(1) Melting of cast steel. Cast steel must be melted in electric furnace, mainly electric arc furnace and induction furnace. According to the different lining materials and slag systems used, it can be divided into acidic furnace and alkaline furnace. Carbon steel and low alloy steel can be melted in any kind of furnace, but high alloy steel can only be melted in alkaline furnace.
(2) Casting process. Cast steel has high melting point, poor fluidity, and liquid steel is easy to oxidize and inhale. At the same time, its volume shrinkage 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 cavity, hot crack, sand sticking, deformation and so on. In order to prevent the above defects, corresponding measures must be taken in the process.
Molding sand for steel castings shall have high fire resistance and sand adhesion resistance, as well as high strength, air permeability and yield. Raw sand usually adopts silica sand with large and uniform particles; In order to prevent sand sticking, the surface of the mold cavity is mostly coated with coatings with higher fire resistance; When producing large parts, it is mostly used in sand mold or sodium silicate sand, which is faster than casting mold. In order to improve the strength and yield of the mold, various additives are often added to the molding sand.
In the design of gating system and riser. As cast carbon steel tends to solidify layer by layer with large shrinkage, the principle of rigid sequential solidification is adopted to set the gating system and riser to prevent shrinkage cavity and porosity. Generally speaking, steel castings should be provided with risers. Cold iron is also widely used. In addition, the bottom pouring system with simple shape and large cross-sectional area should be used as far as possible to make the molten steel fill the mold quickly and stably.
(3) Heat treatment. The heat treatment of cast steel is usually annealing or normalizing. Annealing is mainly used for steel castings with w (c) ≥ 0.35% or with particularly complex structure. This kind of castings have poor plasticity, high casting stress and easy cracking. Normalizing is mainly used for steel castings with w (c) ≤ 0.35%. This kind of steel has low carbon content, good plasticity and is not easy to crack when cooling.