How to use an annealing furnace for metal quenching?

Annealing and quenching are two distinct metal heat treatment processes, differing in both purpose and operational methodology. In simple terms, annealing primarily aims to refine the internal structure of the metal, enhancing its machinability; whereas quenching is employed to increase the metal's hardness and wear resistance. Below, I shall outline the fundamental procedures for annealing and quenching respectively, though it should be noted that quenching is not typically performed within an annealing furnace.

Basic Steps for Annealing:

Place the metal to be annealed into the annealing furnace.

Set the required annealing temperature within the furnace control system.

Close the furnace door and adjust the temperature control switch to the appropriate position to commence heating.

Monitor the temperature changes within the furnace. When the temperature approaches the set point, adjust the temperature control parameters in the furnace control system as necessary to stabilise the temperature near the target value.

Once the metal reaches the set temperature, maintain it for a specified holding time to ensure internal microstructural transformation occurs.

After annealing concludes, gradually reduce the furnace temperature while monitoring the cooling rate. Compressed gas or other cooling devices may be employed to accelerate cooling.

When the furnace temperature drops to a safe range, open the furnace door, remove the annealed metal, and place it in a secure location for natural cooling.

Basic steps for quenching:

Heat the metal workpiece to the quenching temperature (typically above the metal's critical point).

After holding at this temperature for a specified duration, rapidly remove the workpiece from the heating furnace.

Immediately immerse the workpiece into a quenching medium (such as water, oil, or salt bath) for rapid cooling. The choice of quenching medium influences the cooling rate and quenching effect.

After a cooling period, remove the workpiece from the quenching medium and subject it to appropriate tempering treatment to eliminate internal stresses generated during quenching, thereby enhancing the workpiece's stability and toughness.

It is important to note that the quenching process must be conducted in specialised quenching equipment, not in annealing furnaces. This is because quenching requires rapid cooling, whereas annealing furnaces are typically designed for slow cooling or holding applications. Furthermore, preparatory steps such as preheating the metal workpiece are essential prior to quenching to ensure consistent and reliable results.

In summary, while both annealing and quenching are crucial processes in metal heat treatment, their objectives and operational methods differ significantly. Consequently, selecting the appropriate technique based on specific requirements and strictly adhering to operational procedures are imperative in practical applications to guarantee product quality and safe production.