Can a muffle furnace be evacuated for annealing?

Muffle furnace vacuum can be used for annealing treatment, and vacuum annealing is one of the typical applications of Muffle furnace vacuum. The following is an explanation from four aspects: principles, advantages, application scenarios, and operational points:

1. Principle of Vacuum Annealing
Vacuum annealing is a heat treatment technique that isolates oxygen in a vacuum environment to achieve annealing of metal materials and maintain surface brightness. Its core lies in:
Vacuum degassing: By using a vacuum system to reduce the pressure inside the furnace to 0.1-1Pa, the contact path between the material and oxygen is eliminated, and the formation of oxide film is suppressed. At the same time, the vacuum degassing effect accompanies the heat transfer process, which can remove gas impurities such as H ₂ and CO ₂ dissolved inside the metal. After degassing, the impurity content can be reduced to below 1.5ppm.
Recrystallization process: The system achieves uniform heating through radiation heating, promoting the material to complete the recrystallization process within the phase transition temperature range, optimizing grain size and density. For example, in the treatment range of 130-250 ℃, the grain size of titanium coating gradually increases with temperature, and the decrease in porosity leads to an increase in reflectivity.

2. The advantages of vacuum annealing
Surface quality improvement: The vacuum environment enables stainless steel and other materials to obtain a non oxidizing surface, and the ellipticity of bearing rings can be controlled within 1/8 to 1/9 of traditional processes. The evaporation of elements in high alloy steel forms a mist like bright layer, which is closer to the original metallic color on the surface compared to gas quenching process.
Corrosion resistance enhancement: Research has shown that the temperature range of 130-250 ℃ can optimize the grain size and density of coatings, and the corrosion resistance time of surface drop tests can be increased from 5 seconds to 46 seconds.
Residual stress relief: Stress relief annealing involves heating to a temperature at which internal particles can move, utilizing the displacement of particles to relax stress, thereby eliminating or reducing residual stress inside. The speed of stress relaxation largely depends on the annealing temperature. The higher the temperature, the easier the particles are to move and the faster the relaxation speed.

3. Application scenarios of vacuum annealing
Aerospace field: used for processing stainless steel bearings and precision parts to meet extreme environmental requirements. For example, vacuum annealing can improve the fatigue life of titanium alloy parts and reduce the tendency towards hydrogen embrittlement.
Semiconductor manufacturing: achieving high purity and oxidation free treatment to ensure device performance. For example, in the manufacturing of transistors and integrated circuits, vacuum annealing can prevent metal lead oxidation and improve conductivity.
Powder metallurgy: used for powder sintering, infiltration, alloying, and preparation of high-performance metals and composite materials. The vacuum environment can reduce the oxide film between powder particles and increase the sintering density to over 99%.

4. Key points of vacuum annealing operation
Vacuum extraction process:
Connect a vacuum pump in a cold state and draw a relative vacuum (usually -0.1Mpa).
First, use a mechanical pump for pre pumping to achieve a certain degree of vacuum, and then start the molecular pump to obtain a higher degree of vacuum.
Temperature control:
Set the temperature rise and fall curve and save the settings.
Adopting a high-precision temperature control system, the temperature is controlled near the set value through PID regulation and other methods, with a temperature control accuracy of ± 1 ℃ or even higher.
Atmosphere regulation:
Flexibly adjust the type and flow rate of gas introduced into the furnace according to experimental requirements.
By using a gas mass flow controller, the flow rate of gas can be controlled to achieve different atmospheric environments (such as inert atmosphere, reducing atmosphere, etc.).
Security protection:
Equipped with a vacuum gauge to monitor the vacuum level inside the furnace in real-time and intuitively.
There are safety protection devices such as furnace door interlocking device and emergency stop button to prevent operators from misoperation.