Nitrogen not only plays an important role in the production of Si3N4 Silicon Nitride ceramics and H-BN Hexagonal Boron Nitride ceramics, but also in the powder metallurgy industry. Nitrogen-based atmosphere is an energy-saving variable protective gas atmosphere developed with the development of powder metallurgy technology and metal heat treatment technology. The nitrogen content of nitrogen-based atmosphere gas is generally between 75%-95%, and the atmospheric dew point is below -40 degree C. In a controlled atmosphere, nitrogen is usually used as a dilute protective gas. Injecting a certain amount of nitrogen can reduce the consumption of raw material gas and the formation of surface carbon black, and increase the decomposition rate of enriched gas in the furnace. The nitrogen-based gas atmosphere system does not require a traditional energy-consuming atmosphere gas generator, and can control different gas atmospheres required by different parts of the same sintering furnace. The nitrogen-based gas atmosphere system abandons the previous complicated consideration of balancing the relationship between atmosphere gas composition and furnace function, and has great flexibility and practicability.
1. Sintering protection
Adopt nitrogen-based atmosphere for sintering, making the surface oxidation degree of the workpiece easier to control. During sintering, the carbon content of the surface and center of the sintered part depends on the sintering gas atmosphere. Combining the zoned gas atmosphere with the appropriate temperature and time can achieve the goal of high efficiency and economy at every stage of the sintering process.
2. Quench protection
After the quenching furnace has been working continuously for about a week, the carbon deposits need to be burned in the quenching furnace. If the temperature of the charcoal burning furnace exceeds 960 degree C, nitrogen must be immediately introduced for deoxidation and flameout protection to avoid accidents.
3. Purge
In the process of carburizing and nitriding, nitrogen is commonly used to purge and exhaust the furnace, the air curtain of the furnace door is sealed, and the anti-oxidation cooling after carburizing is used. The purity of nitrogen is usually above 99.5%. At the same time, the infiltration rate of nitrogen-based atmosphere nitrocarburizing is faster than that of endothermic or exothermic nitrocarburizing, and the wear resistance, hardness and corrosion resistance of the infiltration layer are not weaker than traditional processes.
4. Other
The protective atmosphere gas used in the iron fine powder reduction process is usually pure nitrogen and hydrogen plus nitrogen. Nitrogen is used to blow the furnace, hydrogen nitrogen is used to reduce iron powder. Generally, the purity of nitrogen is above 99.99%.
In addition, in the discharge of magnetic materials, high-purity nitrogen has been widely used as a protective gas to prevent the explosion of hydrogen and air. Generally, the purity of nitrogen used is above 99.9995%, the dew point of nitrogen at normal pressure is about -60 degree C, and the hydrogen content has low hydrogen requirements, generally below 5×10-6.