Surface nitriding treatment process of stainless steel plates

Stainless steel plates are used in a wide range of applications, and surface modification of the plates is a key method that is low-cost and can significantly enhance the surface hardness, wear resistance and other properties of the material.

Because there will be an oxide film on the surface of the stainless steel plate, it is very difficult to perform ordinary gas nitriding. Although the stainless steel material after the surface activation treatment of the plate can be gas nitrided, the process is complicated and difficult to control, so the industry has also begun to use some new nitriding process technologies. Ion nitriding technology is the most commonly used one.

Conventional ion nitriding is carried out in a mixed atmosphere of N2 and H2 or NH3 at a temperature of 500 to 560°C. Because ion nitriding can directly remove the passivation film on the surface of stainless steel, and can easily achieve local nitriding and control the nitrogen potential, it can show obvious superior performance in strengthening the surface of stainless steel.

The results of ion nitriding experiments on some martensitic stainless steels show that ion nitriding can significantly generate a nitriding layer of a certain thickness on the surface of the stainless steel plate without the need for pretreatment to remove the oxide film. The hardness and wear resistance of stainless steel after nitriding will be significantly enhanced. However, conventional ion nitriding easily forms CrN on the surface of stainless steel, resulting in chromium deficiency in the stainless steel matrix, thereby reducing the corrosion resistance of the stainless steel material. Therefore, even if the surface hardness, wear resistance, scratch resistance, and gluing resistance of stainless steel are greatly enhanced after ion nitriding treatment, if not handled properly, it is extremely easy to cause surface peeling, uneven thickness of the hardened layer, and resistance to gluing. Quality problems such as a significant reduction in corrosion ability.

In order to prevent CrN from forming at high temperatures and damaging the original corrosion resistance of stainless steel, a low-temperature treatment process must be developed. The plasma low-temperature nitriding process developed in the 1980s has successfully overcome the technical problem of weakened corrosion resistance of austenitic stainless steel after treatment. The key is to conduct it at low temperature to prevent the formation of CrN and the decrease in corrosion resistance after the matrix is depleted of chromium.

Although low-temperature nitriding technology solves the problem of reduced corrosion resistance of stainless steel after nitriding, ion nitriding itself also has shortcomings, such as boundary effects, hollow cathode effects, and uneven workpiece temperatures. In order to solve the shortcomings of ion nitriding, the industry has also specially developed activated screen ion nitriding technology.