4 Different Ways That Steel Is Classified, Sorted & Graded
When you roll up to the beam yard looking to buy some steel for your project, you can't just say, "I'd like some steel, please!" Well, of course you can, but eventually you're going to need to be more specific. There are many different kinds of steel to choose from! Steel made from different blends of metals, steel with different physical properties, steel suited for different applications -- there's a lot to consider. One smart place to begin is by learning how steel is classified and sorted into different types. This is done in a variety of ways, which we'll introduce you to below.
At Eagle National Steel, we strive to give you an unparalleled customer service experience. It begins by giving you the information you need to make an informed decision. These articles are a great place to start, but if you have any questions, our friendly team is here to help. Give us a call or stop by our Hutchins location.
4. AISI-Recognized Types Of Steel
All steel is a blend of iron and carbon, plus small amounts of "alloying metals" that can enhance strength, hardness, corrosion resistance and other factors. These alloying metals can include chromium, nickel, tungsten, molybdenum and a whole lot more. The proportions of these ingredients define the steel's characteristics.
The American Iron and Steel Institute identifies four general categories that all steel falls into: Carbon Steel, Alloy Steel, Stainless Steel and Tool Steel
Carbon steel is almost entirely iron, with usually no more than about 2% carbon or other alloying ingredients. Alloy steel may feature a much higher concentration of elements like nickel, silicon and manganese. Stainless steel resists corrosion thanks to its very high chromium content. Lastly, tool steel is engineered for unique properties needed for making tools, like increased hardness and deformation resistance.
3. AISI-SAE Steel Numbering System
When you're selecting steel for your project, it'll be helpful to understand the basics of the classification system developed by the AISI and the Society of Automobile Engineers. All steel is sorted into general groups identified by a four-digit number.
The first digit tells you the main alloying element in the steel. 1xxx-grade steel is carbon steel. Steel with codes beginning with numbers 2–9 are alloy steels -- for example, the 7xxx-grade steels are alloyed with tungsten as their primary alloying element.
The second digit in the code tells you the sub-category according to what other elements have been added. For instance, steel with a 13xx code number is carbon steel alloyed with a small amount of manganese, which increases hardness.
The final two digits tell you the amount of carbon in the steel by hundredths of a percent. For example, 1340 steel is often used to make nuts and bolts. Its code indicates to you that it's a carbon steel alloyed with small amounts of manganese and has 0.40% carbon content.
2. Carbon Level
Alloy steels can have huge differences among them because of the various alloying metals added. The amount of carbon present in carbon steel is also important. Carbon steel can be further divided into three sub-categories: low carbon steel, medium carbon steel and high carbon steel.
Low carbon steel (AKA "mild steel") is the most common and least expensive steel you can buy, and it's also quite versatile. Medium carbon steel is a bit stronger, and can withstand heat treatment better for a harder final product. High carbon steel is very strong, very hard and can be quite brittle, too. Despite its strength, high carbon steel may not be ideal for some projects due to its low ductility and weldability.
1. Types Of Tool Steel
When fabricating your own tool, you won't be shocked to learn that tool steel is the ideal material for the job. But, depending on what kind of tool you're making, you'll want to select the right type of tool steel. There are different ways tool steel can be processed to make it better suit a specific purpose.
When shopping for tool steel, take a look at the AISI letter code. W stands for water-hardened steel. This is the most common tool steel for its high abrasion resistance. However, when making tools like chisels, punches or anything else that will need to withstand a sudden impact, shock-resistant tool steel is a better choice. Shock-resistant steel is indicated by the letter S. Other kinds of tool steel available include O for oil-cooled steel and T for high-speed tungsten steel -- just to name a few.
