or shock. Cast iron is also heavy and rusts easily, so it may require painting or electroplating as protection.

Future Trends in Cast Iron: What’s Next for This Timeless Material?

The cast iron industry is experiencing revolutionary changes and adopting new technologies. For instance, integrating computer-aided manufacturing (CAM) and computer-aided design (CAD) programs into the casting process has improved dimensional accuracy. These advanced simulation software programs help lower waste while optimizing casting designs.

Sustainability efforts, such as utilizing green energy and recycled scrap iron, are also taking center stage, contributing to more eco-friendly production methods. In addition, manufacturers are increasingly using composite cast irons derived from combining cast iron with other polymers and materials. This hybrid material has enhanced resilience and damping features, opening new application possibilities.