What Is Carbon Steel? Grades, Types & Uses

Short answer: Carbon steel is iron alloyed only with carbon (up to ~2.1%) plus small manganese and silicon. Its carbon content sets hardness, strength, and weldability, splitting it into low, medium, and high-carbon classes. This single variable is what makes carbon steel the most produced and versatile engineering metal.

At a Glance

How Carbon Content Defines the Metal

Carbon is the key alloying element. As carbon rises from ~0.05% to ~1.5%, strength and hardness climb while ductility and weldability fall. Below about 0.3% the steel is ‘low-carbon’ and easy to form; around 0.3-0.6% it is ‘medium-carbon’ and machineable; above ~0.6% it is ‘high-carbon’ and very hard but brittle.

The Three Classes

The chart contrasts them. Low-carbon (A36, 1018) builds structures and car bodies. Medium-carbon (1045) makes shafts, gears, and rails. High-carbon becomes springs, blades, and cutting edges. See hot-rolled vs cold-rolled for how processing changes properties.

Common Grades and Standards

Grades are tied to standards: ASTM A36 and A572 in the USA, EN S235/S355 in Europe, JIS SS400 in Japan, and GB Q235 in China are broadly equivalent structural steels. See our standards guide and the ASTM/ASME carbon-steel page for cross-references.

Choosing the Right Class

Match carbon content to the job: low-carbon for welding and forming, medium-carbon for machined strength parts, high-carbon for wear and springs. Tell HXSCO the form and duty and we will recommend the grade and temper.

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