Low carbon steel refers to carbon steel with carbon content less than 0.25%. Alloy steel is based on carbon steel, in the smelting of one or more alloying elements deliberately added to improve its performance, the total alloy content of less than or equal to 5% is known as low alloy steel, the total alloy content of 5 to 10% is known as medium alloy steel, the total alloy content of more than 10% is known as high alloy steel.

Low alloy steel welded structural components usually need to go through the process of molding - welding - post-weld heat treatment and other processes, which requires the steel has good process performance. Process performance includes metal weldability, cutting performance, cold and hot working performance, heat treatment performance, malleability, organization uniformity and stability and large cross-section of the hardenability and so on. In considering the cost of materials should also take into account the material processing, welding, the degree of difficulty of different manufacturing costs.

Low-alloy steel in construction machinery, ships, bridges, high-rise buildings, boilers and pressure vessels, electric power, a variety of vehicle manufacturing has been widely used. This is inseparable from its properties (e.g., plasticity, toughness, welding performance). The uses and properties of some common low alloy steels are shown in the atlas.