Steel: Definition, Composition, Types, Properties, and ...

Steel is a strong and versatile metal. It is an alloy consisting of iron with a small amount of carbon and occasionally other elements. The carbon directly influences the steel&#;s strength and durability. However, a vast array of different steels have been developed through the addition of other alloying elements such as chromium, nickel, molybdenum, and silicon. These can provide enhanced properties like abrasion resistance or corrosion resistance. There is a grade of steel for almost any application. This article will define steel, its composition, types, properties, and applications.

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What Is Steel?

Steel, in its simplest form, is iron metal that&#;s been alloyed with less than 2% carbon. However, many other elements can be added as well to create multiple grades of steel alloys with varying properties. Common alloying elements include chromium, manganese, and nickel.

What Is the History of Steel?

The history of steel begins with the history of iron. Iron&#;s discovery and rise to prominence in what we now call the Iron Age began in about the 12th century BCE (though it varies depending on geographical location). It is only considered to have started in Europe around the 5th century BCE. Early steels (iron with added carbon to increase strength) were made in China around that time but generally had too low an iron content to be considered true steel. It was in India around 400 BCE that true steel was created by melting iron and charcoal together in small crucibles. 

Variations of steel and cast iron (which have a higher carbon content) were developed throughout the world during medieval times and into modern history. A significant step forward was discovered by Benjamin Huntsman in England in when he used geologically-sourced coal rather than charcoal from timber to heat the crucibles. An even bigger breakthrough was made by Henry Bessemer, who was awarded a British patent in for a steel-manufacturing process. His process blew air directly through the molten iron (and its additives). This became fundamental to modern commercial steel production.

It wasn&#;t until about - that stainless steel was first created with the addition of chromium and nickel. These materials were gradually developed and refined through the end of World War Two.

What Is Steel Made of?

Fundamentally, steel is made of iron and carbon, but many other alloying elements also get 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.

How Are Steels Made?

Steel is made via one of two main smelting processes &#; either a blast furnace or an electric arc furnace. 

For a blast furnace, iron ore and coke (coal that has been treated to remove volatile components) are added to the furnace, which is fired by air. Lime is also added to reduce the iron from the ore to its metallic form. This produces so-called pig iron, which is then sent to a direct oxygen furnace for the production of molten steel.

In an electric arc furnace, the iron ore is fired first by natural gas in a direct-reduction furnace. The iron metal is then sent to the electric arc furnace for steel production. Large electrodes are submerged into the furnace where electricity is used to create high-temperature arcs between the electrodes and thus melt the metal. Alloying elements are added to the electric arc furnace section.

After either process, the molten steel is then continuously cast by a hot strip mill and then rolled into different forms such as plates, bars, pipes, and others. This can be done by hot rolling or cold rolling. Other finishing processes such as tempering or annealing can also take place depending on the steel grade being produced.

What Are the Characteristics of Steel?

The common characteristics of steel are listed below:

1. Strength: Steel is a high-strength material, particularly in tension, and can be used for structural loads.
2. Durability: Steel is highly durable with a potential lifespan of over 100 years. It does not swell or creep, instead remaining very rigid.
3. Versatility: Steel is an incredibly versatile material. Its many grades can be applied to thousands of uses. 
4. Machinability: Most steel is easily machinable, depending on the grade. Some specific grades of steel (free-cutting steels) are highly machinable.
5. Weldability: Most grades of steel are easily weldable, although some need specialized welding procedures.
6. Corrosion Resistance: Steel can be alloyed with other elements such as chromium, nickel, and molybdenum to better resist corrosion.
7. 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. 
8. 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. Figure 1 contains examples of steel:

Choosing the correct steel grade is essential for the success of your project. A bad grade can result in poor performance, reduced durability, or even catastrophic failure.

When selecting a steel grade, factors such as strength, rust resistance, heat resistance, and weldability must be considered. Additionally, the intended use and environmental conditions should be taken into account.

With the right steel grade, you can ensure that your project will meet its intended purpose and provide long-lasting performance. Make sure to consult with a steel expert before starting a project.

