What Is Carbon Steel and How Is It Classified?

Introduction

Carbon steel is one of the most widely used types of steel in the world. From construction and automotive manufacturing to pipelines and kitchenware, its strength, durability, and cost-effectiveness make it an essential material across industries.

But not all carbon steels are the same. Understanding what carbon steel is and how it’s classified helps engineers, fabricators, and buyers choose the right grade for their specific application. In this blog, we’ll explore:

• What carbon steel is

• How it differs from other steels

• The main classification categories

• Applications by type

What Is Carbon Steel?

Carbon steel is a type of steel in which carbon is the main alloying element, typically making up 0.05% to 2.0% of the material’s composition.

Unlike stainless steel, carbon steel contains no significant amount of chromium, nickel, or other corrosion-resistant elements, which means it’s more prone to rust but also more affordable and easier to work with in many industrial applications.

Key Properties:

• High tensile strength

• Excellent machinability (especially in low-carbon types)

• Good weldability (varies by carbon content)

• Cost-effective for mass production

• Heat treatable (especially medium and high carbon types)

How Is Carbon Steel Made?

Carbon steel is produced by removing impurities from molten iron and adding controlled amounts of carbon and other trace elements. The main manufacturing processes include:

• Basic Oxygen Furnace (BOF) – High-volume production

• Electric Arc Furnace (EAF) – Used for recycling scrap steel

• Hot and Cold Rolling – To shape the steel into sheets, pipes, or bars

Classification of Carbon Steel

Carbon steels are generally classified based on their carbon content. The carbon percentage greatly influences the mechanical properties such as hardness, ductility, and strength.

1. Low Carbon Steel (Mild Steel)

• Carbon Content: 0.05% – 0.25%

• Features: Soft, ductile, easily weldable

• Common Grades: ASTM A36, 1018, 1020

• Applications: Structural beams, sheet metal, car bodies, pipes

2. Medium Carbon Steel

• Carbon Content: 0.25% – 0.60%

• Features: Higher strength and hardness, less ductile, heat-treatable

• Common Grades: 1045, 1050

• Applications: Shafts, gears, axles, machinery components

3. High Carbon Steel

• Carbon Content: 0.60% – 1.0%

• Features: Very hard and wear-resistant, brittle if not properly heat-treated

• Common Grades: 1095, 1084

• Applications: Springs, blades, cutting tools, high-strength wires

4. Ultra High Carbon Steel (Rare)

• Carbon Content: 1.0% – 2.0%

• Features: Extremely hard and brittle

• Applications: Specialized tools and knives, some exotic industrial parts

Comparison Table of Carbon Steel Types

Other Ways to Classify Carbon Steel

Aside from carbon content, carbon steel can also be classified based on:

1. Form and Shape

• Sheets and coils

• Pipes and tubes

• Bars and rods

2. Surface Finish

• Black (hot-rolled)

• Pickled and oiled

• Galvanized

3. Production Method

• Hot-rolled vs. Cold-rolled

• Seamless vs. Welded (for pipes)