Stainless steel and carbon steel are the most commonly used types of steel in almost every industry.
But what exactly is the difference between the two? And which one should you choose for your application?
Stainless steels are characterized by their high strength and ductility along with high chromium content, making them resistant to corrosion. In contrast, carbon steel is characterized by its carbon content, varying from 0.05%-2.00%. The higher the carbon content, the better its wear resistance and hardness but the lower its machinability.
This article provides a detailed differentiation between stainless steel and carbon steel and helps you make a calculated choice between the two for your application.
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Difference between Stainless Steel and Carbon Steel
|Properties||Stainless steel||Carbon steel|
|Composition||Must contain chromium > 11%.||Must contain carbon<2%.|
|Corrosion resistance||High corrosion resistance||Low corrosion resistance.|
|Thermal conductivity||Lower thermal conductivity ~30W/m °C||Higher thermal conductivity <40W/m °C|
|Magnetism||Austenitic stainless steels are nonmagnetic.||Almost all types of carbon steel are magnetic.|
|Machinability||Tough to machine||Easy to machine|
Differences Based on Composition
Stainless steels are known for their corrosion resistance owing to their alloying element chromium, which must be at least 11 wt.%.
Adding nickel and molybdenum further enhances the corrosive resistance of the material.
On the other hand, carbon steels consist of carbon as the primary alloying element with very meager amounts of other elements.
Differences Based on the Properties
Stainless steel is a type of metal that does not rust easily and exhibits excellent resistance to oxidation and corrosion due to the presence of chromium.
Austenitic stainless steel is the best when it comes to corrosion resistance, followed by ferritic, and last is martensitic.
However, stainless steel is not completely immune to rusting and can undergo oxidation under extreme conditions.
In contrast, carbon steels are more vulnerable to rusting and corrosion and have poor corrosion resistance properties.
The density of stainless steel is higher than that of carbon steel and tends to increase with the increase in alloying elements.
As a result, stainless steel exhibits better ductility and malleability, whereas carbon steels exhibit better hardness and strength.
Generally, the thermal expansion value of ferritic stainless steel and carbon steel is almost similar at around 11×10-6/°C.
However, for applications where retaining heat is crucial, stainless steel is preferred for its lower thermal conductivity values (~30W/m °C) than carbon steel (<40W/m °C).
The high iron content of carbon steel results in good magnetic properties, whereas all grades of stainless steel are considered to be non-magnetic metals, except for the austenitic grade of stainless steel.
Due to the alloying elements, electrical resistivity is higher in stainless steel than in carbon steel components.
Which is Easier to Machine? Stainless Steel or Carbon Steel
Low-carbon steels are generally easier to machine due to their softness and lesser tendency to form built-up edges (BUE) during machining.
However, machining high carbon steels owing to their hardness and brittleness can be difficult and usually results in poor surface quality.
On the other hand, stainless steel is more difficult to machine because of the tendency of work hardening and generation of high temperatures during cutting, which results in faster tool wear.
Although some stainless-steel grades like 303 and 416 are specifically designed for improved machinability, low-carbon steel is the preferred choice for applications that require heavy machining.
Free machining steel is a type of carbon steel that consists of alloying elements for further improving its machinability, making it the best-suited grade of steel for machining applications.
Which is More Costly? Stainless Steel or Carbon Steel
Costs involved in stainless steel can be higher as compared to carbon steel due to the higher percentage of alloying elements and can range from $1 to $5 per pound.
On the other hand, carbon steel can cost around $0.30 to $2 per pound, making it ideal for applications that require good strength at a lower cost.
Although carbon steel is prone to corrosion, you can galvanize the steel or anodize it to improve its corrosion resistance, thereby attaining strength, looks, and durability at a comparatively lower cost.
Whereas, stainless steel cannot be anodized and therefore requires other protective methods such as powder coating.
How to Identify Stainless Steel and Carbon Steel
|Steel type||AISI/SAE designation||ASTM Designation|
|Stainless steel||31XX-34XX, 43XX, 47XX, 50XXX-52XXX, 61XX, 72XX||X-XX-SS|
|Carbon steel||10XX-12XX, 15XX||X-XX-S|
Check for any labels or codes present on the metal. The codes usually fall under any of the two standard systems: AISI/SAE or ASTM.
The AISI/SAE system usually involves a four-digit code where the first two numbers indicate the type of steel.
Similarly, ASTM (American Society for Testing and Materials) system comprises a combination of numbers and letters, where the numbers denote the size of the bar and the letters denote the type of steel.
Stainless steel generally has a brighter, shinier appearance than carbon steel, which has a comparatively dull-matte finish.
Moreover, carbon steel appears dark brown or red due to the rust formed on its surface over time.
Apart from that, you can also differentiate between the two on the basis of their weight.
When comparing two workpieces of identical size, the stainless steel workpiece is heavier than carbon steel due to its higher density.
Spark testing involves grinding the workpiece and observing the color of sparks produced during the process.
Generally, grinding stainless steel produces shorter sparks with reddish-orange color, whereas grinding carbon steel produces longer, yellow sparks.
Stainless steel owing to its lower carbon content has a lower yield strength than carbon steel and is more vulnerable to bending and denting under the action of force.
Carbon steel, on the other hand, has relatively high yield strength and lower tensile strength, which means that it can break easily when subjected to a tensile force.
