What is the working principle of the box type tempering furnace?

The box type tempering furnace is the core equipment for metal heat treatment, and its working principle is based on thermodynamic control and material phase transformation. By precisely regulating temperature, time, and atmosphere, the internal structure of the metal is optimized.

1. Core working mechanism
Heating system
Electric heating element: using resistance wire (such as iron chromium aluminum or nickel chromium alloy) or silicon carbon rod as the heating element, generating Joule heat through current.
Radiant heat transfer: The heating element transfers heat to the metal workpiece inside the furnace in the form of infrared radiation, and the temperature uniformity of the furnace is guaranteed by air duct circulation or refractory fiber insulation layer (typical uniformity ≤± 5 ℃).
Temperature controller
PID intelligent control: Real time monitoring of furnace temperature through thermocouples (K-type or S-type), combined with PID algorithm to dynamically adjust power output, achieving precise control of heating rate (≤ 10 ℃/min) and insulation accuracy (± 1 ℃ or ± 5 ℃).
Program temperature control: supports multiple heating curves (such as step heating, constant temperature maintenance, and rapid cooling), adapting to different material and process requirements.
Atmosphere protection system (optional)
Inert gas protection: Nitrogen or argon is injected into the furnace through a flow meter to replace air to prevent oxidation (leakage rate ≤ 0.5%), suitable for easily oxidizable materials such as titanium alloys and stainless steel.
Vacuum tempering: By pumping to below 10 ⁻ ² Pa with a vacuum pump, the risk of hydrogen embrittlement is eliminated and the surface finish is improved.

2. Typical process flow and case studies
Tempering of carbon steel (taking 45 # steel as an example)
Process: After quenching (HRC 58), hold at 560 ℃ for 2 hours and air cool to room temperature.
Effect: Hardness reduced to HRC 28-32, toughness increased by 30%, residual stress reduced by 90%.
Principle: Martensite decomposes into tempered martensite, carbides spheroidize, and grain boundary stress is released.
Tempering of alloy steel (taking H13 mold steel as an example)
Process: After quenching at 1020 ℃, hold at 540 ℃ for 4 hours, and then air cool.
Effect: The hardness has decreased from HRC 52 to HRC 48, while the red hardness (600 ℃ hardness) remains above HRC 45.
Principle: Secondary hardening phenomenon, carbide precipitation strengthens the matrix, and improves high-temperature wear resistance.
Stainless steel solid solution+tempering (taking 316L as an example)
Process: After solid solution at 1050 ℃, tempering at 750 ℃ for 1 hour, and water cooling.
Effect: Corrosion resistance (salt spray test) improved by 40%, and intergranular corrosion risk reduced.
Principle: Carbides dissolve in the austenite matrix, hindering the precipitation of Cr ₂ ∝ C ₆ and forming a uniform solid solution.

3. Technological advantages and industry value
Organizational optimization
By controlling the tempering temperature and time, directional transformation of martensite, bainite, austenite and other structures can be achieved, balancing hardness and toughness.
Case: After tempering at 480 ℃, the elastic limit of spring steel 60Si2Mn is increased by 15%, and the fatigue life is extended by three times.
Residual stress relief
During the tempering process, the dislocation density decreases, the grain boundary stress is released, and the risk of deformation and cracking is reduced.
Data: After tempering, the dimensional stability of the workpiece increased by 30%, and the processing qualification rate increased by 15%.
Energy saving and intelligence
Adopting ceramic fiber insulation layer reduces energy consumption by 30%; Integrate MES system to achieve process data traceability and remote monitoring.

4. Summary
The working principle of the box type tempering furnace is essentially thermodynamic driven material phase transition control, and its core value lies in:
Precise control: Through precise matching of temperature, time, and atmosphere, customized optimization of metal properties can be achieved.
Process compatibility: covering the full range of metal materials such as carbon steel, alloy steel, stainless steel, titanium alloy, etc.
Quality assurance: eliminate heat treatment defects, improve product consistency and reliability.

In high-end manufacturing, aerospace, automotive industry and other fields, box type tempering furnaces have become the core equipment to ensure the performance of metal materials, and their technological progress directly promotes the development of the industry towards high precision, high efficiency and green direction.