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Stainless steel and cast iron are exceptional materials and excel in terms of their own features. So, obviously, choosing one among them can be a real challenge just based on assertions.
Stainless steel stands out for its modern appearance and exceptional resistance to rust while the cast iron attracts the users with its tough durability and heat retention. Both materials bring unmatched benefits, making your choice depend on the comprehensive understanding of their features.
However, you can navigate the detailed differences in this write-up and find a reliable summary. So, without searching any further, read today’s detailed comparison discussion.
What Is Stainless Steel?
Also known as inox, stainless steel is a rustless and corrosion-resistant alloy of iron, containing chromium for about 10% to 30%, a minimum of 10.5%.
The chromium content makes the steel approximately 200 times more highly resistant to heat and rust, whereas the low carbon content maintains this resistance.
Other elements like molybdenum, nickel, aluminum, titanium, copper, nitrogen, sulfur, phosphorus, or selenium are sometimes added for extra benefits. Stainless steel does not require to be treated, painted, or coated once it is put into service.
You can see five main types of stainless steel.
- Austenitic: Contains 16-26% chromium and more than 35% nickel.
- Ferritic: Contains less than 0.2% carbon, 10.5-27% chromium, and no nickel.
- Martensitic: Contains 11.5-18% chromium and 1.2% carbon.
- Duplex: Contain 21-27% chromium, 0.05-3% copper, 1.35-8% nickel and 0.05-5% molybdenum.
- Precipitation Hardening: Contains 15-17.5% chromium and 3-5% nickel and others.
What Is Cast Iron?
Cast iron is a type of iron-carbon alloy that has a silicon content of around 1% to 3% and a carbon content of more than 2%. Its usefulness mainly derives from its relatively low melting point.
The form of the carbon in the cast iron depends on the alloying elements. For instance, white-cast carbon contains carbon in the form of cementite. It makes it very hard but brittle.
As for the gray cast iron, it has graphite flakes that deflect cracks. Ductile cast iron features spherical graphite nodules. It effectively stops the crack from further progressing. However, the main alloy elements of cast iron are carbon between 1.8 to 4 wt% and silicon 1–3 wt%.
Quick Comparison of Stainless Steel Vs Cast Iron
| Features | Stainless steel | Cast iron |
|---|---|---|
| Durability and strength | Superior durability and tensile strength | More brittle and more prone to cracking under impact |
| Corrosion resistance | Durable but does not match the cast iron | Can last for generations with proper care |
| Heat retention | Retains heat reasonably well | Excels in heat retention |
| Machinability | Difficult | Easier |
| Tensile strength | Higher | Lower than stainless steel |
| Compression strength | Lower | Higher than stainless steel |
| Surface finish | Dull, bright, or unique | As-cast surface |
| Wear resistance | Higher | Poor |
| Application | Medical, automotive, and power industries | Construction, and machinery |
| Melting point | High melting point around 1,400 to 1,530 °C | The low melting point of about 1145~1250℃ |
| Price | Moderate to high-priced | Affordable |
Cast Iron vs. Stainless Steel: A Detailed Comparison
Stainless steel and cast iron have different properties and show differences in terms of strength, use case, performance, suitability, and so on.
Check it out below for a detailed comparison between them.
1. Chemical Composition
Cast iron is primarily composed of iron (Fe). Along with this base element, other major alloying elements are carbon and silicon (Si) with a trace amount of elements like manganese, sulfur, and phosphorus also present.
Chemical Composition of Cast Iron
| Element | Composition |
|---|---|
| Carbon | 2.00-2.65% |
| Silicon | 0.90-1.40% |
| Manganese | 0.25-0.55% |
| Phosphorous | Less than 0.18% |
| Sulfur | 0.05% |
In contrast, the primary alloying element of stainless steel is iron. Other elements include nickel, molybdenum, manganese, and carbon, all of which depend on the specific grades of stainless steel. Here is the quick table highlighting the composition percentage for common types of stainless steel.
Chemical Composition of Stainless Steel
| Element | Composition |
|---|---|
| Iron (Fe) | 50% – 75% |
| Chromium (Cr) | 16-30% |
| Nickel (Ni) | 8-10.5% |
| Molybdenum | 2-3% |
| Manganese (Mn) | 1% – 2% |
| Carbon (C) | 0.03-0.08% |
| Silicon (Si) | 0.5-1% |
| Phosphorus (P) | ≤ 0.045% |
| Sulfur (S) | ≤ 0.03% |
2. Strength And Durability
Regarding strength and durability, both stainless steel and cast iron have good sides. However, cast iron has higher compressive strength than steel which makes it resistant to dents and bending. Coming to the tensile strength of the cast iron which is lower than that of stainless steel. You can easily bend it and apply it to your projects rather than cast iron.
