Carburizing: it is a kind of surface treatment of metal. Most of the carburized parts are low carbon steel or low alloy steel. The specific method is to put the workpiece into the single-phase austenite area with active carburizing medium, which is heated to 900-950 ℃. After holding for enough time, the active carbon atom decomposed from the carburizing medium will penetrate into the surface of the steel piece, so as to obtain high carbon on the surface and keep the original composition in the center 。 Similarly, low-temperature nitriding treatment. This is a common heat treatment process for metal materials. It can make the surface of carburized workpiece obtain high hardness and improve its wear resistance.
It also makes the surface layer of low carbon steel have high hardness and wear resistance after quenching and low temperature tempering, while the central part of the workpiece still maintains the toughness and plasticity of low carbon steel.
The material of carburized workpiece is generally low carbon steel or low carbon alloy steel (carbon content is less than 0.25%). After carburizing, the chemical composition of the surface of the steel can be close to that of the high carbon steel. After carburizing, the workpiece should be quenched to obtain high surface hardness, high wear resistance and fatigue strength, and maintain the strength and toughness of low carbon steel after quenching in the center, so that the workpiece can bear the impact load. Carburizing technology is widely used in aircraft, automobile, tractor and other mechanical parts, such as, shaft, camshaft and so on.
Carburizing process can be traced back to 2000 years ago in China. The first one is carburizing with solid carburizing medium. Liquid and carburizing appeared in the 20th century and are widely used. The United States began to use rotary hearth furnace for gas carburizing in the 1920s. In 1930s, continuous gas carburizing furnace began to be applied in industry. Gas carburizing at high temperature (960-1100 ℃) was developed in 1960s.