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The Difference Between Carbon and Stainless Steel


Steel is an amazing metal that has been an integral part of American industry since our country’s inception. Due to the material’s extreme versatility, designers and manufacturers need to be familiar with many different types of high-performance steel alloys and grades. Steel is commonly found in just about every industry, and yet two different kinds of steel may bear little resemblance to each other.

Two of the main categories of steel are carbon steel and stainless steel, and it is essential for manufacturers to understand the difference between them. Each has its own unique properties and advantages that make it suitable for particular applications. At Clinton Aluminum, we can help producers assess their application needs and select just the right material for a specific job.

History Of Carbon Steel

Steel is, by definition, an alloyed metal that combines iron and carbon. With pure iron, its crystal structure provides very little resistance to the iron atoms, allowing them to easily slip past one another. This means that iron is soft and ductile. By adding carbon and creating steel, the iron is hardened by the carbon atoms filling in the crystal structure, reducing the number of dislocations that occur at the molecular level.

While the chemical understanding of steel was not understood until much later, steel in its most basic form has been used by humans for nearly 4,000 years. Many ancient societies developed methods for forging steel into various tools and weapons that were much more effective and durable than their iron counterparts.

In general terms, any steel that is not stainless steel can be considered carbon steel. But there is a more technical designation of carbon steel, and it must meet the following criteria:

  • There must be no minimum content specified or required of any alloying elements, such as chromium, cobalt, molybdenum, nickel, niobium, titanium, tungsten, vanadium, or zirconium.
  • The specified minimum for copper content cannot exceed 0.40 percent.
  • The maximum content specified for the following elements must not exceed the specified percentages: manganese 1.65 percent, silicon 0.60 percent, copper 0.60 percent.

Furthermore, as a general rule carbon-iron alloys that possess greater than 2.1% carbon content are classified as cast iron. With the exception of a few modern high-performance alloys that are considered very high carbon, cast iron is not malleable even when it is very hot. It gets its name from the fact that it is formed by casting and has a lower melting point than other types of steel. It should also be noted that carbon steel and wrought iron are not the same thing, even though wrought iron does contain a small amount of carbon.

The Development Of Stainless Steel

While carbon steel has been around for millennia, stainless steel is a much more recent development. It wasn’t until the early 1800’s that researchers recognized the natural corrosion resistance of iron-chromium alloys. But even then, it took nearly a century for scientists to reliably reproduce these alloys in a cost effective manner. Once a solution was found, however, stainless steel quickly became a mainstay of numerous industries.

Generally speaking, stainless steel is defined as any steel alloy that contains between 10 and 30 percent chromium. In addition, it has a low carbon content, distinguishing it further from traditional carbon steel. Modern stainless steel can be alloyed with any number of other elements, including nickel, molybdenum, titanium, aluminum, niobium, copper, nitrogen, sulfur, phosphorus, and selenium, leading to a great diversity of available stainless steels, which number in the hundreds.

The process of forming stainless steel starts with melting the material in a furnace and refining it in a vessel in order to lower the carbon content. During the argon-oxygen decarburization process, oxygen and argon are injected in gas form into the molten steel. This lowers the carbon content without losing any chromium.

What Are The Differences Between Carbon And Stainless Steel?

The first and most obvious difference between the two types of steel is that carbon steel does not possess nearly the same level of corrosion resistance as stainless steel. The whole reason that stainless steel was developed in the first place was to overcome the natural vulnerability of carbon steel to atmospheric corrosion.

Iron will react with oxygen to form rust. The chromium that has been added to stainless steel attaches itself to oxygen. This means that the metal will form a chromium oxide layer on its surface that can protect the metal from degrading the way iron typically does. Carbon steel does not possess enough chromium to form this protective layer.

Another benefit of stainless steal that becomes immediately apparent when comparing the two is its appearance. Forgetting about carbon steel’s susceptibility to rusting, stainless steel more naturally has a shiny, polished appearance. This means that it is more generally preferred when an aesthetic appeal is a consideration. While carbon steel can also be polished, it will require a coating of some kind to protect its appearance.

On the other hand, because stainless steel tends to be more expensive, in instances where the steel will be hidden from view, on construction projects for instance, carbon steel is often the more popular choice. This might include internal building supports and the like.

Another difference is in thermal conductivity. At room temperature, stainless steel’s thermal conductivity is much lower than that of carbon steel. But at extremely high temperatures, such as those above 1000°C, stainless steel begins to have superior thermal conductivity to carbon steel. This means that the preferred material will depend on the application and what, if any, extreme temperatures it will be exposed to.

Your Technical Resources Partner

At Clinton Aluminum, we understand that the success of your project depends on much more than choosing the right material. That’s why we pride ourselves on being a partner to our clients throughout the entire production process. Our experienced and dedicated team of technical professionals is ready to assist you at any time.

If you have questions about any of our product or service offerings, don’t hesitate to contact one of our knowledgeable customer service representatives today.

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