High Precision Stainless Steel Investment Casting Parts

Stainless steel investment casting parts have high dimensional accuracy, generally up to CT4-6 (sand casting is CT10-13, die casting is CT5-7). Due to the complicated process of investment casting, there are many factors affecting the dimensional accuracy of castings, for example. The shrinkage of the molding material, the deformation of the investment mold, the change in the amount of the mold during heating and cooling, the shrinkage of the alloy, and the deformation of the casting during solidification, etc., so the dimensional accuracy of ordinary investment castings is high, but The consistency still needs to be improved (the dimensional consistency of castings using medium and high temperature waxes is much higher).
When casting stainless steel castings, the molding with high cavity surface finish is adopted, so the surface finish of the investment mold is also relatively high. In addition, the shell is made of a refractory paint made of a special binder and a refractory material which is resistant to high temperature, and is coated on the investment mold, and the inner surface of the cavity which is in direct contact with the molten metal has a high surface finish. Therefore, the surface finish of the investment casting is higher than that of the general casting, and generally reaches Ra.1.6-3.2μm.
The purpose of the mirror treatment is to enhance the hardness and gloss of the cast stainless steel castings. What factors are excluded to make this treatment process meet the requirements?
First, through experiments, it is found that the sulfuric acid oxide film is an important factor affecting the high purity and transparency of the oxide film of stainless steel castings. Its thickness, porosity, purity, sealing quality, etc. will directly interfere with the mirror effect of the casting. For example, when the oxide film contains a large amount of impurities, its purity is low and the transparency is lowered.
Second, the impurities in the oxide film are mainly derived from the stainless steel casting itself, and some are derived from the oxidation bath, so the content of the alloying elements in the casting can be appropriately reduced to minimize the impurity content. At the same time, reducing the impurity ions in the bath and keeping the bath fresh can also improve the purity of the oxide film.