The alloy material of the stainless steel stands out with its incredible tensile strength. It approximately ranges from 415 MPa ( 60 Ksi) to 1380 MPa (200 Ksi). Let’s see the table highlighting the tensile strength of stainless steel in various grades:
| Alloy | Tensile Strength |
|---|---|
| Grade 301 Stainless | 515 MPa (75 Ksi) |
| Grade 302 Stainless | 585 MPa (85 Ksi) |
| Grade 303 Stainless Steel | 690 MPa ( 100 Ksi) |
| Grade 304 Stainless | 621 MPa (90 Ksi) |
| Grade 309 Stainless | 620 MPa (89 Ksi) |
| Grade 316 Stainless | 579 MPa (84 ksi) |
| Grade 317 Stainless | 585 MPa ( 85 Ksi) |
On the other side, cast iron also has good stability in all conditions. The tensile strength is the cast iron starts 90.0, which goes as long as 1650 MPa, depending on its type. However, it lasts long as long as you take good care of it. You can preserve the natural appearance of the cast iron surface with occasional seasoning.
3. Corrosion Resistance
Stainless steel outperforms cast iron in corrosion resistance. That’s because cast iron has a higher carbon content which develops a stable and protective rust layer.
| Feature | Cast Iron | Stainless Steel |
|---|---|---|
| Rust Formation | Forms a protective layer | Minimal rust due to chromium oxide |
| Resistance in Salty Environment | Poor | Excellent |
| Resistance in Acidic Conditions | Poor | Excellent |
| Durability (in Corrosive Areas) | Moderate | High |
Stainless steel is considered to be superbly resistant to corrosion when the corrosion rate is below 0.1 mm/year in a given environment. It has a protective chromium layer which helps prevent rust and corrosion.
However, that does not mean they are indestructible. Both stainless steel and cast iron will develop corrosion if you avoid proper care.
4. Heat Retention
Here also, cast iron excels more compared to the stainless steel. It has exceptional heat retention and is popular for heating up quickly and evenly.
Cast iron even can maintain the temperature for a long time once heated. So, it can be a good option to be used for car parts manufacturing or industrial materials.
But that’s not the same with the stainless steel. They do not retain heat like cast iron. It heats up quickly but is prone to cool down faster. That’s the reason, why stainless steel may not be the ideal choice for the task requiring high or consistent heat.
5. Machinability
Cast iron is generally easier to machine compared to cast iron. It ranges from almost 200% in soft alloys and 60% in hard alloys. That means cast iron is easier to cut or grind. It breaks away more uniform way and more easily.
Stainless steel can be machined, but it is more difficult due to its high tensile strength and hardness. For instance, Austenitic steel has 35-75% machinability whereas Duplex stainless steel has machinability for about 20-30%.
6. Electrical Conductivity
Stainless steel is generally a better conductor than cast iron. The electrical conductivity of the cast iron is typically around 100 x 10^-8 Siemens per meter (S/m) due to the presence of graphite flakes within the iron matrix.
In contrast, the electrical conductivity of stainless steel is approximately 1.45 x 10^6 Siemens per meter (S/m). This makes it more suitable for applications requiring moderate electrical conduction. You can easily use it in electrical enclosures, grounding equipment, and certain medical or industrial devices.
Though cast iron has lower electrical conductivity, still you can use it for many structural and mechanical applications like engine blocks and components, pipelines and valves, machine frames, and housings. Many automotive parts like brake discs, and pump and valve bodies can also be made with it.
7. Surface Finish
Surface finish refers to the appearance of the material. Stainless steel is generally available in a wide variety of surface finishes. Three main categories include Mill finishes, Mechanically polished finishes, and Special finishes.
On the other hand, all cast iron has an as-cast surface. Typically, this surface of the cast iron shows a light sand texture.
8. Wear Resistance
Cast iron and stainless steel are both highly durable materials. However, cast iron is highly resistant to wear and tear, especially in situations with friction. Its graphite content acts like a lubricant that allows the sliding of the solid surface without wearing down. However, it is a brittle material and tends to crack under sudden thermal shocks or impacts.
