Steel is a popular material being used across various industries. Cast steel and carbon steel are two popular types that have unique properties. In some cases, both of these types are the same in terms of their chemical composition. However, their production process creates differences and leads to confusion about cast steel vs carbon steel.
Understanding the difference between these two materials is key. It will help you choose the right steel type for your specific project. Generally, it is believed that both of these materials mainly consist of iron and are similar, which is wrong. In this article, I will debunk all of their key distinctions. This piece will help you choose the right steel type. So, let’s begin!
What is Carbon Steel?
Carbon steel is an alloy primarily consisting of iron and carbon. Apart from these two elements, silicon, manganese, sulfur, and phosphorus are also present in traces. Carbon steel is mainly known for its strength and hardness, which comes due to the presence of carbon.
This carbon steel has three further key types. Those types of carbon steel vary in terms of the carbon content. Here is a table showing those types and their carbon proportion:
| Type of Carbon Steel | Carbon Content (%) |
| Low Carbon Steel | 0.05% – 0.25% |
| Medium Carbon Steel | 0.3% – 0.6% |
| High Carbon Steel | 0.6% – 1.5% |
Interestingly, the carbon steel with higher carbon content is harder and stronger. For example, the low carbon steel has a lower carbon proportion (up to 0.25%) and is very soft. On the other hand, high carbon steel has a higher carbon content proportion. So, this material is robust, hard, and brittle. A higher carbon ratio will result in higher hardness and brittleness, and vice versa.
One of the prominent points to discuss is its production process. The carbon steel is made through forging, rolling, or machining. For example, carbon steel pipes used in pipelines are made through a hot rolling process. The production process of carbon steel is what differentiates it from cast iron.
What is Cast Steel?
Let’s have a brief look at the basics of cast steel.
Cast steel can be either type of carbon steel or alloy steel. However, its production involves the casting process. Due to this, this type of steel is known as cast steel. The composition of this material is to some extent similar to carbon steel, as both consist of carbon and iron.
As I said earlier, carbon steel is made using a forging or machining process. Right? Those processes cannot make parts with complex shapes. That’s where the cast steel comes into the scene. Manufacturers can make very complex-shaped parts efficiently due to the casting process. In this process, the steel undergoes melting at a very high temperature.
After that, this molten steel is poured into the mold. The shape of the mold is exactly similar to the desired shape of your parts. When the molten steel goes into the mold, it undergoes a curing process. In this stage, the molten steel cools, solidifies, and adopts the shape of the mold. After a specific duration, the part is ejected from the mold.
This process is called casting, which is involved in the production of this material. Therefore, it is called cast steel. The steel used in this process can be either carbon steel or alloy steel. Despite the same composition, the properties of cast steel and carbon steel differ from each other. This is due to the unique casting process involved in cast steel production.
Differences Between Cast Steel and Carbon Steel
Have you understood the basics of carbon steel and cast steel? It is a casting process that creates differences between these two materials. Let’s discuss all the key differences between these two steel-based materials:
1- Shape Complexity
As I said earlier, cast steel is made through the casting process. In this process, molten steel is poured into the mold. This molten steel solidifies into the mold and adopts the shape of the mold. You can create a complex shape mold. The steel will easily adopt that complex shape. It means that cast steel can help us make complex shapes easily.
On the flip side, the carbon steel is made through either rolling, forging, or machining. These processes are decent options for creating parts of simple shapes. For example, they can help us develop pipes, sheets, etc. However, when it comes to making complex shapes, these processes lag. They cannot make complex-shaped parts of carbon steel material.
2- Strength and Toughness
Strength and toughness are generally considered similar parameters, which is wrong. Strength indicates the ability of a material to sustain a specific load. It indicates how much force a particular material can withstand before it starts to bend. Carbon steel generally has a higher carbon proportion.
Remember, the higher the carbon content, the greater the hardness and strength. So, carbon steel has better strength than cast steel. However, toughness is something different than mechanical strength. It indicates the ability of a material to withstand sudden impact or force. Cast steel is a superior option in terms of toughness.
The reason is that this material is made by pouring molten steel into a mold. This molten material solidifies inside the mold and becomes very dense. Due to this denser formation, cast steel sustains the impact and sudden force easily. Cast steel also has a lower carbon proportion, which is another reason for its better toughness.
3- Surface Finish
Surface finishing is an important aspect when it comes to material selection. Manufacturers prefer materials with smooth and shiny surfaces. The carbon steel material comes with ideal surface finishing. The reason is that the forging or machining processes are used to make this material.
The machines cut it with sharpness, ensuring its surface is not uneven or rough. Contrarily, cast steel has a rough, uneven surface with pits on it. The reason is that this material is made by pouring molten steel into a mold. However, this mold is not very smooth and has some surface defects.
