Iron is undoubtedly one of the most used materials worldwide. Ductile iron and cast iron are two of the most common types. They have many applications in different industries. We are going to discuss ductile iron VS cast iron.
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What are the advantages and disadvantages of both of these? From finding the difference between cast iron and ductile iron, we will learn about them in detail.
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What Is Cast Iron?
Do you know cast iron forms when carbon and silicon are mixed with iron? When the iron is melted, carbon and silicon are mixed, forming cast iron. Moreover, the grey color of the iron is because of the presence of graphite particles.
It has excellent compressive strength and vibration-damping properties. Where is cast iron in use? You will see it in decorative items, pots, pans, pipes, and more.
Advantages
The primary advantage of this type of cast iron is its durability. Castability is also one of the leading benefits, and it is often used. Also, regarding affordability, cast iron is the primary choice.
Disadvantages
However, it also has one disadvantage: its brittleness. Cast iron is prone to breaking at times, so it is unsuitable for use in areas under stress.
What Is Ductile Iron?
Ductile iron has different names, such as ductile cast iron and nodular cast iron. Moreover, it was a major invention of the mid-20th century. Why is it so popular? What sets it apart from other types? Because of its microstructure, it offers unique flexibility, ductility, and even strength.
How is it made? When we add magnesium to molten iron, the graphite forms nodules rather than flakes. With this comes the characteristic of ductility in this type of iron. Thus, because of such qualities, it has different applications. They include pipes and fittings, engine blocks and crankshafts, gears, and more.
Advantages
One of the primary advantages of ductile iron is its ductility and strength. Both of these factors make it usable in places under high stress. Hence, we see this type of ductile iron in automobiles, etc.
Disadvantages
The disadvantage is that it lacks castability. Because it is tough, it is more difficult to cast this iron and make it as needed than other types.
Ductile Iron VS Cast Iron- Differences to Know
In this section, we will talk about the differences between cast iron and ductile iron.
Properties of Strength- Ductile Iron VS Cast Iron
The first difference we will consider is the strength of these irons. Regarding strength, ductile iron is a stronger choice than cast iron. Moreover, it is one of the major reasons why it is a significant choice for industrial purposes.
Cast iron can be brittle. What does that mean? It means that cast iron can break under pressure. Yes, due to its lack of ductility, cast iron cannot bend without breaking. Thus, ductile iron is always preferred over cast iron as it has more ductility.
Hence, there is a critical difference in ductility, where ductile iron offers more. Another major point to consider is tensile strength. Ductile iron offers more tensile strength than cast iron.
Properties of Structure- Ductile VS Cast Iron
There is a major difference in the structural properties. Where does this difference come from? Well, the difference comes because of the internal structure of graphite.
In ductile iron, rounded graphite nodules form during the manufacturing process. Hence, this formation gives ductile iron amazing strength and ductility. How is cast iron different in this? Well, it is because it has a flake-like graphite structure. With this, the cast iron is not able to get as ductile and becomes brittle. Hence, it is how both these iron are different.
Other Properties- Ductile Iron VS Cast Iron
Are there any other differences between cast iron and ductile iron? Yes! The difference is due to impact resistance, machinability, and corrosion. How do these factors make a difference?
Ductile iron has better impact resistance. It is because of its ductility. It offers amazing resistance. Hence, ductile iron is well-suited for high-stress applications.
The next aspect of the difference is machinability. In this, cast iron performs better than its counterpart.
This
is because of the structural property that we discussed earlier. With a flake-graphite structure, machining cast iron is way easier than ductile iron.
Both types provide top-notch corrosion resistance. However, when we compare them, ductile iron has a higher edge than cast iron.
Application- Ductile Iron VS Cast Iron
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They differ in their applications, too.
Pressure Handling: Ductile iron is an ideal type of pressure handling. Its strength makes it the right candidate for pipes and valves. In all those applications that need to handle high pressure, ductile iron is there. Why not cast iron, then? Well, cast iron is brittle and can break in high pressure.
