Carbon steel and alloy steel have a lot in common: they’re abundant, versatile, durable, and 100% recyclable. Even among the commonalities, though, they start to differ. There are more than 3,500 grades of steel, so how do you know which steel is right for your project? The first thing to consider is whether you’ll be best served using carbon steel or alloy steel.
What is Carbon Steel?
Technically, carbon steel is an alloy of iron and carbon. Still, it’s unique from what we call alloy steel in that there are no other elements added to carbon steel (there can be trace amounts of other elements present, but they aren’t deliberately added as alloys). In carbon steel, the carbon content ranges from .05% to 2.1% by weight. The higher the carbon content, the stronger the steel; conversely, lower carbon content yields better ductility and weldability.
Types of Carbon Steel
Carbon steel is divided into three categories: high-carbon steel, medium-carbon steel, and low-carbon steel.
- High-carbon steel is the strongest and hardest, and is extremely resistant to wear, but has the lowest ductility.
- Low-carbon steel has a low hardness that also allows high ductility, weldability, and toughness.
- Medium-carbon steel is, as expected, in the middle; it’s stronger than low-carbon steel and more ductile than high-carbon steel.
What is Alloy Steel?
Alloy steel also contains iron and carbon, as well as one or more alloying elements used to create specific properties in the steel. Low-alloy steel has fewer than 8% by weight of alloying elements, and high-alloy steel contains 8% or more.
From here, things can get very specific. Depending on the alloying element(s) and the amounts of those elements, the properties of alloy steel can be customized to certain applications. Some of the most common alloying elements are chromium, aluminum, titanium, copper, nickel, and manganese; however, this is not an exhaustive list. By altering the elements and proportions of such, manufacturers can customize the strength, hardness, flexibility, weldability, corrosion-resistance, and much more. For a deeper look at one example, check out the common alloy steel grade 4140.
Carbon Steel vs. Alloy Steel: Mechanical Properties
In comparing the mechanical properties of alloy steel vs. carbon steel, we need to keep in mind that alloy steel can increase or decrease a particular attribute, depending on the alloying elements and their amounts. Likewise, carbon steel’s properties can be altered depending on how much carbon by weight is in the steel. Thus, the table below is a good general reference, but properties can vary as needed for the application. For example, while alloy steel in general is not as hard, strong or weldable as carbon steel, adding manganese increases all three of those traits in alloy steel.
| Mechanical Property | Carbon Steel | Alloy Steel |
| Strength | High | Low to medium |
| Hardness | High | Low to medium |
| Toughness | High | Low to medium |
| Ductility | Low | High |
| Weldability | High | Low to medium |
| Malleability | High | Low to medium |
| Corrosion Resistance | Low | High to very high |
Carbon Steel vs. Alloy Steel: Cost & Financial Factors
Up front, carbon steel is substantially less expensive than alloy steel. The production process is less complicated, and the raw materials (iron and carbon alone) are more affordable than alloying elements. Thus, based solely on initial cost, carbon steel is the more affordable option.
When it comes to maintenance, though, alloy steel has the advantage. Because carbon steel is susceptible to corrosion, it needs more frequent maintenance, including protective coatings. Alloy steel is already resistant to corrosion and thus doesn’t require nearly as much maintenance. In general, alloy steel also has a longer lifespan in high-stress environments, so its maintenance costs will be lower while lasting longer.
Carbon Steel vs. Alloy Steel: Common Applications
Both carbon and alloy steel are heavily used across many industries. In particular, carbon steel’s strength and hardness make it ideal for construction, the automotive industry, machinery, and tools. Carbon steel is good for cables, pipes, shafts, gears, and fasteners.
Alloy steel is also popular for construction and automotive uses, as well as in the aerospace and marine industries. Alloy steel is often used to manufacture girders, ship propellers, bridge parts, wires, and a variety of rails, rods, bolts, nails, and screws. Because alloy steel is so versatile in the way it’s created, alloy steel can be designed and manufactured for very specific purposes.
Connect With Our Team of Steel Experts
Whether you need carbon steel, alloy steel, or a little of both, we’re here to work with you and make sure you get the right steel for your project. Contact our steel experts to partner with Capital Steel for all your steel needs.
