Casting defects such as sand holes, air holes, cracks, shrinkage porosity, and shrinkage cavities often appear in steel castings. How to improve the steel casting process? Here are some tips to ensure casting quality. We’ll also get into the difference between forged steel and cast steel.
Tips & Guide to Steel Casting
It is difficult to control production, especially for alloy steel castings in a sand mold. Cast steel has a high melting point, easy oxidation of molten steel, poor fluidity of molten steel, and large shrinkage. Its volume shrinkage is 10-14% and linear shrinkage is 1.8-2.5%. In order to prevent defects in steel castings, more complicated technological measures must be taken.
1) Due to the poor fluidity of the molten steel, the wall thickness of the steel casting shall not be less than 8mm in order to prevent cold insulation and insufficient pouring of the steel casting; The structure of the gating system shall be simple; Dry casting mold or hot casting mold is adopted; Properly raise the pouring temperature, generally 1520 ° ~ 1600 ℃, because the pouring temperature is high, the superheat degree of molten steel is large, and the time to keep the liquid state is long, and the fluidity can be improved. However, if the pouring temperature is too high, it will cause defects such as coarse grain, hot crack, porosity, and sand sticking. Therefore, for small, thin-walled, and complex castings, the pouring temperature is about the melting point temperature of steel + 150 ℃; The pouring temperature of large and thick wall casting is about 100 ℃ higher than its melting point.
2) Due to the large shrinkage of cast steel, in order to prevent shrinkage cavities and porosity defects, riser, cold iron, and subsidies are mostly adopted in the casting process to achieve sequential solidification.
3) In order to prevent shrinkage, porosity, and crack defects of steel castings, the wall thickness shall be uniform, sharp angle and right angle structure shall be avoided, sawdust shall be added to the molding sand for casting, coke shall be added to the core, and hollow core and oil sand core shall be used to improve the yield and air permeability of the sand mold or core.
4) The melting point of cast steel is high, and the corresponding pouring temperature is high. The interaction between molten steel and mold material at high temperature is easy to produce sand sticking defects. Therefore, artificial quartz sand with high fire resistance should be used as the casting mold, and the coating made of quartz powder or zirconium sand powder should be brushed on the surface of the casting mold. In order to reduce the source of gas, and improve the fluidity of molten steel and the strength of casting mold, most steel castings are cast with dry mold or fast dry mold, such as CO2 hardened water glass quartz sand mold.
What is the difference between forged steel and cast steel?
Forged steel refers to various forged materials and forgings produced by the forging process, cast steel is the steel used for casting.
Forged steel is often used in the manufacture of some important machine parts. Cast steel is mainly used to manufacture some parts with complex shapes, which are difficult to forge or cut and require high strength and plasticity.
Forged steel can withstand large impact force, and its plasticity, toughness, and other mechanical properties are higher than those of steel castings. There are many impurities in the cast steel material, the material is brittle, the strength is poor, the internal stress is large, and the internal structure is loose.