While most of us are familiar with stainless steel, not many know much about carbon steel. Both these steel types have their own importance, and are manufactured for use in different applications. In this ScienceStruck post, we shall learn more about both through a carbon steel vs. stainless steel comparison.
Did You Know?
With over 60% of it being recycled globally each year, steel is one of the most recycled materials in the world.
Steel comes in various forms and types. There is mild steel, carbon steel, stainless steel, etc. In all its various forms, steel is the element of choice used in building the majority of our tools, devices, and indeed all the structures that we see around us. As a matter of fact, along with iron, it is one of the most extensively utilized material by man. It is important therefore, to learn about steel and its types.
In the following lines, we shall first explore what steel is and how it is made. Then we shall study about two of its most commonly used types – Carbon Steel and Stainless Steel. Lastly, we shall highlight the main points of distinction between these two types of steel.
An alloy of carbon and iron, steel is characterized by its high tensile strength and considerably low cost. Pure iron is highly ductile, and therefore, unsuitable for certain applications where a lot of tension is involved. When carbon and other elemental inclusions such tungsten, chromium, etc., are made to pure iron, they act as a toughening agent, solidifying its crystalline lattice structure and preventing the dislocations of iron atoms.
Steel is graded based upon the percentage of carbon in it. Usually, carbon contributes to about 0.2% to 2.1% of the weight of steel. However, this seemingly small amount is enough to bestow a great amount of strength and rigidity to it. The elemental inclusions also affect steel’s density, which usually ranges from 7750 kg/m3 to 8050 kg/m3.
Steel is used in the construction of buildings, bridges, stadiums, etc. It is used to manufacture automobiles, airplanes, ships, etc. It finds use in the manufacturing of large and small machinery used in industries. Even several of our domestic items such as kitchen utensils, furniture, etc., are made from steel.
As the name itself suggests, in carbon steel, the main alloying element is carbon. Other inclusions may be present, but there are no strict rules governing their percentage within it. Carbon has the ability of making steel harder through heat treatment, but at the cost of reduced ductility. Hence, carbon steel, though stronger, is less ductile. Also, a higher carbon percentage means the weld-ability of steel gets reduced.
There are mainly four different grades of carbon steel, differing from each other based on the actual percentage of carbon within them.
- Mild/Low Carbon Steel: This type contains carbon in the range of 0.05% – 0.3%. It is very malleable as well as ductile. It finds a wide range of use in industries.
- Medium Carbon Steel: This one has 0.25% – 0.6% carbon. It has the best balance between rigidity, ductility, and malleability. It is used in making large machines and automobile parts.
- High Carbon Steel: It has carbon in the range of 0.9% – 2.5%. This type is very strong. It is used in making load-bearing wires, large springs, etc.
- Ultra High Carbon Steel: Nearly 2.5% – 3% of its weight is carbon. It is extremely strong, but has the lowest ductility. It is used in making knives, axles, etc.
Discoloration and markings tend to appear on carbon steel items, especially knives and blades, upon contact with acids. Those made of high carbon steel can become completely black over time. Also, they tend to corrode when brought into contact with water. High carbon steel, on being hardened via heat treatment, retains its magnetic properties.
Stainless steel is also known as inox steel or inoxydable steel. This is due to the fact that its chemical composition enables it to resist oxidation. Normal carbon steel gets oxidized on coming in contact with water or moisture. The iron in it combines with the oxygen to form iron oxide. This process continues until a film of iron oxide is formed on the surface. This film further accelerates the oxidation process, until the entire steel rusts.
Stainless steel characteristically has a minimum of 10.5% chromium by weight, which is what grants it the ability to resist corrosion. At the molecular level, chromium combines with oxygen forming a chromium oxide layer which is inert. Thus, stainless steel is able to retain all the properties of normal steel, while at the same time is protected from rusting.
Stainless steel finds use in all the places where the presence of moisture or water prevents carbon steel from being used. There are over 150 different grades of stainless steel, which are used in making bridges, kitchen utensils, automotive bodies, aircraft, etc. Also, thanks to its luster, it even finds use in ornaments and sculptures too. In terms of magnetism, most types of stainless steels are nonmagnetic in nature.
Carbon Steel Vs. Stainless Steel: Comparison
► Stainless steel has a larger percentage of chromium in it as compared to carbon steel.
► This chromium allows the formation of a chromium oxide layer when stainless steel comes into contact with water or moisture. Such a layer is absent in carbon steel.
► The protective chromium layer makes stainless steel less susceptible to corrosion and rust. Carbon steel, on the other hand, gets easily rusted.
► Stainless steel is the material of choice in a moist and wet environment. Carbon steel is better used in drier places.
► Generally, alloys conduct less heat as compared to pure metals. The presence of at least 10.5% chromium in stainless steel reduces its thermal conductivity. Carbon steel, though also an alloy, has a much smaller percentage of impurity in the form of carbon, and thus, is more thermally conductive.
► Chromium is added to stainless steel to make ii corrosion-resistant. But this limits the carbon percentage that can be added to it, as it tends to chemically react with chromium. Thus, stainless steel has lesser carbon, and is therefore not as strong and hard as carbon steel.
► Almost all types of carbon steel are magnetic, while only a few types of stainless are magnetic.
► Mild carbon steel is more malleable and ductile as compared to stainless steel. It also has better weld-ability.
► Carbon steel is the more common high-volume steel in production which is used extensively in industries. Stainless steel has more ornamental and aesthetic appeal, and finds uses in homes, architecture, etc.
► For larger projects, where a large volume of steel is required, carbon steel, with its comparatively lower price is the better choice as compared to stainless steel.
Both carbon and stainless steel have the advantage of increased tensile strength compared to raw iron. Apart from that, they also have their own individual characteristics that make them suitable for specific applications. Understanding the properties of each can be helpful while choosing one over the other.