Carbon steel is one of the most widely used materials in construction, manufacturing, and machinery due to its strength and affordability. However, one common concern among users is whether carbon steel rusts—and if so, how to prevent it. In this article, we’ll explore what carbon steel is, its types, why it rusts, and the best methods to protect and maintain it for long-term use.
What is Carbon Steel
Carbon steel has two meanings. Technically, steel must meet certain criteria to qualify as carbon steel, as defined by the American Iron and Steel Institute (AISI). There is no minimum requirement for the addition of elements such as chromium, cobalt, niobium, molybdenum, nickel, titanium, tungsten, vanadium or zirconium for alloying effect. It meets the requirements when the minimum copper content does not exceed 0.40%, and the maximum content of elements such as manganese (1.65%), silicon (0.60%), and copper (0.60%) do not exceed the specified values.
In essence, true carbon steel consists mainly of iron and carbon, with almost no alloying elements, although the carbon content can vary and there are some acceptable alloying materials.
In addition to the precise technical definition, the term “carbon steel” is also used to refer to a large group of alloy steels that are not stainless steels. Unlike carbon steels, low-alloy steels can contain small amounts of various alloying elements, which allows them to be tailored for a wide variety of applications and highlights the significant difference between stainless steel and other steel grades.
Types of Carbon Steel
Low carbon steel (0.05% – 0.25% carbon): It has good plasticity and toughness, but relatively low strength. It is softer and easier to process, making it ideal for applications that require good weldability, such as building structures and car bodies.
Medium carbon steel (0.25% – 0.60% carbon): This carbon steel has good overall properties, but poor weldability. It has high strength and hardness, making it suitable for manufacturing mechanical parts and structural components such as bearings and gears.
High carbon steel (more than 0.60% carbon): High carbon steel is brittle and difficult to weld. However, it has excellent hardness and wear resistance, so it is often used to produce high-strength parts such as knives, tools, and springs.
Does Carbon Steel Rust
All carbon steel, whether it is low carbon steel, medium carbon steel or high carbon steel, will rust. When the iron in carbon steel reacts with oxygen, water or moisture in the air, iron oxide, commonly known as rust, is formed.
The speed at which carbon steel rusts depends on the amount of water, oxygen and other environmental factors it is exposed to. However, carbon steel can be protected from rust by coating or other treatments, such as painting or galvanizing. We will discuss this in more detail later in this article.
Why Does Carbon Steel Rust
Carbon steel is primarily made of iron. When iron comes into contact with water and oxygen, it oxidizes. Think of it like a chemical formula, where iron interacts with oxygen and water to create rust. This process is similar to how materials weather over time in the natural environment. The chemical equation 4FE + 3O2 + 6H2O = 4Fe(OH)3 shows the reaction that creates iron oxide (rust).
How To Keep Carbon Steel From Rusting
Clean and dry carbon steel: Before storing or using carbon steel, make sure it is clean and dry. Wipe the surface with a clean, dry cloth to remove dirt and debris.
Apply a protective coating: Applying a protective coating such as a rust inhibitor or oil can help. Be sure to apply an even, thin layer and allow the coating to dry completely before using or storing the steel.
Store in a dry place: To prevent rust, store carbon steel in a dry, low-humidity area. Avoid storing in humid areas, as this will accelerate rust.
Use a dehumidifier: In areas with high humidity, use a dehumidifier to reduce the amount of moisture in the air and prevent carbon steel from rusting.
Galvanizing: Plating a layer of zinc on the surface of carbon steel is an effective way to prevent rust because zinc has better chemical properties than iron. It can form a protective zinc oxide film in the air, preventing iron from oxidizing and rusting.
Avoid contact with water: Since water is one of the main causes of rust, avoid contact with carbon steel as much as possible. If carbon steel gets wet, dry it thoroughly as soon as possible.
How To Remove Rust From Carbon Steel
Using a wire brush or sandpaper: Gently rub the carbon steel surface with a wire brush or sandpaper until the rust is removed.
Using vinegar or lemon juice: Pour vinegar or lemon juice on the carbon steel and gently rub the surface with a sponge or brush. The acid contained in these liquids will help remove the rust. When you are finished, rinse with water and wipe the surface dry.
Using chemical rust removers: There are many chemical rust removers available on the market. Read the product instructions carefully when using them and strictly follow all safety precautions.
Using electrolytic rust removal: This is a very effective method, but it requires special equipment and skills. Place a negative electrode and an anode on the surface of the carbon steel and connect them to a power source. The current will break down the rust. If you do not have relevant experience, seek professional help.
Remember that removing rust from carbon steel requires care and patience. After removing the rust, take measures to protect the carbon steel to prevent rust from reappearing.
Conclusion
Although carbon steel is a highly versatile and cost-effective material, it is prone to rusting due to its iron content. Understanding the rusting process and how to prevent it can significantly extend the lifespan of carbon steel products. Whether through coatings, proper storage, or regular maintenance, protecting carbon steel from rust is essential for ensuring both performance and durability in demanding environments.
