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Process

Technology

Low pressure carburizing

Gas nitriding

Low pressure carburizing

Oxidation treatment
Carburizing is a chemical heat treatment process that infiltrates carbon atoms into the metal surface. It can make the metal surface obtain excellent physical and chemical properties, such as improving the surface hardness, wear resistance, corrosion resistance and so on.

There are many types of carburizing processes, which can be divided into solid carburizing, liquid carburizing, atmosphere carburizing and special carburizing according to the difffferent carburizing media used.Solid carburization is the process of burying a workpiece into a solid carburizing agent such as charcoal, or applying a layer of carburizing paste on the surface of the workpiece, and then heating and carburizing it in a furnace; Liquid carburization refers to heating and carburizing the workpiece directly into a salt solution that can decompose active carbon atoms; Atmosphere carburization is carried out in a gas medium, which can be carburized in natural gas, petroleum cracking gas, endothermic and nitrogen based controllable atmospheres, or in decomposition gases injected with liquid carburizing agents; Special carburization is usually carried out under specific physical conditions, such as ion carburization under ion bombardment conditions, electrolytic carburization under electrolytic discharge conditions, fluidized bed carburization under flowing particle state, and low-pressure carburization introduced in this article. Low pressure carburizing is carried out by introducing a small amount of carburizing medium in an environment close to vacuum, so it is also called vacuum carburizing.


Before the emergence of low-pressure carburizing technology, atmosphere carburizing, as the mainstream process of carburizing, has been deeply studied and widely used in all walks of life. Atmosphere carburizing takes carbon monoxide produced by carburizing medium (such as methane, propane, methanol, etc.) as the main carbon source, and then adjusts the carbon potential of atmosphere through enriched gas and air, which can realize the accurate control of carburizing process. Nevertheless, atmosphere carburizing still has many unsatisfactory aspects, such as: intergranular oxidation is easy to appear on the workpiece surface; Large deformation of workpiece after treatment; Poor processing capacity for deep blind hole parts; Carburizing cycle is long, energy consumption is huge and so on.

Therefore, when the new low pressure carburizing technology was published in the 1970s, it received extensive attention from the heat treatment industry and was known as "an epoch-making new technology in the 1970s". Compared with traditional atmosphere carburizing, low pressure carburizing has distinct characteristics and unparalleled advantages.

(1) The carburizing medium used for low-pressure carburizing is saturated (such as propane) or unsaturated hydrocarbons (such as acetylene), the composition does not contain oxygen, and there is no other rich gas and air introduced in the carburizing process, which fundamentally solves the problems of internal oxidation and the formation of nitrogen oxides;

(2) Low pressure carburizing is carried out under the condition of high temperature and low pressure. A large amount of carbon is obtained by rapid cracking of carburizing medium, which can quickly establish a high carbon potential on the workpiece surface and greatly shorten the carburizing cycle;

(3) The low-pressure carburizing process is carried out alternately by strong carburizing and diffusion, which can not only avoid the generation of surface carbides, but also solve the internal carburizing problem of deep blind hole parts. The atmosphere medium used is only 1% of that of the traditional carburizing furnace, which greatly reduces the use of flammable and explosive gases, that is, reduces the gas cost and improves the operation safety.

(4) Low pressure carburizing is heated and carburized in the vacuum furnace, which can be easily combined with high-pressure gas quenching process for oil-free quenching, so as to ensure bright surface, save cleaning cost, and be more environmentally friendly and clean.


Low pressure carburizing technology has been widely used in automotive gears, aviation standard parts, fuel injection systems and other fields. It is gaining more and more attention and favor from heat treatment users with the characteristics of high efficiency, environmental protection, economy, safety and flexibility.