Steel is the world’s most important engineering and construction material. It is used in every aspect of our lives; in cars and construction products, refrigerators and washing machines, cargo ships and surgical scalpels. It can be recycled over and over again without loss of property.
In this article, you’ll learn what steel is Steel? The definition, Characteristics, and Properties of Steel are all explained with pictures.
What is Steel?
Steel is an alloy typically consisting of iron and carbon along with small amounts of manganese, silicon, phosphorus, sulfur, and oxygen. The amount of carbon content present ranges from 0.02% to 2.14%, and the presence of manganese is around 1%.
Other than these, the common alloying elements include manganese, cobalt, boron, nickel, chromium, molybdenum, titanium, vanadium, tungsten, and niobium.
It is known for its high tensile strength and versatility, making it a crucial material in construction, manufacturing, and various industries. Steel’s composition can vary, often including other elements to enhance its properties, which contributes to its widespread use in buildings, tools, vehicles, and machinery.
The density of steel is in the range between 7,700 and 8,050 kg/m3. The presence of carbon creates a strong molecular structure. It can take two crystalline forms, body-centered cubic and face-centered cubic, depending on the temperature.
Pure iron is often ductile, soft, or easily formed due to the iron atoms in the crystal structure slipping past one another.
Here, the presence of carbon and other elements acts as hardening agents, which prevent the dislocation of atoms. As a result, the amount of carbon and other elements present in the alloy makes up for the final physical qualities of the alloy.
These qualities include quenching behavior, need for annealing, tempering behavior, hardness, tensile strength, and yield strength. Evident production of steel dates back to the sixth century BC, produced in South India, known as Wootz steel.
What Is Steel Made of?
Fundamentally, steel is made of iron and carbon, but many other alloying elements are also added to create thousands of different grades of steel.
Mild steel, or carbon steel, is generally more than 99% iron, containing less than 0.25% carbon, similar amounts of manganese, and traces of phosphorus and sulfur.
By contrast, a common grade of stainless steel (304) has only about 70% iron with a minimum of 18% chromium and 8% nickel. Manganese, silicon, phosphorus, and, of course, carbon are also present in varying amounts within this type of steel.
Other alloying elements for different steels include molybdenum, vanadium, and boron. Multiple grades of each type of steel exist, with variations in their composition meant to produce different characteristics.
Characteristics of Steel
The common characteristics of steel are listed below:
- Strength: Steel is a high-strength material, particularly in tension, and can be used for structural loads.
- Durability: Steel is highly durable with a potential lifespan of over 100 years. It does not swell or creep, instead remaining very rigid.
- Versatility: Steel is an incredibly versatile material. Its many grades can be applied to thousands of uses.
- Machinability: Most steel is easily machinable, depending on the grade. Some specific grades of steel (free-cutting steels) are highly machinable.
- Weldability: Most grades of steel are easily weldable, although some need specialized welding procedures.
- Corrosion Resistance: Steel can be alloyed with other elements such as chromium, nickel, and molybdenum to better resist corrosion.
- Conductivity: Steel generally has lower thermal and electrical conductivity compared to other metals. It can be employed as a strong and heat-resistant shielding material.
- Recycling: Steel can be completely recycled, and due to its value, a large portion (>60%) of steel globally is recycled.
What is the Color of Steel?
Steel is generally silver-gray, but the appearance depends on the grade of the steel and the level of oxidation. For instance, some stainless steels, when polished, are reflective silver, almost with a mirror finish. Carbon steels are generally a dull gray to start with and turn a dark brown as they oxidize.
What Does Steel Look Like?
Steel looks like a dark gray or dark brown metal, often gaining a dull or rough appearance from oxidation or rust forming on its surface. Superficial rust is often visible on the surface of steel that has been exposed to the elements for an extended period.
Properties of Steel
A few of the main properties of steel are as follows:
- Hardness
- Toughness
- Yield strength
- Tensile strength
- Ductility
- Durability
- Malleability
- Magnetic
- Thermal conductivity
#1. Hardness.