Due to those irregularities in the mold, the surface of cast steel becomes textured or rough. Manufacturers generally use polishing to make cast steel surfaces smoother. Have you ever seen smoothness on the sheets of carbon steel? That’s because those sheets are made by conventional machining, not by the casting process.
4- Weldability & Machinability
As I said earlier, cast steel is made by pouring molten steel into a mold. So, when molten steel goes into the mold and solidifies there. During solidification, it becomes denser and thicker. So, machining such dense material is very challenging. Cutting and shaping of cast steel may require advanced or high-end tools.
On the other hand, carbon steel is less dense and softer. So, its machining can be relatively more straightforward and require high-end tools. When it comes to weldability, cast steel wins the race. How? This material has very low carbon content as compared to carbon steel. Due to this, cast steel is less hard and brittle.
During welding, exposure to heat does not cause deterioration (cracking) in this material. On the flip side, the carbon steel has a higher carbon proportion, which makes it brittle. During welding, heat can cause cracking in this material due to its brittleness. Therefore, generally, weld treatment is used for creating a strong and reliable weld on this material.
5- Impact Resistance & Durability
I consider cast steel superior in terms of durability and impact resistance. As I said earlier, cast steel generally has a very low carbon content. Additionally, its production process in the mold makes it very dense. So it can easily withstand sudden impacts or shocks. In fact, this material can easily bear the extreme vibrations.
On the other hand, carbon steel has more strength and hardness due to its higher carbon content. However, this higher carbon proportion increases its brittleness as well. So, when exposed to sudden impact, this material can crack and break. Therefore, its durability is questionable in conditions where sudden impact is more common.
6- Different Classification
Both cast steel and carbon steel have different categories. The carbon steel is made by forging and machining. It has further subdivisions based on content. Those types are as follows:
- Low carbon steel (0.05% – 0.25%)
- Mid carbon steel (0.3% – 0.6%)
- High carbon steel (0.6% – 1.5%)
On the other hand, cast steel has two major types, i.e., carbon steel cast or alloy steel cast. As I said earlier, this cast steel is made by pouring the molten steel into a mold. If carbon steel is melted and poured into a mold, we will get a carbon steel cast. On the other hand, if alloy steel is molded and poured into a mold, we will get an alloy steel cast. Remember, the properties and characteristics of all types of carbon steel and cast steel differ from each other.
7- Cost & Applications
Cast steel is costly and premium as compared to carbon steel. The reason behind its higher pricing lies in its production process. As previously mentioned, this material is made through casting. The steel is first melted at a very high temperature. Once done, the molten steel is poured into the mold.
This process is time-consuming and needs more resources and energy. Due to this, the cost of cast steel is very high. The cast steel is generally used when high impact resistance is needed. Manufacturers also prefer when they require complex-shaped parts. The carbon steel is ideal for making simple parts with decent strength.
Here is the application comparison between cast steel and carbon steel materials:
| Cast Steel Applications | Carbon Steel Applications |
| Pump and valve bodies | Structural beams and columns in buildings |
| Mining equipment components | Pipelines and pressure vessels |
| Railway couplers and brake components | Automotive body and engine parts |
| Gear housings and casings | Machine tools and equipment frames |
| Turbine housings and heavy-duty engine parts | Agricultural tools and machinery |
| Complex-shaped components | Shipbuilding and bridge construction |
Frequently Asked Questions
Which is better, cast steel or carbon steel?
I consider cast steel a better option than carbon steel. It comes with better surface finishing and ideal impact resistance. Additionally, this material can be used to make very complex-shaped parts easily.
What are the disadvantages of cast steel?
Cast steel is mainly known for its many useful properties. However, there are some drawbacks, which are as follows:
- Higher production cost
- Require more time for production
- Surface finishing of this material is also compromised
- Their pricing is too high due to the complex production process
Does cast steel rust?
Yes, both cast steel and carbon steel can rust. The reason is that both come with iron as the primary material. This iron reacts with oxygen and makes iron oxide (rust). Manufacturers apply some additional coating on their surfaces to protect them against rust.
Conclusion
Both cast and carbon steel offer excellent value propositions. You might consider them direct competitors. However, they are specific in their properties and functionality instead of being competitors to each other. Cast steel is a premium, expensive material.
You should use it when you need higher impact resistance. On the other hand, carbon steel is a cheaper alternative to cast steel. Generally, this material is used when manufacturers aim to make parts less costly. They complement each other’s values rather than overshadow each other. If you ask my opinion, I suggest choosing cast steel due to its ideal durability.