Defects and countermeasures of induction hardening hardening layer of gear

Guide: Gear material hardenability is too low or too high, carbon content is too high or too low.  Countermeasures: 1) Choose suitable hardenability steel according to the size and technical requirements of the gear.  2) The carbon content of gear should meet the requirements of GB/T 699 -- 1999 and GB/T 3077 -- 1999, and its composition deviation should meet the requirements of GB/T 222 -- 2006.  

Hardening layer too shallow or too deep   

1. Causes  

The hardenability of gear material is too low or too high, and the carbon content is too high or too low  

Countermeasures:  

1) Select suitable hardenability steel according to the size and technical requirements of the gear.  

2) The carbon content of gear should meet the requirements of GB/T 699 -- 1999 and GB/T 3077 -- 1999, and its composition deviation should meet the requirements of GB/T 222 -- 2006.  

2. Causes  

The induction heating frequency is improperly selected, too high or too low, and in this case, reasonable specific power and heating time is not selected, and the current penetration depth is too thin or too deep, which directly affects the depth of the heating layer, leading to the hardening layer depth does not meet the technical requirements.  

Countermeasures:  

(1) Induction heating frequency should be reasonably selected according to the depth requirements of hardened layer. The relationship between depth of various hardened layers and current frequency will be introduced gradually in the future.  

(2) When the depth of the hardening layer is required to be greater than the current penetration depth that can be achieved by the current frequency of the existing equipment, the following methods can be used to obtain a deeper hardening layer under the condition that the surface is not overheated  

1) Reduce the specific power and prolong the heating time.  Continuous heating and quenching can reduce the relative speed of motion between the inductor and the gear  

2) Appropriately increase the gap between the gear and the inductor to extend the heating time, or use the intermittent heating method when heating at the same time to increase the heat conduction time  

3) Before induction heating, the gear is preheated in the inductor  

4) When heating continuously, double or multi-turn inductor is used  

5) When the gear size is large and the power of the equipment is insufficient, the continuous sequence heating and quenching should be adopted to minimize the surface area heated in the inductor to improve the specific power and take preheating measures at the same time  

3. Causes  

If the induction heating time is too short or too long, it has a great effect on the heating temperature and heating depth of the gear surface, and determines the hardening layer depth  

Countermeasures: Reasonable induction heating time is determined according to the depth of gear hardening layer  

4. Causes  

Unit power is too high or too low, the length of heating time, affect the surface heating temperature and heating speed and material austenitizing temperature  

Countermeasures: According to the depth requirements of gear hardening layer reasonable selection of unit power  

5. Causes  

The gap between the inductor and the gear is too small or too large, resulting in different heating depth, so the hardening depth is obviously different  

6. Causes  

The gear (or inductor) moves too fast or too slow during continuous quenching  

Countermeasures: when the gear adopts continuous quenching mode, the appropriate moving speed can be determined through the test  

7. Causes  

Improper quenching cooling process, such as improper selection of temperature, pressure and composition of quenching cooling medium  

Countermeasures: improve quenching cooling process, increase cooling speed, and adopt preheating mode  

Reasons for uneven hardening layer  

1. Causes  

When the gear is heated at the same time, its position is eccentric  

Countermeasures: In the use of simultaneous heating, gear position should be put straight  

2. Causes  

The sensor's blowhole is uneven  

Countermeasure: When the inductor is designed and made, the spray hole should be evenly distributed to ensure that the hardened part can get uniform cooling  

3. Causes  

The top and bottom centers of the quenching machine are different  

Countermeasure: the concentricity of top and bottom center of quenching machine should be <0.05mm  

4. Causes  

Unqualified internal organization of gear raw materials (such as serious banded organization and reticulated carbides)  

Countermeasures: to ensure the quality of raw materials, and high-magnification structure inspection;  Before induction hardening, the gear should be normalized or tempered  

The hardening depth changes beyond the required range  

1. Causes  

Gear material factors.  In addition to the quantitative variation of C and Mn, other alloying elements, especially Mo and Cr, greatly affect the hardenability of materials. If the cutting gear inspection finds that the depth of heating layer is similar, but the hardenability depth changes greatly, it may be the material factor  

Countermeasures: Ensure the quality of raw materials, check the chemical elements that affect hardenability, and the deviation of the main chemical components should comply with GB/T 222-1999  

2. Causes  

Quenching cooling medium pressure, flow, liquid temperature, concentration will affect the depth of hardened layer, must be checked  

Countermeasures: strictly enforce quenching cooling specifications.  Check whether the pressure, flow rate, liquid temperature and concentration of quenching cooling medium meet the requirements  

3. Causes  

There are great changes in the induction heating electrical specifications and changes in the moving speed of the continuously quenched gear bracket  

Countermeasures: check whether the induction heating electrical specification changes greatly, and the continuous quenching gear should ensure that the bracket moving speed is stable