QPQ Salt Bath Nitriding Treatment of 42CrMo Products

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Brief Introduction of QPQ Salt Bath Nitriding Process
QPQ technology can complete heat treatment and anti-corrosion treatment at one time, with low temperature and short time. It can also improve the surface hardness, wear resistance and anti-corrosion of parts, reduce friction coefficient, small deformation and no pollution. It has the advantages of optimizing processing procedures, shortening production cycle and reducing production costs.

QPQ technology is a combination of heat treatment technology and anti-corrosion technology in technology. It is a combination of high wear resistance and anti-corrosion in performance. On the infiltration layer, it is a composite infiltration layer composed of a variety of compounds. Therefore, it is regarded as a tremendous progress in the field of metal surface strengthening technology abroad, and it is called a new metallurgical method.

QPQ salt bath composite treatment technology was invented by German company in 1970s. After decades of continuous development and improvement, it has been applied more and more widely. Therefore, QPQ salt bath composite treatment technology is regarded as a tremendous progress in the field of metal surface strengthening technology abroad. It is called a new metallurgical method. At present, QPQ salt bath composite treatment technology has been widely applied in China, especially in automobiles, motorcycles, shaft products, electronic parts, spinning machines, machine tools, electrical switches, tools and dies.

QPQ salt bath nitriding technology characteristics

1. Good wear resistance
In QPQ process, metal materials react with salt bath liquids at 570 (+10℃) working temperature, forming a dense compound layer with good quality on the metal surface. The compound is composed entirely of epsilon iron nitride, which can improve the hardness and compactness of the metal surface efficiently and make the metal surface have good wear resistance. The surface hardness of the treated metal mainly depends on the alloying elements in the steel. The higher the content of alloying elements, the higher the hardness of the carburized layer. According to the hardness of the infiltrated layer, common materials can be divided into the following categories:

(1) Carbon steel and low-platform gold steel
Represent steel numbers: 20, 45, titanium, 20Cr, 40Cr, etc. Surface hardness of carburized layer: 500-700 HV

(2) alloy steel
Represent steel numbers: 3CrW8V, Crl2MoV, 38CrMoAl, 1Crl3-4Cr13, etc. Surface hardness of carburized layer: 850-1000HV

(3) High-speed steel and austenitic stainless steel
Representation steel number: hardness of quenched Wl8Cr4V, W6Mo5Cr4V2 and 1Crl8Ni9Ti isopenetrating layer: 1000-1250HV

(4) cast iron
Surface hardness of infiltrated layer: > 500HV
The following figure is the sliding wear test data of 40Cr workpiece after different treatment methods. Based on the wear value of QPQ 0.22mg, the wear resistance of QPQ process is 2.1 times of hard chromium plating, 2.8 times of ion nitriding, 23.7 times of high frequency quenching and 29.4 times of conventional quenching.

2. Good corrosion resistance
The figure below is a comparison of neutral salt spray test of 45 # steel with 1Cr18Ni9Ti stainless steel and 1Cr13 material after QPQ salt bath composite process, decorative chromium plating, hard chromium plating and common blackening treatment. It can be seen that the corrosion resistance of 45 # steel treated by QPQ is 5 times of that of 1Cr18Ni9Ti stainless steel, 70 times of hard chromium plating and 280 times of that of ordinary blackening. After other materials were treated by QPQ process, the neutral salt spray test could reach 100-300 hours.

3. Good fatigue resistance
After QPQ salt bath composite process, high residual compressive stress was introduced and produced on the metal surface, which resulted in a great improvement of various types of fatigue strength. It was proved by experiments that the fatigue strength could be increased by about 100%, and the surface defects such as pitting corrosion and rust could be alleviated.

4. Minimal Deformation
QPQ salt bath composite treatment technology will not change the structure under the phase transition point of steel due to its low process temperature. Therefore, compared with quenching, high frequency quenching, carburizing quenching and carbonitriding, the deformation of the treated workpiece is much smaller. At the same time, after nitriding at 570-580 ℃, the workpiece should be kept at 350-400 ℃ for 15-20 minutes, which will greatly reduce the thermal stress produced when the workpiece is cooled. Therefore, the workpiece treated by QPQ salt bath composite process almost does not deform, and it is the hardening technology with the smallest deformation, which can effectively solve the hardening deformation problem that is difficult to be solved by conventional heat treatment methods.

5. Low-carbon environmental protection
Degaussa, Germany, which invented the process, won the German Environmental Protection Award for this process. In China, the QPQ treatment process has been tested and identified by the relevant environmental protection departments, and proved to be pollution-free, pollution-free and heavy metal-free by the actual use of users all over the country. It is also used to replace some heavily polluted processes such as electroplating.

6. It can replace multi-process and reduce time cost.
The metal material treated by QPQ salt bath composite process can not only improve its hardness and wear resistance, but also improve its corrosion resistance. Therefore, it can replace conventional quenching (ion nitriding, high frequency quenching, etc.), tempering, blackening (chromium plating) and other processes, greatly shorten the production cycle and reduce production costs. A large number of production data show that QPQ treatment can save 50% energy compared with carburizing and quenching, save 30% cost compared with hard chromium plating, and have a high cost performance ratio.

Application Range of QPQ Salt Bath Nitriding

1. The most suitable materials:
Various structural steels: blunt iron, Q235, 20, 20Cr, 20CrMnTi, 20CrNiMo, 35CrMo, 42CrMo, 45, 40Cr, 50CrV, 65Mn, 38CrMoAl.
Various tool steels: T7-T12, 5CrMnMo, 5CrNiMo, 3Cr2W8V, GCrI5, HI3 (0.35% C, 1.5% Mo, 5% Cr, 1% Si, 1% V), Cr12MoV, various high speed steels.
Various stainless steels: 0Crl3-4Crl3, 201, 301, 304, 316, 1Cr18Ni9Ti, 0Crl8Nil2MoTi, 4Cr9Si2, 5Cr21Mn9Ni4N.
All kinds of cast iron: gray iron, malleable iron, ductile iron, wear-resistant alloy cast iron.
Various iron-based powder metallurgical parts.

2. Applied industries:
Automobile, motorcycle, locomotive, internal combustion engine, textile machinery, construction machinery, light industry machinery, pump and valve equipment, hydraulic machinery, printing and packaging machinery, chemical machinery, electric tools, agricultural machinery, machine tools, tools and moulds, high and low voltage electrical switches and other parts required wear resistance, corrosion resistance, fatigue resistance, anti-occlusion.

3. Typical applications:
Engine valves, crankshafts, cylinder liners, gears, cams, bearings, spindles, sliders, steering arms, automotive wiper ball-end spindles, guideways, hydraulic cylinders, universal joints, connecting pins, various dies, pistons, screw threads, bolts, pumps, high-speed steel drills, guns, various tools, flanges, key pins, gaskets, shells and so on.