What are the differences between carbon steel and stainless steel?
Carbon steel vs. stainless steel is a choice of which characteristics are critical to your application and what you’re trying to achieve. To help you make your decision, we’ve put together this guide to give you a better understanding of both materials. We’ll cover:
The properties of carbon steel
Carbon steel is an alloy of iron and carbon, with a carbon content that typically ranges between 0.05% to 2.0%. It has a high tensile strength, which makes it resistant to deformation and able to handle high levels of stress without breaking or cracking. The amount of carbon in steel can vary, but generally falls into three categories:
| Amount of carbon | Properties | |
|---|---|---|
| Low carbon steel, also called mild carbon steel | Maximum of 0.3% | Low hardness and cost. High ductility, toughness, machinability and weldability |
| Medium-carbon steel | 0.3% to 0.6% | Low hardenability. Medium strength, ductility and toughness |
| High-carbon steel | 0.6% to 2% | High hardness and strength. Low ductility |
Steel with higher carbon content has higher corrosion resistance than low-carbon steels.
Melting points vary as well, depending on factors such as impurities, other alloying elements, and the rate of heating and cooling used during testing. Generally, however, melting point can range between 1425-1540°C for carbon steels.
Carbon steel is ductile and can be formed into different shapes and sizes with ease. It’s also easily welded and machined. Because of its high iron content, carbon steels are magnetic, which makes them especially suitable for applications that include motors, transformers, generators, construction vehicles and automotive applications. It’s good at conducting electricity, which makes it ideal for applications that include electrical wiring. Some other applications include:
Made of mild-carbon steel, as shown here. With the base remaining stationary, the leg can be adjusted under load. Also available with a rigid base for mounting machinery or conveyors.
Philips-drive shoulder screw resists vibration, making it ideal for appliances and electronics. Designed to work with vibration mount grommets.
Easy to operate. Ideal for tool boxes and chests, electrical panels and inspection covers. Can be fixed with low-carbon self-drilling screws.
A type of washer suited for applications requiring very high loads in small spaces, such as vehicle braking systems and shock absorbers.
Gas spring end fittings and mounts
Works with gas struts and uses pneumatically stored potential energy to operate.
Density wise, carbon steel varies, and again, this is related to the steel’s specific composition. Typically, however, it ranges from 7.85 g/cm3 to 8.05 g/cm3.
You can learn more in our guide, What are the differences between iron and steel?
What makes carbon steel so tough?
The carbon content is what gives steel its strength. The more carbon present in steel, the harder and stronger it gets when heat treated. This also makes it less ductile, losing strength when deformed. Other materials are added in small amounts to enhance certain characteristics – such as chromium for corrosion resistance – without affecting the steel’s strength.
To assess carbon steel’s strength, we look at tensile strengths and yield strengths. Tensile strength is a measurement of how much stretching or pulling force it can endure before breaking. Yield strength measures how much force the steel can take before bending or denting. There are no cut and dry measurements for carbon steel because again, it depends on the specific steel’s composition, grade and standard.
But to give you an idea of the range of yield and tensile strengths in carbon steel, let’s use AISI (American Iron and Steel Institute) standards.
| Tensile strength | Yield strength | |
|---|---|---|
| AISI 1020 low-carbon steels | 450 MPa 65,300 psi |
342 MPa 47,900 psi |
| AISI 1045 medium-carbon steel | 565 MPa 81,900 psi |
310 MPa 45,000 psi |
| AISI 1080 high-carbon steel | 965 MPa 140,000 psi |
585 MPa 84,800 psi |
Does high carbon steel rust?
Yes. As already mentioned, high-carbon steels are more corrosion resistant than low-carbon-content steels. However, even high-carbon steels will still rust if exposed to moisture over time. As carbon steels have a higher iron content than other steels, they will always be under threat to oxidation and corrosion.
The properties of stainless steel
Stainless steel belongs to a family of iron-based alloys known for their heat and resistance to corrosion. Stainless-steel alloys include a minimum of 10.5% chromium. It’s chromium that gives this steel outstanding corrosion resistance. Nickel is an important alloy in stainless steel, as it enhances resistance to oxidation and enables formability, weldability and ductility.
It’s also highly durable, used in automotive, surgical tools, medical equipment and implants, construction, and the food and catering industry. Other stainless-steel applications include:
Self locking and ideal for bundling and securing cables, wires, and other assemblies. Provides outstanding strength and durability while resisting extreme temperatures.
