Analysis of high-frequency induction heating surface heat treatment process of tower-type disc gears

1. Let's briefly introduce the specifications of the disc gear: the module is m=2.5mm, and the outer dimension is 205x16mm in diameter.

2. Heat treatment technical conditions. The tooth surface hardness requirement is 48-52HRB, and the gear oscillation pendulum deformation is controlled between 0.01-0.03mm.

3. Processing process. Forging blank, normalizing, machining, quenching and tempering treatment, high frequency induction heating surface quenching, low temperature tempering, fine machining - finished product.

Heat treatment process specifications and mechanical properties of tower type disc gears

a. High frequency induction heating surface quenching. Simultaneous quenching is performed on a 120KW high-frequency induction heating equipment to give the tooth surface of the tower-shaped disc gear high hardness and high wear resistance. The power supply voltage is 380v, the anode voltage is 10.5-12.5KV, the anode current is 9-9.5v, the ridge current is 1.0-1.2A, and the heating time is 15-17S.

The purpose of selecting 10%-15% emulsion as quenching cooling medium is to more effectively reduce the deformation of the workpiece, make it meet the technical requirements, and control the vibration deformation of the gear within the technical requirements.

b. Low temperature tempering. In order to meet the technical requirements and reduce the brittleness and deformation of the workpiece, the tempering temperature is 240-280°C and the tempering time is 60 minutes.

Key points for the implementation of heat treatment technology for tower-shaped disc gears - Why is modulation treatment used for pre-heat treatment of gears? The structure after high-frequency induction heating quenching depends on the heating conditions (current frequency), heating speed, surface temperature, steel composition and original structure. After high-frequency induction heating surface quenching, the quenching structure along the cross-section of the workpiece can be divided into three Region: martensite layer, transition layer, core.

The martensite layer is on the outermost layer with a temperature of Ac3. After quenching, the martensite structure is obtained. The martensite in this area is thicker on the surface (because of the high surface temperature and overheating) and has an obvious fine needle shape. The martensite near the inside is very fine, even called cryptocrystalline martensite, and its hardness can be as high as 62HRC or more.

The transition layer temperature is between Ac1 and Ac3. The mixed structure of martensite + unmelted ferrite obtained after quenching is different from the general two-phase area. Due to the fast heating speed, the austenite composition is uneven. As a result, the hardenability decreases, and there is often a small amount of finer pearlite around the unmelted ferrite. This layer of structure is also called the transition layer, and the hardness begins to decrease.

The heating temperature of the core is lower than Ac1, and no phase change occurs during heating. Therefore, the original structure of the scale after quenching still maintains the hardness of the quenched money. If the pre-heat treatment is normalizing, the core structure is sorbite + ferrite. If the pre-heat treatment is annealing, the original structure is pearlite + ferrite. If the pre-heat treatment is modulation treatment, the original structure is tempered. Sorbite.

Due to the different pre-heat treatment of steel, the depth of the hardened layer and the size of the transition zone are often different even if the same heat treatment process is used. Although the same heat treatment process is used, the depth of the single hardened layer and the size of the transition zone are often different. different.

To sum up, the pre-heat treatment of tower gear steel adopts quenching and tempering treatment in order to obtain a wider hardened layer depth on the tooth surface, and at the same time, the matrix can maintain high strength and toughness, that is, good comprehensive mechanical properties, and it has relatively good overall mechanical properties. Good ability to resist impact loads.