Complete Guide to Carbon Steel Grades

Whether you work in the automotive or general appliance industry, steel remains an integral part in many applications. The most common type of steel used is carbon steel due to its high strength and excellent durability. But have you ever wondered why some steel feels softer than others? Well, the difference lies in their varying grades and composition. To help you understand this, we are going to discuss carbon steel grades in detail. So let’s start!

Classification of Carbon Steel by Carbon Content

The carbon steel market size is quickly growing and is expected to hit USD 1,370.43 billion by 2030. Here’s an overview of the different types of carbon steel based on their carbon content.(. For a deeper understanding, see our Comprehensive Guide on Carbon in Carbon Steel):

High Carbon Steel

High-carbon steel refers to any steel that has a carbon content of over 0.6% but not more than 1.5%. It’s also known as carbon tool steel or M2 and is known for its incredible corrosion resistance and improved hardness.

Compared to traditional steel, which absorbs carbon at high temperatures and releases it after cooling, the manufacturing of high-carbon steel is different. In this, manufacturers use quenching to prevent the steel from letting go of the carbon as it cools.

The cooling temperature is increased from 200°C to 1000°C per minute, ensuring the carbon doesn’t have enough time to escape the lattice structure. Other elements present in high-carbon steel include manganese (0.30% to 0.90%) and silicon.

Medium Carbon Steel

It has a carbon content ranging from 0.30% to 0.60% and a manganese content of around 0.10% to 3.0%. The low carbon content makes it less brittle than high-carbon steel, yet it retains high strength.

When we look at the manufacturing of medium carbon steel, it’s pretty simple. First, you need to mine iron ore, which is then melted into pig iron in a blast furnace.

Controlled amounts of carbon and other alloying elements are added to it to achieve the desired composition. You’ll commonly see them in the form of bars, wires, and even steel sheets.

Low Carbon Steel

Low-carbon steel actually has a very low quantity of carbon in it, typically within the range of 0.05% to 0.32%. This means it has the lowest strength and is also more malleable than high-carbon steel.

However, it’s also cost-effective as it requires less carbon and other alloying elements. The manufacturing of low-carbon steel is quite similar to that of medium-carbon steel.

Raw materials and iron ore are melted, and carbon monoxide gas is often introduced, which reduces the iron ore to liquid steel. Overall, carbon content is carefully controlled to ensure a low quantity.

Key Carbon Steel Grades and Composition Tables

Now that you are aware of the core classification of carbon steel, let’s look at the different carbon steel grades:

Properties of Different Carbon Steel Grades

Here’s an overview of the key properties of different carbon steel grades, including  mechanical characteristics, fabrication, and environmental durability:

Mechanical and Fatigue Properties Comparison

As far as the mechanical and fatigue properties of common carbon steel grades are concerned, you’ll need to pay attention to tensile strength, yield strength, and elongation.

Elongation

• A36: 23% in 50 mm
• 1018: 15% in 50 mm
• 1045: 16.0% in 50 mm
• 1095: 10% in 50 mm

Tensile Strength

• A36: 400 MPa
• 1018: 440 MPa
• 1045: 500 to 700 MPa
• 1095: 665 MPa

Yield Strength

• A36: 220 MPa
• 1018: 370 MPa
• 1045: 310 to 420 MPa
• 1095: 380 MPa

Fabrication & Heat Treatment Guide

Low-carbon steel grades, such as 1018 and A36, are easier to weld. But other grades like 1045 and 1095 have high carbon content and are prone to cracking. They need heat treatment such as:

• Annealing: Annealing is a heat treatment that reduces the hardness of carbon steel grades and makes them more ductile. The process typically involves heating the steel to a specific high temperature, holding it there, and then slowly cooling it down. This allows the formation of grains and relieves internal stresses.
• Quenching and Tampering: Quenching and tampering are two sequential heat processes that enhance the mechanical properties of carbon steel grades. In quenching, steel is rapidly cooled from a high temperature to prevent the formation of a soft and stable microstructure. Next comes tampering, which involves heating the steel at low temperatures and allowing it to cool slowly to achieve a lower hardness.

Environmental Durability & Corrosion Prevention

It may surprise you, but carbon steel is more prone to corrosion in the presence of moisture and oxygen. This is primarily because of their high iron content and little to no presence of chromium. However, to enhance the corrosion resistance of carbon steel grades, here are a few techniques:

• Galvanization: Galvanization is a suitable approach, as it involves coating steel with zinc, which acts as a sacrificial anode, corroding before the steel.
• Protective Coatings: Applying a barrier like oil, paint, or an electroplating between the steel and the environment is a good solution.

Application Guide by Grade

The applications of different carbon steel grades include:

• A36: Used in construction, infrastructure, and heavy equipment manufacturing. While A36 is a carbon steel, it also falls under certain structural steel grades, making it suitable for bridges, buildings, and other load-bearing structures.
• 1018: Machine components like tool bodies, jigs, and fixtures, as well as general fabrication, including doors and furniture frames.
• 1045: Cutting tools like dies and knives, automotive, and construction.
• 1095: Springs such as automotive leaf springs, anti-roll bars, high-stress flat springs, and cutting tools.