Casting provides superior design detail capabilities, often without the need for additional fabrication and assembly. Many materials can be cast, including many metals and composites, but steel in particular has excellent mechanical properties that make it suitable for a wide range of applications.
While cast iron and steel may appear similar on the surface, they each have unique advantages and disadvantages from production to application. Understanding these pros and cons and making appropriate choices can mean the difference between intolerable strength and durability and a broken or deformed part that quickly loses its luster. In today’s guide, we will discuss what is the difference between cast iron and cast steel. Read on to learn more.
1. Main differences
First, carbon content is the main difference.
Both iron and steel are ferrous metals composed primarily of iron atoms. However, in the manufacturing process, things are not that simple – many different alloys and grades are used in production. It is important to distinguish between everyday iron and iron (Fe) used in scientific research. Elemental iron is a substance found in nature, usually in an oxidized form, and requires an intensive process called smelting to extract.
Most applications cannot be carried out with pure elemental iron because it is too soft. When it is alloyed or mixed with carbon, it becomes harder and therefore more useful. In fact, the carbon content is the main difference between cast iron and steel. Cast iron typically contains more than 2% carbon, while cast steel typically contains 0.1-0.5% carbon.
2. Characteristics
A comparison of relevant characteristics of iron and steel is provided below.
1) Application fields
Gray Cast Iron: Engine blocks, cylinder heads, manifolds, gas burners, gear blanks, casings, casings, outdoor hardscape products, frying pans, electrical boxes, decorative castings, stove parts, counterweights
Ductile Iron: bollards, field furnishings, steering knuckles, crankshafts, heavy-duty gears, car and truck suspension components, hydraulic components, automotive door hinges, cast iron valves
Steel: bollards, industrial wheels, cast gears, valve bodies, mining machinery, turbine impellers, forging presses, tram frames, pump casings, marine equipment, engine casings, heavy trucks, construction equipment
2) Castability
Most people have not encountered iron or steel in the molten state, which is understandable since iron melts at about 2300°F and steel at 2600°F, and both are at much higher temperatures Pour into molds. People working with liquid iron and steel quickly discover that there are huge differences in pourability and shrinkage.
As a result of its ease of pouring, cast iron is relatively easy to cast. It shrinks less than steel, so it is easier to cast. This means it can easily fill complex voids in molds and requires less molten material to do so. This fluidity makes cast iron an ideal metal for architecture or ornate ironwork structures such as fences and benches.
Pouring steel is much more difficult. It has poorer fluidity than molten iron and is more reactive with mold materials. It also shrinks more as it cools, which means more molten material needs to be poured in—usually into an excess reservoir called a riser, from which the casting is cooled Absorb from.
However, the entire internal structure of a casting typically does not cool evenly. The outer areas and thinner sections cool and shrink at different rates than the inner areas and larger sections, often creating internal tensions or stresses that can only be relieved by heat treatment. Steel is more susceptible to shrinkage stresses than iron, and in some cases, these tensions can result in significant internal and/or external voids that may ultimately lead to fracture.
Due to these reasons, casting steel requires more attention and inspection throughout the process, making production more resource-intensive.
3) Machinability
Depending on the end application, castings may need to be machined to specific tolerances or to create a desired finish. At a minimum, objects like gates and chutes need to be cut out and ground down.
NOTE: Strength without ductility means the material will be very brittle and prone to breaking.
Machinability is a measure of how easy a given material is to cut or grind; some materials are more difficult to machine than others. As a rule of thumb, metals that are highly alloyed to improve mechanical properties are less machinable.
Cast iron is generally easier to machine than steel. The graphite structure in cast iron sheds more easily and more evenly. Harder irons, such as white iron, are more difficult to work due to their brittleness.
Steel does not cut easily with the same consistency and causes more tool wear, resulting in higher production costs. Hardened steel or steel with a higher carbon content can also increase tool wear. However, softer steel is not necessarily better, and mild steel, although softer, can become sticky and difficult to work with.
