Compared to cast iron (such as gray cast iron or ductile cast iron), pump components made of cast steel are primarily used in industrial applications involving high pressure, high temperature, high strength, or highly corrosive environments. Due to their superior mechanical properties, cast steel parts are the preferred choice for chemical pumps, boiler feed pumps in power plants, and oil and petrochemical process pumps.
Below are the key technical details and application highlights regarding cast steel pump components:
1. Common Classification of Cast Steel Pump Components
Pressure-retaining parts: Casing, pump cover, suction section, discharge section. These components must withstand high system pressure; cast steel offers better density than cast iron, effectively preventing leakage under high pressure.
High-speed rotating parts: Impeller. At high rotational speeds, cast steel provides sufficient strength to resist centrifugal forces and prevent impeller failure.
Load-supporting components: Bearing frame, bearing housing. These require good structural rigidity to maintain shaft alignment accuracy.
2. Commonly Used Cast Steel Materials (Selected Based on Operating Conditions)
The selection of cast steel materials typically follows relevant international standards (such as ASTM, DIN, GB):
Carbon steel castings (e.g., WCB): The most commonly used material in industry, suitable for general service under normal temperature and pressure conditions. Offers excellent weldability and machinability.
Alloy steel castings (e.g., WC6, WC9): Contain elements such as chromium and molybdenum, providing good heat resistance; commonly used in high-temperature, high-pressure boiler feed pumps in power plants.
Stainless steel castings (martensitic stainless steel, e.g., CA15 / ZG0Cr13): Possess good cavitation resistance and moderate corrosion resistance, making them the mainstream material for medium to low-corrosion pump components.
Duplex stainless steels (e.g., CD4MCu, CE3MN): Combine austenitic and ferritic microstructures, offering excellent resistance to stress corrosion cracking; primarily used in chloride-containing media, chemical pumps, and seawater pumps.
Ultra-low carbon austenitic stainless steels (e.g., CF8M, CF3M): Provide outstanding corrosion resistance, mainly used in highly corrosive environments involving acids and alkalis.
3. Characteristics of Cast Steel Production Processes
The melting point of cast steel is significantly higher than that of cast iron (above approximately 1500°C), presenting substantial challenges during the casting process:
High shrinkage: Steel melt has a high volumetric shrinkage rate (approximately 10%–12%), making steel castings highly prone to shrinkage cavities and porosity. Riser design is therefore critical, requiring sufficient feeding channels calculated precisely.
Poor fluidity: Steel melt exhibits lower fluidity than cast iron during pouring. To ensure proper filling of thin-walled sections or complex shapes, higher pouring temperatures are required, which in turn may lead to sand mold sintering.
Tendency to hot cracking: During solidification, steel castings experience significant shrinkage stresses. If the sand mold lacks adequate "yieldability," hot cracks are likely to occur. Special disintegrating resin sands are typically required.