Steel

Different Types of Steel, Properties and Applications

Steel is a versatile and widely used material crucial in various industries and everyday life. It is an alloy of iron and carbon and is renowned for its strength, durability, and flexibility, making it essential in construction, manufacturing, and infrastructure projects. In this article, we will explore what steel is, how it is made, its properties, different types, advantages and disadvantages, and its wide range of applications.

What is Steel?

Steel is an alloy made primarily from iron and carbon, with the carbon content typically ranging from 0.2% to 2.1% by weight. Adding carbon to iron alters its properties, making it stronger, harder, and more durable. Other elements, such as manganese, chromium, nickel, and molybdenum, are often added to enhance specific steel properties. For example, adding 11% chromium can make stainless steel resistant to corrosion and oxidation.

Steel is one of the most useful and common ferrous alloys in modern use because of its very high strength, still substantial toughness, and ability to be greatly changed by heat treatment. In addition, due to its high tensile strength and low cost, steel is used in buildings, infrastructure, tools, ships, trains, cars, bicycles, machines, electrical appliances, furniture, and weapons.

what is steel

How to Make Steel?

The first step in making steel is obtaining iron ore. Iron ore is a rock containing iron oxide or Fe2O3.  Smelting, which utilizes a blast furnace, isolates the iron from the ore. Smelting uses heat and a chemical-reducing agent like coking coal to remove oxygen from the iron oxide ore. This leaves just the iron behind as a molten metal that can be made into steel.

Once the pig iron is obtained, the next step is the conversion to steel. Pig iron contains about 4-5% carbon, which makes the iron very brittle and unsuitable for most applications. The pig iron is melted, and oxygen is blown through it to reduce the carbon levels to 0.2-2.1%. This oxidizes the carbon, which escapes from the iron as carbon monoxide gas. Scrap metal and other alloys are often added to the molten pig iron during this process to obtain the desired composition of the final steel product.

The liquid steel is cast into semi-finished forms like slabs, billets, and blooms. These undergo further processing, like hot or cold rolling and additional heat treatments, to produce the final steel product with the desired shape and properties.

Properties of Steel

The properties of steel can vary greatly depending on its composition and processing. Some key properties of steel are:

Strength: Steel has high strength compared to other building materials like aluminum or plastic, allowing it to withstand heavy loads and resist deformation. The tensile strength of steel ranges from 200 MPa for mild low-carbon steels to over 1500 MPa for certain martensitic steels that have been tempered and hardened. The strength comes from the carbon content in the steel. Higher carbon steels are stronger than lower carbon steels.

Hardness: Besides high strength, the carbon in steel makes it harder than pure iron. Hardness improves wear resistance and the ability to hold a sharp cutting edge. Like strength, hardness increases with increasing carbon content. Hardness can range from 60 HB for mild steels to over 650 HB for specialized steels.

Toughness: While strength and hardness are improved by additional carbon, toughness is lowered. Toughness is a measure of the energy a material can absorb before fracturing. It is important in withstanding sudden impacts and preventing brittle fractures. Mild steels with lower carbon content usually have higher toughness than ultra-high-strength steels.

Durability: Steel is highly durable and can withstand harsh environmental conditions, making it suitable for long-lasting structures.

Thermal Conductivity: Steel conducts heat efficiently, making it suitable for applications where heat transfer is essential.

Weldability and Ductility: Low-carbon steels are highly weldable, while higher-carbon steels can crack during welding. Special precautions must be taken when welding high carbon or alloy steels.

Formability: Lower carbon steels can be more easily bent, pressed, or forged into shape. Higher carbon steels are less malleable and harder to form.

Corrosion Resistance: Pure iron and mild steels have low corrosion resistance and readily rust. Alloying elements like chromium, nickel, and copper can greatly improve corrosion resistance. Certain types of steel, such as stainless steel, exhibit excellent corrosion resistance, making them ideal for applications in corrosive environments.

Electrical conductivity: While not as conductive as copper or aluminum, steel still possesses reasonable electrical conductivity, making it useful in electrical applications.

Recycling: Steel can be completely recycled, and due to its value, a large portion of steel globally is recycled.

Types of Steel

Thousands of steel grades are tailored to meet the needs of various applications. Here are some of the major types and categories of steel:

Carbon Steels

Carbon steels have a carbon content of up to 2.1% by weight. The various carbon steel types based on carbon content are:

  • Low Carbon Steel – 0.05 – 0.25% C  
  • Medium Carbon Steel – 0.30 – 0.60% C
  • High Carbon Steel – 0.60 -1.00% C
  • Ultra-high-carbon Steel – 1.25–2.0% C

Increasing the carbon content improves strength and hardness but lowers toughness and weldability. Low carbon steels are the most commonly produced types due to their excellent combination of strength and ductility. Carbon steel can be employed for structures, automotive components, and many other applications.

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 Steels – below 8% alloying elements
  • High-alloy Steels – more than 8% alloying elements

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.

