Working principle of vacuum gas quenching furnace
11-10-2025 Author: KJ technology
Vacuum gas quenching furnace is an advanced heat treatment equipment that combines vacuum technology and gas quenching process. Its core principle is to heat the workpiece in a vacuum environment, and then use high-pressure inert gas to achieve rapid cooling, thereby obtaining ideal microstructure and properties. The following is a detailed step-by-step explanation of its working principle:
1. Establishment of vacuum environment
Vacuum pumping process:
After the furnace door is closed, the mechanical pump starts to reduce the pressure inside the furnace from atmospheric pressure (about 1013 mbar) to the rough vacuum range (about 10 ⁻¹ mbar).
Subsequently, the Roots pump or diffusion pump works in relay to further reduce the air pressure to the high vacuum range (approximately 10 ⁻³ mbar to 10 ⁻⁵ mbar).
Purpose:
Eliminate reactive gases such as oxygen and water vapor from the air to prevent oxidation or decarburization of workpieces at high temperatures.
Reduce the absorption of thermal radiation by gas molecules and improve heating efficiency.
2. Workpiece heating
Heating method:
Graphite heater: generates heat through resistance and radiates thermal energy to the workpiece, suitable for high temperature (such as ≥ 1000 ℃) scenarios.
Induction heating: using the principle of electromagnetic induction to directly heat the workpiece, with a fast heating speed, suitable for local heating or thin-walled parts.
Temperature control:
Real time monitoring of workpiece temperature using infrared thermometer or thermocouple, and adjusting heating power through PID controller.
Typical heating curve:
Preheating stage: Heat up at a slower rate to 500-600 ℃ to relieve stress.
Insulation stage: Maintain the target temperature (such as 850-1250 ℃) for a certain period of time to homogenize the tissue.
Heating stage: When approaching the quenching temperature, slow down the heating rate to avoid overheating.
3. High pressure gas quenching
Gas selection and injection:
Common gases: nitrogen (N ₂), argon (Ar), or mixed gases, selected according to material characteristics (such as argon for titanium alloys and nitrogen for carbon steel).
Gas injection: During quenching, high-pressure gas (usually 1-6 bar) is sprayed into the furnace at high speed (up to 100 m/s) through a nozzle, forming forced convection cooling.
Cooling mechanism:
Convection heat transfer: Gas flow carries away surface heat of the workpiece, and the cooling rate can reach 50-200 ℃/s.
Heat conduction optimization: The higher the gas pressure and density, the higher the heat conduction efficiency, but it is necessary to balance the pressure bearing capacity of the equipment.
Cooling curve control:
Segmented cooling: In the initial stage, high-pressure gas is used to rapidly cool down, and in the later stage, the pressure is reduced to reduce the risk of stress cracking.
Temperature feedback: Monitor the temperature of the workpiece through thermocouples and dynamically adjust the gas flow rate and pressure.
4. Vacuum recovery and furnace discharge
Post quenching treatment:
After quenching, the pressure inside the furnace may increase due to gas expansion, and it needs to be restored to a vacuum state through an exhaust valve.
Some processes require tempering under vacuum to eliminate quenching stress.
Out of furnace operation:
After cooling the furnace to a safe temperature (such as ≤ 100 ℃), fill it with nitrogen to atmospheric pressure, open the furnace door and remove the workpiece.
Emergency situation: If rapid discharge is required, compressed air can be introduced to accelerate cooling, but it may introduce oxidation risks.
Key technical features
Non oxidative heat treatment:
Vacuum environment eliminates oxidation and decarburization, with a surface finish of Ra0.8 μ m or less, suitable for precision parts.
Efficient cooling:
High pressure gas quenching has a speed similar to oil quenching, but it is pollution-free and has minimal deformation, making it suitable for thin-walled and complex shaped workpieces.
Process flexibility:
Programmable control of heating, insulation, and quenching processes, supporting multiple temperature curve settings.
Material adaptability:
Suitable for high-speed steel, mold steel, titanium alloys, high-temperature alloys, etc., especially for materials with high surface quality requirements.
Typical application cases
Aerospace blades:
Process: Vacuum heating to 1250 ℃, argon quenching (pressure 4 bar), cooling rate 150 ℃/s.
Effect: No oxidation on the surface, uniform organization, and a 30% increase in fatigue life.
Automotive gears:
Process: Vacuum heating to 850 ℃, nitrogen quenching (pressure 2 bar), cooling rate 80 ℃/s.
Effect: Hardness reaches 58-62 HRC, deformation ≤ 0.1%, meeting the requirements of mass production.
3D printed titanium alloy:
Process: Vacuum heating to 1000 ℃, argon nitrogen mixed gas quenching (ratio 7:3).
Effect: Avoid nitride generation, improve cooling efficiency, and reduce thermal stress cracking.
