Vacuum carburizing heat treatment process
(1) it is easy to control the depth, carbon concentration and concentration gradient (hardness gradient) of the carburized layer.
Heat treatment plant that due to the physical and chemical reaction characteristics of vacuum carburizing process, therefore, according to the technical condition of the parts can be simply calculated or some relation curve to determine the vacuum carburizing heat treatment process parameters. Production practice shows that the special to process the experiment to verify the demand of batch production and modification process parameters calculated, this is important for high precision parts of batch production is very important. The production practice also shows that the consistent carburizing results of each furnace can be obtained as long as the operation is carried out according to the process parameters determined by the process experiment -- good reproducibility.
(2) high surface quality of carburized parts.
Heat treatment plant that due to the vacuum carburizing heat treatment was conducted in vacuum heating and soaking and after carburizing diffusion, so parts don't produce the problem such as decarburization and black organization, the surface is clean. In this way, the cleaning process can be eliminated and it is beneficial to the finishing process after heat treatment.
(3) the vacuum carburizing parts have high mechanical properties.
Heat treatment plant that due to the vacuum carburizing heat treatment parts with high surface quality (no decarburization, oxidation), the characteristics of, therefore, on the state of stress and fatigue strength of surface layer has a favorable effect.
(4) it has a good carburizing effect on parts with blind holes, deep holes and narrow joints. For stainless steel and silicon steel which are difficult to be carburized by gas carburizing heat treatment, the vacuum carburizing method can be used successfully.
(5) thin, thick (up to 7mm) and high carbon concentration carburizing layer can be obtained. The steep or gentle carbon concentration gradient can be obtained by making the cementing period and diffusion period have different coordination.
(6) high temperature carburizing heat treatment can be carried out to shorten the carburizing time.
The heat treatment plant thinks that the vacuum carburizing is developed on the basis of exploring the possibility of high temperature carburizing. High temperature carburizing is possible in vacuum because the structure and component material of modern vacuum carburizing furnace can meet the requirement of high temperature carburizing.
High temperature carburizing heat treatment can significantly shorten the carburizing time. This is because austenite has a higher solubility to carbon at high carburizing temperature, and the carburized gas used can supply the activated carbon atoms sufficiently. It is also because high temperature carburizing can significantly increase the diffusion rate of carbon in steel. In addition, the parts are heated and heated in a vacuum state, which results in degassing and removal of oxides, so as to activate the surface of the parts and accelerate the absorption of carbon atoms.
Under the condition of general gas carburizing, the carburizing furnace cannot withstand high temperature for a long time. Therefore, the high temperature carburizing test with gas carburizing furnace has not been successful for many years.