What are the differences between carbon steel and stainless steel?

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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. Read more about the differences between low, medium and high carbon steel in our guide, Low, medium, and high-carbon steel: everything you need to know.

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 2597-2800°F (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:

Levelling feet

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. 

Threaded detent pins

Economical mild-carbon steel detent pins for conveniently adjusting heavy-duty equipment, locking telescopic tubing, and securing bracket assemblies.

Vibration grommet screw

Philips-drive shoulder screw resists vibration, making it ideal for appliances and electronics. Designed to work with vibration mount grommets. 

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 65,300 psi 
(450 MPa) 47,900 psi
(342 MPa) AISI 1045 medium-carbon steel 81,900 psi
(565 MPa) 45,000 psi
(310 MPa) AISI 1080 high-carbon steel 140,000 psi
(965 MPa) 84,800 psi
(585 MPa)

 

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:

Quarter-turn latches

Padlockable wing knob for adding security. The knob enables a sure grip. Use steel cams for additional strength, sold separately. 

Stainless-steel cable ties

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.

 

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%     1598°F (870°C) – when chromium content is 18% Ferritic stainless steels Low Medium Chromium:10.5% to 18% 
Nickel: up to 1% 1022°F – 1562°F (550°C – 850°C) Martensitic stainless steels Low Low Chromium:10.5% to 18% 
0.15% carbon 
0.1% manganese
No nickel 572°F – 1292°F (300°C – 700°C) Duplex stainless steels     High  Medium Chromium: 19.5% to 23%
Nickel: 3% to 6.5% 482°F – 600°F (250°C – 316°C) Precipitation hardening stainless steels Low Medium Chromium:17%
Nickel: 4%  Up to 600°F (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, sulfer, 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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Steel is one of the most versatile and useful materials on the planet. Steel mainly consists of iron (Fe) and carbon (C), but the modern steel is more complex than that. Steel’s characteristics and strength are affected by the concentration of carbon and iron or the inclusion of other elements, which allows steel to be used in an infinite number of scenarios.

Most people believe that steel is just a set combination of iron and carbon. But there are in fact over 3,500 different grades of steel! You can determine the grade of steel by analyzing the quantity of carbon in it, the other alloying elements it includes as well as how it’s processed.

In this article, we’ll discuss the four different types of steel, along with how they’re classified, the various steel grades and the methods of heat treatment used to improve steel’s mechanical properties.

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The four types of steel

Steel is graded and classified into four groups:

• Carbon steels
• Alloy steels
• Stainless steels
• Tool steels

What are these many forms of steel made of, and what purpose do they serve? Let’s find out!

Carbon steels

Aside from carbon and iron, carbon steels contain only trace amounts of other components. Carbon steels are the most common of the four steel grades, accounting for 90% of total steel production! Carbon steel is classified into three subgroups based on the amount of carbon in the metal:

• Low carbon steels/mild steels (up to 0.3% carbon)
• Medium carbon steels (0.3–0.6% carbon)
• High carbon steels (more than 0.6% carbon)

Find out more about carbon steels in our mild steel vs. carbon steel guide!

Companies frequently produce these steels in large quantities since they are relatively inexpensive and robust enough to be used in large-scale construction.

Alloy steels

Alloy steels are made by combining steel with additional alloying elements such as nickel, copper, chromium and/or aluminum. Combining these elements improves the strength, ductility, corrosion resistance and machinability of the steel.

Stainless steels

Stainless steel grades are alloyed with 10–20% chromium as well as nickel, silicon, manganese, and carbon. Because of their increased capacity to survive adverse weather these steels have phenomenally high corrosion resistance and are safe to use in outdoor construction. Stainless steel grades are also commonly used in electrical devices.

For example, 304 stainless steel is widely sought after for its ability to withstand the environment while keeping electrical materials safe.

While different stainless steel grades, including 304 stainless steel, have a place in buildings, stainless steel is more often sought after for its sanitary properties. These steels are widely found in medical devices, pipes, pressure vessels, cutting instruments and food processing machinery.

