Tempering Time and Tempering Frequency

Tempering Time: The tempering time is generally determined according to the size and furnace loading of the mold. Usually, the tempering time is between 1 - 3 hours. For larger - sized and more - loaded molds, the tempering time needs to be appropriately extended. This is because heat transfer inside the mold takes time, and sufficient tempering time can ensure that the microstructure inside the mold changes fully and uniformly and effectively eliminates internal stress. For example, for a large - scale die - casting mold, the tempering time may need to be about 3 hours to better release the stress inside the entire mold.

Tempering Frequency: High - carbon steel molds generally need to be tempered multiple times. This is because it is difficult to completely eliminate the residual stress generated by quenching with a single tempering. Usually, the tempering frequency is 2 - 3 times. After the first tempering, there will still be some residual stress inside the mold. Through subsequent tempering, these stresses can be further released. After each tempering, the microstructure stability and performance of the mold will be further improved. For example, during the second tempering, the remaining stress inside the mold will continue to decrease, and the balance between the hardness and toughness of the mold will be further optimized, thus improving the quality and service life of the mold.

 

 

 

Cooling Method after Tempering

The cooling method after tempering also has an important impact on the quality of the mold. Generally, air - cooling is adopted, that is, the mold is allowed to cool naturally in the air. This can avoid the generation of new internal stresses due to too - fast cooling. If a rapid - cooling method such as water - cooling or oil - cooling is used, a large temperature difference will be generated between the surface and the core of the mold, which will lead to new stress concentration and affect the dimensional accuracy and performance of the mold. Air - cooling can enable the mold to cool in a more stable state, ensure the microstructure stability after tempering, and thus improve the quality of the mold.

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