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What's the difference between cast iron valves and cast steel valves?
The primary difference between cast iron and steel valves lies in their carbon content, which directly influences the strength and ductility of the material. Carbon steel, also known as carbon steel, is an iron-carbon alloy with a carbon content (WC) below 2%. In addition to carbon, carbon steel typically contains small amounts of silicon, manganese, sulfur, and phosphorus. Based on their applications, carbon steel can be categorized into three main types: carbon structural steel, carbon tool steel, and free-cutting structural steel.
Release date:
2021-11-09
The primary difference between cast iron and steel valves lies in their carbon content, which directly influences the strength and ductility of the material. Carbon steel, also known as carbon steel alloy, is an iron-carbon alloy with a carbon content (WC) below 2%. In addition to carbon, carbon steel typically contains small amounts of silicon, manganese, sulfur, and phosphorus. Based on their applications, carbon steels are classified into three main categories: carbon structural steel, carbon tool steel, and free-cutting structural steel. Carbon structural steel itself is further divided into two types: construction structural steel and machinery manufacturing structural steel. According to carbon content, carbon steel can be categorized into low-carbon steel (WC ≤ 0.25%), medium-carbon steel (WC 0.25%–0.6%), and high-carbon steel (WC > 0.6%). Additionally, carbon steels can be classified based on their phosphorus and sulfur levels into ordinary carbon steel (with higher levels of phosphorus and sulfur), carbon steel (with lower levels of phosphorus and sulfur), and special-grade carbon steel (with even lower levels of these elements). Generally speaking, the higher the carbon content in carbon steel, the greater its hardness and strength—but this often comes at the expense of reduced ductility.
Cast iron
Cast iron is an iron-carbon alloy with a carbon content of more than 2%.
Cast iron can be classified into
1. Gray Cast Iron 2. White Cast Iron 3. Malleable Cast Iron 4. Ductile Cast Iron 5. Compacted Graphite Iron 6. Alloy Cast Iron
Typically, the cast iron valves we refer to are made from ductile iron, which is produced by subjecting gray cast iron molten metal to a spheroidizing treatment. This process causes the graphite to precipitate in a spherical shape, hence the term "ductile iron." Compared to ordinary gray cast iron, ductile iron boasts higher strength, as well as significantly improved toughness and ductility.
Cast steel
Steel used for casting metal parts—this is a type of casting alloy. Cast steel is categorized into three main types: cast carbon steel, cast low-alloy steel, and cast special steel. Cast carbon steel is a type of cast steel where carbon serves as the primary alloying element, with small amounts of other elements added as well. Specifically, it’s classified based on its carbon content: steels with less than 0.2% carbon are known as low-carbon cast steel; those containing 0.2% to 0.5% carbon fall into the medium-carbon category; and steels with more than 0.5% carbon are referred to as high-carbon cast steel. As the carbon content increases, the strength and hardness of cast carbon steel also rise significantly. This material boasts excellent strength, ductility, and toughness, while remaining cost-effective. As a result, it’s widely employed in heavy machinery to produce components that endure substantial loads—such as rolling mill frames and hydraulic press bases—and in railway vehicles, where it’s used to manufacture critical, high-stress parts like bolster brackets, side frames, wheels, and couplers that must withstand both significant forces and impact.
Based on the material properties described above, cast iron exhibits greater rigidity than cast steel but is also more brittle. In contrast, cast steel offers superior ductility and toughness compared to cast iron. As a result, cast iron is typically used in pipelines that operate under relatively low pressure—and only at ambient temperatures, since even slight increases in pressure or temperature could lead to minor deformations, which are detrimental to cast iron valves. On the other hand, cast steel valves can withstand higher pressures and temperatures, making them suitable for more demanding applications.
Applications of Cast Iron Valves
For example, we often see valves used in municipal water pipelines—these valves are typically coated with black paint on their surfaces. Such valves are classified as cast-iron valves.
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