Practical Analysis and Countermeasures for Problems in the Production and Cleaning of Large Steel Castings

Large steel castings can be divided into two major categories according to chemical composition: carbon cast steel and alloy cast steel. Among them, carbon cast steel is widely applied, accounting for more than 80% of the total output of steel castings, and it is used for machine parts that require high strength, plasticity and toughness.

Based on years of casting experience, manufacturers of large steel castings have found that cast steel features a high melting point, easy oxidation of molten steel, poor fluidity of molten steel, and large shrinkage tendency. These characteristics easily cause casting defects such as misrun, cold shut, shrinkage cavity, shrinkage porosity, cracks and sand adhesion.To guarantee the quality of steel castings, manufacturers adopt targeted solutions for each process section. For example, to prevent shrinkage cavity and shrinkage porosity, risers, chills and padding are applied to realize directional solidification.

To prevent large steel castings from generating defects such as shrinkage cavities, shrinkage porosity, blowholes and cracks, manufacturers avoid sharp corner and right-angle structures, select suitable coatings for the mold according to actual working conditions, and improve the collapsibility and air permeability of sand molds or cores.

Casting defects such as blowholes, cracks, shrinkage cavities, shrinkage porosity, coarse grains, uneven microstructure and residual internal stress exist inside steel castings in the as-cast state, which greatly reduce the strength of steel castings, especially their plasticity and toughness. Therefore, heat treatment is required to ensure their service life and comprehensive performance.

When smelting steel castings, appropriate smelting equipment such as electric arc furnaces, induction furnaces and refining furnaces shall be selected according to factors including material requirements, production scale and quality standards. By doing so, manufacturers of large steel castings can effectively improve the quality and service life of steel castings.