Tool steels

Tool steels, as the name suggests, excel in cutting and drilling equipment. The presence of tungsten, molybdenum, cobalt and vanadium helps improve heat resistance and general durability. And because they hold their shape even under heavy use, they are the preferred material for most hand tools. Learn how tool steel is made here!

Steel classifications

Beyond the four groups, steel can also be classified based on a different variables including:

• Composition: carbon range, alloy, stainless, etc.
• Finishing method: hot rolled, cold rolled, cold finished, etc.
• Production method: electric furnace, continuous cast, etc.
• Microstructure: ferritic, pearlitic, martensitic, etc.
• Physical strength: per ASTM standards
• De-oxidation process: killed or semi-killed
• Heat treatment: annealed, tempered, etc.
• Quality nomenclature: commercial quality, pressure vessel quality, drawing quality, etc.

Steel grading systems

Steel grading systems allow us to categorize steel varieties based on their use case. For example, the rate at which steel is cooled by steel manufacturers might affect its molecular strength. The length of time they can maintain steel at critical temperatures throughout the cooling process is also essential. In reality, two sheets of steel with the same alloy content can have various grades depending on the heat-treatment technique.

The ASTM Grading System assigns each metal a letter prefix based on its general category (“A” for iron-based alloys and steel materials) as well as a sequentially allocated number corresponding to that metal’s unique qualities.

In contrast, for classification, the SAE Grading System employs a four-digit number. The first two figures represent the steel type and alloying element concentration, while the latter two digits indicate the metal’s carbon concentration.

Steel grading standards are frequently used to assure the quality and consistency of materials by scientists, engineers, architects, automotive engineers and government bodies. These standards provide consistent terminology for communicating the properties of steel in great detail, as well as directing product manufacturers toward suitable processing and application techniques.

Grades of steel

Steel grading systems consider chemical composition, treatment, and mechanical qualities to help fabricators choose the best product for their application. Aside from the actual percentage of carbon and other alloys in the material, the microstructure has a considerable impact on steel’s mechanical properties.

Microstructure

It is critical to understand the meaning of microstructure and how steel microstructure can be modified through hot and cold forming as well as post-manufacturing. These methods can be used to create goods with unique mechanical qualities. Manipulation of chemical composition and microstructure, on the other hand, will result in a trade-off between distinct qualities.

The microstructure of a substance is the way molecules are bonded together with forces acting between them. Heating and cooling operations are used to shift the microstructure from one form to another, affecting the material’s characteristics.

The microstructure cannot be seen with the human eye but can be studied under a microscope. Steel can have a variety of microstructures, including ferrite, pearlite, martensite, cementite, and austenite.

Ferrite

The molecular structure of pure iron at normal temperature is referred to as ferrite. This microstructure will also be found in steel with very low carbon content. A body-centered cubic (BCC) crystal structure is the ferrite’s distinguishing feature. The molecules in BCC are more loosely packed than in other microstructures that contain more molecules per cube.

At room temperature, however, the quantity of carbon that may be supplied without affecting the ferrite microstructure is limited to 0.006%.

Austenite

Austenite is a microstructure generated when iron-based alloys are heated over 1500 degrees Fahrenheit but below 1800 degrees Fahrenheit (982 degrees Celsius). If the correct alloy, such as nickel, is present in the steel, the material will retain its microstructure even after cooling.

Austenite is distinguished by its face-centered cubic (FCC) crystal structure. The molecules in austenite are more densely packed than those in ferrite. Austenite, a common stainless steel microstructure, can contain up to 2% carbon.

Cementite

When carbon steel is heated to austenite temperatures and subsequently cooled without any alloy present to maintain the austenite shape, the microstructure reverts to ferrite.

However, if the carbon level exceeds 0.006%, the excess carbon atoms bond with iron to create iron carbide (Fe3C), also known as cementite. Cementite does not form on its own since a portion of the material is ferrite.

