How to prevent cracks in stainless steel precision castings?

Most of the important parts of the turbine are made of stainless steel castings, such as ZG06Cr13Ni4Mo, ZG06Cr16Ni5Mo, etc. Stainless steel precision casting of this material has weak processing performance, poor circulation, relatively large body shrinkage and line shrinkage, large internal stress, and is very easy to crack. Once the casting cracks, not only will the maintenance work be intensive, but it will also be damaged in serious cases, resulting in serious property losses. The formation factors of casting cracks are usually the casting structure, forging process, etc., and the following methods are generally used to prevent them during the production process:

1. Casting structure

When forging, the structure, shape, size, thickness and connection of castings should be considered in all aspects, and the factors affecting the liquid and solid shrinkage of castings should be considered, and appropriate process parameters should be selected to avoid welding defects such as shrinkage and porosity. The design of the casting riser control system must be scientific. If you want to use sprue and other process countermeasures, its placement must be scientific. It is necessary to ensure the compactness of the internal structure of the casting and avoid stress as much as possible.

2. Smelter

In the smelting plant link, the content of harmful elements such as P and S should be reduced as much as possible, and the content of gas and inclusions such as N, H and O should be reduced. By adopting low-phosphorus steel master alloy, it can play a certain effect.

3. Thermal insulation

Properly increase the heat insulation time of castings in the sand mold, usually by controlling the unpacking temperature to be less than 70°C, to ensure that the stainless steel precision casting parts are fully packed in liquid and solid in the sand mold, and to prevent stress caused by external forces.

4. Shaking sand

In the sand removal process of castings, it is forbidden to pour sand molds and castings when boxing, and it is forbidden to use strong external force impact methods such as boxing to prevent external force and casting thermal stress from interacting and cracking.

5. Laser cutting gate

According to the casting standard, select the appropriate processing method of thermal cutting riser to ensure that the starting temperature of thermal cutting is not less than 300°C. During operation, the gas cutting torch and oxygen blowing tube are cut by vibrating laser. Immediately after oxy-cutting important parts, use glass fiber cotton to cover the gap or enter the furnace for heat treatment. For castings with complicated structures such as upper crowns and axial flow fan blades, unique technical measures are used for castings, and secondary thermal cutting is used.