Hardness is defined as the ability to withstand the friction and abrasion of the material and is a measure of how durable it is.
It is the most poorly defined material property because it can indicate resistance to scratching, resistance to abrasion, resistance to indentation or shaping, or resistance to localized plastic deformation.
#2. Toughness.
Toughness is the property of steel that is defined as its ability to absorb energy without fracturing or breaking. Simply put, it is the resistance of a material to fracture when stressed. It depends heavily on strength as well as flexibility.
The toughness of a material is usually measured in foot lbs, per sq, in or Joules per sq, centimeter.
Steel may have satisfactory toughness under static load, but fail under dynamic load or impact. It is indicated by hardness as a material that deforms severely without breaking, and it can be considered extremely tough but not hard.
#3. Yield Strength.
Yield strength refers to the measure of the force required to initiate deformation (i.e., bending or warping) of a material. To put it in simple words, it is the peak force that is applied to an object before it changes its shape and structure.
The yield strength is the important one that helps in choosing a suitable material for construction based on the requirement.
#4. Tensile Strength.
Tensile strength is defined as the measure of the force required to break a material. The tensile strength of steel is almost as high, which makes it relatively impervious to cracking or breaking, which is important for its use in the construction of structures.
A typical tensile strength for structural steel is 400 megapascals (MPa), while a typical tensile strength for carbon steel is 841 MPa.
#5. Ductility.
One of the valuable mechanical properties of steel is its ductility, which is its capacity to change shape under the influence of force applied to it in such a way that it does not crack. This is one of the most important mechanical properties of steel.
The property that makes it possible for it to be shaped into various shapes and structures is known as ductility. This allows it to be utilized as thin wires or as large automotive parts and panels, depending on the shape and structure.
#6. Durability.
The durability of a metal refers to its ability to withstand abrasion, pressure, and damage over a long period of time. Steel is also a highly durable type of metal. Since steel is also strong and ductile, which makes it is highly resistant to accidental damage.
Since steel is a compound metal, which is made up of iron and carbon in a particular combination, it is remarkably impervious to most components, making it perfect for areas such as coastal areas and cities that experience high winds, frequent storms, and challenging conditions.
#7. Malleability.
When metals are malleable, it means that they can be beaten, squeezed, or bent into thin or thick sheets without breaking, thereby indicating they have the physical property of malleability. Simply put, it is the property of a metal to deform under pressure and take another shape.
#8. Magnetic.
Steel is also a magnetic material, yet it depends on what type of steel is referred to. In the case of steel jars, for instance, the components that make up the jar are ferromagnetic, such as iron, which is strongly attracted by magnets.
Austenitic stainless steel does not act magnetically due to the high concentration of chromium and nickel.
#9. Thermal Conductivity.
Thermal conductivity is the rate at which thermal energy is transported through a material. It is usually measured in watts per meter per degree Kelvin (W/(mK)).
A high thermal conductivity material can transport heat faster and more efficiently than a low thermal conductivity material.
Carbon steel has very low conductivity compared to aluminum. This is usually about 45 watts for every Kelvin per meter.
Electrical conductivity at room temperature of about 6 million siemens per meter. It is the first physical property that determines the conductivity of steel.
Different Types of Steel
| Steel Type | Characteristics | Applications |
| Carbon Steel | Varies in carbon content; low, medium, high categories | Construction, tools, machinery |
| Stainless Steel | Corrosion-resistant with chromium content | Kitchenware, medical devices, cutlery |
| Alloy Steel | Varies in carbon content: low, medium, high categories | Aerospace, structural, machinery |
| Tool Steel | High hardness; water, oil, or high-speed variants | Tools, dies, machining |
| HSLA Steel | Lightweight with improved strength | Bridges, buildings, automotive parts |
| Electrical Steel | Magnetic properties and low conductivity | Transformers, electric motors |
| Weathering Steel | Forms a rust layer for corrosion protection | Outdoor structures, sculptures |
| Galvanized Steel | Zinc-coated for rust prevention | Roofing, fences, automotive parts |
| Maraging Steel | High strength and toughness after aging | Aerospace components |
| Dual-Phase Steel | Mix of strength and formability | Automotive safety parts |
There are many types of steel, each designed to meet specific requirements based on its unique properties and applications. Understanding these types is essential for selecting the right steel for various projects. Here’s an expanded overview of the most common types of steel:
