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

The primary distinction between cast iron and steel valves lies in their carbon content, which directly influences the strength and ductility of the steel. Carbon steel, also known as carbon steel, is an iron-carbon alloy with a carbon content (WC) of less than 2%. In addition to carbon, carbon steel typically contains small amounts of silicon, manganese, sulphur, and phosphorus. Based on their application, carbon steels can be categorised into three types: carbon structural steel, carbon tool steel, and free-cutting structural steel. Carbon structural steel is further divided into two types: building 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 sulphur content, carbon steel can be classified into ordinary carbon steel (higher phosphorus and sulphur content), carbon steel (lower phosphorus and lower sulphur content) and steel (lower phosphorus and sulphur content). Generally, the higher the carbon content in carbon steel, the higher the hardness and strength, but the lower the ductility.

Cast iron

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

Cast iron can be divided into

1. Grey cast iron 2. White cast iron 3. Malleable cast iron 4. Ductile cast iron 5. Vermicular cast iron 6. Alloy cast iron

The cast iron valves we commonly refer to are made of ductile iron, which is obtained by spheroidising grey cast iron molten iron. The graphite precipitates in a spherical form, hence the abbreviation ‘ductile iron.’ It has higher strength, better toughness, and greater ductility than ordinary grey cast iron;

Cast steel

Steel used for casting components. 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. Cast steel with carbon as the primary alloying element and containing small amounts of other elements. Those with carbon content below 0.2% are classified as cast low-carbon steel, those with carbon content between 0.2% and 0.5% are cast medium-carbon steel, and those with carbon content above 0.5% are cast high-carbon steel. As the carbon content increases, the strength and hardness of cast carbon steel also increase. Cast carbon steel has high strength, plasticity, and toughness, with relatively low cost. It is used in heavy machinery to manufacture parts subjected to heavy loads, such as rolling mill frames and hydraulic press bases; in railway vehicles to manufacture parts subjected to high stress and impact, such as bogie frames, side frames, wheels, and couplers;

Based on the above material characteristics, cast iron has greater rigidity than cast steel but is more brittle, while cast steel has better ductility and toughness than cast iron. Therefore, cast iron is generally used in pipelines with lower pressure and only at ambient temperatures, as increased pressure or temperature can cause slight deformation of the valve. 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 used in water supply pipelines are often coated with black paint on their surfaces, and these are cast iron valves.