How to avoid pitting on the appearance of Custom carbon steel castings
The lower the carbon content of Custom carbon steel castings during casting, the higher the melting point, because its casting performance will be relatively poor, the fluidity will be reduced, and the probability of cracking will increase. The carbon content is less than 0.2% is precision casting low carbon steel, the carbon content is 0.2%-0.5% is precision casting medium carbon steel, and the carbon content is more than 0.5% is precision casting high carbon steel. The appearance of Custom carbon steel castings has pockmarks, how can we avoid this situation?
1. The most important factor affecting the pitting of Custom carbon steel castings is the quality of molten steel.
2. Refractory materials, especially surface layer refractory materials, in addition to the main components should meet the requirements, the impurity content mainly Fe2O3 must be low. Excessively high Fe2O3 content will aggravate the oxidizing atmosphere of the interface reaction and lead to pitting.
3. The calcination temperature of the shell should not be lower than 1150°C, and the holding time should not be less than 35 minutes. The manufacturer of Custom carbon steel castings tells you that the shell that has not been completely burned through will have a small amount of gas generation during casting, and it will participate in the interface reaction between the molten steel and the shell, bringing oxygen into the molten steel to form secondary oxidation. Carbon steel has a high content of C and does not contain Cr, so when it is cooled in air, the interface reaction can only form a decarburization layer without pitting; if there are pitting, the shell is not burnt.
4. Since the temperature of the shell during casting is about 800°C and the temperature of the molten steel is about 1600°C, the temperature of the surface of the Custom carbon steel castings is extremely high at this time, and the metal will not solidify instantly, especially for thick-walled parts. At this time, the oxygen in the atmosphere easily reacts with the metal surface through the mold shell to form oxides, and gathers with the inclusions in the molten steel to form pits. Therefore, when pouring large pieces, add sawdust (or charcoal) to the insulation. , After the module is poured, immediately participate in the heat preservation of the waste wax block cover box, which is an important measure to avoid pitting.