What is cast iron? Metal characteristics, production features, and applications

Cast iron is an alloy of iron and carbon, with the latter's content being 2.14%. Other components are also present.

The mechanical properties of this alloy are determined by the form in which carbon exists. It can be cementite or graphite, as well as austenite decomposition products. Depending on how quickly the alloy was cooled, it can be martensite, troostite, sorbite, pearlite, or ferrite. Alloying components allow control over the graphitization process and influence the properties of cast iron in various directions.

The carbon content in cast iron ranges from 2.14% to 6.67%. The rest consists of iron, alloying components, and cementite (Fe3C, iron carbide). Impurities such as silicon, sulfur, manganese, and phosphorus are also present.

The primary use of cast iron is as a raw material for steel production; it is also used to manufacture various parts.

Classification of Cast Irons

The characteristics of the final product are formed during the production stage. Depending on the eutectic transformation, cast irons are divided into gray, where carbon is present as graphite, and white, where carbon is in the form of cementite. There are also mottled cast irons, which contain both forms of carbon.

The size and configuration of inclusions determine the grade of cast iron and its application. They can be lamellar, spheroidal, vermicular, or flaky. The metallic base, in turn, is divided into:

• pearlitic;
• pearlitic-ferritic;
• ferritic;
• austenitic;
• bainitic;
• martensitic.

Alloying components such as aluminum, titanium, vanadium, tungsten, molybdenum, chromium, and nickel may be used.

How It Differs from Steel

The main difference is the carbon content. In steels, it is significantly lower, ranging from 0.025% to 2.14%. Additionally, cast iron contains more impurities. This affects the melting point, with steels reaching up to 1500°C, while cast iron melts at 1150-1250°C.

Due to the high carbon content during smelting, carbon atoms cannot integrate into the iron’s molecular lattice, making cast iron more brittle than steel products.

Steel is lighter in color, while cast iron alloys have a dark, matte appearance.

Cast iron is better suited for casting but is less weldable and has higher thermal conductivity.

Types of Cast Irons

1. Pig Iron
   This alloy is produced in blast furnaces. Its primary purpose is as an intermediate product for steelmaking. It can be used in solid or liquid states. It has strictly regulated impurity content: silicon, manganese, sulfur, and phosphorus. Depending on the silicon content, the following grades are distinguished:
   • for steelmaking: P1, P2 (EN-GJMB-350-10);
   • for foundry production: PL1, PL2 (EN-GJL-200);
   • phosphorus cast iron: PF1, PF2, PF3 (EN-GJMB-450-6);
   • high-quality cast iron: PVK-1, PVK-2, PVK-3 (EN-GJS-500-7).


2. White Cast Iron
   Formed under rapid cooling conditions. Its key feature is a white fracture surface, high hardness, and brittleness, making it unsuitable for machining with cutting tools. Carbon is present as cementite.
   Used for casting wear-resistant parts: grinding balls, turbine blades, rolling mill rolls, and forging cast iron variants. Wear resistance can be enhanced with alloying components like nickel and molybdenum.


3. Gray Cast Iron
   Exhibits a characteristic gray fracture surface. Compared to white cast iron, it is more machinable but has low ductility and moderate strength. Formed at slow cooling rates, it has good anti-friction properties and low susceptibility to shrinkage defects, making it suitable for complex castings with wall thicknesses up to 500 mm.
   According to EN 1561, it is classified into grades like EN-GJL-100 to EN-GJL-350, where the numbers indicate tensile strength.


4. Ductile Cast Iron
   Its distinctive feature is the addition of pure magnesium or spheroidizing modifiers like cerium and yttrium. Graphite in this cast iron is spheroidal. Magnesium content ranges from 0.02% to 0.08%.
   A high-strength alloy used for manufacturing critical wear-resistant parts. Resistant to aggressive environments and high temperatures.
   EN 1563 specifies requirements for chemical composition and properties. Grades range from EN-GJS-350-22 to EN-GJS-1000-5, with numbers indicating minimum tensile strength.


5. Malleable Cast Iron
   Produced based on ferrite, ferrite-pearlite, or pearlite structures.
   Offers high strength, improved ductility, uniform property distribution, and good machinability. The alloy has virtually no internal stresses, making it suitable for parts subjected to vibration and impact loads. Two types are distinguished: blackheart and whiteheart. Quality and production are regulated by EN 1562. Grades denote minimum tensile strength and elongation, e.g., EN-GJMW-500-5, where 500 indicates tensile strength in MPa and 5% elongation.
   Special cast irons are also distinguished, with properties achieved through alloying, special smelting, or cooling techniques. These include heat-resistant, anti-friction, ferroalloy, artistic, and types with unique electromagnetic properties.

How Impurities Affect It

Silicon is a key element in cast iron. It positively affects graphite formation and improves casting properties.

Sulfur reduces mechanical properties and causes red brittleness.

Manganese reduces casting properties and inhibits graphitization but increases hardness and strength.

Phosphorus enhances fluidity but negatively impacts strength and increases brittleness.

Advantages and Disadvantages

Cast iron has been known since the 14th century. Since then, production technology and its applications have significantly evolved. It has both positive and negative aspects.

Cast iron products are easy to clean, heat up slowly, and retain heat well. This material is environmentally friendly and has a relatively simple forging production process. Due to its eco-friendliness, it is often used for cookware, is resistant to acidic and alkaline environments, safe for human health, and durable.

Drawbacks include brittleness and susceptibility to rust. Products are heavy, requiring special transportation and maintenance conditions.

Production Technology

Cast iron is smelted in blast furnaces and cupolas. Enriched iron ore serves as the iron source. Coke, a processed coal product, is used as the carbon source, along with natural gas and coal dust. This smelting process produces cast iron and slag containing unrecovered oxides, flux residues, and ash.

Where It Is Used

Widely used in mechanical engineering and other industries. Its primary application is steel production in converters, open-hearth furnaces, or electric arc furnaces. Depending on the grade, it is also used to manufacture various parts, crankshafts, heavy equipment bases, grinding components, sliding bearings, bushings for tractor and automotive engine crankshafts, and refractory pressing molds.

In harsh climates, it ensures reliable operation of machine parts even at low temperatures.

Cast iron is used to produce numerous plumbing items: sinks, radiators, pipes, and bathtubs. Its excellent casting properties enable the creation of artistic works, such as ornate forged gates and architectural landmarks.

The "UTMK" company assists in organizing the supply of metal rolled products weighing from one ton to any city in Ukraine and across Europe, including Moldova, Germany, Spain, and Portugal. On a self-pickup basis, rolled products can be purchased at UTMK warehouses in Kyiv, Zaporizhzhia, Dnipro, Odesa, and Polish cities like Łódź, Kraków, Warsaw, and Poznań. We work with wholesale and retail clients. Call us, and our managers will assist with selecting rolled products and placing an order.