On the other hand, stainless steel is strong and malleable. It makes it less likely to crack compared to cast iron. Moreover, stainless steel offers exceptional resistance to corrosion and staining.
9. Applications
Stainless steel has more versatile use than cast iron and also has more applications. It includes medical, construction, automotive, and power industries. For instance,
| Stainless Steel Types | Applications |
|---|---|
| Austenitic | Exhaust systems, Pipes, domestic items such as cutlery, saucepans, and so on. |
| Ferritic | Dishwashers, sinks, pharmaceutical and food and processing equipment etc. |
| Martensitic | Automotive components, knives, aerospace, cutlery, scissors, etc. |
| Duplex | Heat exchangers, pressure vessels, bleaching equipment, and so on. |
| Precipitation-hardened | Aerospace, nuclear, oil and gas industry. |
As for cast iron, its different types are used for different purposes. Here is a quick overview of the cast iron application.
| Cast iron types | Application |
|---|---|
| Grey cast iron | Engine blocks and cylinder heads. |
| White cast iron | Manufacturing mill linings, crushers, slurry, and pump housings. |
| Ductile cast iron | Heavy-duty gears, crankshafts, crankshaft and hydraulic applications. |
| Malleable cast iron | Manufacture heavy-duty-bearing surfaces, construction, and farm machinery. |
10. Melting Point
The melting point of materials determines their ability to maintain their structural integrity in high temperatures. Stainless steel has a higher melting point than the cast iron. The melting point of stainless steel is between 1,400 to 1,530°C (2,550 to 2,790°F) whereas for cast iron it is around 1,204°C (2,200°F).
Here is a detailed idea of the melting points of the stainless steel and cast iron.
Melting point of stainless steel:
Below are the melting points of stainless steel of different grades.
| Grade Of Stainless Steel | Melting Point (In Fahrenheit) | Melting Point (In Celcius) |
|---|---|---|
| Grade 304 | 2552°-2642°F | 1400°-1450°C |
| Grade 316 | 2507°-2552°F | 1375°-1400°C |
| Grade 430 | 2597°-2750°F | 1425°-1510°C |
| Grade 434 | 2600°-2750°F | 1426°-1510°C |
| Grade 410 | 2696°-2786°F | 1480°-1530°C |
| Grade 420 | 2642°-2750°F | 1450°-1510°C |
The melting point of cast iron:
Here is the melting point of different types of cast iron.
| Cast Iron | Melting Point (In Fahrenheit) | Melting Point (In Celcius) |
|---|---|---|
| Iron, Cast | 2200 °F | 1204 °C |
| Iron, Cast (Gray) | 2150 – 2360 °F | 1175 – 1290 °C |
| Iron, Ductile | 2,100 – 2,190 °F | 1,150 – 1,200 °C |
Applications suggestions of cast iron and stainless steel based on melting points:
Stainless steel, with its high melting point, is perfect for applications exposed to extreme temperatures. For example, you can use it in-
- Aerospace for engine parts and turbine blades,
- Chemical processing equipment like reactors and piping systems
- Medical instruments, such as surgical tools and implants
- Power generation plants.
However, if you don’t need extreme heat resistance with great durability and heat retention, choose cast iron for your specific projects. For example, engine blocks, plumbing systems, machine frames and parts, and so on.
11. Price
In terms of price, cast iron is generally a more affordable option than stainless steel.
For example, one tonne of stainless steel may cost you something around $2000. But the same one tonne of cast iron will cost between $1300 to $1600.
However, as a general rule of thumb, brand, quality, features, and size can affect greatly the cost of both cast iron and stainless steel.
What Sets Stainless Steel Apart?
Stainless steel excels in durability, aesthetics, and so on. It makes the material a low-maintenance option for many industries.
| Factor | Details |
|---|---|
| Ease of fabrication | Stainless steel is very easy to fabricate. So, it offers exceptional flexibility in customization and design. |
| Effortless cleaning and maintenance | The smooth and corrosion-resistant surface of the stainless steel is very easy to clean and maintain. |
| Resistance to UV Degradation | Stainless steel is highly resistant to UV degradation, unlike any other material. It does not discolor when exposed to sunlight. |
| Health & safety compliance | Stainless steel contains nontoxic content and is free from harmful chemicals. That is why it is widely used in the food and healthcare industries. |
| Aesthetic appeal | Stainless steel offers a modern and aesthetic appearance to any setting. |
| Energy efficiency in production | The production of the stainless steel utilizes recycled materials. That’s the reason it is also energy efficient. |
Limitations Of Stainless Steel
Though stainless steel offers many impressive benefits, it has some limitations. It includes-
- Stainless steel has a higher initial cost.
