Vacuum nitriding furnace technology description

Nitriding is to use vacuum furnace to heat the whole steel and fill a small amount of gas to produce active nitrogen atoms at low pressure, so as to infiltrate and diffuse into the steel to achieve hardening; ion nitriding is the active nitrogen produced by glow discharge. Ion bombardment heats only the surface of the steel part, and chemical reactions occur to produce nuclei for hardening. By infiltrating nitrogen into the box furnace and atmospheric furnace, the hardening density can be achieved and the texture is harder.

When infiltrating into the atmosphere, the vacuum furnace vacuumizes to a higher vacuum degree of 0.133 PA (1 × 10-3 Torr) and raises the workpiece to 530? 560 ℃. At the same time, it is supplied with ammonia which mainly contains active substances. The pressure of the vacuum furnace is controlled at 0.667 PA (5 Torr). After holding for 3 to 5 hours, the inert gas in the furnace is used for rapid cooling.

Through different materials, after this treatment, the hardened layer with penetration depth of 20-80 μ m and hardness of 600-1500hv can be obtained. Vacuum nitriding is called vacuum exhaust nitrocarburizing. It is characterized by activation and purification of metal surface by vacuum technology. In the whole heat treatment process of heating, heat preservation and cooling, impure trace gas will be discharged and sent into the pure compound gas containing active substances, so as to adjust and control the surface phase structure, improve the quality and efficiency. X-ray diffraction analysis shows that the compound layer in the nitrided layer is of single-phase structure and has no other brittle phases (such as Fe3C and Fe3O4), so it has high hardness, good toughness and uniform distribution. The hardness of the “white layer” single-phase epsilon compound layer is related to the composition of the material. The higher the Cr content is, the higher the hardness is. X-ray diffraction analysis shows that the compound layer in the nitrided layer is of single-phase structure and has no other brittle phases (such as Fe3C and Fe3O4), so it has high hardness, good toughness and uniform distribution. The hardness of the “white layer” single-phase epsilon compound layer is related to the composition of the material. The higher the Cr content is, the higher the hardness is. X-ray diffraction analysis shows that the compound layer in the nitrided layer is of single-phase structure and has no other brittle phases (such as Fe3C and Fe3O4), so it has high hardness, good toughness and uniform distribution. The hardness of the “white layer” single-phase epsilon compound layer is related to the composition of the material. The higher the Cr content is, the higher the hardness is.

When Cr content is 13%, the hardness can reach 1200hv; when Cr content is 18%, the hardness can reach 1500hv. When Cr is 25%, the hardness can reach 1700hv. The wear resistance of the single-phase epsilon compound layer without brittle phase is higher than that of the gas nitrocarburizing structure, and it has excellent friction and combustion resistance, thermal adhesion resistance, welding resistance and melt loss resistance. However, the existence of this “white layer” also has disadvantages for some molds and parts. In the early stage of forging, it is easy to cause cracks in the forging die, and pinholes are easily produced in the welding repair process. Another advantage of vacuum nitriding is that by controlling the type and quantity of the compound gas containing active substance fed into the furnace, the structure with almost no compound layer (white layer) but only diffusion layer can be obtained. The reason may be that the vacuum furnace exhausts to 0.133 PA (1 × 10-3 Torr). Another reason is the structure formed by the diffusion of composite gas and active material into steel in a short time. The advantages of this structure are excellent thermal shock resistance and crack resistance.

Therefore, the comprehensive properties of hot working dies, such as high speed steel or 4cr4mosiv (H13) steel, which are tempered at high temperature, have high surface hardness, good wear resistance, good thermal shock resistance, crack resistance and toughness. However, when there is only diffusion layer structure, the die has insufficient bite resistance, welding resistance and melt loss resistance. The structure and performance of the surface layer must be adjusted in the process of surface heat treatment because of the different service conditions and performance requirements of the die or mechanical parts. In addition to the application of vacuum nitriding in the mould, it also has an obvious effect on improving the performance of precision gears and mechanical parts that need wear resistance and corrosion resistance.

Vacuum nitriding furnace