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Cast Iron vs Steel: Differences and Distinctions
In the vast field of metal processing, steel and cast iron are the core materials. Although they are similar in appearance and certain characteristics, there are essential differences between them.
Are you curious about the differences between cast iron and steel? Which is better, steel or cast iron? Next, I’ll show you what’s unique about these two materials and answer your questions.
What are Iron and Steel?
Iron is a chemical element with an atomic number of 26 and the chemical symbol Fe. Cast iron is an iron-carbon alloy with a carbon content greater than 2.11%. It is obtained by remelting casting pig iron (part of steelmaking pig iron) in a furnace and adding ferroalloy, scrap steel, and returned iron to adjust the composition. Cast iron has good castability and machinability, and is often used to manufacture castings with complex structures and wear resistance.
Steel is an alloy of iron, whose main component is iron and contains a certain proportion of carbon (usually between 0.02% and 2.1%).
Comparison Of Cast Iron And Steel
Carbon Content：
In nature, iron usually occurs in the form of oxides. Cast iron is a material commonly used in the hardware industry. It is a general term for an alloy composed of iron, carbon and silicon, which also contains small amounts of manganese, phosphorus, sulfur and other elements. The carbon content of cast iron is greater than 2.11%, usually between 2.5% and 4.0%. However, the carbon content of steel is much lower than that of cast iron, generally below 2.11%.
Types Of Cast Iron
There are many types of cast iron. Here are some of the main types of cast iron and their characteristics:
Classification by chemical composition
Ordinary cast iron
Definition: Cast iron that does not contain any alloying elements, such as gray cast iron, malleable cast iron, ductile iron, etc.
Features: It has good castability, machinability and wear resistance, and is widely used in industrial fields.
alloy cast iron
Definition: A high-grade cast iron prepared by adding some alloying elements (such as manganese, chromium, nickel, molybdenum, etc.) to ordinary cast iron to improve certain special properties.
Features: It has special properties such as higher strength, hardness, wear resistance, heat resistance or corrosion resistance, and is suitable for specific working environments or conditions.
Classification by fracture color
gray cast iron
Features: Most or all of the carbon exists in the form of free-flake graphite, and the fracture surface is dark gray. It has good castability, machinability and wear resistance, but low strength and toughness.
white cast iron
Features: Except for a small amount of carbon dissolved in the ferrite body, the rest of the carbon exists in the form of cementite in the cast iron, and the fracture surface is silvery white. Hard, brittle and difficult to machine, but extremely wear-resistant.
Hemp cast iron
Features: Part of the carbon exists in the form of graphite, and the other part exists in the form of free cementite. There are black and white pits in the fracture. The performance is between gray cast iron and white cast iron, but it is more brittle and hard and has fewer applications.
Classification by production method and organizational performance
Ordinary gray cast iron
Definition: The most common type of cast iron that has the characteristics of gray cast iron described above.
Incubate cast iron
Definition: Based on gray cast iron, it is made through “metamorphosis treatment”, also known as metamorphic cast iron.
Features: Strength, plasticity and toughness are much better than ordinary gray cast iron, and the structure is more uniform.
Malleable cast iron
Definition: It is made of white cast iron with a certain composition and graphitized annealed. It is also called ductile cast iron.
Features: High toughness, but not forgeable.
Ductile Iron
Definition: Obtained by adding a certain amount of nodularizing agent and inking agent to the molten iron before casting to promote the crystallization of spheroidal graphite.
Features: The mechanical properties are close to steel, and it is an excellent material that has the advantages of steel and cast iron.
Special performance cast iron
Definition: Cast iron with certain special properties, such as wear-resistant cast iron, heat-resistant cast iron, corrosion-resistant cast iron, etc.
Features: It has different special properties according to different uses.
Types Of Steel
Carbon steel: In addition to iron, steel mainly contains carbon, and a small amount of silicon, manganese, phosphorus, sulfur and other impurity elements. According to the different carbon contents, carbon steel can be divided into:
Low carbon steel: Carbon content is less than 0.25%, soft and tough, and widely used in construction.
Medium carbon steel: The carbon content is 0.25% to 0.6%. It is relatively hard and is mostly used to make rails and mechanical transmission parts.
High carbon steel: The carbon content exceeds 0.6%. The more carbon it contains, the harder and brittle it is. It is generally used to make tools.
Alloy steel: Steel in which one or several alloying elements (such as manganese, silicon, chromium, nickel, tungsten, vanadium, titanium, etc.) are specially added in order to improve certain mechanical properties of the steel or obtain some special properties. Alloy steel can be divided into:
Low alloy steel: the total alloying element content does not exceed 5% (some say it does not exceed 4%).
Medium alloy steel: The total content of alloy elements is 5% to 10%.
High alloy steel: The total alloying element content is greater than 10%.
Performance:
Steel:
Excellent plasticity and toughness: Steel can withstand large plastic deformation without breaking easily, and at the same time shows good toughness when subjected to impact or vibration.
