The differences in valve material: cast iron, carbon steel, and cast steel

The choice of valve material is crucial for its performance, applicable scenarios, and service life. The following provides a detailed analysis of the differences among cast iron, carbon steel, and cast steel from three aspects: material characteristics, performance differences, and application scenarios:

Material characteristic comparison

Cast iron: Contains 2% to 4% carbon, with a high silicon content and many impurities. It is directly cast after melting and has a simple process. It has high brittleness, good wear resistance, and high compressive strength, but low tensile strength. It is not resistant to impact and vibration and has average corrosion resistance.

Carbon steel: Contains 0.02% to 2.11% carbon and mainly consists of iron and carbon. The steel ingot is formed through rolling and forging processes. It has better comprehensive performance, good strength, plasticity, and toughness, good welding and cutting processing properties, and poor corrosion resistance.

Cast steel: Contains 0.15% to 0.6% carbon and has fewer impurities. The steel water is cast, and the performance needs to be improved through heat treatment. It has high strength, good toughness, and resistance to impact. It can withstand dynamic loads and can be alloyed (such as adding chromium, nickel, etc.) to enhance corrosion resistance and high-temperature resistance.

Key performance differences

Mechanical properties

Strength and toughness

Cast iron: Has high compressive strength (such as gray cast iron with a compressive strength of 200 to 400 MPa), but low tensile strength (only 100 to 250 MPa), poor toughness, and is prone to fracture under impact.

Carbon steel: Tensile strength increases with the increase in carbon content, has good plasticity and toughness, and can withstand certain deformation.

Cast steel: The tensile strength is usually 450 to 800 MPa, and its toughness is significantly better than that of cast iron and carbon steel. It is suitable for withstanding dynamic loads and can be used in scenarios requiring reduced friction (such as valve body sealing surfaces).

Wear resistance

Cast iron (especially wear-resistant cast iron) has a low friction coefficient due to the presence of graphite, and has better wear resistance than ordinary carbon steel and cast steel. It is often used in scenarios requiring reduced friction (such as valve body sealing surfaces). Corrosion resistance performance

Cast Iron: The graphite in the matrix is prone to form micro batteries, and its corrosion resistance is generally poor. It needs to rely on surface coatings (such as painting, galvanizing) or select corrosion-resistant cast iron (such as high-silicon cast iron).

Carbon Steel: It is prone to rusting, and its corrosion rate is fast in humid, acidic, and alkaline environments. Extra anti-corrosion treatment (such as electroplating, coating epoxy resin) is required.

Cast Steel: Ordinary cast steel has similar corrosion resistance to carbon steel, but it can be made into stainless steel cast steel (such as CF8, CF3M) by adding alloy elements (such as Cr, Ni), significantly improving its corrosion resistance.

High-temperature performance

Cast Iron: Gray cast iron has poor heat resistance (long-term use temperature ≤ 300℃), while ductile cast iron can be slightly higher (≤ 400℃), but it is prone to oxidation at high temperatures.

Carbon Steel: Ordinary carbon steel has a long-term use temperature of ≤ 450℃, and its strength significantly decreases at high temperatures, so it needs to select heat-resistant steel (such as 15CrMo).

Cast Steel: Through alloying, it can withstand high temperatures and is suitable for high-temperature media (such as steam, hot oil).

Processing performance

Cast Iron: The casting performance is excellent, with good fluidity, and it can form complex structures (such as valve bodies with heat dissipation plates), but its cutting performance is poor (hard and brittle), and its welding performance is poor (easily cracked).

Carbon Steel: The forging, welding, and cutting performance are good, and it is convenient for processing into various shapes (such as flanges, threaded connections), suitable for scenarios that require frequent disassembly.

Cast Steel: The casting process is more complex than that of cast iron (it requires controlling the casting temperature and cooling speed), but it can improve its performance through heat treatment (such as normalizing, quenching and tempering), and its welding performance is better than that of cast iron.

Application scenario comparison

Application scenarios of cast iron valves:

Low pressure, static or small-diameter pipelines (such as DN ≤ 300mm), with media being water, steam, oil, etc., which are non-corrosive or weakly corrosive fluids.

Typical valves: Gate valves, globe valves, check valves (often used in water supply, heating systems).

Advantages: Low cost, easy casting, good wear resistance.

Disadvantages: Not suitable for high pressure, impact or corrosive environments.

Carbon steel valves applicable scenarios:

Medium and high-pressure pipelines (such as PN ≤ 16MPa), with media being air, steam, oil, etc., which need to withstand certain pressure and vibration (such as industrial pipelines, heating systems).

Typical valves: Ball valves, butterfly valves, safety valves.

Advantages: High strength, balanced comprehensive performance, moderate processing cost.

Disadvantages: Insufficient corrosion resistance, requires regular anti-corrosion.

Cast steel valves applicable scenarios:

High pressure, high temperature, high impact or complex conditions (such as PN ≥ 25MPa, temperature ≥ 450℃), or scenarios requiring corrosion resistance (such as stainless steel cast steel).

Typical valves: Power plant valves (such as gate valves, globe valves), chemical plant valves (such as stainless steel ball valves), marine engineering valves.

Advantages: High strength, good toughness, can adapt to extreme environments through alloying.

Disadvantages: High cost, complex casting process.