The melting point of cast steel is high, the molten steel is easy to oxidize, the fluidity of molten steel is poor, and the shrinkage is large. The volume shrinkage rate is 10-14%, and the linear shrinkage rate is 1.8-2.5%. In order to prevent defects such as undercasting, cold shut, shrinkage cavity and shrinkage porosity, cracks and sand sticking in steel castings, more complicated technological measures must be taken.

1. Due to the poor fluidity of molten steel, in order to prevent cold shut and insufficient pouring of steel castings, the wall thickness of steel castings should not be less than 8mm; the structure of the pouring system should be as simple as possible; dry casting or hot casting should be used; The temperature is generally 1520 ° ~ 1600 ° C, because the pouring temperature is high, the superheat of the molten steel is large, and the time to maintain the liquid state is long, and the fluidity can be improved. However, if the pouring temperature is too high, it will cause defects such as coarse grains, hot cracks, pores and sand sticking. So for general small, thin-walled and complexly shaped casting, its pouring temperature is about the melting point of steel + 150 ℃; for large, thick-walled casting, its pouring temperature should be about 100 ℃ higher than its melting point.

2. Due to the large shrinkage of Casting Steel, in order to prevent shrinkage cavities and shrinkage defects in castings, measures such as risers, chillers and subsidies are mostly used in the casting process to achieve sequential solidification.

3. In order to prevent shrinkage cavity, shrinkage porosity, porosity and crack defects in steel castings, the wall thickness should be uniform, sharp corners and right-angle structures should be avoided, sawdust should be added to the casting sand, coke should be added to the core, and Use hollow cores and oil sand cores to improve the concession and air permeability of sand molds or cores.

4. The melting point of casting steel is high, and the pouring temperature is correspondingly high. The molten steel interacts with the mold material at high temperature, and it is very easy to produce sticky sand defects. Therefore, artificial quartz sand with high refractoriness should be used as the Casting Mold, and the coating made of quartz powder or zirconium sand powder should be brushed on the surface of the casting mold. In order to reduce the source of gas, improve the fluidity of molten steel and the strength of the mold, most steel casting are cast in dry or quick-drying molds, such as water glass quartz Sand Cast molds hardened by CO2.