The Differences between Carbon and Stainless Steels

In all likelihood, if someone were asked the difference between carbon and stainless steel, the answer would involve appearance: one is dull and one is shiny. That might sound simple, but it’s also true! While the finish of each steel is the most obvious difference, there are other, more significant ways they differ. Learning more about the characteristics of each steel type will help determine which steel is most appropriate for a project.

Corrosion Resistance
The most significant difference between the two is the high degree of corrosion resistance found in stainless steel. Both types of steel are vulnerable to corrosion due to their iron content, which reacts with oxygen to form rust. However, the addition of chromium in stainless steel alloy provides much more protection against corrosion. The chromium in stainless steel reacts more quickly with oxygen than iron, and the resulting chromium oxide forms a protective layer on the surface of the metal. The chromium oxide prevents further oxygen interaction with the metal, effectively stopping any continued corrosion.
Carbon steel alloys may also contain chromium, but not in the amounts found in stainless steel. This means carbon steel is vulnerable to the corrosive effects of rust, which leads to damaged metal unless regularly maintained. So in situations where corrosion resistance is a big concern, stainless steel will be the best choice.

Adding chromium as an alloying element in stainless steel not only boosts corrosion resistance, it is also the source of the metal’s distinctive shine. Carbon steel naturally has a flatter finish, and its vulnerability to corrosion leads to tarnishing and other discoloration. It can be sanded to smooth the metal and produce more shine, but unless some type of coating is applied to the polished carbon steel, the same rust and discoloration will develop.
Stainless steel, on the other hand, has a natural luster which polishing can increase to a mirror shine. Polishing also provides even more corrosion resistance to the metal, without the need for an additional protective coat. This is because any existing irregularities are sanded down during polishing, so corrosive particles are less likely to cling to the metal’s surface. For projects where aesthetics is an important factor, stainless steel may be preferable over polished or painted carbon steel.

Mechanical Properties
Both carbon and stainless steels are produced in multiple types and grades, so it can be difficult to make a clear distinction between the two kinds of steel. In general, stainless steels tend to be more ductile, while carbon steels have greater tensile strength. This is due to the carbon alloying percentage found in carbon steels. Carbon makes steel harder, to the point of becoming very strong and brittle with high-carbon steels.
However due to the variety of available carbon and stainless steels, these properties may not apply across the board. A low-carbon steel can be more ductile than certain types of martensitic stainless steel. Some stainless steel grades will be harder and with greater tensile strength than a low-carbon steel. Ultimately, the mechanical properties of any kind of steel should be considered for its specific use in a project.

As a general rule, stainless steel will be more expensive than carbon steel due to its alloying elements. Carbon steel may contain other elements, but is mainly made up of iron and carbon which are fairly affordable. Stainless steel is created with the addition of chromium, and also has higher amounts of alloying elements such as nickel and manganese. Each additional element to the stainless steel’s chemical composition increases the cost. For a lower budget project where aesthetics is a lesser priority, carbon steel will be the best way to go.