Alloy steel and carbon steel are common steel types used across the globe. Yet, they share certain similarities that make your selection of either of them difficult.This guide provides insight into alloy steel and carbon steel. After you read this, you’ll be equipped with the knowledge to make informed decisions for your next project.
What is Alloy Steel
You can call alloy steel a type of steel with different proportions of other elements. These elements are in different ranges, and they may range from about 1.0% to even 50% by weight. Elements you may find as a constituent include molybdenum, manganese, nickel, cobalt, tungsten chromium, vanadium, silicon, or boron.
It’s good you know that the blend and proportion of these alloying elements changes the steel’s properties. Properties you can alter include strength, hardness, wear resistance, heat resistance, corrosion resistance, toughness, and ductility.
Since you can alter these properties, you can create steels tailored for a wide range of industrial uses. You may even use the altered steel in heavy-duty construction and aerospace.
Classification of Alloy Steel
You may classify alloy steel into different types (grades). However, when you classify these steels, they are either in one of the two broad classes. These classes are:
- Classification based on the increasing proportion of alloying elements present
- Classification based on the number of alloying elements you use
Classification of Alloy Steel by Proportion of Alloying Elements
When you classify based on the proportion of alloying elements present in the material, subgroups include:
- Low-Alloy Steel: This is the type of steel where your alloying elements are less than 5% by weight.
It’s good you keep in mind that low alloy steel is only slightly modified. Hence, you may not see it differently from 99.9% steel. It also offers moderately modified mechanical properties. As such, you can use it to manufacture automotive parts, construction equipment, pipelines, heat exchangers, and pressure vessels.
- Medium-Alloy Steel: Some renowned classification standards may exclude this classification because it lies at the border. Nevertheless, this alloy steel contains between 5% and 12% alloying elements by weight.
- High-Alloy Steel: Is the steel that contains any alloying elements above 12% of its composition. You may find it difficult to get high-alloy steels as they are uncommon. This is also because most steels only dedicate a small percentage of their mass to alloying elements.
A popular high-alloy steel you should never forget is stainless steel. Stainless steel has over 10.5% chromium by mass.
As you modify steel, you increase its strength and make it have superior corrosion and heat resistance. This makes high-alloy steel ideal for more demanding industrial and engineering applications.
Classification of Alloy Steel by Number of Alloying Elements
You can also classify alloy steel based on how many alloying elements are present in the metal.
- Ternary Alloy Steel: The steels you find in this class contain three elements: iron, carbon, and an additional alloying element.
An example you might be familiar with is manganese steel. You may know manganese steel for its high strength and wear resistance, particularly in impact-heavy applications.
- Quaternary Alloy Steel: This is the steel type that contains four elements: iron, carbon, and two additional alloying elements.
An example of quaternary alloy steel is chromium-molybdenum (chrome-moly) steel. If you are an automotive manufacturer, you have likely used this steel in bicycles and automotive components. Quaternary alloy steel has an excellent strength-to-weight advantage that you should leverage.
- Complex Alloy Steel: Your complex alloy steel features more than four elements: iron, carbon, and more than two alloying elements. Complex alloy steel has specialized properties, so you need it for critical engineering applications. You can use it for applications like aerospace, high-performance automotive parts, and so on.
What is Carbon Steel?
Carbon steel is a steel type with up to 2.0% total carbon. This metal also contains trace amounts of other alloying elements. Other elements you may see are chromium, cobalt, niobium, molybdenum, nickel, titanium, tungsten, vanadium, and zirconium.
The carbon in carbon steel balances the steel’s strength and your ease of shaping it. Carbon steel also works well with your different manufacturing methods including CNC machining, sheet cutting and fabrication, and welding.
Classification of Carbon Steel
There are different grades of carbon steel available for you. You can classify these grades in two categories too: deoxidation steel practices employed and their carbon content.
Classification of Carbon Steel by Deoxidation Practices
When it comes to the deoxidation practices employed in the manufacturing process, you further classify carbon steel into:
- Rimmed Steels: Rimmed steels are partially deoxidized steel. When you only partially deoxidize steel, you have an excellent surface finish and ductility. However, rimmed steels are relatively prone to impurities and segregation.
- Capped Steels: Are similar to rimmed steels. But with capped steels, you have improved surface quality and less segregation.
- Semikilled Steels: Unlike rimmed steel, semikilled steels are only partially deoxidized, so you end up with something that has the characteristics of rimmed and killed steels.
Semikilled steel helps you balance the steel’s quality and cost. Basically, you use them to make structural components and pipes.
- Killed Steels: Are the type of steel that you completely deoxidize. Deoxidizing steel requires you to use deoxidizing agents with silicon and aluminum. This process provides a more uniform composition and properties throughout the metal, so it’s ideal for your critical applications too.
Classification of Carbon Steel by Carbon Content
You can also classify carbon steel based on its carbon content. This approach is more common than the former. This classification puts all the carbon steel you know into four categories. Each of these categories has its specific characteristics and applications.
- Low-carbon steel:It is also known as mild steel, and low-carbon steel contains up to 0.30% carbon. You may know it as the steel that is famous for its high formability and weldability. It’s also cost-effective.
Low-carbon steel makes up the largest group of carbon steels manufactured. You can use it for automobile body parts, boiler plates, seamless tubes, construction structural components, wire products, and kitchenware.
- Medium-carbon steel: This steel has a carbon content ranging from 0.30% to 0.60%. When you increase the carbon in medium-carbon steel, you enhance its tensile strength and hardness. In contrast, the metal experiences a drop in ductility and weldability.