Factors to Consider When Choosing Steel Grades

Project Requirements

• Strength and Durability

Strength and durability are the most critical factors when selecting the steel type for your project area. Your project requirements will dictate the level of strength and durability that your steel must possess to withstand the intended conditions of use.

To determine the appropriate level of grading systems, several factors must be considered: the expected load-bearing capacity of the steel, the environmental conditions the steel will be exposed to, and the lifespan of the finished product.

For example, If your project involves constructing a bridge carrying heavy traffic, you&#;ll need high-strength steel to handle the weight without buckling or bending. If you&#;re building a fence or a railing, you may only need lower-strength steel that can provide sufficient durability and resistance to weathering.

Other considerations that may impact your choice of steel grade include the required level of rust resistance, the ease of fabrication, and the cost-effectiveness of the steel.

Ultimately, selecting the correct steel grade for your project requires careful analysis and consideration of all the relevant factors. Ensure that it is strong and performs reliably over time.

• Corrosion Resistance

You must consider the level of anti-corrosive property, especially if it will be exposed to harsh environmental conditions. Corrosion can cause structural damage, reduce the product&#;s lifespan, and increase maintenance costs. The level of rust-proof quality required will be determined by factors like moisture, salt water, and chemicals.

Galvanized steel is another option for corrosion resistance. It is coated with a layer of zinc that acts as a barrier against rust and corrosion. However, galvanized steel may not be suitable for products exposed to extremely corrosive environments.

Other common grades with high corrosion resistance include weathering steel, which forms a protective layer of rust over time, and aluminum, naturally corrosion resistant.

Consideration of the environmental conditions to which the metal will be exposed and selection of the one with the appropriate level of corrosion resistance is essential to ensuring the longevity and durability of the finished product.

• Temperature and Pressure

Consider the ability to withstand the temperature and pressure requirements of the application. Different steel grades have varying melting points and yield strengths, which can affect their performance in high-temperature or high-pressure environments.

For example, if you&#;re working on a project involving boilers, pressure vessels, or piping systems, you must choose a steel grade with high-temperature and high-pressure capabilities. Alloy and stainless steels are often used in these applications due to their excellent strength and durability at elevated temperatures.

Similarly, if your project involves cryogenic applications, you need a steel grade to maintain strength and flexibility at shallow temperatures. Low-temperature steels, such as those with nickel or manganese content, are often used in these applications.
In addition to the temperature and pressure requirements, consider factors like corrosion resistance, ease of fabrication, and cost-effectiveness when selecting a steel grade for your project.

 

Cost Considerations

• Raw Material Costs

When choosing the suitable steel grade for your project, raw material costs are a factor. Different steel grades have varying raw material costs based on their composition and availability.

High-strength steel grades with alloying elements such as chromium, nickel, or molybdenum tend to be more expensive due to the cost of these materials. On the other hand, lower-strength steel grades with lower alloying elements tend to be more cost-effective.

Another factor that can impact raw material costs is the demand and availability of the steel grade. If a particular steel grade is in high demand, its raw material costs may be higher due to supply and demand.

When choosing the correct steel grade, it&#;s important to balance cost considerations with other factors, such as the project&#;s requirements, performance, and safety. While cost may be a critical consideration, choosing a steel grade based on price alone can result in a suboptimal product.

• Fabrication Costs

Fabrication costs are another consideration when choosing the right steel grade for your project. Different steel grades require varying levels of fabrication processes, which can significantly impact the project&#;s overall cost.

For example, high-strength steel grades may require more specialized equipment and processes, which can increase fabrication costs. Conversely, lower-strength steel grades may be easier to work with, resulting in lower fabrication costs.

Other factors that can impact fabrication costs. Projects with complex designs or tight tolerances may require more skilled labor and specialized equipment, resulting in higher fabrication costs.

When choosing the correct steel grade, it&#;s a good idea to balance fabrication costs with other factors, such as the project&#;s requirements, performance, and safety. While cost may be critical, choosing a steel grade based solely on fabrication costs can result in a suboptimal product.

Availability

• Local Availability

Local availability can help you choose the correct steel grade for your project. Depending on your location, some steel grades may be more readily available than others.

