*What is QPQ

QPQ Salt bath treatment is a method of modifying the surface of black metal parts by placing them in two salt baths with different properties and infiltrating multiple elements into the metal surface to form a composite infiltration layer. This processing method has not undergone quenching, but has achieved the effect of surface quenching, hence it is called “QPQ”.

QPQ salt bath treatment is suitable for various structural steels, tool steels, heat-resistant stainless steels, pure iron, cast iron, and various powder metallurgy parts. It is suitable for various working environments with high wear resistance, high corrosion resistance, fatigue resistance, and micro deformation, and is widely used in industries such as automobiles, motorcycles, locomotives, engineering machinery, agricultural machinery, light chemical machinery, machine tools, instruments and meters, firearms, gears, and molds.

The process steps of QPQ salt bath treatment include cleaning, preheating, nitriding, and oxidation polishing. Firstly, use water-based cleaning agents and ultrasonic waves to clean the dirt on the surface of the workpiece. Then, preheat the workpiece in an air furnace; Next, place the preheated workpiece in a salt bath for processing. Finally, polish the oxidized workpiece. QPQ is actually a process that combines heat treatment and anti-corrosion treatment in one go. Its main advantages are low processing temperature, short time, and the ability to simultaneously improve the hardness, wear resistance, and corrosion resistance of the part surface, reduce friction coefficient, minimize deformation, and be pollution-free. It has the advantages of optimizing processing procedures, shortening production cycles, and reducing production costs, and has been recognized and praised by many manufacturers worldwide.

*Characteristics of QPQ salt bath treatment

① Good wear resistance and fatigue resistance: In the QPQ process, metal materials react with salt bath liquid at a working temperature of 570 ± 10 ℃, forming a high-quality and dense compound layer on the metal surface. This compound is entirely composed of ε – iron nitride, which can efficiently improve the hardness and density of the metal surface, thereby giving the metal surface good wear resistance and reducing the friction coefficient.

The wear resistance of the product after QPQ treatment is more than 16 times higher than conventional quenching and high-frequency quenching, more than 9 times higher than carburizing quenching of 20 # steel, and more than 2 times higher than hard chromium plating and ion nitriding. Fatigue experiments have shown that this process can increase the fatigue strength of medium carbon steel by more than 40%, which is better than ion nitriding and gas nitriding. This process is particularly suitable for parts with complex shapes, solving technical key issues and solving deformation problems easily.

② Good corrosion resistance: Continuous spray experiments were carried out on samples of several different materials and different processes under the same experimental conditions according to ASTM BII7 standard. The temperature of salt spray experiment was 33~37 ℃, the relative humidity was 95%, and 5% NaCL aqueous solution was spray. The test results show that the corrosion resistance of the parts treated with QPQ is 5 times that of 1Cr18Ni9Ti stainless steel, 70 times that of hard chromium plating, and 280 times that of blackening.

③ Minimal deformation: After QPQ treatment, the product will hardly deform, which can effectively solve the problem of hardening deformation that is difficult to solve by conventional heat treatment methods.

For example, after QPQ treatment, the surface hardness of 2Cr13 stainless steel sheet with dimensions of 510*460*1.5mm is greater than HRC60, and the unevenness is less than 0.5mm. At present, QPQ technology has been successfully applied to numerous shaft parts and slender rods, effectively solving the contradiction between heat treatment hardening and product deformation that has always existed.

④ It can replace multiple processes and reduce time costs: After QPQ treatment, the product not only improves its hardness and wear resistance, but also enhances its corrosion resistance, and forms a black and bright appearance. It can replace the conventional multiple processes such as quenching, tempering, and blackening (chrome plating), shorten the production cycle, and reduce production costs. On the surface of a large amount of production data, QPQ treatment can save 50% energy compared to carburizing and quenching, and save 30% cost compared to hard chrome plating treatment, with high cost-effectiveness.

⑤ Low carbon and environmentally friendly: The QPQ treatment process has been identified by relevant environmental protection departments and has been proven by actual use by users across the country that the emissions of various harmful substances are below the allowable values of national emission standards. Due to advanced technology and stable quality, QPQ technology has been applied to hundreds of products and has established multiple production lines around the world.

⑥ QPQ technology is applicable to a wide range of materials: This process is applicable to all black metal materials, from pure iron, low-carbon steel, structural steel, tool steel to various high alloy steels, stainless steel, cast iron, and iron-based powder metallurgy parts.

The following are examples of the application of QPQ technology on some typical workpieces:

1.High speed steel cutting tools include various HSS drill bits, milling cutters, zippers, and gear cutting tools, which can increase the service life by 1-4 times, especially for difficult to machine materials, the effect is particularly outstanding.

2.The tool holder and blade body of various machine clamps improve their wear resistance, abrasion resistance, non deformation, and meet the requirements of positioning and accuracy well, with strong rust prevention ability.

3.Molds are suitable for various die-casting molds, injection molds, extrusion molds, rubber molds, glass molds, etc., greatly improving the service life of molds and enhancing the surface smoothness of processed parts.

4.Automotive parts such as valves, crankshafts, camshafts, gears, air spring piston rods, shock absorber rods, differential brackets, spherical pins, and dozens of other parts have been applied for many years with significant results.

5.Sports equipment such as golf heads can be directly exported to the European and American markets.

6.Textile machinery is used for the cold and hot tracks of elastic yarn machines to increase hardness and prevent deformation.

7.Switch components are used for various air switch components, replacing galvanizing and chrome plating, with significant effects.

8.Printing machinery, various offset printing machine parts, gears, edge suction nozzles, etc.

9.Seal various valves and shaft components of machinery.

10.Electric tool parts include gear shafts, helical teeth, flat teeth, and bearing housings.

11.Various shafts, pins, gears, and other components of construction machinery.

12.Camera parts such as shutter, lock and other stamped parts.

*Why Choose COOLDO

COOLDO is a company with over 20 years of experience specializing in metal melting, casting, and heat treatment furnaces. We are committed to providing high-quality equipment and the most suitable turnkey solutions based on customer needs.

QPQ salt bath nitriding project mainly consists of the following equipment:

1. Preheating furnace
2. Nitriding furnace
3. Oxidation furnace
4. Ultrasonic cleaning machine
5. Rinse tank
6. Cooling tank
7. Water-soluble sealing tank
8. Oil-based sealing tank
9. Tooling fixture
10. Physical and chemical analysis facilities

QPQ process supporting raw and auxiliary materials:

1. Basic salt
2. Regeneration Salt
3. Oxidation salt
4. Water-soluble cleaning agent
5. Water-soluble sealant
6. Oil-based sealant