1. Carbon Steel.
Carbon steel is the most widely used type of steel, accounting for approximately 90% of global steel production. It is primarily composed of iron and carbon, with the carbon content influencing its properties. Carbon steel can be categorized into three main groups based on carbon content:
- Low Carbon Steel (Mild Steel): Contains up to 0.3% carbon, making it ductile and malleable. It is easy to weld and shape, which makes it ideal for construction materials, automotive parts, and everyday items like pipes and food cans.
- Medium Carbon Steel: Has a carbon content ranging from 0.3 to 0.6%. This type strikes a balance between strength and ductility, making it suitable for applications such as railway tracks, crankshafts, and machinery components.
- High Carbon Steel: Contains between 0.6 to 2.1% carbon, resulting in increased hardness and wear resistance. However, this type is less ductile and more brittle, making it ideal for cutting tools, springs, and high-strength wires.
2. Stainless Steel.
Stainless steel is a specialized material known for its exceptional corrosion resistance thanks to the addition of chromium (at least 10.5% by weight). This alloy is widely used in environments where rust and staining are concerns. Stainless steel can be further divided into several categories:
- Austenitic Stainless Steel: Contains high levels of nickel and chromium, providing excellent corrosion resistance and good formability. Common grades include 304 and 316, often used in kitchen equipment, medical devices, and food processing.
- Ferritic Stainless Steel: Contains less nickel but more chromium than austenitic types. This group offers good corrosion resistance but is less ductile. It is commonly used in automotive applications and architectural structures.
- Martensitic Stainless Steel: Known for its hardness and ability to be heat-treated. It typically contains higher carbon levels and is used in cutlery, surgical instruments, and certain industrial applications.
3. Alloy Steel.
Alloy steel includes various alloying elements beyond carbon that enhance specific properties such as strength, toughness, and wear resistance. The composition can vary widely depending on the intended application:
- Low-Alloy Steel: Contains less than 8% alloying elements like manganese or chromium. It offers improved mechanical properties compared to carbon steel and is often used in structural applications.
- High-Alloy Steel: Contains more than 8% alloying elements, providing superior corrosion resistance and strength. These steels are used in specialized applications such as aerospace components and high-stress machinery.
4. Tool Steel.
Tool steel is engineered specifically for manufacturing tools and dies due to its hardness and resistance to deformation at high temperatures. It typically contains higher levels of carbon along with other alloying elements:
- Water-Hardening Tool Steel: Hardens when cooled in water; suitable for simple tools.
- Oil-Hardening Tool Steel: Requires oil for cooling; offers good toughness.
- High-Speed Tool Steel: Designed for high-speed machining; retains hardness at elevated temperatures.
5. High-Strength Low-Alloy (HSLA) Steel.
HSLA steel is designed to provide better mechanical properties than conventional carbon steels while being lighter in weight.
This particular type of steel includes small amounts of alloying elements such as vanadium or titanium. It is commonly used in structural applications like bridges, buildings, and automotive parts due to its strength-to-weight ratio.
6. Electrical Steel.
Electrical steel is designed specifically for electrical applications where magnetic properties are crucial.
Moreover, silicon steel is often used in transformers and electric motors due to its low electrical conductivity and reduced magnetic losses.
7. Weathering Steel.
Weathering steel is a steel type that develops a protective rust layer when exposed to the elements, which prevents further corrosion. This steel is ideal for outdoor structures such as bridges or sculptures, where aesthetics will also be a consideration due to its unique patina.
8. Galvanized Steel.
Galvanized steel has a protective zinc coating that prevents rusting. It is commonly found in roofing materials, fences, and automotive parts where moisture exposure is frequent.
