The deformation of mould after heat treatment is generally thought to be caused by cooling, which is incorrect. Mold, especially complex mold, the correctness of processing technology often has a great influence on the deformation of mold. It can be clearly seen from the comparison of heating processes of some molds that faster heating speed often leads to greater deformation.

(1) causes of deformation

Any metal will expand when heated, because when steel is heated, the temperature of each part in the same mold is uneven (that is, uneven heating), which will inevitably lead to inconsistent expansion of each part in the mold, thus forming internal stress due to uneven heating. At the temperature below the transformation point of steel, uneven heating mainly produces thermal stress, and when it exceeds the transformation temperature, uneven heating will also produce non-isochronous microstructure transformation, which will not only produce structural stress. Therefore, the faster the heating speed, the greater the temperature difference between the mold surface and the core, and the greater the stress and deformation of the mold after heat treatment.

(2) Preventive measures

When the complex mold is heated below the phase transition point, it should be heated slowly. Generally speaking, the deformation of the mold after vacuum heat treatment is much smaller than that after quenching in salt bath furnace. ? Adopt preheating, one-time preheating (550-620? c)； Secondary preheating (550-620? C and 800-850? C) carry out the test.

2. Influence of heating temperature

Some manufacturers think that it is necessary to increase the quenching heating temperature in order to ensure the high hardness of the die. However, production practice shows that this method is not suitable. For complex molds, heating quenching is also carried out at normal heating temperature, and the heat treatment deformation after heating at the upper allowable temperature is much greater than that at the lower allowable temperature.

(1) deformation reason

As we all know, the higher the quenching heating temperature, the larger the grain size of steel. Because larger grains can increase hardenability, the greater the stress produced during quenching and cooling. Furthermore, because most complex dies are made of medium-high alloy steel, if the quenching temperature is high and the Ms point is low, the amount of retained austenite in the microstructure will increase, thus increasing the deformation of the dies after heat treatment.

(2) Preventive measures

Under the condition of ensuring the technical conditions of the mold, the heating temperature should be reasonably selected and the quenching heating temperature should be as low as possible to reduce the stress during cooling, thus reducing the complicated heat treatment deformation.