| Classification |
Analysis |
Countermeasures |
Overheating
or
Overburning |
1) Thermocouple temperature measurement is not accurate, resulting in high temperature. |
1) Regular inspection. |
| 2) Inappropriate material-feeding method. |
2) Achieve even heating. |
| 3) Batch mixing of different grades of steels. |
3) Differentiating grades of steels before quenching. |
Quenching
Distortion |
1) Overhigh quenching temperature. |
1) Referring to the introduction of products to adjust the heating temperature, regularly check the temperature measurement device. |
| 2) Inappropriate hoisting during heating and cooling. |
2) Improve the hoisting device; consider the weight of the work piece. |
| 3) Methods of heating and cooling |
3) Strengthen the preheating, and controlling the cooling velocity after classification. |
Quenching
Cracking |
1) Shape defect; radius is too small |
1) Increase radius. |
| 2) Overheating or overburning. |
2) Referring to the introduction of products to decide whether to increase temperature or not; regularly check temperature-measuring device. |
| 3) The residual decarburized layer leads to the difference of transition, which is between surface and central structure. |
3) Control the machining allowance before quenching. |
| 4) Poor organization of raw materials (carbide segregation is serious). |
4) Control the sources of raw materials, and strengthen inspection. |
| 5) Inappropriate cooling conditions. |
5) For the work piece of complex shape and uneven thickness, after classification quenching, cooling velocity of martensite transformation temperature range should be reduced or isothermal quenching should be adopted. |
| 6) Tempering is not timely or inadequate. |
6) Cool to room temperature and timely tempering, and supplementary tempering is needed. |
| 7) Stress corrosion cracking. |
7) After quenching, washing for cleaning is necessary. The temperature of the work piece and the temperature of water should be controlled well. |
Poor
Hardness |
For low hardness： |
|
| 1) The chemical composition of the steel is not qualified or materials are mixed. |
1) Strengthening material-feeding management |
| 2) Quenching temperature is too low. |
2) Referring to the introduction of products to decide whether to increase temperature, and adjust the amount of materials for feeding while heating evenly. |
| 3) Quenching temperature is too High (Serious overheating or overburning). |
3) Referring to the introduction of products to decide whether to increase temperature or not; regularly check temperature-measuring device. |
| 4) Quenching cooling velocity is slow. |
4) Accelerate quenching cooling. |
| 5) Tempering furnace-feeding temperature is too high or not sufficient. |
5) Cool to room temperature and timely tempering, and supplementary tempering is needed. |
| 6) When decarburization (residual raw material and heat treatment process) |
6) Strictly ensure the minimum machining allowance. Check salt bath deoxidation or the vacuum degree in vacuum furnace. |
| When the hardness is relatively high： |
|
| 7) Quenching temperature is relatively high. |
7) Reduce the heating temperature properly. |
Insufficient
Tempering |
1) Inaccurate temperature measurement. |
1) Regularly check the temperature measurement device. |
| 2) The amount of materials for feeding furnace is not proper. |
2) Adjust the amount of materials for feeding while heating evenly. |
| 3) Carbide pile-up of raw materials. |
3) Control the sources of raw materials, and strengthen inspection. |
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