Cast Iron vs. Steel: Understanding the Differences(feedrate Tina)

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Cast iron and steel are two widely used materials in various industries, thanks to their exceptional strength and durability. While they may appear similar at a glance, there are significant differences between cast iron and steel regarding composition, properties, and applications. This article aims to shed light on these disparities, enabling you to make informed decisions when it comes to CNC machining.

Composition and Production

Both cast iron and steel compose primarily of iron (Fe), but the presence of additional elements sets them apart. Cast iron contains more carbon and silicon compared to steel, leading to its distinctive properties. The incorporation of these elements into the molten iron during casting influences the final structure and characteristics of the material.

Casting Techniques for Cast Iron and Steel
To produce cast iron, the traditional method involves melting iron along with scrap metals, such as steel or ferroalloys, then adding carbon-rich substances like coke or charcoal. Once melted, the composition is poured into molds and allowed to solidify. This process produces a brittle material that boasts excellent compression strength but minimal tensile strength.

Steel, on the other hand, can be produced through various methods, including basic oxygen furnace (BOF) and electric arc furnace (EAF). In BOF, iron ore and additives, such as limestone, are smelted together using pure oxygen to reduce impurities. EAF relies on recycled steel scrap, which undergoes an electric arc melting process to achieve the desired composition. These techniques result in a malleable material with superior tensile strength compared to cast iron.

Properties and Characteristics

One distinguishing characteristic of cast iron is its high carbon content, typically ranging from 2% to 4%. This abundance of carbon makes cast iron extremely hard and brittle, making it prone to cracking under tension. However, this brittleness also contributes to its excellent wear resistance, making it suitable for applications involving heavy loads, such as engine blocks and machinery components.

Steel, on the other hand, contains less carbon, usually between 0.2% to 1.5%. This lower carbon content significantly improves steel's malleability and ductility, resulting in a material that can be easily formed into various shapes. Steel also exhibits excellent tensile strength, allowing it to withstand both tension and compression forces efficiently. Consequently, steel is commonly used in structural elements, automotive parts, and tools requiring flexibility along with strength.


Due to their contrasting properties, cast iron and steel find usage in different applications. Cast iron, with its brittleness and wear resistance, is ideal for items requiring high compression strength, such as pipes, engine blocks, manhole covers, and brake discs. Its ability to absorb vibrations makes it favorable for construction, railings, and machine bases.

On the other hand, steel's versatility allows it to excel in numerous industries. Its high strength-to-weight ratio adds value in building infrastructures like bridges, skyscrapers, and towers. Automotive manufacturing relies heavily on steel due to its exceptional formability, toughness, and crashworthiness. Steel is also widely used in household appliances, ships, submarines, and surgical instruments, among others.


In summary, understanding the differences between cast iron and steel plays a crucial role in CNC machining decisions. Cast iron offers remarkable wear resistance and compression strength but lacks ductility. Meanwhile, steel provides superior tensile strength while maintaining formability. Both materials have their unique advantages and applications, making them valuable resources across various industries. CNC Milling