Steel and cast iron are two popular materials. Their usage is standard in various manufacturing industries. Although both consist of some proportion of iron, they have many distinctions. Those differences spark debate on steel versus cast iron.
Everyone knows that steel is a more popular material. However, fewer people have the basic know-how about cast iron. Their differences from one another further fuel the confusion among laypeople. In this article, I’ll take on the debate of steel and cast iron. This will help you know which material is best suited for your needs!
What is Steel & Cast Iron?
Before comparing these two materials head-to-head, let’s first highlight their basics.
Both steel and cast iron are man-made materials. Iron is the central element that is present in both of these materials. Cast iron has a carbon content of 2 to 4%, while steel has a carbon content of 0.15 to 2%. These differences in carbon proportion make these two materials different from each other.
Apart from iron and carbon, both of these materials also have other elements. The proportion of those elements also affects the properties of these two materials. Here is a table showing the typical composition of these materials:
| Element | Cast Iron | Steel |
| Iron (Fe) | 90–96% | 98–99% |
| Carbon (C) | 2.0–4.0% | 0.1–2.0% |
| Silicon (Si) | 1.0–3.0% | 0.1–0.6% |
| Manganese (Mn) | 0.2–1.0% | 0.3–1.5% |
| Sulfur (S) | 0.02–0.15% | 0.005–0.03% |
| Phosphorus (P) | 0.02–1.0% | 0.005–0.04% |
It is noteworthy that steel and cast iron have further types. For example, cast iron has subtypes, including gray iron, white iron, and malleable iron. Similarly, steel has various subtypes, including stainless steel, carbon steel, and alloy steel. The composition and overall properties of each of these types can vary from steel to cast iron.
Steel has a higher melting point, which enhances its value and durability. Manufacturers prefer using it when making heat-resistant parts. Such steel parts can easily withstand high temperatures efficiently. On the other hand, cast iron has excellent castability. Remember, their differences do not imply that one is superior to the other.
Those differences highlight their specific use. China was the first country to produce cast iron, which it used to manufacture weapons and other tools. However, its industrial usage started in the 1770s. The Iron Bridge, located in England, was made in 1779 using cast iron materials. Similarly, steel also has a long history.
What are the Differences Between Steel and Cast Iron?
Let’s compare steel and cast iron head to head. This portion will help you understand their fundamental differences.
1- Strength and Hardness
As said earlier, steel has a lower carbon content (0.15 to 2%). Remember, carbon material increases the hardness and brittleness of the materials. As steel has a lower carbon proportion, it means it is less brittle. It has better strength and can withstand heavy loads. That’s why this material is widely used in the building and construction industry.
On the other hand, cast iron has a higher carbon content (2 to 4%). This higher carbon increases the brittleness of cast iron. As a result, this material breaks easily under load. Therefore, cast iron is generally used to make parts that don’t face heavy loads. Due to its brittleness, its overall strength is also compromised.
2- Flexibility (Ductility)
Ductility indicates the ability of a material to deform and bend without cracking. Materials with a higher carbon content tend to be brittle. Upon facing a load, this material is more likely to crack. It would be less flexible and ductile. The steel has a very low carbon proportion, which makes it more ductile. Its internal structure does not break and can bend before breaking.
As I said earlier, cast iron has a higher proportion of carbon. Due to this, this material becomes highly brittle. It tends to break or crack when force is applied to it. Therefore, it is less ductile and flexible. Due to better ductility, steel is widely used to make wires and other intricately shaped parts. The cast iron has lower usability due to compromised flexibility.
3- Corrosion Resistance (Rust)
Steel is a superior option to cast iron in terms of corrosion resistance. As I mentioned earlier, steel comes in various types, and stainless steel is one of them. Stainless steel is very popular due to its exceptional corrosion resistance. It contains 10.5% chromium, which enhances its value. This chromium reacts with moisture to make a chromium oxide layer.
This layer protects the material from further rusting. Almost all types of steel offer some level of corrosion resistance. The cast iron has no particular resistance to rust (corrosion). The surface of this material generally has some impurities. Those impurities react with moisture, causing corrosion. Therefore, a paint coating is applied to this material to enhance its resistance to rust.
4- Weight and Density
Cast iron is heavier and bulkier compared to other types of iron. The reason is that the structure of this material is more condensed. The presence of a higher carbon content makes it denser and more solid, increasing its density. A higher weight affects its weight-to-strength ratio, thereby reducing its overall value.
Steel, on the other hand, is also heavier. However, its weight is less than that of cast iron, considering the exact size of both materials. The weight-to-strength ratio of steel is better than that of cast iron. Therefore, steel is used to make various aircraft parts. Its low weight, combined with higher strength, ensures that aircraft parts are both strong and lightweight.
5- Surface Texture & Appearance
Cast iron looks dull and less attractive than steel. The reason lies in the production process of cast iron. Remember, during production, the molten material (iron mixed with carbon) is poured into the sand mold.
