Steel is one of the most versatile and useful materials on the planet. Steel mainly consists of iron (Fe) and carbon (C), but modern steel is more complex than that. Steel’s characteristics and strength are affected by the concentration of carbon and iron or the inclusion of other elements, which allows steel to be used in an infinite number of scenarios.
Most people believe that steel is just a set combination of iron and carbon, but there are actually over 3,500 different grades of steel! You can determine the grade of steel by analyzing the quantity of carbon in it, the other alloying elements it includes, and how it’s processed.
In this article, we’ll discuss the four different types of steel, how they’re classified, the various steel grades, and the methods of heat treatment used to improve steel’s mechanical properties.
What Is Steel, Exactly?
To understand the types of steel, one must first understand exactly what it means for an alloy to be classified as steel. All steel types are iron alloys with the addition of different elements.
They are always primarily composed of iron and carbon, with a carbon content of 2% or less. They also contain 1% manganese and small amounts of other elements. Most steel alloys are manufactured using iron ore, scrap steel, coal, and limestone.
All steel is infinitely recyclable, and new steel products contain an average of about 37% recycled steel. It is the most commonly used metal in the world.
The many combinations of elements and processes used to make various types of steel mean an almost infinite number of possible steel grades. In fact, over 75% of the current steel grades have been developed only within the last 20 years. Many more may be developed in the future.
Different Types Of Steel
Steel can be changed in many ways by adding other elements like chromium, nickel, or manganese. These elements are called alloying elements. They help improve certain properties of steel, such as strength, resistance to rust, or the ability to handle heat.
Because of these changes, steel is divided into different types. Each type is designed for a specific use.
Think of it like cooking. If you change the ingredients or the amount of each ingredient, you get a different dish. In the same way, changing the composition of steel creates different types.
Main Types of Steel
Four main types of steel are commonly used:
- Carbon Steel
- Alloy Steel
- Stainless Steel
- Tool Steel
Let us understand each one in simple terms.
1. Carbon Steels.
Carbon steel is the most common and widely used classification of steel. Its properties come from a relatively simple composition: iron and carbon, with trace amounts of other elements. Because carbon is the primary alloying ingredient, these steels are known for their strength, versatility, and cost-effectiveness.
Carbon steels typically contain up to 2% carbon. As carbon content increases, strength and hardness also rise while weldability and ductility decrease. These qualities make carbon steel suitable for structural beams, automotive components, machinery parts, and general construction applications.
Carbon steel is classified into three subgroups based on the amount of carbon in the metal:
- Low-carbon steel grades, or mild steel grades, contain up to 0.3% carbon. They are known for their excellent ductility, weldability, and malleability, making them ideal for structural applications and everyday products.
- Medium carbon steel grades, with 0.3–0.6% carbon. They balance strength and flexibility and are often used in automotive components and machinery parts.
- High carbon steel grades exceed 0.6% carbon. They are significantly harder and stronger but less ductile, commonly utilized in cutting tools and high-strength wires.
One disadvantage of carbon steel is that it can rust easily when exposed to moisture and air. That is why it is often coated or painted to protect it.
2. Alloy Steels.
Alloy steel refers to steel that contains additional alloying elements (over and above carbon), such as chromium, nickel, molybdenum, manganese, boron, silicon, and vanadium, to improve strength, toughness, and other properties.
And the alloying elements can make up 1% to 50% of the alloy. Alloy steels are broken down into two groups:
- Low Alloy Steel: They contain small amounts of alloying elements, typically less than 8 %. Titanium, copper, niobium, and vanadium are common elements that are added to obtain ‘Low Alloy Steels’ to improve their strength and toughness. Low-alloy steels undergo heat treatment, normalising, and tempering during the manufacturing process.
- High Alloy Steel: They contain more than 8% of alloying elements, which are typically added to improve their corrosion resistance, high-temperature strength, and wear resistance. Examples of high alloy steel include stainless steel and tool steel, which we have discussed already.
