The performance characteristics of austenitic stainless steels are corrosion resistance, high toughness, and good processing performance is widely used in many fields, but the abrasion resistance and fatigue resistance of austenitic stainless steel is poor, which greatly affects the application life of the material products.
Practice has proved that the austenitic stainless steel in high temperature nitriding quenching, which is on the surface of the 1050-1150 DEG C in vacuum furnace of nitrogen dissolved into the stainless steel workpiece, followed by rapid cooling, and let not this nitride precipitation can be formed on the surface of stainless steel containing nitrogen in solid solution strengthening austenitic nitriding layer.
After high nitrogen surface treatment, it not only enhances the surface strength, hardness and wear resistance of austenitic stainless steel plates, but also maintains the microstructure and properties after solution treatment. Because the lattice parameters of this kind of nitriding layer are different from that of gamma phase, they are called “S phase”. In the S phase, the nitrogen atoms are dissolved into the austenite lattice, which also inhibits the precipitation of chromium nitride at the grain boundary. Therefore, the surface hardness of austenitic stainless steel plates is obviously enhanced without weakening the corrosion resistance of austenitic stainless steel plates.
The technology of S phase modification on stainless steel surface is of great significance for the development of stainless steel surface treatment technology. The experimental results show that a layer of S hardening layer similar to the nitriding layer can be obtained by replacing nitrogen with carbon gas in the atmosphere of ion treatment.
The traditional nitriding technology although stainless steel parts will enhance the surface hardness, wear resistance and fatigue strength, but because of nitriding, carburizing temperature is very high, the nitride and carbide precipitates, which solves the corrosion resistance of stainless steel materials. In addition, a thin and dense layer of the oxide film is produced on the surface of the stainless steel plate to prevent the infiltration of nitrogen and carbon atoms into the stainless steel matrix. These factors greatly restrict the popularization and use of the nitriding and nitriding surface treatment technology of stainless steel materials.
Unlike traditional nitriding and carburizing technology, S phase permeation layer technology belongs to a kind of low-temperature nitriding and carburizing technology. For example, low-temperature nitriding technology, the nitriding temperature is reduced to 450 DEG C, the penetration of nitrogen will generate the solid solution of austenite, thereby significantly enhance the hardness of austenitic stainless steel material, and also inhibits the precipitation of chromium nitride nitriding process, ensure that the corrosion resistance of stainless steel materials.
The low-temperature ion nitriding technology can obtain a single phase nitrogen-containing expansion austenite structure of dozens of microns. The low-temperature ion carburizing has the advantages of homogeneous permeability layer, excellent toughness, high bearing capacity, the gentle gradient of hardness, high carburizing efficiency and so on. In addition, after fluoridation of stainless steel surface, the oxide film on the surface of stainless steel can be removed, and fluorinated film can be formed. Such fluorinated film enhances the adsorption and diffusion of activated nitrogen and reduces the nitriding temperature of stainless steel to 300 degrees.
The nitriding austenitic stainless steel can provide a stronger subsurface layer to support the oxide film formed when sliding, which can bear the greater load than the unit riding sample. The wear of nitriding steel is the mechanism of oxidation and wear, while the wear of the non-nitriding steel is the mechanism of adhesion and plastic deformation.
After the low-temperature nitriding and carburizing, austenitic stainless steel plate can get the diffusion layer containing nitrogen and carbon solution, which is also the S phase seeping layer. It can not only enhance the surface hardness of stainless steel but also enhance the corrosion resistance of stainless steel.
Source: China Stainless Steel Plates Manufacturer – Yaang Pipe Industry Co., Limited (www.yaang.com)