Components Dealing With High Stress: Ductile iron is used when dealing with high stress. Where do we see this application? Well, if we see engine blocks, gears, or automotive parts, the use of ductile iron is prominent. Why not cast iron? Cast iron does not have enough strength to handle excessive pressure or stress. Thus, because of its capability to handle pressure, ductile iron is in use.
However, cast iron is used in applications like vibration damping. Why? Cast iron&#;s flake-graphite structure makes it an ideal candidate. We also see the use of cast iron in places like hand equipment, pipe fittings, and farm equipment.
Other Differences
Are there any other differences between ductile iron and cast iron? Let&#;s discuss other factors, such as cost, weight, and castability.
Cost is one of the primary points of difference between the two types of iron. Ductile iron is more expensive than cast iron. This difference arises because it offers better
ductility
.
Castability is one such property with which you can mold irons in different shapes. So, which iron is better in this? Cast iron delivers way better with a lower melting point and better fluidity. Thus, people choose cast iron over ductile iron for these properties.
Another aspect that we must recognize is weight. Which of the two types of iron is a heavier option than the other? Because of the density of the structure, ductile iron is heavier than cast iron. Moreover, you should note that we are comparing the same size component.
Hence, these are all the points of difference between these types of iron.
Conclusion
Thus, are you aware of the difference between cast iron and ductile iron? Considering these differences, merits, and demerits, one can decide between them. In the long run, it all depends on the use and the application that will determine the preference.
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Gray Cast iron VS Ductile iron
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MVPs
(Mechanical)
(OP)
19 Jan 02 09:32For diaphragm valve lined with PTFE, I understand that the fluid will not contact body material. I would like to use gray cast iron instead of ductile iron. Are there any disadvantages for this applicatoin.
Replies continue below
(Mechanical)
21 Jan 02 19:42It depends on your application. Grey cast iron is more brittle than ductile iron so piping should impose minimal forces on the valves. If the fluid contained is flammable you should not used cast iron.
(Mechanical)
24 Jan 02 15:19PAM,
The only set of rules that should concern you is the design code that governs your installation.
Both ASME B31.1 and B31.3 put limitations on use of cast iron in toxic, flammable and steam service. Limitations imposed typically are in the form of pressure/temperature maxima or inclusion only in non-shock service.
If a material is deemed suitable for service (by the piping code) and the component is design rated for that combination of temperature and pressure, then you should be able to use it. Valve manufacturers have excellent experience with succesful and non-successful installations and are usually happy to share it with a customer..
MJC
(Mechanical)
24 Jan 02 16:32Gray cast iron, regard;ess of what you coat your wetted surfaces with, won't meet NACE MR if that is a consideration.
guest
(visitor)
2 Apr 02 17:40The Iron body is not wetted as it is fully insulated by the teflon lining. So there is no discussion on the chemical properties.
Why should you consider cast iron. It will not save you money. The standard for any valve manufacturer is ductile.
My advise, stick to the standard material configuration.
ood luck !
Ed
(Mechanical)
4 Apr 02 17:11A thing you like to consider is if the lining is glass reinforced there may be a danger of cracking the flange in tighteneing the bolts. The teflon will form its own gasket and as such will be raised above the face of the flange. When the bolts are tightened tha CI is subject to a bending moment and shear at the "gasket". CI is weak in tension and examples exist of CI flanges cracking when in a raised face scenario.
For critical service I would always use DI over CI. I beleive that Saunders diaphragm valves are only available in CI but other manufacturers such as Kim or Gemu could well have DI. Of course you would expect to pay more for a DI bodied valve. But this will be a lot less than the repair of a cracked flange.
(Mechanical)
(OP)
5 Apr 02 21:44Thanks for all comments. In our plant's specification, there are both ductile iron and gray cast iron body. I will study more to update the specification.
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