Ductile Iron Vs. Cast Iron: What Are the Main Differences?

Ductile iron and cast iron are alloys of the element iron. Since iron isn’t found in a pure form, metallurgists have tried to form new alloys with desirable qualities and features. This way, they have achieved forming alloys of iron, which are much higher in strength, durability, corrosion resistance, and shock resistance.

However, there are many differences between these alloys as well. Though these alloys share some similarities, their chemical and physical properties are notably influential in their applications. Cast iron and Ductile Iron Pipe, as the most popular and well-known components, hold specified characteristics, which we will learn about in this article.

What Is Ductile Iron?

Ductile iron, a modern alloy created in the past 50 years, is formed by mixing molten iron with a small amount of magnesium. Ductile iron properties are many, but the most unique one is flexibility. The added magnesium forms this flexibility. This causes the graphite to form in nodules rather than flakes, which is how ductile iron is created. Ductile iron is used for many purposes. Industrial equipment, vehicles, and pipes are some of the most common uses of ductile iron. Ductile iron has many advantages, such as flexibility and durability. High strength and durability, flexibility and resistance to cracking, and corrosion resistance in ductile iron are examples of the advantages ductile iron pipes hold.

What Is Cast Iron?

Cast iron is produced when melted iron is combined with silicone and carbon. The gray color is an important cast iron characteristic mainly due to the graphite particles present in its carbon content. Cast iron has many uses due to its wear resistance. In addition to that, being cost-efficient is an important feature that makes cast iron a popular choice for kitchenware or engine blocks. A significant advantage of cast iron is its hardness. However, being hard is equal to being brittle, which can make this feature one of the cast iron disadvantages in some cases. Lastly, cast iron has the potential for corrosion, which may cause rust and degradation over time.

What Are the Main Differences Between Ductile Iron and Cast Iron?

Although cast iron and ductile iron share similar-sounding names, there are significant differences between ductile iron and cast iron. Experts at Commercial Industrial Supply explain that these differences range widely, from colors and textures to physical and chemical characteristics. There are plenty of factors to consider when choosing between cast iron and ductile iron due to the different properties they own. When it comes to strength, machinability, and cost, you are faced with two totally different choices.

Chemical Composition

Elemental iron is highly susceptible to oxidation or rusting in damp air, so it is hardly found in its pure form in nature. Although there is a considerable amount of iron on Earth, a significant percentage of it is within iron oxides—minerals such as hematite, magnetite, and taconite. Due to the frequency of this element, metallurgists have learned to form alloys to create a desired form of it.

Cast Iron

Cast iron and ductile iron are examples of these alloys formed with desired qualities. In cast iron, graphite carbon is the second most abundant element by mass. It is approximately 96 to 98 percent iron, 2 to 4 percent carbon, and a slight amount of silicone.

Ductile Iron

In addition to iron, which is the primary element, 3.2 to 3.6 percent of this material is carbon, 2.2 to 2.8 percent is silicone, and the remaining amount is elements such as manganese, magnesium, phosphorus, and sulfur.

Physical Properties

When it comes to the physical properties of cast iron and ductile iron, the main differentiator is the arrangement of the graphite microstructure. Graphite forms into flakes due to the gradual cooling process of gray cast iron; this process disperses throughout the metal’s entire structure. After that, the casting is under too much pressure and tension, and the graphite flakes in cast iron overlap, which creates weak points similar to tiny tectonic plates; cracks and fractures have high potential in this case. However, in ductile iron, a nodulizer, which is often magnesium, influences the graphite in the way it forms spheroidal nodules. This process enables ductile iron to be bent with a smaller chance of cracking or fracture.

Durability and Strength

Cast iron is known for its hardness; however, this makes it more brittle and susceptible to fracture. On the other hand, ductile iron is known for its high ductility and strength.

Corrosion Resistance

Ductile iron’s corrosion resistance is fairly high compared to cast iron, especially in water and sewage applications. Cast iron, on the other hand, is more susceptible to corrosion, which is why it may need coatings.

Weight

Cast iron is typically heavier than ductile iron. Ductile iron is lighter in weight, especially when compared to gray cast iron.

Applications

Cast iron is a proper choice for non-mechanical purposes where brittleness is not an issue. Ductile iron fittings, on the other hand, can even be an alternative to steel in some engineered applications because of its considerable strength-to-weight ratio.

Price

Cast iron is more economical to produce than ductile iron. This means that for customers, cast iron is less expensive to buy rather than ductile iron. The alloying process of ductile iron makes the price go much higher.

 

The table below gives an overall comparison of the technical characteristics of ductile iron and cast iron.

 

Characteristic:	Ductile Iron	Cast Iron
Microstructure	Spheroidal graphite nodules	Flake graphite
Tensile Strength	Higher (60-100 ksi)	Lower (20-40 ksi)
Ductility	Higher	Lower
Impact Resistance	Higher	Lower
Hardness	Lower	Higher
Machinability	Good	Excellent
Corrosion Resistance	Good	Moderate
Wear Resistance	Moderate	Good
Cost	Higher	Lower