Carbon steel is a steel that is created by alloying iron with carbon. The key feature of carbon steel is that carbon is the main alloying element in the steel besides iron. Carbon is primarily added to increase strength and hardness in the material. Carbon steel is the most popular manufacturing metal in the world.

All carbon steels possess good strength, hardness and machinability. They also have a significantly lower cost as a raw material than aluminum or stainless steel (usually 20-25% of the cost per kilogram). On top of this, they are extremely easy to fabricate and weld.

In many manufacturing projects, carbon steel provides all the functionality needed at an affordable price.

In this article, we’ll look at the different types of carbon steel. We’ll look at low, medium and high carbon steels, as well as cold rolled vs hot rolled versions, so you can make the right choice for your manufacturing project.

Key Takeaways

• Carbon steels are manufactured with different carbon contents, and the carbon content has a big impact on the physical properties of the steel.
• Choose low carbon steel for a higher level of ductility and lower cost.
• Choose higher carbon steels for increased hardness and tensile strength.
• Forming processes (hot rolling, cold rolling or galvanizing) strongly influence the physical and mechanical properties of carbon steel.
• Cold rolled steel has an overall better appearance than hot rolled steel and is less vulnerable to surface level corrosion.

Table of Contents

• Introduction
• Key Takeaways
• The Carbon Steel Material Family
• What are the Different Types of Carbon Steel?
• Carbon Steel Types by Forming Process
• Carbon Steel Heat Treating
• Carbon Steel Type Comparison Tables
• How to Select the Right Carbon Steel Grade
• Normal Applications for Carbon Steels

The Carbon Steel Material Family

Carbon steel is a steel alloy that is made primarily of iron and carbon. Small amounts of other elements, including manganese, silicon, sulfur, and phosphorus may also be present, but carbon is always the main element besides iron. The addition of carbon is crucial in carbon steel, adding strength and hardness.

Carbon is abundant and easily available, which is the reason carbon steels are cheap to produce.

Carbon steel is also a versatile material. Carbon steels are produced with varying carbon contents, and the amount of carbon significantly alters the ductility of the steel. Different forming processes are also used, and these affect the physical and mechanical properties of carbon steel as well. All carbon steels have the following characteristics:

• High strength and durability.
• Cost-effectiveness compared to other materials.
• Poor corrosion resistance (can be enhanced through protective coatings or galvanization).
• Good machinability and weldability (weldability decreases with higher carbon content).
• Heat treatability - Carbon steels can be heat-treated to enhance certain properties.
• Easily recycled.

The more carbon is added, the more carbon steel’s hardness as well as its yield and tensile strength increases. At the same time, however, adding more carbon will also decrease ductility. This makes carbon steel a versatile material, offering varying levels of hardness, strength and ductility.

What are the Different Types of Carbon Steel?

Cold rolled steel is primarily classified into grades according to the amount of carbon it contains. As well as this, carbon steels are classified by the processing methods used to form them in manufacture.

In this section, we’ll look at the classifications of carbon steel by grade and by forming processes.

Carbon Steel By Grade

Carbon steel is defined as steel with a carbon content between 0.05 and 2.1% by weight. Within this range, carbon steel comes in different grades according to the carbon content. The more carbon there is, the more the material’s hardness and strength increases. At the same time, as the carbon content increases, the level of ductility decreases.

This means that different grades of carbon steel come with different physical properties, making them suited to very different applications.

• Mild steel (low carbon) - 0.04% – 0.25% carbon
• Medium carbon steel - 0.25% - 0.60% carbon
• High carbon steel - 0.60% - 1.00% carbon
• Ultra-high carbon steel - 1.00% - 2.1% carbon

See the table below for a quick comparison of the qualities and uses of the different carbon steel grades:

Carbon Steel Types by Forming Process

Here are the different types of steel according to the processes applied during production.

Hot Rolled Steel

Hot rolled steel is steel that is processed with roll presses at high temperatures (around 1,700°F or 927°C) to shape it and reduce its thickness.