Pearlite

Pearlite is a laminated material composed of alternating layers of ferrite and cementite. It happens when steel is progressively cooled, generating a eutectic combination. A eutectic mixture occurs when two molten materials crystallize at the same time. Under these conditions, ferrite and cementite form concurrently, resulting in alternating layers within the microstructure.

Martensite

Martensite has a tetragonal crystalline structure that is body-centered. This microcrystalline form is achieved by rapidly cooling steel, which traps carbon atoms inside the iron lattice. The end product is a needle-like iron and carbon structure. Steel with a martensite microcrystalline structure is typically a low-carbon steel alloy with about 12% chromium content.

Hot and cold forming

To prevent corrosion, molten steel must be shaped into its final shape and then finished. Steel is often cast in machine-ready shapes such as blooms, billets and slabs. Rolling is then used to shape the casts. Depending on the material and intended application, rolling can be done hot, warm or cold.

Compression deformation is done during rolling by using two work rolls. The rolls rotate quickly, pulling and squeezing the steel between them.

Cold forming

Cold forming is the process of rolling steel at temperatures lower than its recrystallization temperature. The pressure applied by the rolls on the steel generates dislocations in the material’s microstructure, resulting in grains in the substance.

As the number of dislocations increases, the steel gets harder and more difficult to deform. Cold rolling also creates brittleness in the steel, which can be remedied with heat treatment.

After rolling is complete, the steel pieces are finished using secondary processing techniques to increase corrosion resistance and improve their mechanical properties, such as:

• Coating
• Surface treatment
• Heat treatment

Various methods of steel heat treatment

Spheroidizing

Spheroidization happens when carbon steel is heated to 1290°F (699°C) for 30 hours. The pearlite microstructure’s cementite layers are changed into spheroid shapes, resulting in the softest and most ductile form of steel.

Full annealing

Carbon steel is annealed by first heating slightly beyond the upper critical temperature for an hour, then at a rate of around 36°F (2°C) per hour. This procedure yields a coarse pearlitic structure that is flexible and free of internal tensions.

Process annealing

In cold-worked, low-carbon steel (> 0.3% C), process annealing relieves stress. For one hour, the steel is heated to 1025–1292°F (552–700°C). Before cooling, dislocations in the microstructure are corrected by reconstructing the crystal.

Isothermal annealing

High-carbon steel is heated above its upper critical temperature first. The temperature is then maintained, reduced to the lower critical temperature and maintained once again. After that, it is gradually cooled to room temperature. This procedure guarantees that the material has reached a uniform temperature and microstructure before proceeding to the next cooling stage.

Normalizing

For one hour, carbon steel is heated to the normalizing temperature. The steel has now entered the austenite phase completely. The steel is then cooled by air. Normalization results in a fine pearlitic microstructure with high strength and hardness.

Quenching

In this process, medium or carbon steel is heated to the normalizing temperature, then quenched (rapid cooling in water, brine, or oil) to the upper critical temperature. The quenching process results in a martensitic structure, which is highly hard but fragile.

Tempering quenched steel

This is the most popular heat treatment since the outcome is predictable. Quenched steel is reheated and chilled to temperatures below the lower critical point. Temperatures vary depending on the desired effect, with 298–401°F (148–205°C) being the most typical.

What is the best grade of steel?

There is no universal “best” grade of steel, as the optimal steel grade for an application depends on many factors, such as the intended usage, mechanical and physical requirements, and financial limits.

Steel grades that are regularly used and deemed the top series from each type include:

• Carbon steels: A36, A529, A572, 1020, 1045, and 4130
• Alloy steels: 4140, 4150, 4340, 9310, and 52100
• Stainless steels: 304, 316, 410, and 420
• Tool steels: D2, H13, and M2

Final thoughts

To find that optimal grade of steel for your application, visit a Metal Supermarkets location to speak to one of our metal experts. We have all your steel needs covered. You can buy as much metal as you need, quickly and easily, with no minimum order size!

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