Connector dust caps and chains
Threaded onto connector adapters when unmated to provide mechanical and environmental protection. The stainless-steel material is suitable for harsh conditions.
Threaded stainless steel stud provides a maximum articulation of 30 degrees. Ideal for use in food production industries and catering.
Designed to secure and suspend objects from anchor or pivot points.
Ideal for use on electrical cabinets and enclosures. IP65 rating makes this suitable for outdoor applications.
We mentioned the medical industry, where stainless steel plays a critical role. You can learn more in our guide, What is surgical steel? The role of stainless in healthcare.
Not all stainless steel is the same, however. It’s made in different grades and is classified according to family, of which there are five. The family they belong to reflects their metallurgical structure. To learn more, read our Guide to stainless steel grades.
For now, we’ll give you a glimpse of the five families, which have different proportions of iron, carbon and chromium. They also include slightly different alloys. Note, operating temperature ranges depend on specific composition and grades. Use these temperature ranges as a general idea of the steel’s ability to handle heat.
| Family | Weldability | Ductability | Notable content | Operating temperature range |
|---|---|---|---|---|
| Austenitic stainless steels | High | High | Chromium: 16% – 18% Nickel: 6% – 8% |
870°C – when chromium content is 18% |
| Ferritic stainless steels | Low | Medium | Chromium:10.5% to 18% Nickel: up to 1% |
550°C – 850°C |
| Martensitic stainless steels | Low | Low | Chromium:10.5% to 18% 0.15% carbon 0.1% manganese No nickel |
300°C – 700°C |
| Duplex stainless steels | High | Medium | Chromium: 19.5% to 23% Nickel: 3% to 6.5% |
250°C – 316°C |
| Precipitation hardening stainless steels | Low | Medium | Chromium:17% Nickel: 4% |
316°C |
Is stainless steel rust-resistant?
Yes, stainless steel is around 200 times more corrosion resistant than steels without chromium. Stainless steel’s high chromium content reacts with oxygen, creating a passive, protective layer against corrosion. This isn’t a coating or plating. It’s inside stainless steel, providing more than surface protection against oxidation.
This is why when stainless steel is scratched, the passivation layer continues to work, standing up to oxidation. A major difference between carbon steel and stainless steel comes down to corrosion resistance.
Does stainless steel have carbon?
The carbon content of stainless steel is less than 1.2%. The addition of carbon to stainless steel in small amounts can improve the steel's strength, but it can also decrease resistance to corrosion. To balance these properties, stainless steel is typically produced with low to moderate levels of carbon.
What is high-carbon stainless steel?
High-carbon stainless steel belongs to the Martensitic family and tends to be a niche material. While it has high levels of hardness and strength, it’s also more brittle than other types of stainless steel and can be prone to cracking under certain conditions. High stainless-steel carbon content is typically used for cutting tools, and other applications where sharpness and durability are important and the cutting edge needs to be retained for longer.
In addition to carbon, stainless usually contains nickel and other alloying elements, such as titanium, which can further improve the steel's strength.
Is carbon steel stronger than stainless steel?
Stainless steel vs carbon steel. The strength of both depends on the carbon content. For example, stainless steel tends to be much stronger than low-carbon steel, in addition to being harder. High-carbon steels, on the other hand, offer the same or even higher strength than stainless steels.
Depending on the strength you require, either carbon steel or stainless steel can suit your application. But if corrosion resistance is important, choose stainless steel.
Can you weld stainless steel to carbon steel?
Yes, but welding stainless steel to carbon steel isn’t a good idea. Due to the difference in the two metals’ electrical conductivity – stainless is more electrically resistant – reaching the right weld temperature is extremely difficult. Then there’s the problem of thermal expansion, which affects both metals differently, and can lead to structural failure in the joint. Welding the two materials is possible, but not without a lot of trial and error, and thus costs.
Stainless steel vs carbon steel
Here’s a quick reference to how carbon and stainless steel compare.
| Carbon steel | Stainless steel | |
|---|---|---|
| Definition | Main alloying element is carbon | Minimum of 10.5% chromium by mass and maximum of 1.2% of carbon by mass |
| Content | Carbon, manganese, silicon, copper | Chromium, carbon, silicon, phosphorous, sulphur, nickel, molybdenum |
| Magnetic properties | Magnetic | Some stainless steels are not magnetic |
| Carbon content | Up to 2% | Between 0.03% and 1% by weight |
| Corrosion resistance | Poor | Strong |
| Cost | Inexpensive | Costs more |
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Questions?
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