Vacuum gas nitriding furnace

Vacuum nitriding furnace has a wide range of applications, including gas and ion nitriding, which needs to be done after vacuuming, so the effect is better. Ordinary nitriding furnace is suitable for small batch workpiece processing, using liquid nitriding, usually salt bath heating nitriding.

Gas nitnitation is to put the workpiece into a sealed space, through ammonia gas, heating to 500-580℃ insulation for several hours to dozens of hours. Ammonia gas above 400℃ will occur the following decomposition reaction: 2NH3=3H2+2N, so there are a large number of active nitrogen atoms in the furnace, active nitrogen atoms [N] are absorbed by the surface of the steel, and spread to the interior, thus forming the nitriding layer.

Nitriding to improve hardness and wear resistance usually nitriding temperature of 500-520℃. The residence time is determined by the thickness of the nitriding layer, generally 0.01mm/h. Therefore, the time required to obtain a thickness of 0.25 — 0.65mm is about 20 — 60h. Increase nitriding temperature, although can accelerate nitriding process, but will make the nitride aggregation, coarsening, so that the parts surface layer hardness is reduced.

For nitriding to improve hardness and wear resistance, alloy steels containing Mo, A, V and other elements should be used during nitriding, such as 38CrMoAlA, 38CrMoAA and other steels. These steels, after passing through nitrogen, contain various alloy nitrides in the nitriding layer, such as AlN, CrN, MoN, VN, etc. These nitrides have high hardness and stability, and are evenly distributed in steel, so that the nitride layer of steel has high hardness and wear resistance. Cr can also improve the hardenability of steel, so that large parts in the quenching and tempering before nitriding can get uniform mechanical properties. Mo can also refine grain and reduce the second temper brittleness of steel. If ordinary carbon steel is used, pure iron nitride is formed in the nitriding layer. When heated to a higher temperature, it is easy to decompose, aggregate and coarsening. Therefore, high hardness and wear resistance cannot be obtained.

Corrosion resistant nitriding temperature is generally between 600-700 ℃, decomposition rate is roughly in the range of 40-70%, residence time from 15 minutes to 4 hours, depth is generally not more than 0.05mm. For corrosion-resistant nitriding steel, any kind of steel can be applied and good results can be obtained.