4) Vibration reduction
Damping properties should be considered when selecting casting materials, as insufficient damping capacity can result in excessive vibration and noise, such as ringing or squealing. Depending on where the material is used, effective damping can result in stronger, more reliable performance.
The graphite structure in cast iron, especially the lamellar structure in gray cast iron, is particularly beneficial for absorbing vibrations. This makes cast iron ideal for engine blocks, cylinder housings, machine tool beds, and other applications where robustness and precision are important. Reducing vibration minimizes stress and prevents wear on moving parts.
5) Compressive strength
Compressive strength is the ability of a material to withstand forces that would reduce the size of an object. The opposite of the force that separates the material is this force. Compressive strength is beneficial in mechanical applications where pressure and sealing are factors. The compressive strength of cast iron is generally higher than that of steel.
6) Impact resistance
So far, using cast iron seems to have more advantages than steel, but steel has one significant advantage: impact resistance. Steel is able to withstand sudden impacts very well without bending, deforming or breaking. This is due to its toughness: it is able to withstand high stress and strain forces.
A lack of ductile strength makes brittle materials prone to fracture, and cast iron is a prime example of a lack of ductile strength. Due to its brittleness, cast iron has a limited range of applications.
At the same time, high ductility or the ability to deform without failure is of little use without the strength to withstand significant impact. For example, a rubber band can undergo significant deformation without breaking, but the force it can withstand is very limited.
While iron may be easier to work in most casting applications, steel has the best combination of strength and ductility in many applications, and cast steel is very tough. Steel’s impact-resistant qualities and all-around load-bearing properties make it ideal for many mechanical and structural applications – which is why steel is the most widely used metal in the world.
7) Corrosion resistance
Iron has better corrosion resistance than steel. Both metals oxidize when exposed to moisture, but iron develops a patina that prevents deep corrosion of the metal’s integrity.
The way to prevent corrosion is to use paint or powder coating. Any chips or cracks that expose the underlying metal can cause corrosion, so regular maintenance is very important for coating metal.
If corrosion resistance is an important factor while maintaining the appearance of the silvery original metal, alloy steel may be a better choice, especially stainless steel, which has chromium and other alloys added to prevent oxidation.
8) Wear resistance
Cast iron generally has better resistance to mechanical wear than steel, especially in the case of frictional wear. A certain amount of graphite content in the cast iron matrix creates a graphite dry lubricant that allows solid surfaces to slide against each other without reducing the surface quality and making it more difficult to wear.
Steel wears more easily than iron, but is still resistant to certain types of wear. The addition of certain alloys can also improve the wear resistance of steel.
9) Cost
Cast iron is generally less expensive than cast steel because the cost of materials, energy, and labor required to produce the final product is lower. Raw steel is more expensive to purchase and requires more time and effort to cast. However, when designing cast products, it is worth considering long-term use and replacement costs. Parts that cost more to make may end up costing less in the long run.
Steel also comes in a variety of prefabricated forms, such as plates, rods, rods, tubes, and beams, and can often be machined or assembled to suit specific applications. Depending on the product and required quantities, manufacturing existing steel products may be a cost-effective option.
3. Conclusion
We compared the qualities of cast iron (gray iron) and cast steel (mild or carbon steel) in their most basic forms, but the specific composition and phase structure of the steel can greatly affect mechanical properties. For example, the carbon in standard gray cast iron is in the form of sharp graphite flakes, while ductile iron has a more spheroidal graphite structure. Flake graphite makes gray cast iron brittle, while the rounded graphite particles in ductile iron increase toughness, making it more suitable for impact-resistant applications.
Alloys can be added to steel to engineer desired properties. For example, manganese improves toughness, while chromium improves corrosion resistance. Different carbon contents are also what differentiates mild steel, standard steel, and high carbon steel – the higher the carbon content, the harder the material. In the end, the choice between cast iron and cast steel will depend on the final installation type and application.
（https://www.reliance-foundry.com/blog/cast-iron-vs-cast-steel）