Working with steel grades that are locally available can save time and reduce transportation costs. However, it is essential to ensure that the chosen steel grade meets the project&#;s requirements and specifications.

Local availability may not be an issue, particularly for large-scale projects. However, for smaller projects or those with unique specifications, it&#;s essential to consider the availability of the chosen steel grade.

• Lead Time

Lead time is also something you should be aware of. Some steel grades may have longer lead times than others, impacting project timelines and deadlines.

Factors such as availability, production capacity, and transportation can all impact lead times for different steel grades. It&#;s crucial to consider lead times when planning your project and selecting the correct steel grade.

Working with steel suppliers with a track record of meeting deadlines can help ensure timely project completion. It&#;s also essential to communicate project timelines and deadlines with your supplier to ensure they can meet your needs.

You must also manage lead time. Any project manager will tell you of past disasters. When a deadline is delayed, it causes a ripple effect, like falling dominoes, as each deadline behind it is pushed further and further away.

• Supply Chain Considerations

When choosing the steel for your project, you must consider the supply chain. Understanding the supply chain of your steel grade selected can help you avoid potential disruptions and delays.

Production location, transportation routes, and inventory levels can all impact the supply chain of different steel grades. It&#;s better to work with suppliers with a reliable supply chain to ensure timely delivery and avoid potential issues.

Consider any potential risks to the supply chain, such as natural disasters or geopolitical events. By understanding potential threats and developing contingency plans, you can address any disruptions to the supply chain.

Common Steel Grades and Their Applications

Carbon Steel

Low Carbon Steel

Low-carbon steel is commonly used with less than 0.25%. This steel grade has excellent weldability and formability, making it the choice for construction, auto, and machinery.

Due to its lower carbon content, low-carbon steel is also more ductile and has better machinability than higher-carbon steel. It&#;s also more economical, making it ideal for projects with tight budgets.

However, low-carbon steel has lower strength and hardness than higher-carbon steel, making it less suitable for applications that require high strength and durability. So consider the specific requirements of your project and choose the steel grade accordingly.
Low-carbon steel is a versatile and cost-effective steel grade used in various applications.

Medium Carbon Steel

Medium carbon steel is a steel grade with a carbon content ranging from 0.3% to 0.6%. This steel grade balances strength and toughness, making it suitable for gears, axles, and crankshaft applications.

Medium carbon steel has higher strength and hardness than low carbon steel but is less ductile and more difficult to weld.

One advantage of medium carbon steel is its excellent machinability, which makes it easier to cut, drill, and machine. This steel grade can also be heat-treated to improve strength and hardness.

High Carbon Steel

High carbon tool steel is a steel grade with an amount of carbon ranging from 0.6% to 1.4%. This steel grade offers high strength and hardness, making it suitable for cutting tools, knives, and springs.

Due to its content, high-carbon steel is brittle and less ductile than lower-carbon steel. It&#;s also more difficult to weld and form. However, it can be heat treated to improve its strength and hardness.

High-carbon steel is often used in applications that require high wear resistance and durability.  High carbon steel is a specialized steel grade that can perform excellently in specific applications.

Applications of Carbon Steel

Carbon steel is a widely used steel grade due to its versatility and affordability. It is used in various industries, including construction, and some of its standard applications include structural components, fasteners, pipelines, and machinery parts.

Carbon steel&#;s strength and durability make it an excellent choice for structural applications, such as building frames and bridges. Its high tensile strength and low cost make it a popular choice for manufacturing applications.

Carbon steel is often used in the car industry for body panels, suspension components, and exhaust systems. It&#;s also used in hand tools, knives, and blades due to its hardness and wear resistance.

Alloy Steel

Types of Alloy Steel

Alloy steel contains elements other than iron and carbon, such as manganese, silicon, nickel, copper, and chromium. These added elements enhance the properties of the steel, making it more robust, durable, and corrosion-resistant.

There are several types of steel and alloy, each with its unique properties and applications. Here are a few examples:

1. Low alloy steel: This type contains less than 5% of other elements, making it less expensive and more readily available. It is used in bridges and buildings.

