Medium carbon steel is a carbon steel with a carbon content of 0.25% to 0.60%. It includes most high-quality carbon structural steels and some ordinary carbon structural steels. This type of steel is mostly used to make various mechanical parts, and some are used to make engineering structural parts.
Medium carbon steel has good hot processing and cutting performance, but poor welding performance. The strength and hardness are higher than those of low carbon steel, but the plasticity and toughness are lower than those of low carbon steel. Cold rolled and cold drawn materials can be used directly without heat treatment, or they can be used after heat treatment. Medium carbon steel has good comprehensive mechanical properties after quenching and tempering. The highest hardness that can be achieved is about HRC55 (HB538), and σb is 600 to 1100MPa. Therefore, in various uses with medium strength levels, medium carbon steel is most widely used. In addition to being used as a building material, it is also widely used to manufacture various mechanical parts.
Medium carbon steel belongs to hypoeutectoid steel, and its annealed structure is pearlite and ferrite. As the carbon content in steel increases, the amount of pearlite in the structure increases, while the amount of ferrite decreases.
The quenched structure of steel with a carbon content greater than 0.40% is martensite; when the carbon content is greater than 0.40%, in addition to martensite, there is a small amount of residual austenite, and the amount of residual austenite increases with the increase of carbon content in the steel.
High-strength medium-carbon quenched and tempered steel has certain plasticity, toughness and strength, good machinability, and good comprehensive mechanical properties after quenching and tempering. It has poor hardenability and is prone to cracks. The welding performance is not high. It needs to be well preheated before welding and heat treated after welding.
Medium-carbon steel is mainly used to manufacture high-strength moving parts, such as pistons of air compressors and pumps, impellers of steam turbines, shafts, worms, gears of heavy machinery, etc., wear-resistant parts on the surface, crankshafts, machine tool spindles, rollers, bench tools, etc.