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Tempering of Induction Hardening in High-Frequency Heating Machines
Release time:
2024-01-25
Because induction heating is rapid and produces a large degree of superheat, causing the critical points of the metal to rise quickly, the induction quenching temperature (the surface temperature of the workpiece) is higher than that of conventional quenching.
Because induction heating is rapid and produces a significant degree of superheat, causing the critical points of the metal to rise quickly, the quenching temperature for induction hardening (the surface temperature of the workpiece) is higher than that used in conventional quenching. In induction hardening with high-frequency heating equipment, the primary purpose of tempering is to relieve quenching stresses. To prevent quenching cracks, tempering is sometimes also performed to reduce hardness, thereby meeting the technical requirements of the workpiece. Tempering methods generally include furnace tempering, induction tempering, and self-tempering.
I. Induction Tempering
Induction tempering requires factors such as surface temperature, surface hardness, power, heating time of the induction heating equipment, and the hardness gradient of the quenched and hardened layer.
1. Traditional tempering
Disadvantages of traditional tempering heating: Long duration. Reason: The external heating source heats the steel through thermal conduction and radiation, allowing sufficient time for heat to propagate throughout the steel and achieve uniform temperature distribution.
2. Modern Induction Heating
Advantages of induction heating equipment: short heating time. The reason is that induction heating differs fundamentally from traditional tempering methods—in induction heating, eddy currents induced in the steel itself generate heat and raise the temperature of the steel surface.
Method 1: Use another power supply with a suitable lower frequency to perform tempering with the inductor. This method is now widely adopted.
Method 2: Utilize the original quenching heating power supply and, under the original induction coil setup, perform induction tempering by reducing the power output. The advantage of this method is that the quenching and tempering processes can be completed in a single loading and unloading operation. Its disadvantage is that it occupies the quenching station, thereby reducing quenching production efficiency.
II. Furnace Tempering
This process typically uses a box furnace for tempering. A drawback of the box furnace is its long tempering time and low tempering temperature.
III. Self-tempering
1. Advantage: A set of tempering equipment has been eliminated.
2. Self-tempering is applicable only to workpieces that have sufficient residual heat in their core after being heated by a high-frequency heating device. The residual heat should be evenly distributed throughout all points of the quenched layer; otherwise, after self-tempering, the hardness of various regions on the quenched surface of the workpiece will be inconsistent, and in some areas, self-tempering may not occur at all.
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