Valve Material Tips: Ductile Iron vs. Cast Steel

Jul. 21, 2022

Customers from a wide range of industries require a variety of valves to increase operations. Valves are available in a variety of materials to suit any application. Carbon steel, PVC, cast iron, stainless steel and ductile iron are some of these substances. In this article, we will examine two of them: ductile iron and cast steel. The "ductile iron vs. cast steel valve material" debate has existed for decades, as not most people are familiar with these differences. 

Fortunately, comparing valves made of ductile iron and cast steel is simple, as there are only a few significant differences between the two materials. We will describe the qualities of each material and then weigh the advantages and disadvantages of each. By the conclusion of this blog post, the reader will become a valve expert!


Valve Material Tips: Ductile Iron vs. Cast Steel

 

What exactly is ductile iron?

Ductile iron is a relatively new iron alloy formed from endogenous graphite. This provides high ductility to the fabric, which means it will not crack when bent. The thermal limit is slightly lower than that of cast iron, although it remains relatively high at 1350F (730°C). Ductile iron valves are also available in pressure grades 150 and 300. 150 grade ductile iron maintains a seal at normal ambient temperatures up to 250 psi. 300 grade can withstand pressures up to 640 psi.

Ductile iron has high strength and stiffness, structural rigidity, and ultimate tensile strength. Because ductile iron does not break when folded, it is better suited for application operations than cast iron. Ductile iron is a durable material for use in piping, joints and valves.

Design teams will also be interested to note that the Poisson's ratio for ductile iron is typically considered to be 0.275. ratio limits are as important as the design professional. The ratio limit for the 0.2% ultimate stretch ratio for the ferritic level (60-40-18) is typically 0.71. For the austenitic level, the same ratio is typically 0.56 (80-55-06).

Ductile iron has excellent structural integrity and can withstand high temperatures without damage. This is due to the ductility of the raw material, which makes them much less likely to bend and twist. During this time, rust is also attracted to ductile iron.

Ductile iron is used in more specialized industrial applications to improve fracture toughness:.

● Drums made of cables

● Frames

● Gearboxes

● Pumps

One disadvantage is cost. Due to its more complex chemical composition, ductile iron is usually more expensive than cast iron. Nevertheless, if your project requires a more robust material, you may need to invest a little extra.

Advantages of ductile iron.

● Improved castability.

● Cost savings

● Improved vibration damping

● Improved corrosion rates

● Excellent compression yield toughness

 

What exactly is a cast steel valve?

Cast steel valves are made by a process called "casting". This process involves melting steel and then forming it into the desired shape. Advanced cast steel valves are quite affordable in terms of effectiveness, longevity, quality and fatigue strength. For example, cast steel taps are widely used in the petrochemical industry, power stations, waste treatment units, treatment plants, rail lines and other applications.

Depending on the application, cast steel valves may be made of high-grade steel or metal alloys. Because they are created using molds, you can simply design these valves to have complex forms or intricate features. They can be produced in any size, and a single valve can contain multiple components.

 

Advantages of cast steel valves

Design flexibility: Because cast steel valves consist of molten material, they can be easily molded into any size or shape. You can also increase the complexity of the design and create complex functional parts for the valve.

Versatility: Cast steel valves offer a wider range of metal compositions. Cast steel valves can be made from a variety of metal alloys. You can specify precise parameters, such as improved corrosion resistance, by using the appropriate metal composition.

Reduced machining: Cast steel valves can be manufactured without extensive machining. This equates to lower processing costs and faster turnaround times.

Cast steel valves are more widely used than forged steel valves. This is due to the lower difficulty and cost of casting compared to forging. Replacement components and valve service are more readily available. Spare parts and valve service are more readily available.

Space-saving design: Cast steel valves are curved and have rounded sides. This makes them easy to install, especially in tight spaces and pipelines.

 

Disadvantages of cast steel valves

Casting generates a lot of waste. Some material is lost as the metal is converted to fluid. The fluid is then modified as it enters and leaves the mold. A portion of the core material is wasted at each stage.

The solidification process of cast steel valves sometimes leads to microscopic impurities such as cracks and crevices in the valve. This can lead to poor mechanical quality that can only be restored by time-consuming and expensive weld repairs.

Heat treatment can change the composition of the cast steel valve part when it is welded in one piece. As a result, the valve creeps more and becomes less ductile. Thorough inspections must be performed to ensure that the valve's robustness and creep tolerances have not deteriorated after welding.

Because cast steel valves are tested to a lower standard than forged steel valves, extra care must be taken when obtaining these valves. Specialized industrial valve manufacturers, such as KXC, ensure that each cast steel valve has the necessary certifications and testing, although this is not always the case.

 

Ductile Iron vs. Cast Steel

1. Chemical Composition

Ductile iron chemistry typically contains 3.0% to 3.9% carbon, while cast steel typically contains 0.08% to 0.60% carbon. Therefore, the carbon concentration of ductile iron is higher than that of cast steel.

 

2. Ultimate Tensile

Ductile iron and cast steel have similar tensile strengths; however, ductile iron has a higher tensile strength of 40k psi, while cast steel has a maximum yield strength of only 36k pounds per square inch. In terms of equivalent grades, ductile iron has greater yield toughness. As a result, ductile iron can replace most cast steel and, in some cases, forged steel in the production of crank propellers and gears.

 

3. Tensile and impact properties

While the elongation of ductile iron is 18%, the maximum elongation of cast steel is 25%. Therefore, cast steel has greater elongation and superior impact properties. The AKV of cast steel is 30J.

 

4. Welding and vibration damping

Because cast steel has better welding characteristics than ductile iron, welding alternatives are often used in production and do not degrade mechanical quality. However, ductile iron is a good material for making equipment bases because of its high impact absorption.

 

5. Alloy cast steel

Although iron foundries may add certain elements to ductile iron, alloyed cast steel is available in a wider variety and classification and therefore can meet the needs of a wide range of unique applications.

 

Conclusion

So there you have it. As you can see this is not a case of ductile iron vs. cast steel valves. One is not necessarily superior to the other. It all depends on what you want to do with it!

KXC offers valves in a variety of sizes, even some that are hard to find! So if you're looking for anything to fit your requirements, be sure to contact the experts here!

 

 Valve Material Tips: Ductile Iron vs. Cast Steel

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