I. Basic Definition and Composition
Carbon steel is mainly composed of iron (Fe) and carbon (C), and the carbon content is the key factor determining its performance. Besides carbon, it also contains a small amount of impurity elements such as silicon (Si), manganese (Mn), sulfur (S) and phosphorus (P). Silicon and manganese can improve the strength and toughness of steel to a certain extent, while sulfur and phosphorus are usually harmful elements and will reduce some properties of steel. For example, sulfur will cause hot brittleness and phosphorus will cause cold brittleness.

II. Characteristics of Different Types of Carbon Steel

Low - carbon steel (carbon content ≤ 0.25%)
It has good plasticity and toughness, and is easy to be formed by punching, welding and other processing operations.
Its strength is relatively low, but it can be improved by cold working or heat treatment (such as quenching + tempering).
It is often used to manufacture some structural parts with high requirements for shape and small stress, such as car body shells, some simple containers, etc.

Medium - carbon steel (carbon content 0.25% - 0.6%)
Its strength and hardness are higher than those of low - carbon steel, and at the same time, it still maintains certain plasticity and toughness.
Good comprehensive mechanical properties can be obtained through quenching and high - temperature tempering treatment.
It is widely used in the field of machinery manufacturing. For example, it is used to manufacture various shafts, gears and other parts.

High - carbon steel (carbon content > 0.6%)
It has high hardness and wear resistance, but poor plasticity and toughness.
After appropriate heat treatment, it can obtain very high hardness, and is often used to manufacture tools and parts that require high hardness and wear resistance, such as cutting tools, measuring tools, springs, etc.