2. High-strength low alloy steel

    (HSLA): HSLA steel contains small amounts of alloying elements, making it strong and lightweight. It is in the auto and aerospace industries, as well as in construction.

3. Chromium-molybdenum steel: This type of alloy steel contains chromium and molybdenum, which enhance its strength and corrosion resistance. It is commonly used in pressure vessels, such as boilers and storage tanks.

4. Nickel-chromium-molybdenum steel: This type of alloy steel contains nickel, chromium, and molybdenum, making it highly resistant to corrosion and oxidation at high temperatures. It is commonly used in chemical processing and power generation.

5. When choosing the correct steel grade for your project, consider the specific application and the required properties of the steel. Alloy steel is an excellent choice for projects that require strength, durability, and corrosion resistance. However, you should still consult a professional to determine the best alloy steel type for your project.

Applications of Alloy Steel

Alloy steel contains a higher percentage of elements other than iron and carbon. These additional elements are typically chosen to impart specific characteristics such as increased strength, corrosion resistance, or improved weldability.

One common application of alloy steel is in constructing pipelines and pressure vessels. Adding elements such as chromium, molybdenum, and nickel makes these materials more resistant to corrosion and high-pressure environments.

Alloy steel is also used in the production of aircraft and aerospace components. The high strength-to-weight ratio of some alloys makes them ideal for structural components, while others are chosen for their resistance to high temperatures and wear.

Contact us to discuss your requirements of Steel Manufacturer and Supplier. Our experienced sales team can help you identify the options that best suit your needs.

Gears, axles, and drive shafts are among the applications of this kind of steel. Elements such as vanadium and tungsten can improve the strength and durability of these components. Meanwhile, other alloys are chosen for their ability to withstand high temperatures and extreme environments.

Stainless Steel

Types of Stainless Steel

Stainless steel is a choice for industrial and commercial applications. There are types of stainless steel grades, each with its unique properties and characteristics.

Austenitic stainless steel is a different type of steel. This type of steel is non-magnetic and has excellent weldability, making it ideal for use in the construction of tanks, steel pipes, and pressure vessels.

Another popular type is ferritic stainless steel, known for its high resistance to corrosion and oxidation. This steel is used in exhaust systems of vehicles, heat exchangers, and other high-temperature applications.

Martensitic stainless steel is a high-strength steel often used in applications where wear resistance and hardness are important factors. This type of steel is found in producing cutlery, surgical instruments, and industrial equipment.

Duplex stainless steel combines the benefits of austenitic and ferritic stainless steel. Its high strength and resistance to corrosion make it commonly used in producing chemical processing equipment, oil and gas pipelines, and other high-pressure applications.

Applications of Stainless Steel

Stainless steel is a versatile material used in various industrial and commercial applications. Its resistance to corrosion, durability, and aesthetic appeal make it a popular choice for many projects.

One common application of stainless steel is in producing kitchen appliances and utensils. Its hygienic properties and resistance to corrosion make it ideal for food preparation and storage.

Another common use of stainless steel is in constructing architectural features such as building facades, handrails, and elevator interiors. Its aesthetic appeal and durability make it a popular choice for these projects.

Stainless steel is also commonly used in the production of medical equipment and devices due to its high level of cleanliness and resistance to corrosion. It is often used to produce surgical instruments, dental equipment, and implants.

In the automotive industry, stainless steel products include exhaust systems, mufflers, and other components due to their resistance to heat and corrosion.

Understanding Steel Grade Designations

American Iron and Steel Institute (AISI) Designations

Examples of AISI Designations

The American Iron and Steel Institute (AISI) is a widely recognized organization that establishes standards for the steel industry. AISI designations are commonly used to classify steel based on its chemical composition and mechanical properties.

One example of an AISI designation is , a chromium-molybdenum alloy steel. This steel type is commonly used to produce shafts, gears, and other machine parts that require high strength and wear resistance.

Another AISI designation is 304 stainless steel, a commonly used austenitic stainless steel known for its corrosion resistance. This steel is often used to produce kitchen appliances, piping, and architectural features.

AISI designations are also used to classify carbon steels, such as AISI and AISI . These steels are commonly used to produce machine parts and structural components.

