1. Smelting
In the smelting process, try to reduce the content of harmful elements such as P and S, and reduce the content of gases and inclusions such as N, H and O. By using low phosphorus steel intermediate alloy, it can achieve a good effect.
2. Casting structure
During casting, factors affecting the liquid and solid shrinkage of castings, such as structure, shape, size, wall thickness and transition, etc. should be fully considered, and appropriate process parameters should be selected to prevent casting defects such as shrinkage cavity and porosity.
3. Heat preservation
By properly extending the holding time of castings in sand mold, mainly by controlling the unpacking temperature below 70℃, the liquid and solid shrinkage of castings in sand mold can be fully completed to avoid the occurrence of stress concentration caused by external factors.
4. Falling sand
In the process of casting sand drop cleaning, it is strictly prohibited to water the sand mold and casting when hitting the box, and it is strictly prohibited to use strong external force such as box bump to sand drop, so as to avoid cracks caused by the interaction between external force and the internal stress of casting.
5. Cut the riser
According to the casting conditions, select the appropriate hot cutting casting riser process to ensure that the initial temperature of hot cutting is not less than 300℃. During operation, the gas cutting gun and oxygen blowing tube are cut by vibration.
6. Increase annealing
Add a final stress relief annealing process for major stainless steel castings, strictly control the holding time and temperature. The aim is to reduce the new stress concentration in the production process, eliminate the internal stress of the casting more thoroughly and prevent the crack.
7. Preheat
The principle of preheating should be adhered to when the stainless steel castings are treated with defects. In the process of blowing and welding, the workpiece should be preheated to more than 108℃ before operation.
Two, share the main reasons for stainless steel casting pores are as follows
1, the paint is poor in air permeability or negative pressure is insufficient, the filling sand is poor in air permeability, and the gas and residue in the cavity can not be discharged in time, forming pores under the filling pressure.
2. The casting speed is too slow, failing to fill the pouring cup, exposing the straight runner, getting involved in air, inhaling slag, forming wrapping pores and slag holes.
3. Foam model gasification decomposition generates a large number of gases and residues can not be timely discharged from the casting, foam, coating layer filled with dry sand drying is poor, surrounded by liquid alloy at high temperature, cracking a large number of hydrogen and oxygen into the casting is the main reason for the formation of pores.
4. The connection between the pouring cup and the straight runner and the pouring system is not well sealed, especially the connection between the straight runner and the pouring cup is not well sealed. This phenomenon can be calculated and explained by Bernoulli equation.
5. Due to the unreasonable design of the gating system, the filling speed of the metal liquid is greater than the foam gasification yield and gas discharge speed, and the re-gasification of the metal liquid forms the black decomposition pores on the inner wall.
