Today, precision castings are a very common and always-processed method, and there are many methods for heat treatment of investment casting carbon steel parts in precision casting. Such as casting full annealing, normalizing and normalizing plus tempering. For particularly large precision castings, most of them use diffusion annealing heat treatment methods. Xiaobian briefly introduce these methods
1, what is full annealing of precision casting.
The casting is heated to the temperature range of the austenite region and stored for a period of time, and then the full annealing heat treatment is taught with the method of furnace cooling, referred to as annealing.
When heating, it is necessary to ensure that the casting does not deform and crack. It should be heated quickly to improve productivity. The heating rate depends mainly on the chemical composition of the steel. The section point of the casting is small and the shape of the casting. Steel has a high carbon content. The thermal conductivity is poor, and the allowable heating rate is low. The larger the cross section of the shoulder pads. The larger the temperature difference of the inner layer during heating, the greater the thermal stress caused, so the heating speed should be slower. Castings with complex shapes and widely varying thicknesses should be heated slowly.
2, normalizing in heat treatment.
The heating temperature and holding time of normalizing are the same as that of full annealing. The difference is that after the holding time is reached, the casting is cooled in the air to normal temperature.
3. Precision casting normalizing and tempering
In order to improve the structural performance of steel, a heat treatment process can be used after tempering. The tempering temperature is 500-650 degrees, which belongs to high temperature tempering, and the heat preservation takes 2-3 hours.
The phenomenon of decarburization on the surface of investment casting is a serious defect. Decarburization will reduce the carbon content of the surface layer of the steel. It is more obvious for medium carbon steel and high carbon steel.
Heat treatment greatly increases the performance of precision mechanical castings. All many companies' casting products are heat treated. But the heat treatment process is more complicated.