What are the temperatures for tempering electric furnaces under vacuum?

The temperature range and classification of vacuum tempering electric furnaces are mainly based on material types, process requirements, and equipment design. The following is a detailed explanation:

1. Temperature range classification
Low temperature tempering (150 ℃ -250 ℃)
Purpose: To eliminate quenching stress, reduce hardness, improve toughness, and maintain high elasticity.
Applicable materials:
Tool steel (such as T10A, 9SiCr): used for manufacturing cutting tools and measuring tools, with better hardness after tempering.
Spring steel (such as 65Mn, 50CrVA): used for automotive suspension springs, the elastic limit is significantly improved after tempering.
Process characteristics:
Under vacuum environment, oxidation and decarburization can be avoided, and surface smoothness can be maintained.
The temperature uniformity requirement is within ± 5 ℃ to prevent local overheating and performance degradation.
Medium temperature tempering (350 ℃ -500 ℃)
Purpose: To achieve a good balance between elasticity and strength, suitable for parts that require high fatigue life.
Applicable materials:
Structural steel (such as 40Cr, 42CrMo): used for gear and shaft parts, with increased hardness after tempering.
Bearing steel (such as GCr15): used for rolling bearings, with improved wear resistance after tempering.
Process characteristics:
It is necessary to strictly control the heating rate (≤ 3 ℃/min) to avoid uneven tissue transformation.
A vacuum environment can reduce the risk of hydrogen embrittlement and extend the lifespan of parts.
High temperature tempering (500 ℃ -650 ℃)
Purpose: To obtain comprehensive mechanical properties (high strength, good toughness) suitable for parts that can withstand complex loads.
Applicable materials:
Alloy structural steel (such as 35CrMo, 42CrMo): used for automotive connecting rods and engine crankshafts.
Stainless steel (such as 304, 316L): used in food machinery and chemical equipment, with enhanced corrosion resistance after tempering.
Process characteristics:
Long term insulation (2-4 hours) is required to ensure sufficient precipitation of carbides.
A vacuum environment can prevent surface decarburization and maintain material corrosion resistance.

2. Special process temperature
Deep cooling treatment with tempering (-196 ℃ to room temperature)
Purpose: To eliminate residual austenite, improve dimensional stability, and be suitable for precision parts.
Temperature control:
After deep cooling, it is necessary to temper in stages (such as -196 ℃ → room temperature → 150 ℃ → 250 ℃) to avoid thermal stress cracking.
A vacuum environment can prevent surface corrosion caused by condensation water.
Pre tempering before vacuum brazing (200 ℃ -400 ℃)
Purpose: To remove oil stains and oxide films on the surface of materials and improve the wettability of brazing materials.
Key points of the process:
The temperature needs to be adjusted according to the type of solder (such as Ag based solder requiring around 350 ℃).
The vacuum degree should be ≤ 10 ⁻ ³ Pa to prevent oxidation of the solder material.

3. Key parameters for temperature control
temperature uniformity
Standard requirement: The temperature difference inside the furnace should be ≤ ± 5 ℃ (for precision parts, it should be ≤ ± 3 ℃).
Implementation method:
Adopting multi zone independent temperature control (heating in the upper, middle, and lower zones).
Optimize airflow circulation (such as increasing fan speed).
heating rate
Low temperature tempering: ≤ 5 ℃/min (to prevent thermal stress cracking).
High temperature tempering: ≤ 3 ℃/min (to avoid rapid tissue transformation).
Deep cold tempering: slow heating is required (such as from -196 ℃ to room temperature, which takes ≥ 2 hours).
holding time
General formula: insulation time (min)=material thickness (mm) x coefficient (1-2).
Example: High temperature tempering of 10mm thick 42CrMo steel requires insulation for 20-40 minutes.

4. The impact and handling of temperature anomalies
The temperature is on the low side.
Impact: Insufficient hardness, decreased wear resistance (such as tool steel being prone to chipping due to insufficient tempering).
Solution: Check whether the power and vacuum degree of the heating element meet the standards.
High temperature
Impact: Coarse grain size and reduced toughness (such as loss of elasticity caused by over tempering of spring steel).
Processing: Calibrate thermocouples and adjust PID parameters.
temperature fluctuation
Impact: Uneven organization and unstable performance (such as noise caused by gear tempering fluctuations).
Solution: Check the stability of solid-state relays and vacuum pumps.