WHY DO WE CHOOSE QPQ HEAT TREATMENT FURNACE？

I. Description of QPQ Production Line
The QPQ process is a thermochemical surface treatment technology performed at a temperature of 570±10°C. It involves diffusing nitrogen, carbon, and other alloying elements into the metal substrate to form a dense compound layer on the surface, thereby significantly enhancing the material’s surface hardness and wear resistance characteristics.
Principle:
(1) Salt bath nitriding (nitrocarburizing)-In a nitrogen salt bath at 520-580 ℃, the metal surface will be covered with:
chemical compound: 10-20μm thickness of Fe₂-3N、Fe₃C with high hardness (500-1200HV)
diffusion layer: 0.1-0.5mm of Nitrogen solid solution with strong fatigue resistance
(2) Salt bath oxidation- In a nitrate bath ( NaNO₃/KNO₃) at 350-400 ℃, the metal surface will be covered with:
oxide layer: 3-5μm thickness of Fe3O4 (improve the corrosion resistance of workpieces)

II.QPQ Equipment
1. Ultrasonic cleaning machine for first cleaning

2. Water tank for second cleaning and cleaning the finished product

3. Preheating furnace for heating workpiece up to 350℃

4. Nitriding furnace

5. Oxidation furnace

6. Polishing machine

• Small or irregular workpieces: spiral vibration polishing machine, centrifugal vibration polishing machine
• Large or regularly shaped workpieces: grinding wheel type polishing machine
• Rod shaped workpieces: centerless grinding machine

7. Waste gas and water Treatment equipment: Spray tower

III. Process
1. Chemical or physical cleaning: Using the ultrasonic cleaning machine to clean the oil stains, dust, and rust on the surface of the workpiece. Then use the water tank for second cleaning before heating the workpiece. Workpieces with severe rust require acid washing to cleaning the rust

2. Checking: Checking the dimension, surface and shape of workpieces to ensure it meets the requirements of QPQ.

3. Preheating: Slowly heating the workpieces up to 350℃ to prevent the workpiece from deforming or breaking due to excessive temperature difference in subsequent steps

4. Nitriding: This is the key step of QPQ operation. Treat the workpiece with nitriding salt bath at 570℃ for 1-3 hours, then the workpiece will be covered with a layer of nitrides (Fe₂-3N, Fe₃C). The corrosion resistance, wear resistance, and fatigue resistance of workpieces will be greatly improved by the nitrides on surface. (Copper, aluminum, zinc and other non-ferrous metals are not allowed to be placed in nitriding furnaces)

5. Oxidation: Treat the nitrided workpieces with oxidation salt bat h at 350-400℃ for 15-20 minutes, then the workpieces will be cover with a dense of oxidation film (Fe3O4)

6. Polishing: polish the workpieces to make its surface smoother.

7. Cooling: Slowly cool the workpiece to room temperature to reduce deformation during the cooling process. Then cleaning the finished product with cooling water.

8. Oiling: After completely drying the workpieces, soak it in engine oil at 140-180 ℃ to improve its rust prevention ability.

9. Waste gas and water treatment: the waste gas generated by the furnace will enter the spray tower through the pipeline, and the liquid in the spray tower can neutralize the gas to meet the emission standards. In general, the wastewater generated by the process can be directly discharged. If acid is used during the cleaning process, the operator needs to neutralize the acid before discharging it

Note:
1.Safety: Cyanide salt baths need to be strictly managed, and ventilation and emergency equipment should be installed on site.

2.Waste: Waste salt needs to be recycled.

3.Maintenance of salt bath: regularly checking the concentration of CNO ⁻ (controlled at 32-38%).

4. Furnace slag removal: Slag removal must be carried out after every three batches of materials heated

VI. Advantage of QPQ
1. High hardness of metal surface: the surface hardness of finished product from QPQ process can reach 500-1200HV

2. Wonderful durability of workpiece: The nitriding layer and oxide film formed by QPQ technology effectively extend the service life of workpieces.

3. Outstanding corrosion resistance of workpiece: The final product of QPQ has five times the corrosion resistance of stainless steel. It can also achieve 100-300 hours of corrosion resistance in neutral salt spray tests.

4. Easy to control: The temperature of QPQ process is low and the workpieces almost do not deform, so it is easy for user to control the temperature of furnace and the shape of workpieces.

VII. Application:
1. Car: Piston rings, gears, transmission shafts (Improve wear resistance and corrosion resistance)
2. Tool: Drill bits, cutting tools (Improve cutting performance and service life)
3. Airplane: Landing gear and engine components (Improve fatigue resistance)
4. Die: Cold forging die, hot forging die (Improve wear resistance and corrosion resistance)

VIII. Compared to other technology

1. Electroplating

2. Carburizing quenching

3. Ion nitriding