Stainless Steels

Stainless steels have excellent corrosion resistance due to their chromium content of at least 10%. They are easy to clean and have temperature resistance and strength. Some common types of stainless steel are:

  • 304 stainless – 18% Cr, 8% Ni
  • 316 stainless – 16% Cr, 10% Ni, 2% Mo
  • Duplex stainless – 22% Cr, 5% Ni, 3% Mo
  • 410 stainless – 11% Cr

The addition of nickel further boosts corrosion resistance. Stainless steels are more expensive but indispensable where rust prevention is essential. It is widely used in applications where resistance to corrosion and staining is crucial, such as kitchen appliances, cutlery, and medical equipment.

stainless steel

Tool Steels

Tool steels are ultra-hard and optimized for cutting, stamping, and die tools. They exhibit extreme hardness, abrasion resistance, and the ability to hold a sharp cutting edge. Some examples are:

  • A2 – 1% C, 5% Cr, 1% Ni, 0.8% Mn
  • D2 – 1.5% C, 12% Cr, 0.9% Ni, 0.8% Mn
  • H13 – 0.4% C, 5% Cr, 1.5% Mo, 1% V

These tool steels retain hardness at high temperatures, making them useful for hot work applications. They are annealed and tempered to achieve the hardness needed for various cutting operations. They are commonly used to manufacture tools, dies, and molds.

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. 

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.

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.

Advantages and Disadvantages of Steel

Steel is a very useful material. Here are its benefits and limitations.

Advantages of Steel:

Strength and Durability: Steel is renowned for its high strength and durability, making it suitable for heavy-duty applications.

Versatility: Steel can be easily fabricated and shaped into various forms, allowing versatility in design and manufacturing processes.

Sustainability: Steel is a highly recyclable material, reducing the environmental impact of its production and promoting sustainability.

Dimensional stability: Steel is very rigid and resists deformation well.

Fire Resistance: Steel has excellent fire-resistant properties, making it a preferred choice for structures that require fire protection.

Cost-Effective: Despite its numerous advantages, steel remains a cost-effective material due to its availability and recyclability.

Disadvantages of Steel:

Corrosion: Certain types of steel are prone to corrosion, requiring protective coatings or corrosion-resistant alloys.

Weight: Steel is relatively heavy compared to other materials, which can be a disadvantage in applications where weight is critical.

Energy Requirement: Steel production consumes energy and natural resources. Although modern techniques have improved, steel’s energy footprint is still relatively high.

Applications of Steel

Steel dominates many construction and manufacturing applications thanks to its unparalleled versatility, availability, and cost-effectiveness.

Structural Steel

Steel is used extensively in buildings, bridges, transmission towers, industrial structures, naval vessels, and offshore platforms. Structural steel shapes like I-beams, channels, and plates provide the framework for large structures. Reinforcing bar, or rebar, strengthens concrete structures.

Steel Pipe and Tubing

Steel pipe transports liquids, gasses, slurries, powders, and cables. It is used for plumbing, HVAC, automotive systems, machinery, etc. Steel tubes provide structural strength and are lighter in weight than solid bars.

Railroad Tracks

Steel is used for railroad tracks and wheels on locomotives and rail cars. The strength, wear resistance, ductility, and fracture toughness make steel ideal for handling the stresses and impacts involved in rail transport.

Automotive Steel

Cars, trucks, and other vehicles have thousands of precision steel components. Frames, engines, drivetrains, wheels, and suspension parts experience enormous stresses and must provide passenger safety. Advanced high-strength steels allow automakers to reduce vehicle weight for greater efficiency and performance.

steel parts

Appliances and Home Goods

Refrigerators, dishwashers, stoves, furniture, shelving, kitchen utensils, pipes, and fittings use steel for its affordability, recyclability, and strength. Enameled steel prevents rusting in damp environments.

Cutting and Forming Tools

Knives, saws, drills, taps, dies, molds, patterns, and measuring tools rely on hardened tool steel to cut, shape, and form other materials. Tool steels like A2 and D2 are optimized for hardness, abrasion, and heat resistance.

Fasteners

Bolts, nuts, screws, and nails are predominantly made of steel due to their strength, hardness, and ability to be machined into various head shapes and threading. Stainless steel versions resist corrosion.

Oil and Gas Drilling

Steel drill pipe and collars are joined to transmit torque and drilling fluids downhole during oil and gas drilling. The components must withstand crushing forces, fatigue stresses, and corrosive fluids.

Packaging

Steel is used to manufacture cans for food and beverage packaging due to its strength and ability to preserve the contents.

Summary

Steel is one of the most vital construction materials. Thanks to its abundance, inexpensiveness, strength, and diverse properties, it builds the modern industrial world. Carbon and alloying additions allow metallurgists to customize their hardness, toughness, and corrosion resistance to fit any application. Steel bridges the gap between pure iron’s softness and cast iron’s brittleness. It enables infrastructure, transportation, energy, consumer goods, machinery, and defense applications that comprise our lives.

FAQs

Yes, steel is generally stronger than iron. Adding carbon and other alloying elements to iron enhances its strength, making steel a preferred choice for many applications requiring high strength.

Certain types of steel are prone to rusting, especially when exposed to moisture and oxygen. However, some corrosion-resistant steels, such as stainless steel, contain a high percentage of chromium, forming a protective oxide layer on the surface and preventing rust formation.

Mild steel, also known as carbon steel, contains a low percentage of carbon and is relatively inexpensive. It is commonly used in construction and general-purpose applications. On the other hand, stainless steel contains a higher percentage of chromium, which provides excellent corrosion resistance. Stainless steel is widely used in environments where rusting or staining is a concern, such as kitchen appliances and medical equipment.

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