PRODUCT CATEGORIES

Vacuum Heat Treatment Furnace

Vacuum Sintering Furnace

Vacuum Brazing Furnace

Commonly Used Methods Of Nitriding In Nitriding Heat Treatment

1.Gas nitriding

The main purpose of gas nitriding is to improve the wear resistance of metals, so it is necessary to obtain high surface hardness. The surface hardness of the workpiece after nitriding can reach HV850～1200. Gas nitriding can adopt general nitriding method (i.e. isothermal nitriding) or multi-stage (two-stage, three-stage) nitriding method. In the former, the nitriding temperature and ammonia decomposition rate remain unchanged throughout the nitriding process. The temperature is generally between 480 and 520°C, the ammonia decomposition rate is 15 to 30%, and the holding time is nearly 80 hours. This process is suitable for parts with shallow infiltration layer, strict distortion requirements, and high hardness requirements, but the processing time is too long. Multi-stage nitriding is to perform nitriding and diffusion at different temperatures, different ammonia decomposition rates, and different holding times during the entire nitriding process. The entire nitriding time can be shortened to nearly 50 hours, and a deeper nitriding layer can be obtained, but the nitriding temperature is higher and the distortion is larger.

There is also gas nitriding for the purpose of anti-corrosion. The nitriding temperature is between 550 and 700 ℃, and the heat preservation is 0.5 to 3 hours. The ammonia decomposition rate is 35 to 70%. The surface layer of the workpiece can obtain a chemically stable compound layer. Prevent the workpiece from being corroded by humid air, superheated steam, gas combustion products, etc.

2. Plasmanitriding

Also known as glow nitriding, it uses the principle of glow discharge. Put the metal workpiece as a cathode into a negative pressure vessel containing a nitrogen medium. After power on, the nitrogen and hydrogen atoms in the medium are ionized to form a plasma zone between the cathode and anode. Under the action of a strong electric field in the plasma zone, the positive ions of nitrogen and hydrogen It bombards the surface of the workpiece at high speed, and the high kinetic energy of the ions is transformed into heat energy, which heats the surface of the workpiece to the required temperature. Due to the bombardment of ions, atomic sputtering occurs on the surface of the workpiece, which is purified. At the same time, nitrogen penetrates into the surface of the workpiece due to adsorption and diffusion.

One of the most important features of ion nitriding is that the structure of the surface compound layer (commonly known as the white layer) and the diffusion layer structure can be controlled by controlling the composition of the nitriding atmosphere, air pressure, electrical parameters, temperature and other factors, so as to meet the service conditions of the parts. And performance requirements.

3. Nitrocarburizing

Also known as soft nitriding or low-temperature carbonitriding, that is, below the iron-nitrogen eutectoid transition temperature, the surface of the workpiece is mainly infiltrated with nitrogen and also infiltrated with carbon. The fine carbides formed after carbon infiltration can promote the diffusion of nitrogen. Accelerate the formation of high-nitrogen compounds. These high-nitrogen compounds in turn can increase the solubility of carbon. The mutual promotion of carbon and nitrogen atoms accelerates the infiltration rate. In addition, carbon can reduce brittleness in nitrides.

Commonly used nitrocarburizing methods include liquid method and gas method, the treatment temperature is 530-570℃, and the holding time is 1 to 3 hours. In the early days, cyanide salt was used for liquid salt baths, and a variety of salt bath formulations appeared later. There are two commonly used: neutral salt with ammonia gas and salt based on urea plus carbonate, but these reaction products are still toxic. The gas media mainly include: endothermic or exothermic gas plus ammonia, urea thermal decomposition gas, and instillation of organic solvents containing carbon and nitrogen, such as formamide and triethanolamine.