Surface treatment process of stainless steel with black and gray technology

1、 Technical concept:
QPQ "is the abbreviation for" Quench P0lish Quench "in English. The original meaning is quenching, polishing, and quenching. After salt bath composite treatment, in order to reduce the surface roughness of the workpiece, a polishing process can be performed on the surface of the workpiece, followed by an oxidation process in the salt bath. This is very necessary for precision parts and workpieces with high surface roughness requirements. It is referred to as QPQ salt bath composite treatment technology in China. The QPQ salt bath composite treatment technology can significantly improve the wear resistance and corrosion resistance of metal surfaces, while the workpiece hardly deforms. It is a new metal surface strengthening and modification technology. This technology achieves the combination of nitriding process and oxidation process; Composition of nitrides and oxides; Composite of wear resistance and corrosion resistance; The combination of heat treatment technology and anti-corrosion technology.
2、 Technical features:
1. Good wear resistance
In the QPQ process, metal materials react with salt bath liquid at a working temperature of 570 ± 10 ℃, forming a dense compound layer with excellent quality on the metal surface. This compound is completely composed of ε Composed of iron nitride, it can efficiently improve the hardness and density of the metal surface, thereby providing good wear resistance on the metal surface. The surface hardness value of processed metal materials mainly depends on the alloying elements in the steel. The higher the alloying element content, the higher the hardness of the infiltration layer. According to the hardness of the infiltration layer, commonly used materials can be divided into the following categories:
(1) Carbon steel, low titanium alloy steel
Representative steel grades: 20, 45, TiO2, 20Cr, 40Cr, etc. Surface hardness of infiltration layer: 500-700HV
(2) Alloy steel
Representative steel grades: 3CrW8V, Crl2MoV, 38CrMoAl, 1Crl3-4Cr13, etc. Surface hardness of infiltration layer: 850-1000HV
(3) Representative steel grades for high-speed steel and austenitic stainless steel: quenched Wl8Cr4V, W6Mo5Cr4V2, and 1Crl8Ni9Ti layers, surface hardness: 1000-1250HV
(4) Surface hardness of cast iron infiltration layer:>500HV
The sliding wear test data of workpieces made of 40Cr material after different treatment methods are based on the wear value of 0.22mg of QPQ. The wear resistance of QPQ process is 2.1 times that of hard chromium plating, 2.8 times that of ion nitriding, 23.7 times that of high-frequency quenching, and 29.4 times that of conventional quenching.
2. Good corrosion resistance
Comparison of neutral salt spray tests on 45 # steel with 1Cr18Ni9Ti stainless steel and 1Cr13 material after undergoing QPQ salt bath composite process, decorative chromium plating, hard chromium plating, and ordinary blackening treatment. It can be seen that the corrosion resistance of 45 # steel after QPQ treatment is 5 times that of 1Cr18Ni9Ti stainless steel, 70 times that of hard chromium plating, and 280 times that of ordinary blackening. Other materials can undergo neutral salt spray testing for 100-300 hours after being processed by the QPQ process.
3. Good fatigue resistance
The metal surface treated by the QPQ salt bath composite process has introduced and generated high residual compressive stress, resulting in a significant improvement in various types of fatigue strength. Through experiments, it has been proven that the fatigue strength can be increased by about 100%, slowing down the occurrence of surface defects such as pitting and rust.
4. Minimal deformation
Due to the low process temperature, the QPQ salt bath composite treatment technology will not undergo structural transformation below the phase transition point of the steel. Therefore, compared with hardening processes such as quenching, high-frequency quenching, carburizing quenching, and carbonitriding that generate huge structural stress, the deformation of the treated workpiece is much smaller. At the same time, due to the fact that after nitriding at 570-580 ℃, the workpiece needs to be kept at 350-400 ℃ for 15-20 minutes, which greatly reduces the thermal stress generated during workpiece cooling. Therefore, the QPQ salt bath composite process almost does not deform the workpiece after treatment, making it a hardening technology with relatively small deformation. It can effectively solve the hardening deformation problem that is difficult to solve by conventional heat treatment methods.
5. Low carbon and environmental protection
The German company Digosa, which invented this process, won the German Environmental Protection Award for this process. In China, the QPQ treatment process has been tested and identified by relevant environmental protection standards, and has been proven to be pollution-free, pollution-free, and free of heavy metals by users across the country. And it is used to replace some heavily polluting processes such as electroplating.
6. Can replace multiple processes and reduce time costs
After being processed by the QPQ salt bath composite process, metal materials not only improve their hardness and wear resistance, but also improve their corrosion resistance. Therefore, they can replace the conventional quenching (ion nitriding, high-frequency quenching, etc.) - tempering - blackening (chromium plating) and other multiple processes, greatly shortening the production cycle and reducing production costs. A large amount of production data shows that QPQ treatment can save 50% energy compared to carburizing and quenching, save 30% cost compared to hard chromium plating, and have high cost-effectiveness