Steel is the backbone of the industrial sector, commonly found in everything from building construction to agricultural equipment. While all steel (including mild steel) is an alloy made up of iron and carbon, the amount of carbon and other elements will change the properties of the metal to better suit different applications.
Stainless Steel vs Carbon Steel: At a Glance
Typically harder than mild steel due to chromium content
Commonly available, affordable, and can be hardened significantly through heat treatment
More brittle than mild steel, but rigid and holds its shape well
Good balance of hardness and flexibility (can become brittle when hardened)
Resists corrosion, chemicals
Oxidizes and corrodes easily
Low-maintenance – less oiling required to avoid rusting
Requires care to prevent rust, often in the form of regular oiling
Long work life, low-medium load capacity
Very long work life, high load capacity
Benefits of Stainless-Steel
Stainless steel is an alloy made up of a minimum of 10% chromium, the same element commonly used in decorative car parts, where it allows exposed metal to stay shiny and rust-free.
Chromium has several properties that make it ideal for use in steel manufacturing. It is one of the hardest elements, increasing the base hardness of steel, although the resulting metal is still not as hard as heat-treated carbon steel.
Chromium is also highly resistant to oxidization, giving stainless steel a natural, self-repairing finish that resists corrosion and will not tarnish over time. In contrast, regular steel (both mild and high carbon), is susceptible to oxidization over time. Exposure to moisture, most commonly from rain or seawater, catalyzes this oxidization process within the steel, creating iron oxide - commonly known as rust. Iron oxide forms at the surface of the metal, causing flaky, brown particulate to form. Given enough time and moisture, rust will corrode the steel to the point of failure.
Stainless steel remains highly resistant to this oxidization. Instead of bonding with iron and forming rust, oxygen instead bonds with the chromium, forming a layer of chromium oxide on the surface of the metal that protects the rest of the steel from corrosion. This naturally occurring moisture-resistant barrier is the main reason why stainless steel is the preferred material for many outdoor applications.
The chromium content in the alloy lends stainless steel its high melting point and resistance to corrosion. In applications involving moisture, corrosive chemicals, and extreme heat, stainless steel outperforms mild and high carbon steel. When exposed to heavy moisture for long periods of time, such as submersion, it is possible for stainless steel to rust. Stainless steel may still be an effective material in these applications with careful selection, but regular maintenance may be required to keep systems running effectively. If workload requirements permit, polymer alternatives such as nylon or urethane may provide longer component life while requiring significantly less maintenance.
The chromium that prevents stainless steel from rusting also comes with one downside: the resulting metal is more brittle than regular steel. It is not able to flex under pressure, and is prone to cracking or breaking when exposed to sudden pressure.
Benefits of Carbon Steel Over Mild Steel
Carbon steel can contain anywhere from 0.25-2% carbon. Even within this small range there is a wide assortment of steel products. This type of steel is incredibly strong, able to retain its shape against anything but severe impact. Increasing carbon content in steel up to approximately 0.3% results in a steel that’s harder than mild steel, as the carbon molecules fill in some of the molecular gaps in the iron, increasing strength and rigidity over mild steel. Past this point, adding additional carbon doesn’t increase the base hardness of the steel much, but does greatly improve its hardenability. Past the 2% carbon level, steel starts to enter the “cast iron” classification, which, while hard, lacks the structural strength of steel and is very brittle.
The ductile properties of mild steel allow it flex under pressure, while carbon steel will remain rigid up closer to its breaking point due to its low ductility. It is commonly used in machinery components where materials are subjected to repeated loads over time, and a more ductile steel would wear out quickly. Sprockets and gears, for example, can experience millions of loads during the course of their life. Carbon steel can offer better performance than mild steel for many types of sprockets, creating a tooth surface that is highly resistant to friction-based wear from the chain barrel.
Increasing the carbon content within steel results in a product with increased tensile strength, but decreased ductility. It also increases the melting point of the steel, making the metal suitable for use in high temperature applications. This has the side effect of making steel with carbon levels approaching 2% more difficult to weld, and one of the reasons that high carbon steel isn’t often used in sprocket manufacturing.
Carbon Steel Sprockets vs Stainless-Steel Sprockets
There is no one-size-fits-all steel composition – each offers a different blend of strength, ductility, chemical resistance, and aesthetic appeal.
For applications where increased tensile strength is required, carbon steel offers an ideal balance between strength and flexibility, offering increased durability in situations where mild steel would wear down too quickly under the intense workload required.
Carbon steel is able to be further hardened through application of heat. Hardened steel comes with a tradeoff: as the steel becomes harder, it loses its flexibility, and will crack or shear under pressure instead of bending. If you’re looking for more information about hardening options, here’s an article comparing the different methodologies used to harden steel. Some stainless-steel compositions may be hardened too, although this is less common and the range of hardness differs from carbon steels.
Sprocket manufacturing generally involves a range of steel grades with low and medium carbon levels, such as C1045, C1050, C1055, AR400, and QT400 to name a few. At DROP Sprockets, our materials are selected based on application and chain load, and our goal is to balance ductility with hardness and end up with a product that offers maximum performance over time. Steel at the high end of the carbon spectrum doesn't see much use in sprocket manufacturing, since not only will it wear out your chain faster, but the steel is brittle and may fracture under high pressure. We offer many steel grades, and can always recommend a product with a more appropriate balance of flexibility for applications involving extremely heavy loads. If a steel with a higher carbon content is required, tempering and alloying may also offer alternative methods to increase the load bearing potential of steel as well.
Carbon steel also responds quickly to oxidization with even minimal exposure to moisture. For situations where exposure to moisture is unavoidable, other alloys such as stainless steel or polymer components (nylon, urethane, etc.) will have a much longer lifespan. If the workload required exceeds the tolerance of stainless steel or polymers, carbon steel may be coated to increase resistance to oxidization. Surface treatments can help carbon steel resist corrosion, including galvanization, polyurethane coating, powder coating, and zinc-rich paint.
It's not often that stainless steel and carbon steel sprockets are interchangeable. If you have questions about which is a better fit for your application, call the DROP team today, and one of our technicians will be happy to find you the best steel for your needs!