The purpose of heat treatment is to change the structure of metal or alloy through heating and cooling to make it have the properties required by engineering and technology. In the process of heat treatment quenching and normalizing of large forgings, the first step is to heat the forgings to an appropriate temperature to complete the transformation of austenitic aluminum alloy forgings. The heating of large aluminum alloy forgings is different from that of small and medium-sized ones. According to the characteristics of large forgings, different heating methods are used. The core problem is to minimize the thermal stress of temperature difference during the heating process to ensure that the existing defects will not expand. It is also necessary to consider not staying too long in the high temperature stage to prevent the growth of austenite grains. Therefore, when formulating the heating process of large forgings, comprehensive consideration should be given to one or the other.

Step heating process of aluminum alloy forgings:

1. Feeding

There are no special requirements for medium and small forgings of general carbon steel and low alloy steel. For some large high alloy steel stainless steel forgings, the temperature in the furnace should be less than 450 ℃ and kept for a certain time.

2. Heating speed during low temperature heating

As the forging heart is still in elastic state at low temperature, the high temperature difference is easy to cause excessive thermal stress, which will lead to cracking of the forging.

3. Keep in the middle

In the heat treatment process of large stainless steel forgings, the intermediate holding step heating process is widely used.

4. Keep the heating speed in the middle

After intermediate holding, the temperature difference between the forging surface and the heart basically disappears. At this time, the heart temperature of the stainless steel forging is high and it is already in a plastic state. Therefore, at this time, higher heating speed can be used to continue heating. Even if a second temperature difference is generated at this time, it will not cause greater damage to the forging.

5. Average temperature

The concept of average temperature is determined by the heating characteristics of large forgings. Generally speaking, the heating furnace for large stainless steel forgings is relatively large, and the furnace temperature uniformity is poor. The operator mainly observes the temperature in the furnace through the thermometer of the thermocouple.

6. Thermal insulation

After the average temperature is completed, the insulation stage will be started. The function of heat preservation is to make the heart temperature of the workpiece reach the heating temperature and complete the transformation of austenite.