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Heat treatment of precision mechanical carbon steel castings

There are many methods for heat treatment of carbon steel castings in investment casting. Such as casting full annealing, normalizing and normalizing plus tempering. For very large precision castings, most of them adopt the heat treatment method of diffusion annealing.

 

1. What is precision casting full annealing.

Heat the casting to the temperature range of austenite zone and store it for a period of time, and then teach full annealing heat treatment with the method of furnace cooling, which is called annealing for short.

During heating, on the premise of ensuring that the casting does not deform and crack. It should be heated quickly to improve the 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 speed is low. The larger the section of the shoulder guard. When heating, the greater the temperature difference in the inner layer, the greater the thermal stress, so the heating speed should be slower. For castings with complex shape and great difference 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 that of full annealing. The difference is that after the holding time is reached, the casting is cooled in air to normal temperature.

 

3. Precision casting normalizing and tempering

In order to improve the structural properties of steel, the heat treatment process of tempering after normalizing can be adopted. The tempering temperature is 500-650 ℃, which belongs to high temperature tempering, and the insulation takes 2-3 hours,

 

4. Carburizing

Surface decarburization of investment castings is a serious defect. Decarburization will reduce the carbon content of the surface layer of steel. It is more obvious for medium carbon steel and high carbon steel.

Heat treatment greatly increases the performance of precision mechanical castings. All the casting products of many companies are heat treated. However, the heat treatment process is more complex.

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