The origins of cast iron can be traced back to ancient China, where it was initially manufactured in the 5th century BC. By the 15th century, the process of casting iron was refined in Europe, and later in the 18th and 19th centuries, it became a popular and more economical choice for engineering projects than wrought iron.
What differentiates cast iron from other metals used in casting is the high percentage of carbon it contains. While most metals used for casting contain less than 2% carbon, cast iron usually holds a carbon content that ranges between 2% and 4%.
This rich carbon composition endows cast iron with distinctive qualities, such as remarkable hardness, superior heat retention, and resistance to wear and tear. Due to its robustness and long-lasting nature, cast iron rapidly gained popularity, thus making it a preferred choice for various uses.
What is Cast Iron?
The term “cast iron” is often used to categorize a variety of metal composites primarily composed of iron. Despite its name, cast iron is not entirely composed of iron – a common misunderstanding. Surprisingly, carbon steels contain a higher percentage of iron than cast irons.
For a metal composite to qualify as cast iron, it must comprise more than 2% carbon in addition to its primary component, iron. Cast irons also have smaller quantities of other alloys, including manganese and silicon among others, which are popular choices.
The production method for cast iron is what gives the metal its name. Cast iron creation involves the heating of iron ore in a furnace until it transforms into a molten state. This molten substance is then cast – meaning it’s poured out and left to solidify.
Properties of Cast Iron
High Strength
Casting iron is renowned for its exceptional strength, and ability to withstand heavy loads. It is highly resistant to deformation and can be used in projects requiring structural strength. For instance, in the construction sector, cast iron is often used for making beams, columns, and other load-bearing components. Moreover, in the machinery industry, cast iron is utilized in the manufacturing of engine blocks, gears, and parts that are subject to high stress and wear.
Durability
Casting iron’s exceptional durability makes it highly sought after in various industries, particularly for outdoor structures that are built for the long term. The high carbon content in cast iron contributes to its strength and toughness, ensuring it can withstand harsh environmental conditions. Cast iron’s heat retention capabilities and corrosion resistance further add to its long life, making it a reliable choice for durable outdoor structures.
Heat Retention
Cast iron’s remarkable ability to retain heat makes it an ideal material for applications in cooking utensils and industrial machinery. The high carbon content in cast iron allows it to absorb and hold heat for extended periods, making it perfect for slow and even cooking or providing a stable heat source for industrial processes.
Corrosion Resistance
Casting iron also exhibits excellent corrosion resistance. This makes cast iron a suitable choice for components that are exposed to moisture or aggressive chemical environments. The ability of cast iron to withstand corrosion is crucial in applications such as water pipes, sewage systems, and chemical processing equipment. By utilizing the right treatment methods or coatings, the lifespan and performance of cast iron components can be greatly enhanced.
Damping Capacity
The unique properties of cast iron, such as its high density and stiffness, contribute to its excellent damping capacity. It means that cast iron has the ability to absorb and dissipate vibrations and noise. The damping capacity of cast iron is a crucial property that makes it highly suitable for machinery and automotive applications where noise reduction and vibration control are required. As a result, cast iron is widely used in components such as engine blocks, flywheels, and brake discs.
Types of Cast Iron: Methods and Application
White Iron
White cast iron contains cementite and pearlite, which makes it very hard and abrasion-resistant but also brittle. When it breaks, it shows a white, crystalline surface, which is why it’s called white cast iron. It typically has less than 4.3% carbon and low silicon to prevent graphite formation. By controlling the carbon content and cooling rate, white iron forms iron carbide, and you get a material without free graphite molecules. In specialized cases, white iron is used on the surface of a product by using a heat-conductive mold to cool that area quickly.
White Iron is used in applications where abrasion resistance is essential, but flexibility is not a major requirement, like cement mixer liners, ball mills, and certain industrial tools.
Gray Iron
Gray iron gets its name because of its gray appearance when it breaks, due to the flake-shaped graphite in the metal. It’s a widely used casting material with about 2.5% to 4% carbon and 1% to 3% silicon. By controlling the carbon, silicon, and cooling rate, we can prevent the formation of iron carbide and make graphite flakes form directly in the melted iron. Gray iron is not very flexible and has lower tensile strength, but it’s a good conductor of heat and absorbs vibrations well, about 20-25 times better than steel. It’s easy to machine and has excellent wear resistance. Gray iron is great at resisting wear, even when there’s not much lubrication (like in engine cylinder walls).
Gray Iron is used to make engine blocks, cylinder heads, manifolds, gas burners, gear blanks, and various enclosures and housings.
Ductile Iron
Ductile cast iron, also known as nodular or spheroidal graphite iron, is quite similar to gray cast iron but with a key difference. Instead of the graphite forming as flakes, it appears as spherical particles. This change is achieved by adding small amounts of magnesium or cerium just before pouring. Spherical graphite particles don’t create a network of cracks in the material like graphite flakes do, resulting in higher strength, toughness, and flexibility. Magnesium is often added as an alloy with iron and silicon (Fe-Si-Mg) rather than pure magnesium.
Ductile Iron is used in various applications like water and sewer pipes, agricultural machinery parts, automotive components, electrical fittings, mining equipment, and steel mill components.
Compacted Graphite Iron
Compacted graphite iron is a type of iron with a unique structure that’s a mix of gray and white iron properties. It has small graphite flakes that are interconnected and formed in a microcrystalline structure. An alloy, like titanium, is used to prevent spherical graphite formation. Compared to gray iron, compacted graphite iron has higher tensile strength, thermal conductivity, and better flexibility. Further, you can adjust its properties through heat treatment or adding other alloys. Its unique structure helps the graphite stick well to the iron matrix and prevents cracks, improving its mechanical properties compared to gray iron.
Compacted graphite iron is utilized for making diesel engine blocks, frames, cylinder liners, brake discs for trains, exhaust manifolds, and gear plates in high-pressure pumps.
Malleable Iron
Malleable iron is a type of cast iron with properties between gray and ductile iron. It’s great for applications requiring toughness, machinability, and some flexibility without breaking. It’s often used for small or thin castings to avoid chills (carbides at the surface due to rapid cooling). It’s made by heat-treating white cast iron, where iron carbide breaks down into iron and carbon. This happens with high temperatures, slow cooling, and high carbon and silicon levels. The result is a microstructure with carbon nodules in a ferrite matrix, known as ferritic malleable cast iron, which improves ductility.
Malleable iron is used in various applications like automotive, agriculture, railways, bridges, hoists, casters, and pipe fittings.
Conclusion
Cast iron’s various use cases in construction, transportation, and other industry is a testament to its unparalleled properties and enduring relevance in today’s world. In the realm of cast iron types, ductile and gray iron stand out as the most versatile and widely applied forms. Ductile iron offers a unique balance of strength and ductility, making it a preferred choice for critical components, while gray iron’s excellent castability and damping capacity have made it indispensable in various industries.
Mahadev Ferro Cast Pvt Ltd, is one of the top producers of cast iron with a remarkable capacity to produce castings of up to 3000 kilograms single part piece. Certified with ISO BS OHSAS 18001, the company’s commitment to quality and expertise in the casting process ensures the production of durable and high-quality cast iron components that meet the stringent demands of modern engineering.