Stainless steel has higher precision casting mechanical properties than cast iron, but its casting performance is not as good as cast iron. Due to the high melting point of stainless steel precision casting, the fluidity of molten steel is poor, the steel is prone to oxidation, and the shrinkage is large. The linear shrinkage is about 1.8-2.5%, and the volumetric shrinkage rate is about 10-14%. To prevent defects such as cold shut, insufficient pouring, shrinkage porosity, shrinkage porosity, sand adhesion, and cracks in cast steel parts, more complex process measures must be taken than cast iron:
1) The structure of the pouring system strives for simplicity, and the cross-sectional size is larger than that of cast iron, generally using dry casting or hot casting; Due to the poor fluidity of molten steel, in order to prevent cold insulation and insufficient pouring of cast steel parts, the wall thickness of cast steel parts cannot be less than 8mm; Appropriately increase the pouring temperature, as high pouring temperature leads to high overheating of the molten steel, while maintaining its liquid state for a long time, which can improve its fluidity. However, excessive pouring temperature can cause defects such as hot cracking, coarse grain size, sand adhesion, and porosity. Therefore, the pouring temperature of large and thick walled castings is generally about 100 ℃ higher than their melting point; Thin walled, small, and complex shaped castings are poured at a temperature of approximately 150 ℃ above the melting point of steel.
2) Because stainless steel has a much larger shrinkage rate than cast iron in precision casting, in order to prevent casting defects such as shrinkage porosity and porosity, measures such as cold iron, riser, and subsidies are mostly used in the casting process to achieve sequential solidification.
In addition, to prevent shrinkage, porosity, cracks, and porosity defects in stainless steel castings, it is necessary to avoid sharp and right angled structures, uniform wall thickness, add coke to the core, add sawdust to the molding sand, and use oil sand cores and hollow cores to improve the permeability and setback of the core or sand mold.