The reason why carbon steel casting has low carbon content and is difficult to cast

Carbon steel castingThe lower the carbon content, the higher the melting point, the worse the casting performance, the lower the fluidity, and the greater the probability of cracking. The carbon content of precision-cast low-carbon steel is less than 0.2%, the carbon content of precision-cast medium-carbon steel is 0.2%-0.5%, and the carbon content of precision-cast high-carbon steel is greater than 0.5%. By analogy, as the carbon content increases, the cost of casting becomes higher.
What is the cause of pitting on the surface of carbon steel casting?
(1) Metal oxide inclusions caused by poor deoxidation of molten steel;
(2) The condition for complete deoxidation is: select boring clean charge, first add ferromanganese, then add ferrosilicon for deoxidation, then add silicon calcium for deoxidation, then cut off the power for 2 minutes, add aluminum and then deoxidize, then heat preservation and pouring. Immediately after pouring, add sawdust or waste wax, cover the box, seal, and cool.
The lower the carbon content in carbon steel casting, the more difficult the casting;
1. The quality of molten steel is an important factor affecting the pitting corrosion of carbon steel precision castings.
2. Since the temperature of the shell is above 800℃ and the temperature of molten steel is above 1600℃ during pouring, the outer surface of carbon steel precision castings has a very high contact temperature, and the metal will not solidify instantaneously, especially for thick-walled parts. At this time, oxygen in the atmosphere can easily react with the outer surface of the metal to form oxides, and the oxides and inclusions in the molten steel aggregate together to form pits. Therefore, when pouring large blocks, sawdust (or charcoal) is added to the insulation material
3. The baking temperature of the shell shall not be lower than 1150℃, and the holding time shall not be less than 35 minutes. The incompletely burned shell will produce a small amount of gas during the pouring process, which participates in the interface reaction between the molten steel and the shell, bringing oxygen into the molten steel to form secondary oxidation. Carbon steel contains high C content and does not contain Cr, so when cooled in the air, the interface reaction can only form a decarburized layer and cannot be pitted; if there are pits, the mold shell will not burn well.
4. For refractory data, especially surface refractory data, in addition to the requirements of the main components, the content of impurities mainly containing Fe2O3 must be low. Excessive Fe2O3 content will aggravate the oxidizing atmosphere of the interface reaction, leading to pitting corrosion.