9. Maraging Steel.
Maraging steel is a high-strength alloy that undergoes a special aging process to enhance its properties. This steel is used in aerospace components due to its excellent toughness and fatigue resistance.
10. Dual-Phase Steel.
Dual-phase steel consists of a mix of ferrite and martensite microstructures. This steel offers high strength combined with good formability; the final steel product is often used in automotive safety components.
At the end of the day, steel is a very flexible material to use in your projects!
What is the Melting Point of Steel?
The melting point of steel and other metals varies depending on its composition, but in general, most steel alloys range from 2,500° to 2,750° Fahrenheit, or 1,150° to 1,370° Celsius. However, while steel melts at these temperatures, it can start losing its structural integrity around 1,000° Fahrenheit.
The exact melting point is dependent on the composition of the steel alloy. An alloy is a metal that’s made from two or more elements, one of which must be a metal.
Made by adding a small amount of carbon to iron, steel is considered to be among the strongest alloys available. While there is a wide range of grades and variations, the strength of steel does not generally impact its melting point.
Instead, steel’s melting point is determined by its chemical composition, particularly the types and proportions of elements present in the alloy. Steel’s strength and melting point are related, but don’t contribute directly to the temperature.
How Is Steel Made?
Stage 1: Iron Ore Preparation.
Mining and Extraction Iron ore is extracted from open-pit or underground mines using heavy machinery. The ore typically contains 50-70% iron content along with various impurities.
Crushing and Screening Raw ore is crushed into smaller pieces and screened to separate different sizes. This improves efficiency in subsequent processing steps.
Beneficiation Low-grade ores undergo beneficiation processes including:
- Magnetic separation to concentrate iron-bearing minerals
- Flotation to separate iron from gangue materials
- Pelletizing to create uniform-sized pellets for furnace charging
Stage 2: Coke Production.
Coal Preparation Specific grades of coal are blended and crushed to optimal size for coking.
Coking Process Coal is heated to 1000-1100°C in oxygen-free ovens for 12-18 hours. This process:
- Drives off volatile compounds
- Creates high-carbon coke with necessary strength and porosity
- Produces valuable byproducts like coal tar and ammonia
Stage 3: Iron Production (Blast Furnace Operations).
Furnace Charging The blast furnace is loaded with carefully calculated proportions of:
- Iron ore or pellets
- Coke
- Limestone
- Sometimes recycled materials
The Reduction Process Hot air (up to 1200°C) is blown into the bottom of the furnace, creating temperatures reaching 2000°C. The process involves several chemical reactions:
- Carbon Combustion: C + O₂ → CO₂
- Carbon Monoxide Formation: CO₂ + C → 2CO
- Iron Oxide Reduction:
- Fe₂O₃ + 3CO → 2Fe + 3CO₂
- FeO + CO → Fe + CO₂
Molten Iron Collection Liquid iron, containing about 4% carbon, collects at the furnace bottom. This product is called “pig iron” or “hot metal.”
Slag Formation Limestone combines with silica and other impurities to form slag, which floats on top of the molten iron and is separately tapped.
Stage 4: Steelmaking.
Modern steelmaking primarily uses two methods:
Basic Oxygen Furnace (BOF) Process
Charging
- Molten pig iron (70-80%)
- Steel scrap (20-30%)
- Fluxes like limestone
Oxygen Blowing Pure oxygen is blown onto the molten metal at supersonic speeds, causing:
- Carbon oxidation: C + ½O₂ → CO
- Silicon and manganese oxidation
- Temperature increase to 1600-1700°C
Refining The process removes excess carbon, silicon, manganese, and phosphorus, converting pig iron into steel with desired carbon content.
Electric Arc Furnace (EAF) Process
Charging Primarily steel scrap (up to 100%) with some direct reduced iron or pig iron.
Melting Electric arcs between graphite electrodes and the charge create temperatures up to 3500°C, melting the scrap metal.
Refining Oxygen injection and flux additions remove impurities and adjust chemical composition.
