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Ion Nitriding and Gas Nitriding

Gas Nitriding

Gas nitriding has low efficiency due to the decomposition of NH3 for nitriding, so it is generally fixed to select steels suitable for nitriding, such as containing Al, Cr, Mo and other nitriding elements, otherwise the nitriding is almost impossible. Generally, JIS, SACM1, new JIS, SACM645 and SKD61 are used for strengthening and toughening treatment, also known as quenching and tempering. Because A, Cr, Mo, etc. are all elements that increase the transformation point temperature, the quenching temperature is high, and the tempering temperature is also relatively common. High alloy steel is used. Tempering brittleness occurs during long-term heating at the nitriding temperature, so it is quenched and tempered in advance to strengthen and toughen. NH3 gas nitriding, because the surface is rough, hard and brittle for a long time, it is not easy to grind, and it is not economical for a long time. It is used for the nitriding of the feeding tube and screw rod of the plastic injection molding machine.

Ion Nitriding

The degree of ion nitriding treatment can start from 350°C. The treatment time can be several minutes or even a long time considering the material and its related mechanical properties. This method is the same as the previous nitriding treatment using thermal decomposition The method is different. Because this method uses high ion energy, materials such as stainless steel, titanium, cobalt, etc., which were considered difficult to handle in the past, can also be easily applied with excellent surface hardening.

Ion nitriding and gas nitriding can’t directly say which one is better, each has its own advantages and disadvantages, but I personally think that ion nitriding is better for parts with high requirements. Ion nitriding not only has a strong nitriding ability, but also activates the surface of the workpiece and produces defects that accelerate absorption and diffusion. Therefore, ion nitriding can greatly shorten the nitriding time, especially when shallow nitriding is more prominent. For example, when the depth of the nitriding layer is 0.3~0.5mm, the time of ion nitriding is only 1/3~1/5 of the time of ordinary gas nitriding. Very small deformation. Because ion nitriding is carried out in vacuum, a non-oxidized processing surface can be obtained without damaging the surface finish of the workpiece to be processed, and it can be processed at low temperature (nitriding can be performed from 380°C) ), the deformation of the processed workpiece is extremely small, which can be used to solve many problems that cannot be solved by conventional heat treatment, and can meet the requirements of high-precision parts. After processing, there is no need for mechanical processing, which is suitable for the processing of finished parts.

The surface of the workpiece treated by gas nitriding and salt bath nitriding usually has a thicker (above 20um) compound layer. This is due to the inhomogeneous mixture layer composed of e+γ’ two phases, and the inner layer is a diffusion layer. Therefore, three-phase micro-stress is generated in the compound. If an external force is applied in this direction, micro-cracks will be generated. This crack gradually expands and the entire compound layer is peeled off. The compound layer of chromium-containing and aluminized nitrided steel is very brittle. , After gas nitriding, it must be ground off before it can be used. The glow ion nitriding can be achieved by controlling the ratio of nitrogen to carbon content in the atmosphere, or the ratio of nitrogen to hydrogen, to obtain 5-30um less brittle epsilon phase single phase layer or 0-8um thick tough γ′ phase The single-phase layer can also obtain a compound-free layer with better toughness and a permeated layer with only a diffusion layer, so that it can be used directly without grinding.