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There are many heat treatment methods for investment ca […]
There are many heat treatment methods for investment casting carbon steel parts in precision casting. For example, the casting is fully annealed, normalized and normalized plus tempered. For extremely large precision castings, most of the heat treatment methods are diffusion annealing.
1. What is precision casting full annealing.
Heat the casting to the temperature range of the austenite zone and store it for a period of time, and then teach the full annealing heat treatment with the furnace cooling method, referred to as annealing.
When heating, under the premise of ensuring that the casting does not produce deformation and cracking. It should be heated quickly to increase production capacity. The heating rate mainly depends 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. If the thermal conductivity is poor, the allowable heating rate is low. The larger the section of the shoulder guard. The greater the temperature difference of the inner layer during heating, the greater the thermal stress caused, so the heating speed should be slower. For castings with complex shapes and large differences in section thickness, the heating speed should be slower.
2. Normalizing in heat treatment.
The heating temperature and holding time of normalizing are the same as those of full annealing. The difference is that after the holding time is reached, the casting is placed in the air and cooled to normal temperature.
3. Precision casting normalizing and tempering
In order to improve the structural properties of steel, a heat treatment process that is tempered after normalizing can be used. The tempering temperature is 500-650 degrees, which belongs to high temperature tempering, and the heat preservation takes 2-3 hours.
The surface decarburization of investment castings is a serious defect. Decarburization will reduce the carbon content of the steel surface layer. It is more obvious for medium carbon steel and high carbon steel.
Heat treatment greatly increases the performance of precision machinery castings. All casting products of many companies are heat treated. However, the heat treatment process is more complicated.