The production method of steel castings

(1) Smelting of cast steel. Cast steel must be melted by electric furnace, mainly electric arc furnace and induction electric furnace. According to the different lining materials and slag systems used, it can be divided into acid furnaces and alkaline furnaces. Carbon and low-alloy steels can be melted in either furnace, but high-alloy steels can only be melted in alkaline furnaces.
(2) Casting process. Cast steel has a high melting point, poor fluidity, and molten steel is easy to oxidize and suction. At the same time, its volume shrinkage rate is 2~3 times that of gray cast iron. Therefore, the casting performance of cast steel is poor, and it is easy to produce defects such as insufficient pouring, porosity, shrinkage holes, hot cracking, sticky sand, and deformation. In order to prevent the occurrence of the above defects, corresponding measures must be taken in the process.
The molding sand for the production of steel castings should have high refractory and sticky sand resistance, as well as high strength, air permeability and concession. The raw sand usually adopts silica sand with larger particles and uniform particles; In order to prevent sticking sand, the surface of the cavity is coated with a more refractory coating; When producing large pieces, sand molds or water glass sand are used faster than casting molds. In order to improve the strength and concession of the mold, various additives are often added to the molding sand.
In the design of the gating system and riser. Since cast carbon steel tends to solidify layer by layer and shrinkage is large, the principle of sequential solidification is used to set the pouring system and riser. To prevent the appearance of shrinkage holes and shrinkage looseness. Generally speaking, steel castings are equipped with risers. Cold iron is also widely used. In addition, the bottom injection pouring system with simple shape and large cross-sectional area should be used as much as possible to make the molten steel quickly and smoothly fill the mold.
(3) Heat treatment. The heat treatment of cast steel is usually annealed or normalized. Annealing is mainly used for w(C)≥0.35% or steel castings with particularly complex structure, such castings have poor plasticity, large casting stress, and castings are easy to crack. Normalizing is mainly used for w(C)≤0.35% steel castings, which have low carbon content, good plasticity, and are not easy to crack when cooled.