What Is Medium Carbon Steel?

Medium carbon steel is carbon steel with a carbon content of 0.25% to 0.65%. It includes most high-quality carbon structural steels and a part of 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.

According to the chemical composition of steel, it can be divided into two categories: carbon steel and alloy steel. Carbon steel is further divided into: low carbon steel with less than 0.25% carbon content; medium carbon steel with 0.25% to 0.6% carbon content; high carbon steel with carbon content greater than 0.6%; medium carbon steel Good hot working and cutting performance, poor welding performance. Strength and hardness ratio

The final heat treatment methods of medium carbon steel include quenching and tempering, low temperature tempering after quenching, low temperature tempering after high frequency quenching, isothermal quenching and medium temperature tempering after quenching.

(1) Tempering. The organization is tempered sorbite. This structure has good comprehensive mechanical properties, high strength, good plasticity and toughness. The quenched and tempered steel must have good hardenability to ensure uniform structure and performance on the entire section of the quenched and tempered part. Compared with alloy steel, carbon steel has poor hardenability, so it is only suitable for quenching and tempering of medium carbon steel parts with small cross-section dimensions.

(2) Tempering at low temperature after quenching. The structure is tempered martensite, which has high strength and appropriate ductility and toughness.

(3) Low temperature tempering after high frequency quenching. The structure of the high-frequency quenched layer is extremely fine hidden needle martensite. After low temperature tempering, tempered martensite is obtained. After this treatment, a similar effect to that of carburizing treatment can be obtained. Quenching or normalizing is generally performed before high-frequency quenching. Therefore, after high frequency quenching and tempering, the core of the part has high strength, good plasticity and toughness, and its surface layer has high hardness and good wear resistance. In addition, compressive stress is generated on the surface of high-frequency quenched parts, which has a high fatigue limit and a long service life.

(4) Isothermal quenching. The structure is bainite, which has high strength and good plasticity and toughness.

(5) Tempering at moderate temperature after quenching. The organization is tempered sorbite.

High strength medium carbon quenched and tempered steel has certain plasticity, toughness and strength, good machinability, good comprehensive mechanical properties after quenched and tempered, poor hardenability, easy to produce cracks, low welding performance, before welding It needs good preheating and heat treatment after welding.

Medium carbon steel is mainly used to manufacture high-strength moving parts, such as air compressors, pump pistons, impellers of steam turbines, heavy machinery shafts, worms, gears, etc., wear-resistant surface parts, crankshafts, machine tools Spindles, rollers, fitter tools and more. ^[2]

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