Ion carburizing process parameters

A. Carburizing temperature
Ion carburizing does not require high temperature. The carburizing temperature can be selected in the range of A1~1050 degree C. However, the diffusion of carbon in austenite mainly depends on temperature. When carburizing time remains unchanged, the thickness of carburized layer increases with the increase of temperature. Therefore, high temperature ion carburizing can be carried out for workpieces requiring larger thickness of carburized layer. Low temperature ion carburizing can be carried out for precision parts with complex structure. The common temperature of ion carburizing is 900~960 degreeC.

B. Carburizing time
The depth of plasma carburized layer increases with the extension of carburizing time, and increases obviously in the initial stage of carburizing, which basically conforms to the parabolic law.

C. Ratio of Intensive Permeation to Diffusion Time
High carbon potential is easily established in the surface layer of workpiece during ion carburizing. In order to obtain the ideal distribution of surface carbon concentration and carburizing layer concentration, ion carburizing is usually carried out alternately by intensive carburizing and diffusion. The ratio of strong infiltration to diffusion time (infiltration ratio) has a great influence on the structure and depth of the infiltrated layer. If the diffusion ratio is too high, massive carbides are easily formed in the surface layer, which hinders further inward diffusion. As a result, the total penetration depth decreases, the penetration-expansion ratio is too low, and the surface carbon supply is insufficient, which will also affect the depth and surface structure. Appropriate infiltration ratio (e.g. 2:1 or 1:1) is adopted. Better carbide dispersion in the surface layer can be obtained, and enough penetration rate can be ensured. For deep carburized parts, the proportion of diffusion should be increased appropriately.

D. Carburizing medium
Ion carburizing uses high purity methane or propane (purity mass fraction is higher than 95%, carbon mass fraction is lower than 0.02%). It can be directly carburized into furnace, or the mixture of hydrogen and argon diluted at 1:10 (volume ratio) can be used as carburizing medium.

E. Gas Pressure in Furnace
When carburizing ordinary workpiece, the gas pressure is selected in the range of 133.3-2666Pa. At lower pressure, with the increase of pressure, the carbon concentration on the surface and the depth of the carburized layer increase, and the carbon supply capacity is insufficient if the pressure is too low. When the furnace pressure is 133.3-1333 Pa, the infiltration layer can be uniform. It should be noted that if the pressure is too high, the glow stability will become worse and carbon black and arc discharge will easily occur.

F. Glow discharge voltage and current density
If the workpiece is heated by ion bombardment alone, the discharge voltage is higher and the current density is higher. For equipment with auxiliary heating device, glow discharge only provides energy to accelerate gas decomposition, ionization and surface reaction. Therefore, glow discharge voltage can be less than 500V, current density can be more than 2.5A/cm. In order to have enough excess carbon supply capacity and ensure that glow completely covers the workpiece surface, current density can be selected between 0.2-2.6A/cm.

Learn More : Plasma Nitriding Furnace