Stage 5: Secondary Steelmaking.
Ladle Treatment Steel is transferred to ladles where:
- Final chemical adjustments are made
- Alloy elements are added
- Temperature is controlled
- Degassing removes hydrogen and nitrogen
Vacuum Treatment Some grades require vacuum degassing to:
- Reduce gas content
- Remove inclusions
- Achieve ultra-low carbon content
Stage 6: Casting and Solidification.
Continuous Casting (Most Common)
Tundish Distribution Molten steel flows from ladles into a tundish, which distributes metal to multiple casting strands.
Mold Casting Steel is poured into water-cooled copper molds, forming:
- Slabs (for flat products)
- Billets (for long products)
- Blooms (for structural shapes)
Solidification Controlled cooling solidifies the steel while maintaining quality and preventing defects.
Alternative Casting Methods
Ingot Casting: Traditional method for specialty steels Near-Net Shape Casting: Advanced techniques for specific applications
Stage 7: Hot Rolling.
Reheating Cast steel is reheated to 1200°C in walking beam or pusher furnaces.
Primary Rolling
- Slabs are rolled into plates, sheets, or strip
- Blooms become beams, rails, or other structural shapes
- Billets are rolled into bars, rods, or wire
Finishing Final rolling passes achieve desired dimensions and surface finish.
Stage 8: Cold Processing and Finishing.
Cold Rolling Some products undergo cold rolling for:
- Improved surface finish
- Better dimensional tolerances
- Enhanced mechanical properties
Heat Treatment Various treatments modify steel properties:
- Annealing (softening)
- Quenching and tempering (hardening)
- Normalizing (stress relief)
Surface Treatment
- Galvanizing for corrosion protection
- Coating applications
- Surface inspection and quality control
Application or Uses of Steel:
#1. Building and infrastructure (51%)
Around half of the steel produced annually is utilized to construct buildings and infrastructure such as bridges. It is mostly found in reinforcing bars and sheet products used in roofs, internal walls, ceilings, and structural sections.
It is also found in HVAC systems and items such as stairs, rails, and shelving.
Moreover, applications of steel in transportation-related infrastructure include tunnels, rail tracks, fuelling stations, train stations, ports, and airports.
#2. Mechanical equipment (15%)
This second-greatest use of steel includes (among many other things) bulldozers, tractors, machinery that makes car parts, cranes, and hand tools such as hammers and shovels. It also includes the rolling mills that are used to shape steel into various shapes and thicknesses.
#3. Automotive (12%)
On average, almost 2,000 pounds, or 900 kilograms, of steel is used to make a car, according to the WSA. About a third of that is used in the body structure and exterior, including the doors. Another 23% is in the drive train, and 12% is in the suspension.
Advanced high-strength steels, which are made using complex processes and are lighter in weight than traditional steels, account for about 60% of a modern car’s body structures.
#4. Metal Products.
This market sector includes various consumer products such as furniture, packaging for food and drinks, and razors.
Foods packaged in steel cans don’t need to be refrigerated.
#5. Other Transport.
Steel is used in ships, trains, and train cars, and parts of planes. Hulls of large ships are almost all made of steel, and steel ships carry 90% of global cargo, the WSA says. Steel is important for sea transportation in one other way: almost all of the world’s approximately 17 million shipping containers are made of steel.
Besides the cars, steel shows up in trains in the wheels, axles, bearings, and motors. In airplanes, steel is crucial for engines and landing gear.
#6. Domestic Appliances.
Clothes washers and dryers, ranges, microwave ovens, dishwashers, and refrigerators all contain steel in varying amounts, including the motors, when applicable.
According to the American Iron and Steel Association, a front-loading washer generally contains 84.2 pounds of steel, while a top-bottom refrigerator-freezer contains 79 pounds.
#7. Electrical Equipment.
The last major steel market sector involves applications in the production and distribution of electricity. That means transformers, which have a magnetic steel core; generators; electric motors; pylons; and steel-reinforced cables.