Processing hot rolled steel is relatively low input, and one of the big advantages of this material is its low cost. As well as this, however, hot rolled steel has good ductility compared to other carbon steels. It also possesses flexibility, which is useful in some applications, such as construction.

The main disadvantages to hot rolled steel are the lower dimensional accuracy, rougher surface finish and reduced formability compared to cold rolled steel.

Mechanical performance and thickness also tends to fluctuate to a greater degree across batches and even within a single sheet of metal because hot rolling is a less precise manufacturing process.

We stock the following hot rolled steels in the China Komacut manufacturing facility:

• #20 Steel: Medium carbon steel with good machinability, often used for shafts, gears and machinery parts.
• Q235: Low carbon steel for construction applications like beams, plates and frameworks.
• Q355: High-strength structural steel, often used in construction, heavy machinery and infrastructure.

We also stock the following grades in our Mexico manufacturing facility for the US and North America:

• A36: A strong, weldable and affordable low carbon steel that is widely used in construction.
• A572: A low carbon steel that is lighter in weight than other mild steels and commonly used in construction and structural applications.

Hot rolled steel has poor resistance to corrosion. It rusts very readily, and it can require extensive pretreatment, such as sandblasting or acid bathing, to remove corrosion prior to surface treatment. Typical surface finishing processes other than hot and cold galvanizing that can be applied to hot rolled steel are powder coating and e-coating.

Cold Rolled Steel

Cold rolled steel is steel that is hot rolled first and then further processed (compressed and rolled) at room temperature.

The additional processing improves the steel’s surface finish, strength and hardness. As well as this, it also improves its dimensional accuracy, which makes cold rolled steel suitable for precision engineering. Cold rolled steel is also easier to form than hot rolled steel. Mechanical performance and sheet thickness also fluctuate much less across batches.

One big drawback to cold rolled steel is a slightly increased cost. As well as this, cold rolled steel has less ductility and flexibility than hot rolled steel, which makes it less suitable in certain applications. This can also result in cracking during stamping, particularly for thicker parts.

Galvanized Steel

Galvanized steel is steel that is given a zinc coating to protect it from corrosion, either by an electrical plating process (cold galvanizing) or by a physical coating process (hot galvanizing).

Cold galvanized steel is uniform in appearance, with a matte grey that is distinct from non-treated steels. It performs well in corrosive environments and is often used for outdoor and maritime applications. Other advantages are low maintenance needs, cost effectiveness, cleanability and ability to be top-coated with paint, powder coating or e-coating.

The big drawback with hot galvanized steel is that it is more difficult to conduct secondary processing. Powder coating and paint, for example, have poor or reduced adhesion, which result in problems like cracking and peeling.

The galvanized layer of galvanized steel can produce poisonous fumes when welded, which is a significant health hazard.

At Komacut, we stock the following galvanized steel:

• SGCC: A steel used in applications including roofing, siding and household appliances.

Zinc coating provides a protective barrier as well as galvanic protection. Even if the galvanized layer is damaged by cuts or bends, the surrounding galvanized area will act as a sacrificial anode and prevent further corrosion.

Carbon Steel Heat Treating

Carbon steels can be heat treated after manufacturing and processing to further enhance physical properties such as strength or hardness. Higher carbon steels respond better to heat treatment than low carbon steels.

Here are some common heat treating processes:

• Annealing
• Normalizing
• Hardening
• Tempering
• Case hardening (carburizing)
• Stress relieving
• Spheroidizing

Carbon Steel Type Comparison Tables

The following table provides technical information about the strength, hardness and standard compliances of the carbon steels covered in this article:

Note: You can refer to GB/T codes for carbon steel, JIS G3141-2009, JIS-G3302 or Q/BQB 310-2009 for detailed information about the carbon steels covered in this article.

The following table provides information about the application suitability of the carbon steels discussed in this article:

How to Select the Right Carbon Steel Grade

In this section, we’ll run through the decision-making process for choosing the right carbon steel and look at some common uses for different carbon steels.