Stamping and weldability: Steel is easy to process into various complex shapes through stamping processes, and has excellent welding properties, making it easy to manufacture large structural parts and complex components.
Cast iron:
Excellent castability: Cast iron has good fluidity and can easily fill molds and form precise and complex shapes with good plasticity, toughness, stamping properties, and weldability; heat treatment can improve the strength, hardness, and wear resistance of steel.
High wear resistance: Cast iron has high wear resistance and can maintain a long service life in friction and wear environments.
Good cutting processability: Cast iron performs well during cutting, with low cutting resistance and slow tool wear, which is beneficial to improving processing efficiency.
Low cost: The production process of cast iron is relatively simple and the cost of raw materials is low, giving it significant advantages in cost control.
Surface Treatment:
Surface treatment is to apply treatment on the surface of materials through physical, chemical or mechanical methods to change their surface properties, structure or appearance to achieve the purpose of enhancing performance and protecting the substrate.
The surface treatment methods of cast iron mainly include phosphating treatment, blackening treatment, etc. Phosphating treatment is a common surface treatment method for cast iron, which can remove rust and provide an anti-rust effect. The surface color after treatment is gray-black or black. Blackening treatment is to use a normal temperature blackening agent to form a protective film after pre-treatment of cast iron parts to improve anti-corrosion ability.
Surface treatment methods of steel include electroplating, polishing, anodizing, etc. Electroplating is to coat the surface of steel with a layer of other metals, such as zinc, nickel, and chromium, to improve corrosion resistance, wear resistance, and aesthetics. Polishing can be mechanical polishing or chemical polishing to improve the finish of the steel surface and obtain different gloss effects. Anodizing is the formation of an oxide film on the surface of steel through an electrochemical process to improve corrosion resistance and hardness.
USE:
Steel: can be used to manufacture mechanical parts, engineering structural parts, manufacturing cutting tools, molds, measuring tools and other tools.
Cast iron: widely used in agricultural machinery, automobile manufacturing, machine tool and heavy machinery manufacturing, defense industry and other industries.
In Conclusion
As basic materials in the metal processing industry, iron and steel support the development of modern society. I believe that by reading the above content, you have understood the unique features of iron and steel, and have made certain choices in selecting materials.The following is a simplified comparison of the characteristics of cast iron and steel.
| Characteristic/Advantage | Cast Iron | Steel |
|---|---|---|
| Composition | High carbon content (typically >2.14%), with silicon, manganese, etc. | Lower carbon content (typically <2.14%), with the option of adding alloy elements |
| Casting Ability | Excellent, suitable for complex shapes and thin-walled parts | Poor, usually processed through forging, rolling, etc. |
| Mechanical Properties | Lower (e.g., tensile strength, toughness), but good wear resistance | Higher, including strength, toughness, etc. |
| Corrosion Resistance | Good, but depends on specific type and alloy elements | Can be enhanced through alloying, e.g., stainless steel |
| Machinability | Good cutting and machining ability, but difficult to forge | Easily forgeable, rollable, weldable, and adaptable to various processing methods |
| Cost | Typically lower, with lower production costs and raw material prices | Higher, but with superior performance and potential for long-term economic benefits |
| Application Areas | Machinery manufacturing, construction, civil engineering, transportation, kitchenware, etc. | Wide range of fields including construction, bridges, machinery manufacturing, aerospace, medical equipment, energy, etc. |
Start Your Custom Metal Parts CNC Precision Machining and Manufacturing
In the field of hardware parts machining, cast iron and steel are indispensable metal materials. They are widely used in many key links such as CNC machining center operation, precision extrusion molding and casting process. Choose us VMT, VMT has 14 years of experience in CNC parts machining. We strictly follow 12 quality inspection checkpoints to ensure that the yield rate of batch machining products is as high as 99.98%, building an indestructible wall of protection for your product quality, so that each product meets the high-precision requirements. Choosing VMT means choosing a trustworthy partner.
Frequently Asked Questions About Cast Iron vs Steel
Is Wrought Iron Steel?
Wrought iron is not steel. Although both are iron-carbon alloys, there are significant differences in carbon content and properties.
Steel has a carbon content between 0.05% and 2%, while wrought iron has a carbon content of less than 0.04%.
How Many Types of Iron Are There?
Iron is classified primarily based on its carbon content and how it is processed. In terms of carbon content, iron can be divided into pig iron (carbon content greater than 2%), wrought iron (carbon content less than 0.02%) and steel (carbon content between 0.02% and 2%). Each type has different characteristics in terms of hardness, toughness, plasticity, etc. and is suitable for different application scenarios. In terms of processing methods, iron also includes cast iron obtained through special processes such as melting, alloying, etc.
Will Steel Rust?
When steel is exposed to moist air, especially in an environment containing oxygen, water or certain chemicals, it will undergo an oxidation reaction to form rust. In order to prevent steel from rusting, we at VMT usually adopt a variety of surface treatment measures. For example, painting, galvanizing, chrome plating, stainless steel processing, etc.
