Steel 101: The Four Types of Steel
There are primarily four types of steel, each with its own applications, benefits, and more. These include carbon steel, alloy steel, tool steel, and stainless steel.
To help dispel any misconceptions and make it easier to understand, this post will break down the various types and provide information on each. We’ll also discuss the different grades of steel and why it matters.
The most commonly used form of steel is carbon steel. Up to 90% of the steel produced today is carbon steel. Wide availability, range of properties, and cost make this form of steel ideal for manufacturing, construction, transportation, and industrial uses.
Types of Carbon Steel
There are three general categories of carbon steel: low, medium, and high. Low carbon steel is easily formable and often used in pipe, wire, and general hardware. It is typically under 0.30% carbon and the most common type of steel. Medium carbon steel has a carbon content of somewhere between 0.31% and 0.6%. This type of steel is much stronger and used in railroad applications, mechanical parts, and other similar applications. High carbon steel has a carbon content between 0.61% and 1%. It is most often used in high tensile strength or wear applications such as blades and springs.
Alloy steels have elements other than iron and carbon intentionally added to modify the steel’s properties. The adaptability of the alloy steel is ideal for engineered and safety-critical applications.
Types of Alloy Steel
Alloy steels are categorized by the main elements intentionally added. Typical alloy families are chromium, chromium-molybdenum, and chromium-nickel-molybdenum. To see a more expansive list, please see our list of steel grades below.
Just as the name suggests, tool steel is designed for the manufacturing of tools. Depending on the type of tool being created, different elements are added to give the item varying properties, like extra durability, wear resistance, extreme heat tolerance, etc. Typical applications include test fixtures, dies, and mill rolls.
Types of Tool Steel
Tool steel comes in several types, including air-hardening, water-hardening, oil-hardening, high-speed, hot-working, and shock-resisting. Choosing one type of tool steel over another typically depends on what the finished tool will do and the overall conditions of use.
Stainless steel is typically used in either corrosive or high heat environments. High levels of chromium and nickel give stainless steel its unique properties to handle these environments. Common applications are kitchen utensils, saltwater applications, and automotive exhaust. Stainless steel is commonly found in household appliances, tool boxes, automotive wheels, and more.
Types of Stainless Steel
The four most common types of stainless steel are martensitic, ferritic, austenitic, and duplex. Each type varies in properties such as magnetism, corrosion resistance, and strength.
Grades of Steel
The above types of steel have been broken down into grades to help simplify specifying and purchasing steel. These grades can specify chemistry ranges, strengths, or a combination of both. Several organizations have their own grading systems, with the most common in the United States being ASTM (American Society of Testing and Materials) and SAE (Society of Automotive Engineers).
ASTM (American Society for Testing and Materials)
With the ASTM grading system, each metal is given a specific code to identify various properties. The formula is generally a letter prefix to signify category, followed up by a sequential number. ASTM typically has specifications referring to an application and material. Inside these specifications, there are several grades listed with corresponding chemistries and mechanical properties. An example is ASTM F2282: requirements for carbon and alloy steel wire, rods, and bars for mechanical fasteners.
SAE (Society of Automotive Engineers)/AISI (American Iron and Steel Institute)
For the SAE/AISI grading system, a four-digit number is given. The first two numbers signify steel type and alloying element, and the last two are designated for the overall carbon concentration.
Carbon and Alloy Steel Grades
|SAE designation||Type, and composition by weight|
|10xx||Plain carbon (Mn 1.00% max.)|
|12xx||Resulfurized and rephosphorized|
|15xx||Plain Carbon (Mn 1.00–1.65% max.)|
|31xx||Ni 1.25%; Cr 0.65%, or 0.80%|
|32xx||Ni 1.75%; Cr 1.07%|
|33xx||Ni 3.50%; Cr 1.50%, or 1.57%|
|34xx||Ni 3.00%; Cr 0.77%|
|40xx||Mo 0.20%, 0.25%, or Mo 0.25% and S 0.042%|
|44xx||Mo 0.40%, or 0.52%|
|Chromium-molybdenum (chromoly) steels|
|41xx||Cr 0.50%, 0.80%, or 0.95%; Mo 0.12%, 0.20%, 0.25%, or 0.30%|
|43xx||Ni 1.82%; Cr 0.50–0.80%; Mo 0.25%|
|43BVxx||Ni 1.82%; Cr 0.50%; Mo 0.12%, or 0.35%; V 0.03% min|
|47xx||Ni 1.05%; Cr 0.45%; Mo 0.20%, or 0.35%|
|81xx||Ni 0.30%; Cr 0.40%; Mo 0.12%|
|81Bxx||Ni 0.30%; Cr 0.45%; Mo 0.12%; and added boron|
|86xx||Ni 0.55%; Cr 0.50%; Mo 0.20%|
|87xx||Ni 0.55%; Cr 0.50%; Mo 0.25%|
|88xx||Ni 0.55%; Cr 0.50%; Mo 0.35%|
|93xx||Ni 3.25%; Cr 1.20%; Mo 0.12%|
|94xx||Ni 0.45%; Cr 0.40%; Mo 0.12%|
|97xx||Ni 0.55%; Cr 0.20%; Mo 0.20%|
|98xx||Ni 1.00%; Cr 0.80%; Mo 0.25%|
|46xx||Ni 0.85%, or 1.82%; Mo 0.20%, or 0.25%|
|48xx||Ni 3.50%; Mo 0.25%|
|50xx||Cr 0.27%, 0.40%, 0.50%, or 0.65%|
|50xxx||Cr 0.50%; C 1.00% min|
|50Bxx||Cr 0.28%, or 0.50%; and added boron|
|51xx||Cr 0.80%, 0.87%, 0.92%, 1.00%, or 1.05%|
|51xxx||Cr 1.02%; C 1.00% min.|
|51Bxx||Cr 0.80%; and added boron|
|52xxx||Cr 1.45%; C 1.00% min.|
|61xx||Cr 0.60%, 0.80%, 0.95%; V 0.10%, or 0.15% min.|
|72xx||W 1.75%; Cr 0.75%|
|92xx||Si 1.40%, or 2.00%; Mn 0.65%, 0.82%, or 0.85%; Cr 0.00%, or 0.65%|
|High-strength low-alloy steels|
|9xx||Various SAE grades|
When it comes to steel, there are four different general types best suited for varying applications. By knowing these and understanding the various properties of that type of steel, you can ensure that you know the right one for your needs while on the job.