The Decision Making Process

The most important factors that determine any choice of material, including carbon steel, are:

• 1. How it will be used (application)
• 2. How it will be fabricated (processing)
• 3. Project cost sensitivity

Carbon steels are all relatively affordable compared to other metals and the price differences between different types of carbon steel aren’t large. So, while budget is a consideration with carbon steel, matching the steel type to application and processing requirements is normally more important than cost.

As a general point, aim to choose a carbon steel that meets your application requirements while being readily available, affordable and easy to fabricate.

Requirements in Application

First of all, you should choose a carbon steel that matches your component’s in-use performance requirements.

Tensile strength, yield strength and hardness are crucial here. You should accurately ascertain the mechanical load conditions your component will be put through in use and choose a carbon steel that has been certified as matching them. Ideally, your components will have been tested to ascertain the minimum requirements. In this case, you can refer to this information. Alternatively, you can conduct basic stress and failure mode analysis in most 3D modeling software.

You can refer to the table in the above section for technical strength and hardness information for the steels covered in this article. You can also find in-depth information in the relevant standards:

• GB/T codes: hot rolled steels
• JIS G3141-2009: SPCC cold rolled steel
• Q/BQB 310-2009: SAPH440 cold rolled steel
• JIS-G3302: SGCC cold galvanized steel

Operating Environment

Your component’s operating environment is a crucial consideration. The most important things to consider are extreme temperatures and corrosiveness.

• In a less corrosive environment, you can choose a galvanized steel that will have sufficient corrosion resistance to extend service life without expensive secondary processing. For very corrosive environments, cold rolled or hot rolled steels that have been finished with hot galvanization (can cause deformation), or powder coating can resist extensive exposure to water and salt (sometimes in excess of 2,000 hours of salt spray testing).
• If you plan on using a component in extreme temperatures, carbon steel might be a poor choice of material.
  • Carbon steels are prone to strength reduction, deformation and oxidation in high temperature extremes.
  • They can also become brittle and less tough in cold temperature extremes.

Processing Requirements

The next thing to consider is what processing you will need your metal to undergo during fabrication.

• Look at every step your component will go through in the manufacturing process and ensure that your choice of steel is compatible. For example, galvanized steel can produce poisonous fumes when welded, so it is a poor choice for weldments.
• You can also aim to choose a carbon steel that is as easy as possible to manufacture. Having an easy to fabricate metal may reduce manufacturing cost and time.

If you are limited in your choice of steels, it may be possible to alter the manufacturing process or redesign a component to accommodate the use of a certain type of carbon steel.

Remember to include finishing processes in your fabrication schedule.

Budget Constraints

The last consideration to make is cost. As we already said, all carbon steels are relatively affordable, and the price difference between different types usually isn’t large. As a result, cost is less likely to be prohibitive than with other materials.

While that is true, there are cost differences, and cost may turn out to be a deciding factor in your selection.

As a basic rule, prices increase by 10-20% between each type from hot rolled steel to cold galvanized steel. For example:

• Hot rolled steel: Base price
• Cold rolled steel: 10-20% increase
• Cold galvanized steel: Another 10-20% increase

On the Komacut platform, you can find out the cost of different carbon steels when you get a quote. Upload your complete 3D drawings, which will include material type, and we’ll give you an instant quotation, design for manufacturing feedback and part analysis.

Normal Applications for Carbon Steels

Here are some of the common applications for the carbon steel types covered in this article:

• High strength construction, machinery and infrastructure components, transportation and gas pipelines: Q345 and Q355 hot rolled (Q355 has slightly higher strength)
• Machinery parts such as gear sprockets or axles, bolts and fasteners, frames and low-pressure pipes: #20 hot rolled
• Lighter duty construction applications such as beams and plates, guard rails and machine plates: Q235 hot rolled steel
• Components with tight tolerances: Cold rolled steel
• Smoothly finished, formed components, such as kitchen appliances, car body panels, electrical equipment and metal furniture: SPCC cold rolled
• High strength formed and welded components such as vehicle structures, wheels, structural frames, railway and transportation components: SAPH440 cold rolled
• Components in corrosive environments, such as roofing and wall cladding, vehicle frames, electrical enclosures and outdoor furniture: Cold galvanized SGCC