The ultimate tensile strength of stainless steel can range between 485 Mpa to 760 Mpa, whereas for carbon steel, it is around 400-550 Mpa.
On the contrary, the yield strength of stainless steel lies between 17-450 Mpa, whereas, for carbon steel, it is between 250-800 Mpa.
Stainless Steel - What is it?
Stainless steel is an alloy made from a combination of iron, carbon, and other elements such as chromium, nickel, molybdenum, or manganese.
Based on chromium's weight percentage, the stainless steel is classified as Martensitic, Ferritic, and Austenitic.
|Stainless Steel grade||Properties||Applications|
|Austenitic||Highest corrosion resistance|
Retains strength at high temperatures
|Engine parts, heat exchangers, cooking utensils, trailers, and cars for railways.|
Best used when annealed
|Furnace heating elements, oil burner parts, screws and fittings, interior decoration, petroleum industries.|
Good thermal conductivity
Suitable for cold working
|Parts of pumps and valves, turbine parts, biomedical devices, and surgical instruments.|
Resistant to stress cracking
Extremely effective in chlorine-rich environments
|Seawater heat exchangers, chemical containers|
Austenitic steel falls under the 300 series steel as per the American Iron and Steel Institute (AISI).
The most common austenitic steel consists of chromium and nickel in the range of 17-25% and 8-20%, respectively, and is known as 18/8 steel.
On the other hand, Martensitic steels fall under the 400 series (410, 414, 416, 420, etc.) that contain 12-14% chromium with minimal amounts of carbon (0.08-2.00%) and no nickel.
Ferritic steels also fall under 400 series stainless steel (405, 409, 434, 442, etc.) that consist of chromium as high as 17% or more, with carbon equivalent to that of martensitic steels and no nickel.
Apart from these, Duplex-grade stainless steel is also available, which is a combination of ferritic and austenitic grades, and exhibits higher strength with better resistance to stress corrosion cracking.
Carbon Steel - What is it?
Carbon steel is a type of steel that contains iron with carbon (up to 2%) as the main alloying element.
Based on the carbon content present, carbon steel is categorized as low, medium, and high carbon steel.
Apart from carbon, the other elements are silicon and manganese, which is not more than 0.5 and 1.5%, respectively.
|Carbon Steel grade||Properties||Applications|
|Low-carbon or mild steel||Soft, malleable, good ductility|
Low wear resistance
Good toughness and formability
|Valves, gears, crankshafts, connecting rods, railway axles, fish plate screws, nuts, bolts, rivets, thin canes, chains, wires, and automobile frames.|
|Medium carbon steel||Stronger than mild steel, but less ductile.||Railways coach axles, axles & crank pins on heavy machines, splines, shafts, crankshafts, etc.|
|High carbon steel||High tensile strength, lowest machinability, and poor ductility.||Hand tools, cutting tools, drills, milling cutters, woodworking tools, chisels, shear blades, and spring wires.|
Low-carbon steel contains carbon in the range of 0.06-0.19%, while medium and high-carbon steels have 0.20-0.55% and 0.55-1.4%, respectively.
The hardness and strength of carbon steel tend to increase with the increase in the carbon percentage.
Carbon steel exhibits good workability, making it easier to machine, forge, or weld, to produce workpieces of different shapes and sizes.
Stainless steel or Carbon steel- Which One should you Choose?
When deciding between stainless steel and carbon steel, you need to consider the corrosion resistance, durability, appearance, and cost requirements of your application.
When Corrosion Resistance is Desirable
The ability to withstand corrosion makes stainless steel a better choice for applications where corrosion resistance is the primary requirement.
However, you can also use carbon steel and enhance its corrosion resistance by powder coating the workpiece, which will, in turn, increase the overall cost of the final product.
When Strength and Durability are Desirable
Carbon steel is suitable for applications where the workpiece is subjected to heavy loads or high stress, such as valves, shafts, and cutting tools, that require high yield strength.
On the other hand, stainless steel is ideal for applications where good ductility with excellent corrosion resistance is preferable, such as kitchen knives, surgical tools, etc.
When Cost is a Concern
Cost is another important factor to consider when selecting the type of steel for your application.
Generally, stainless steel is more expensive than carbon steel and is therefore advised to use only when the application specifically demands corrosion-resistant properties.
For general-purpose and DIY applications, carbon steel is a budget-friendly choice.
While carbon steel is stronger and more affordable, stainless steel is more corrosion-resistant and durable.
However, if your application demands vibrant colors with good corrosion resistance, you can opt for powder-coated carbon steel as it provides excellent corrosion resistance at a lower cost.
For applications that require good machinability, low-carbon steel is the preferable choice.
Therefore, choosing between the two will depend on the requirements of the project, making it important to thoroughly analyze your application before making a decision.
Frequently Asked Questions (FAQ)
Why is silicon added to carbon steel?
Silicon is added in a very small quantity (0.05-0.30%) to avoid porosity in the casted carbon steel and enhance the material's toughness.
What are the grades of stainless steel that are used in biomedical applications?
316L grade stainless steel is mostly used in biomedical applications. However, for better wear resistance CoCrMo alloys are also used.
What are the cutting tools used for carbon steel and stainless steel machining?
High-speed steel (HSS) or carbide-cutting tools are suitable for carbon steel, whereas carbide and ceramic tools are suitable for machining stainless steel.
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