- It tends to have corrosion in a specific environment like in high-level acids and chlorides.
- Complex welding requirements
- Is brittle at low temperature
- Dents and scratches are more noticeable
What Sets Cast Iron Apart?
Cast iron sets itself apart from the other materials in the following features.
| Factor | Details |
|---|---|
| Cost-EffectiveCost-Effective | Cast iron is relatively less expensive, making it a cost-effective option for many applications. |
| Excellent machinability | The graphite content in the cast iron performs as a natural lubricant. It enables easy machining and reduces wear when working with cast iron. |
| High wear resistance | Cast iron, especially white cast iron has the higher wear resistance due to its high carbide content in the structure. |
| Good castability | Cast iron has excellent fluidity after melting which allows it to be cast into any shape even to the complex ones. |
Limitations of Cast Iron
Check out the limitations of cast iron below to make an informed decision.
- Cast iron is brittle in nature and tends to crack under high pressure.
- It has relatively low tensile flexibility and strength.
- It can become susceptible to rust when the protective oxide is damaged.
- Cast iron is heavier compared to other materials and denser.
- Welding the cast iron can be challenging.
Similarities Between Stainless Steel and Cast Iron
Although stainless steel and cast iron stand out in their own distinct features, still they share some similarities. For instance.
| Aspects | Stainless steel | Cast iron |
|---|---|---|
| Durability | Highly durable | Highly durable |
| Heat retention | Retain heat well | Retain heat well |
| Versatility | Versatile | Versatile |
| Corrosion Resistance | Resistant with proper care | Resistant with protective layer or coatings |
| Recyclability | Fully recyclable | Fully recyclable |
| Industrial Applications | Used in machinery and tools | Commonly used in tools and pipelines |
Stainless Steel Vs Cast Iron: Choosing The Right Material For Your Applications?
When choosing between stainless steel and cast iron, you should consider the application. Stainless steel is durable and corrosion-resistant. So, it can be ideal for medical tools, construction, and food processing equipment, especially where hygiene is essential. Its ability to handle extreme heat and resist rust makes it perfect for harsh environments.
On the other hand, cast iron is heavy and retains heat better. You can use it ideally for engine components and machinery parts. It performs well in applications where weight isn’t your major concern but heat distribution or strength is essential.
So, first, evaluate your requirements and then make a wise decision accordingly which one you need- stainless steel or cast iron!
Conclusion
Stainless steel is tough and resists rusts well which you can use to make the parts for tools in various industries. In contrast, when you demand material to use in heavy machines and things that need to absorb vibrations, like car parts, cast iron would be great. Though they are tough but tend to be more brittle compared to stainless steel.
However, you can choose the right material by determining your application’s demand. And, if you want custom CNC machining services, Richconn can be the best option for you. Contact us anytime to get the detailed information.
FAQs
Does cast iron need special care?
Yes, cast iron needs special care compared to the other materials. Water is like the enemy of the cast irons. You will need to ensure the cast iron is properly cleaned and dried thoroughly to maintain the nonstick property. It also includes applying a thin layer of cooking oil after each use.
Does stainless steel rust yes or no?
Yes, even the stainless steel can rust. Some types of stainless steel are prone to corrosion and can rust depending on the chromium content. The higher the chromium content in the stainless steel, the less likely the stainless steel is to rust.
Which steel is better, 304 or 316?
Among 304 or 316 stainless steel, which one will be better depends on your specific requirements. 304 stainless steel is more affordable and versatile. However, 316 stainless steel can be a better choice if you need high corrosion resistance. So, choose based on your requirements.
What damages cast iron?
Cast iron can be damaged by a number of factors. For instance, air and moisture. When cast iron is exposed to the air or water, it becomes susceptible to moisture. Moreover, high temperatures or sudden change in the temperature can also damage the cast iron.
Does cast iron rust?
Yes, cast iron is susceptible to rust without the protective layer of carbonized iron. It is called seasoning. However, if you put the cast iron to soak or allow air to dry even the well seasoning cast iron is prone to rust.