The alloying elements inhibit grain boundary formation, improving strength and toughness. Nickel and manganese steel offer increased toughness, while chromium increases hardness and corrosion resistance.
This type of steel is used in many applications, such as stainless steel for dairy producers or advanced high-strength steel in the automotive industry.
What Is It Used For? The combination of alloying materials produces steels with improved hardness, toughness, corrosion resistance, and heat resistance. This makes alloy steel ideal for high-performance industrial and structural applications. Common uses include:
- Oil and gas pipelines
- Automotive parts
- Aerospace components
- Power plant equipment
- Heavy machinery
Alloy steels’ adaptability and strength make them a favorite for demanding environments where durability matters most.
3. Stainless steel.
Stainless steel grades are alloyed with 10–20% chromium along with nickel, silicon, manganese, and carbon. Because of their increased capacity to survive adverse weather, these steels have phenomenally high corrosion resistance and are safe to use in outdoor construction. Stainless steel grades are also commonly used in electrical devices.
There are different types of stainless steel, including austenitic, ferritic, and martensitic stainless steel.
- Austenitic: The most common and weldable stainless steel (e.g., Grade 304). Known for its high corrosion resistance. Used for kitchenware, appliances, and chemical equipment.
- Ferritic: Contains (10.5%) to (27%) chromium but little to no nickel. Magnetic and highly resistant to stress-corrosion cracking. Used for automotive exhausts and water heaters.
- Martensitic: Highly magnetic and heat-treatable, but less corrosion-resistant than austenitic or ferritic steels. Used for surgical tools, blades, and cutlery.
For example, 304 stainless steel is widely sought after for its ability to withstand the environment while keeping electrical materials safe.
While different stainless steel grades, including 304 stainless steel, have a place in buildings, stainless steel is more often sought after for its sanitary properties. These steels are widely found in medical devices, pipes, pressure vessels, cutting instruments, and food processing machinery.
What Is It Used For? Stainless steel is used extensively in:
- Food processing and medical equipment
- Architectural and decorative applications
- Kitchen appliances and utensils
- Chemical and marine environments
- Industrial piping and tanks
Because of its hygienic properties and resistance to moisture, stainless steel is a top choice in environments where cleanliness and durability are essential.
4. Tool Steels.
Tool steels, as the name suggests, excel in cutting and drilling equipment. The presence of tungsten, molybdenum, cobalt, and vanadium helps improve heat resistance and general durability.
These types of steel are specifically engineered to withstand high temperatures and repeated stress, making them ideal for industrial applications. And because they hold their shape even under heavy use, they are the preferred material for most hand tools.
One of the most important features of tool steel is its ability to keep a sharp edge. This makes it perfect for cutting and shaping other materials. Tool steel is used to make drills, cutting blades, dies, molds, and machine tools.
There are different types of tool steel, each designed for a specific purpose. Some are made to resist heat, while others are designed for impact resistance or wear resistance. For example, high-speed tool steel can cut materials at high speeds without losing its hardness due to heat.
Tool steel is usually more expensive than other types of steel because of its special properties. However, it is essential in industries where precision and durability are required.
What Are Tool Steels Used For? Tool steels are engineered specifically for cutting, shaping, and forming materials. Their strength and ability to withstand extreme heat and repeated impact make them invaluable in manufacturing.
Tool steels are commonly used for:
- Cutting tools and blades
- Dies and molds
- Drills, punches, and chisels
- Industrial machinery components
Their superior strength and edge retention make them vital to industries that require precise, long-lasting tools.
5. Weathering Steel.
Weathering steel is also known as corrosion-resistant steel. It contains alloying elements like copper, chromium, nickel, and phosphorus, providing a protective rust-like coating that resists corrosion.
The corrosion mechanism creates a passive oxidized layer on the steel’s surface, inhibiting further corrosion. It is used for outdoor structures like bridges, outdoor sculptures, and building exteriors. The rust coating protects the base metal.
