Low Carbon Steel

Low carbon steel contains less than 0.25% carbon and is characterized by low strength, low hardness, and softness, often referred to as "mild steel." It includes the majority of ordinary carbon structural steels and some high-quality carbon structural steels. Most low carbon steels are used for engineering components that do not undergo heat treatment, while some are used for wear-resistant mechanical parts after processes like carburizing.

The microstructure of low carbon steel after annealing consists of ferrite and a small amount of pearlite, resulting in lower strength and hardness but better plasticity and toughness. This makes it suitable for cold forming processes such as curling, bending, and stamping. Low carbon steel has good weldability. However, with very low carbon content, its hardness is also low, leading to poor machinability, which can be improved through quenching treatment.

Low carbon steel is typically rolled into angles, channels, I-beams, pipes, strips, and plates, used to manufacture various structural components, containers, boxes, stoves, agricultural machinery, and different strength requirements in mechanical parts. It is important to note that low carbon steel is generally not heat-treated before use.

Medium Carbon Steel

Medium carbon steel contains 0.25% to 0.60% carbon. It is classified into ordinary carbon structural steel and high-quality carbon structural steel based on product quality. Medium carbon steel has good hot working and machining properties, though its weldability is slightly inferior. It has higher strength and hardness than low carbon steel but lower plasticity and toughness. This type of steel can be used directly as hot-rolled or cold-drawn steel, or it can undergo heat treatment to optimize its properties.

Medium carbon steel generally includes products like killed steel, semi-killed steel, and boiling steel. After quenching and tempering, medium carbon steel exhibits excellent comprehensive mechanical properties, making it the most widely used among various medium strength grades. In addition to construction materials, it is also extensively used for manufacturing various mechanical parts.

High Carbon Steel

High carbon steel, often referred to as tool steel, has a carbon content ranging from 0.60% to 1.70%. Due to its extremely high hardness and strength, it is commonly used to manufacture tools such as hammers and crowbars, as well as cutting tools like drill bits, taps, and reamers. However, high carbon steel has relatively poor weldability. Due to its poor thermal conductivity, significant temperature differences can occur during welding, leading to internal stresses and cracking. Additionally, high carbon steel is sensitive to quenching, and martensite can form in the heat-affected zone, resulting in cold cracking. Therefore, post-weld tempering is necessary to relieve stress, stabilize the microstructure, and prevent cracking, improving the performance of the weld.

Summary

Carbon steel can be classified into high carbon steel, medium carbon steel, and low carbon steel based on carbon content and performance. High carbon steel has a higher carbon content, resulting in greater hardness and strength but also increased brittleness. Low carbon steel, with lower carbon content, offers better plasticity and toughness, making it suitable for manufacturing various mechanical parts.

In practical applications, selecting the appropriate carbon steel material plays a critical role in the performance and longevity of products. For high-demand components, it is essential to choose the right carbon steel based on the stress conditions and working environment to ensure good mechanical properties and durability. Understanding the characteristics and classification standards of these three types of carbon steel is important for rational material selection, optimizing product design, and improving product quality. Overall, high carbon steel, medium carbon steel, and low carbon steel are three common alloy steel materials, each with distinct characteristics and uses. Correctly selecting the suitable carbon steel material is vital for the performance and quality of products in industrial production.