Carburizing is ordered carbon atoms penetrate into the process of the steel surface layer. Also the low carbon steel workpiece having a surface layer of high-carbon steel, and then having a high hardness and wear resistance after quenching and tempering, so that a surface layer of the workpiece, while the central portion of the workpiece still maintain the toughness of the low carbon steel, and plasticity.
    Carburizing the workpiece material is usually low carbon steel or low carbon alloy steel (carbon content less than 0.25%). Carburizing, the chemical composition of the steel surface accessible high-carbon steel. Even after quenching the workpiece after carburizing, to obtain a high surface hardness, high wear resistance and fatigue strength, and to keep the core section of the strength and toughness of low-carbon steel after quenching, so that the workpiece can withstand the impact load. Carburizing process is widely used in aircraft, cars and tractors and other mechanical parts, such as gears, shaft, camshaft.
    Carburizing process in China can be traced back to 2000 years ago. Media first solid carburizing carburizing. Liquid and gas carburizing emerged in the 20th century and has been widely used. The United States began in the 1920s, the drum furnace gas carburizing. 1930s, continuous gas carburizing furnace applications in industry. 60 'high temperature (960 ~ 1100 ℃) the gas carburizing develop. To the 1970s, there has been vacuum carburizing and ion carburizing.
    Principle
    Carbon and other chemical heat treatment, also consists of three basic process.
    ① decomposition
The carburized media decomposition of the active carbon atoms.
    ② adsorption
Activated carbon atoms absorbed by the surface of steel instant to the surface austenite, the austenite carbon content increases.
    ③ proliferation
The surface of the carbon content increases they poor concentration and the carbon content of the core part, the surface of the carbon, however, internal diffusion. The diffusion rate of carbon in the steel depends primarily on the temperature, while the workpiece is permeability related to the element concentration difference inside and outside the content of alloying elements and steel.
    The carburized parts of the material is generally used in low-carbon steel or low-carbon alloy steel (carbon content less than 0.25%). After carburizing, quenching in order to give full play to the beneficial effect of carburization. The microstructure of the surface of the workpiece carburizing high hardness martensite plus retained austenite and a small amount of carbide, the heart organized by the Ministry of toughness and good low-carbon martensite or containing martensite, but should avoid the ferrite. Usually carburized layer depth range of 0.8 to 1.2 mm up to 2 mm or more in depth, the depth of carburization. The surface hardness up to HRC58 ~ 63, the core hardness to HRC30 to 42. After the carburizing and quenching, the workpiece surface generating compressed internal stress, is advantageous to improve the fatigue strength of the workpiece. Carburizing is widely used to improve part strength, impact toughness and wear resistance, in order to extend the service life of the part.
    Classification
    Different carbon media, carburizing can be divided into solid, liquid carburizing carburizing, gas carburizing and carbonitriding.
    Solid carburizing
    Parts buried in a container filled with a solid carburizing agent (main ingredient is charcoal, reminder infiltration agent and sodium carbonate, barium carbonate, etc.), heating, decomposition of the activated carbon at high temperatures by the chemical reaction of the carbon reminder infiltration agent atoms penetrate the surface of the part. Solid carburizing in various furnace is simple, but the quality is not easy to control, long cycle, poor working conditions.


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