What is the difference between cast iron valves and cast steel valves?

The main difference between cast iron and steel valves is the carbon content, which directly affects the strength and plasticity of the steel. Carbon steel, also known as carbon structural steel, is an iron-carbon alloy with a carbon content (WC) of less than 2%. In addition to carbon, carbon steel generally contains small amounts of silicon, manganese, sulfur, and phosphorus. According to their Applications, carbon steel can be divided into three categories: carbon structural steel, carbon tool steel, and easy-cutting structural steel. Carbon structural steel is further divided into two types: construction structural steel and machine manufacturing structural steel. Based on carbon content, carbon steel can be classified into low carbon steel (WC ≤ 0.25%), medium carbon steel (WC 0.25% - 0.6%), and high carbon steel (WC 0.6%). Based on phosphorus and sulfur content, carbon steel can be divided into ordinary carbon steel (higher phosphorus and sulfur content), carbon steel (lower phosphorus and sulfur content), and steel (even lower phosphorus and sulfur content). Generally, the higher the carbon content in carbon steel, the higher the hardness and strength, but the plasticity is lower.

Cast Iron

Cast iron is an iron-carbon alloy with a carbon content of more than 2%.

Cast iron can be divided into

1. Gray cast iron 2. White cast iron 3. Ductile cast iron 4. Nodular cast iron 5. Vermicular cast iron 6. Alloy cast iron

Generally, the cast iron valves we refer to are made of ductile cast iron, obtained by spheroidizing gray cast iron molten iron. The precipitated graphite is spherical, abbreviated as ductile iron. It has higher strength, better toughness, and plasticity than ordinary gray cast iron.

Cast Steel

Steel used for casting castings. A type of casting alloy. Cast steel is divided into three categories: cast carbon steel, cast low-alloy steel, and cast special steel. Cast carbon steel is cast steel with carbon as the main alloying element and contains small amounts of other elements. Cast low-carbon steel has a carbon content of less than 0.2%, cast medium-carbon steel has a carbon content of 0.2% to 0.5%, and cast high-carbon steel has a carbon content of more than 0.5%. As the carbon content increases, the strength and hardness of cast carbon steel increase. Cast carbon steel has high strength, plasticity, and toughness, and is cost-effective. It is used in heavy machinery to manufacture parts that bear large loads, such as rolling mill frames, hydraulic press bases, etc.; in railway vehicles, it is used to manufacture parts that bear large forces and impacts, such as rocking beds, side frames, wheels, and couplings.

From the characteristics of the materials mentioned above, cast iron has stronger rigidity and greater brittleness than cast steel, while cast steel has better plasticity and toughness than cast iron. Therefore, cast iron is generally used in pipelines with lower pressure and can only be used in pipelines at room temperature, as an increase in pressure or temperature indicates that the valve will undergo a certain amount of micro-deformation, which is detrimental to cast iron valves. In contrast, cast steel valves can be used in pipelines with higher pressure or temperature.

Applications of Cast Iron Valves

For example, the valves we often see used in water supply pipelines are coated with black paint, and these valves are cast iron valves.