You may use medium-carbon steel in applications where you need to balance strength and toughness. These applications include manufacturing rails, railroad wheels, forgings, shafts, couplings, gears, and axles. To improve their use and mechanical properties, you need to heat-treat medium-carbon steels.
- High-carbon steel: This steel contains between 0.60% and 1.00% carbon. You may find high carbon steel rather difficult to weld, machine, or form. However, it has an incredibly high tensile strength. You can use high-carbon steel to manufacture springs, dies, high-strength wires, and cutting tools.
- Ultrahigh-carbon steel: Ultrahigh-carbon steel, also known as tool steels, has a carbon content ranging between 1.25% and 2.0%.
You can call it the strongest amongst the carbon steel classes. However, its strength makes it almost impossible for you to weld, machine, or form. If you must weld it, you need to include a detailed carbon steel heat treatment program in the welding procedure.
You will enjoy this steel type the most for specialized manufacturing processes like high-performance cutting tools for machining.
Comparing Alloy Steel vs. Carbon Steel
Since you have looked at both steels individually, a comparison of their major properties shows how different both metals are. The differences to note between the metals are:
Strength and Hardness
- Carbon Steel: The more the carbon content in the steel, the greater the strength and hardness. However, you’ll see a reduction in the metal’s ductility too.
- Alloy Steel: Because you have more alloying elements, alloy steels have superior strength and hardness, even with lower carbon content. But alloy steels are generally less ductile. Nevertheless, you can add specific alloys that can improve their ductility.
Tensile Strength and Toughness
- Carbon Steel: Carbon steel possesses relatively good tensile strength. But when you increase the carbon content further, you get a more brittle steel.
- Alloy Steel: The different alloying elements in alloy steel increase its strength and toughness. Alloy steels do better even when you subject them to stress and dynamic loading conditions.
Ease of Corrosion
- Because you have carbon in carbon steels, the steels are more likely to rust or corrode from chemicals. So if you want them to last long, you must use protective coatings on the steel.
- Alloy Steel metals possess excellent corrosion and heat resistance properties. Hence, you can use them in harsh environmental conditions.
Machinability and Weldability
- Carbon Steel: You may find it easier to machine and weld carbon steel, especially those with lower-carbon versions.
- Alloy steel, however, is challenging to machine and weld. It’s prone to cracking and other weld defects. To work it, you need specialized equipment and advanced techniques.
Fatigue Resistance
- Carbon steel gives you a moderate fatigue resistance. So it’s not your ideal choice for less demanding cyclic loads.
- Alloy steel has a high fatigue resistance. With this property, you can subject it to repetitive stresses like automotive and aerospace parts without it failing.
Wear Resistance
- Carbon steel’s wear resistance is okay. You’d prefer it for general applications.
- Alloy steel, on the other hand, has a higher wear resistance. Its resistance comes from alloying elements like chromium and molybdenum. Where you have abrasive or high-wear applications, alloy steel is your best option.
Thermal Expansion and Electrical Conductivity
- You can predict the thermal expansion for carbon steel because it’s uniform. It also possesses higher electrical conductivity.
- It’s more difficult for you to predict the thermal expansion of alloy steel though. You can attribute this difficulty to the different alloying elements in the metal. It also has a lower electrical conductivity that is influenced by the presence of alloying metals.
Cost
- Carbon steel has fewer alloying elements, so you can buy it at a lower cost. The manufacturing process is simple for you to carry out too.
- Alloy steel is more expensive. You can attribute this to the higher cost of alloying materials and more complex production processes.
Application Areas of Alloy and Carbon Steels
Common Applications of Alloy Steel
- Oil and Gas Industry: casing tubes and high-pressure pipelines.
- Aerospace: Landing gear, jet engines, and structural components.
- Medical Equipment: Surgical tools, orthopedic implants, and support frames
- Power Plants: Turbine shafts, boiler components, heat exchangers, and pressure vessels.
- Military and Defense: Armor plating, artillery shells.
Common Applications of Carbon Steel
- Construction: Steel wires, beams, rebars, and structural frameworks for bridges and buildings.
- Automotive: Body panels, vehicle chassis and frame, engine parts.
- Tools: Hammers, screwdrivers, chisels, drill bits, and saw blades.
- Piping: water, gas, and utility lines.
- Kitchenware: Knives, cookware, and utensils
- Agriculture: Plow blades, sickles, tractor parts, and fencing materials.
Conclusion
Choosing between alloy and carbon steel depends on the specifics of your project. They have distinct unique properties that make them suited for your different use. Nevertheless, it’s a win for you if you choose the best steel type with this guide.
FAQs
How Can I Identify Carbon Steel?
You can identify carbon steel by its appearance and magnetic properties. However, if that’s not enough, spark testing and chemical analysis will help you confirm.
What’s the Major Difference Between Alloy Steel and Carbon Steel?
The major difference is in the chemical composition of both metals. Alloy steel combines different alloying elements to produce a metal with distinct properties. On the other hand, carbon steel has carbon as its main alloying element, with others present but in trace amounts.
Is Alloy Steel Magnetic?
Yes, alloy steel is magnetic, but it depends on the alloying elements present in the metal.
What Are the Advantages of Using Carbon Steel?
One of the selling points of carbon steel is its affordability. It’s also a versatile material, as varying carbon content makes it suitable for a wide array of industrial and engineering applications.
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