This mold has an irregular surface, which is the cause of the bumpy appearance of cast iron. The surface of the cast iron material is not smooth and looks dull. On the other hand, steel appears very attractive. Stainless steel is soft and shiny. The reason is that steel undergoes multiple processes, such as rolling and polishing.
6- Machinability & Repairability
Cast iron is a better option than steel in terms of machinability. The reason is that cast iron is a brittle material and can break easily. Therefore, the cutting machines lack sufficient power to cut this material. On the other hand, steel is a robust, rigid, and tough material. Their cutting needs high-powered machines.
Using heavy-duty machines to cut steel can be very costly. Let’s discuss repairability, which is closely related to welding. The steel is a superior option in terms of ease of weldability. It does not break or crack when exposed to heat. So, we can create strong welds on steel material and repair broken steel parts.
On the other hand, cast iron is brittle and can break when exposed to high temperatures. So, its welding is very challenging. Have you ever seen stainless steel pipes welded together? That’s due to the ease of weldability of this material. Additionally, creating weld on steel material is less costly than making it on cast iron.
7- Melting Point & Castability
Cast iron offers ideal castability due to its lower melting point. Castability refers to a material’s ability to melt and then be poured into a mold to create parts. Right? Cast iron has a lower melting point of 1200°C (2200°F) as compared to steel (1370°C to 1500°C). Melting cast iron is easier, and manufacturers achieve this by heating it to a temperature of 1200°C.
The molten material is then poured into the mold. In this way, we can efficiently obtain different parts of intricate shapes. The steel material has a higher melting point. It requires more heat to melt than cast iron. So, its ease of castability is a bit compromised. Moreover, steel in its molten state does not flow effectively into the mold cavities.
8- Cost & Applications
Cast iron is an inexpensive material, which is the key reason behind its popularity. Its production is a less energy-demanding process. Moreover, fewer steps are required to produce cast iron. On the other hand, steel is a premium material. Its production is a complex process.
It requires additional steps, such as refining, alloying, rolling, and polishing. Due to this, steel is a costly material. When it comes to usability, steel is widely utilized in the construction industry. You’ll see bridges, buildings, and other tools made of this material. Cast iron is widely used on a smaller scale, for example, in the manufacture of kitchen items.
Here is a table showing the application comparison of cast iron and steel:
| Cast Iron Applications | Steel Applications |
| Cookware (pans, pots, Dutch ovens) | Building structures (beams, columns) |
| Engine blocks and cylinder heads | Bridges and towers |
| Pipes and plumbing fittings | Automobiles and airplanes |
| Manhole covers and drainage systems | Tools (wrenches, hammers, drills) |
| Decorative ironwork (fences, frames, gates) | Kitchen appliances (fridge, sink, etc.) |
| Stoves, fireplaces, and grills | Medical instruments and surgical tools |
It is noteworthy that steel is used in heavy-duty applications. Its higher toughness, strength, and robustness enable it to withstand heavy loads. Cast iron is a weaker material due to its brittle nature. Therefore, it is used for mild applications, particularly in the manufacture of kitchen items. However, I consider steel a reliable option.
Which One Should You Choose, Steel or Cast Iron?
I recommend using steel as the material of choice for most applications. Here is why:
Steel is a rigid material with excellent durability and lasting. It is corrosion-resistant and offers optimal flexibility as well. Additionally, it can withstand extreme loads efficiently without showing any signs of cracks. Parts or products made from this material will remain in good condition for many years to come.
However, some people have budget constraints. The steel material has excellent properties and offers a wide range of advantages. However, its cost is higher, which is a big drawback, especially for those with tight budgets. If you’re in such a situation, consider opting for cast iron. It is an inexpensive alternative to steel material for parts that don’t face high stress.
The cast iron has excellent castability if that’s your primary requirement. Its lower melting point allows it to melt quickly. You can then pour it into a mold and make complex-shaped parts using a casting method. If casting and low pricing are not your preferences, I don’t recommend choosing this material. Go with steel, as it lasts longer and performs better.
Frequently Asked Questions
Which is better: cast iron or steel?
I consider steel a superior option due to its specific properties. It is stronger, more rigid, corrosion-resistant, and, above all, lightweight. The cast iron has several limitations, making it a less desirable option.
What are the disadvantages of cast iron metal?
Cast iron comes with multiple limitations. Here are some drawbacks:
- Brittle nature
- Lesser strength
- No corrosion resistance
- Heavyweight and less friendly to welding
Does cast iron cost more than steel?
No. Cast iron is a very inexpensive material due to its easier production. Its making does not demand higher energy, which is a big plus. The steel material is premium and costly, as it is produced through multiple steps and processes.
Conclusion
Both steel and cast iron are excellent materials. However, their usability differs due to their differences in composition. In my opinion, I consider steel the premium option. The cast iron is also suitable, but it’s particularly well-suited for those with a tight budget. Understand the differences between steel and cast iron and consider your needs. This will help you choose the right material that will serve you for years.