Introduction to Nitriding Heat Treatment Process

Nitriding is a chemical heat treatment process that involves the infiltration of nitrogen elements into the surface of a workpiece in a medium containing active chlorine, in order to improve the hardness, wear resistance, fatigue strength, and redness of the workpiece. It is called anti wear ammonia infiltration, abbreviated as nitriding (formerly known as nitriding).
The nitriding process is carried out below the phase transformation temperature of steel (450-600 ℃), resulting in smaller deformation of the workpiece. In addition, the hardness of the nitriding layer is high, and the wear resistance and fatigue performance of the workpiece are good. Therefore, this process has been widely used. The most commonly used nitriding steels are 38 CrMoA1, 38 CrAl, etc. Due to the development of nitriding technology, low and medium carbon alloy structural steel containing elements such as Cr, Mo, V, Ti, A1 can be nitrided.
The depth of the nitriding layer is relatively thin (0.2-0.7mm), which can generally be considered as two layers: the outer layer is composed of e phase and (e+Y ') phase, which is not easy to corrode and is called the white bright layer; The inner layer is a phase and (a+Y ') phase (e - Fe2N and solid solution of iron or nitrogen, Y' - Fe4N, a - solid solution of nitrogen in iron) with darker corrosion color and highly dispersed alloy nitrides (AIN, VN, Mo2N, CrN). The nitriding process takes a long time, and it often takes 20-80 hours to obtain a 0.3-0.5mm nitriding layer.
Due to the fact that high hardness can be obtained on the surface of the workpiece after nitriding, there is no need for any treatment. However, before nitriding, it is necessary to perform tempering or normalizing to ensure the performance of the core, and sometimes stress relieving tempering is also necessary. The cooling after nitriding needs to be carried out under the protection of a small amount of NH3 to avoid oxidation of the workpiece.
After nitriding, a surface hardness of HV60-1200 can be obtained, with high wear resistance. This high hardness can be maintained up to 500 ℃ (long-term), and up to 6O0 ℃ (short-term), the loading limit can be increased by 30% to 300%, and the corrosion resistance has also been improved.