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Steel Casting Defects

The mechanical properties of steel casting are higher than iron casting, but its casting character is worse than iron casting. Because of the higher melting point of steel, the steel liquid is easily oxidized and its fluidity is very poor, the volume shrinkage rate is 10% to 14% and the linear shrinkage is 1.8% to 2.5%. In order to prevent missing portion of casting, cold shut, shrinkage, cracks, sticky sand and other defects, more complex measures must be taken.

Due to the poor fluidity of liquid steel, the wall thickness of steel castings can not be less than 8.0 mm in order to prevent cold shut and missing portion of casting. The structure of the gating system should be as simple as possible, and the cross-sectional size is larger than cast iron. Use dry cast type or hot mold and increase appropriate casting temperature, typically 1520~1600 Celsius degree, because of the high pouring temperature, overheating degree of molten steel, and long liquid state, the liquidity can be improved.

But if the gating temperature is too high, it will cause casting defects such as coarse grains, thermal cracking, pores and sticky sand. Therefore, for generally small castings with thin wall and complex shape, the casting temperature is about steel melting temperature +150 Celsius degree, while for the large, thick-walled castings, the pouring temperature is about 100 Celsius degree higher than its melting point.

Since the shrinkage of steel casting is much larger than iron casting, in order to prevent shrinkage and other defects, in the casting process, riser and chiller and subsidies and other measures are usually taken to achieve progressive solidification.

In addition, to prevent shrinkage, porosity and crack defects, the wall thickness should be even, avoiding sharp corners and rectangular structure. Adding sawdust in the foundry sand, adding coke in the core, and using hollow core and oil sand cores will improve the yield and permeability of foundry sand and sand cores.

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