CNC Machining: The Difference Between Cast Iron and Steel(6061 vs 7075 Gloria)

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When it comes to understanding the nuances of CNC machining, one of the most crucial aspects is selecting the right material. Two commonly used materials are cast iron and steel. While they might seem similar at a glance, there are several key differences that can affect the outcome of your project. In this article, we will dive into the dissimilarities between cast iron and steel.

The Distinctions: Cast Iron vs. Steel

1. Composition:
Cast Iron: Cast iron is an alloy made primarily from iron, carbon, and silicon. It typically contains 2-4% carbon and up to 3% silicon.
Steel: Steel is an alloy composed mainly of iron and carbon, with additional elements such as manganese, chromium, or nickel for added strength and durability. The carbon content in steel ranges from 0.2% to 2%.

2. Strength and Hardness:
Cast Iron: Cast iron is known for its high hardness, making it ideal for applications requiring strength and wear resistance. The graphite flakes present in cast iron act as lubricants, thereby reducing friction and allowing easier machining.
Steel: Steel offers exceptional tensile strength and hardness, which makes it suitable for applications where strength is paramount. Unlike cast iron, it does not contain graphite flakes but can be hardened further through heat treatment processes like quenching and tempering.

3. Machinability:
Cast Iron: Due to its graphite flakes, cast iron is inherently more machinable than steel. It produces shorter chips during machining and requires less power consumption, resulting in extended tool life. However, it can pose challenges due to its brittleness.
Steel: While often considered harder to machine compared to cast iron, steel's machinability largely depends on its specific grade and composition. High-speed steel (HSS) cutting tools need to be utilized when working with steel to ensure efficient machining.

4. Thermal Conductivity:
Cast Iron: Cast iron has excellent thermal conductivity, meaning it can absorb and transfer heat quickly. This property is beneficial for applications that require rapid cooling or even distribution of heat.
Steel: Steel generally has lower thermal conductivity compared to cast iron. However, specific grades of steel, such as alloys with copper or aluminum, can exhibit higher thermal conductivity.

5. Rust Resistance:
Cast Iron: Cast iron is susceptible to rust and corrosion when exposed to atmospheric moisture. It requires coatings or treatments, such as painting or galvanization, to enhance its resistance against corrosion.
Steel: Steel, particularly stainless steel, exhibits greater corrosion resistance due to the presence of chromium in its composition. Stainless steel contains at least 10% chromium, which forms a passive layer on the surface, protecting it from oxidation and corrosion.


In summary, while both cast iron and steel are commonly used materials in CNC machining, each has distinct characteristics that make them suitable for different applications. Cast iron provides exceptional strength, hardness, and machinability along with high thermal conductivity but lacks natural corrosion resistance. On the other hand, steel offers varied strengths, excellent machinability (depending on grade), better rust resistance (especially stainless steel), and can be further hardened through heat treatment processes. Therefore, careful consideration must be given to material selection, taking into account the specific requirements of your project.

By understanding the differences between cast iron and steel, you can confidently choose the most appropriate material for your CNC machining needs, ensuring optimal performance and longevity of your end product. CNC Milling