6. Electrical Steel.
It is also called silicon steel or transformer steel. Electrical steel contains silicon (typically 3%), increasing electrical resistivity and reducing eddy current losses.
It is used for transformer cores, electric motor laminations, generators, inductors, etc., where low core loss and high permeability are required.
7. High-Speed Steel.
High-speed steel is a subcategory of tool steel and contains high amounts of tungsten, molybdenum, vanadium, and cobalt. It allows very high hardness and the ability to maintain hardness at high temperatures.
It is often used for cutting tools like drill bits, lathe tools, milling cutters, and saw blades. High-speed steel withstands high temperatures without losing hardness. It is very wear-resistant and can cut harder materials.
How Are These Types Different?
The main differences between types of steel come from their composition and treatment. The amount of carbon in steel affects its hardness and flexibility. More carbon usually means harder steel, while less carbon makes it softer and easier to shape.
The addition of alloying elements also plays a big role. Elements like chromium, nickel, and molybdenum give steel special properties such as resistance to rust, strength, and the ability to withstand high temperatures.
Another important factor is heat treatment. Steel can be heated and cooled in different ways to change its internal structure. This process can make steel harder, tougher, or more flexible depending on the need.
Each type of steel is designed for a specific purpose. Carbon steel is simple and affordable. Alloy steel is strong and durable. Stainless steel resists rust. Tool steel is extremely hard and used for cutting and shaping.
Understanding these differences helps engineers and manufacturers choose the right type of steel for each job.
Steel classifications
Beyond the four groups, steel can also be classified based on different variables, including:
- Composition: carbon range, alloy, stainless, etc.
- Finishing method: hot rolled, cold rolled, cold finished, etc.
- Production method: electric furnace, continuous cast, etc.
- Microstructure: ferritic, pearlitic, martensitic, etc.
- Physical strength: per ASTM standards
- De-oxidation process: killed or semi-killed
- Heat treatment: annealed, tempered, etc.
- Quality nomenclature: commercial quality, pressure vessel quality, drawing quality, etc.
Different Grades of Steel
Steel grading is a system for categorizing varieties of steel and materials based on their properties. The American Society of Testing (ASTM) grading system assigns the metals a classification letter based on the following:
- A represents ferrous metals and products such as iron and steel materials
- B represents nonferrous metals and products such as coatings
- C represents ceramic, concrete, and masonry materials.
- F represents end-use materials and products, such as bolts
The letter is followed by a 1–3-digit reference number, such as A572 steel, a high-strength, low-alloy structural steel that is popular in construction.
Metric standards will be followed by the letter M. Updated standards will have a two-digit number representing the year of updating, such as 99 for 1999. For example, in ASTM A 582M-95, the M represents the metric system and the 95 represents 1995 as the year of its most recent update.
Grades are indicated by numbers that represent the metal properties. For example, A572 steel is available in five different grades, 42, 50, 55, 60, and 65, with the grade number representing the different yield strengths.
The Society of Automotive Engineers (SAE) uses a four-digit classification for steel types. The first digit indicates a type of carbon steel alloy. The remaining digits indicate the percentage concentration of other elements. For example, SAE 5130 is a chromium steel alloy with 1% chromium and 0.30% carbon.
Types of Steel Used in Construction
The construction industry uses about 50% of the world’s steel. Steel is a popular building material for its strength, low cost, and ability to bind to concrete.
Galvanized steel is carbon steel coated in zinc to reduce corrosion. It is used in large structural pieces as well as railings, fences, and gutter systems.
The following are steel products used in building and construction.
- Structural steels are used for framing buildings.
- Reinforcing bars, such as rebar, add tensile strength to concrete.
- Steel pipes are frequently used in plumbing, as railings on construction sites, and to provide support for construction piling.
- Steel sheet products are found in roofing, ceilings, and walls.
- Steel plates are frequently used in construction, mining equipment, and many types of machinery.
- Steel rods are used for reinforcement at construction sites.
- Non-structural steels are used in ductwork and heating and cooling equipment.