It&#;s important to note that AISI designations are just one way to classify different grades of steel, and other organizations may use different designations or classification systems.

Society of Automotive Engineers (SAE) Designations

Examples of SAE Designations

The Society of Automotive Engineers (SAE) is a professional organization that develops standards for the automotive industry. SAE designations are commonly used to classify based on their chemical composition and mechanical properties.

One example of an SAE designation is , which is low-carbon steel.  Another example of an SAE designation is , a chromium-molybdenum alloy steel.

Stainless steels are also classified using SAE designations, with examples such as SAE 304 and SAE 316. The production of automotive exhaust systems and other high-temperature applications commonly uses these steel types.

Unified Numbering System (UNS) Designations

Examples of UNS Designations

ASTM International and SAE International developed the Unified Numbering System (UNS) to assign a unique identification number to different metals and alloys. Industry professionals commonly use UNS designations to classify different steel grades based on their chemical composition and properties.

One example of a UNS designation is S, a type of austenitic stainless steel. Manufacturers commonly use this to produce chemical processing equipment, medical devices, and other applications.

Another example of a UNS designation is G, commonly used to produce machine parts and tools.

Manufacturers use UNS designations to classify specialty steels, which include N (a nickel-chromium alloy) and K (a low-carbon steel).

Other Designations

Apart from the American Iron and Steel Institute (AISI), Society of Automotive Engineers (SAE), and Unified Numbering System (UNS) designations, various other systems exist to classify steel grades. Some examples include the Japanese Industrial Standards (JIS), the European Standard (EN), and the International Organization for Standardization (ISO).

In Japan, industries commonly use JIS designations, similar to the AISI and SAE designations used in the United States. In Europe, industries use EN designations to identify different steel types, providing a standardized system for classification. Globally, industries use ISO designations to identify different types of metals and alloys, providing a standardized system for classification.

Final Thoughts

Selecting the right steel grade for your project requires consideration of several factors, including the application, required strength and toughness, and corrosion resistance. Finally, understanding the classification systems and designations, such as AISI, SAE, UNS, JIS, EN, and ISO, can help identify the right steel grade.

Frequently Asked Questions

Why Does Steel Grade Matter?

Selecting the appropriate steel grade impacts the performance, durability, and cost of your project. For instance, a high-strength steel may be needed for a bridge, while a more corrosion-resistant grade may be suitable for use in a chemical plant.

How Do I Determine the Right Steel Grade for My Project?

Start by identifying the requirements of your project, such as load-bearing capacity, corrosion resistance, and welding capabilities. Once you have these details, consult various standards like ASTM, AISI, or EN to find a matching steel grade. It&#;s also a good idea to consult experts in the field for additional insights.

Can I Use Multiple Steel Grades in One Project?

Yes, using multiple steel grades is not uncommon, especially for complex structures. Different sections may have varying requirements, making it advisable to use the most suitable steel grade for each specific purpose.

 Are There Any Downsides to Picking a Higher-Grade Steel?

Higher-grade steels generally come at a higher cost and may require specialized handling or fabrication techniques. For instance, some high-grade steels are not as easily weldable as lower grades. So, using a higher-grade steel when unnecessary can lead to unnecessary expenses and complications.

 Is Recycled Steel of Lesser Quality?

Not necessarily. Recycled steel often undergoes rigorous processing to restore its properties, making it comparable to virgin steel in many applications. It&#;s also a more environmentally friendly option.

References

1. American Iron and Steel Institute. (n.d.). Steel Industry Glossary.

   https://www.steel.org/steel-industry/glossary.aspx

2. Engineering Toolbox. (). Steel Grades &#; Properties and Global Standards.

   https://www.engineeringtoolbox.com/steel-grades-d_.html

3. Metal Supermarkets. (). How to Choose the Right Steel Grade.

   https://www.metalsupermarkets.com/how-to-choose-the-right-steel-grade/

4. Society of Automotive Engineers. (n.d.). SAE Steel Grades.

   https://www.sae.org/standards/content/j403_/

5. Unified Numbering System. (n.d.). UNS Numbering System. https://www.unsnumber.com/

 

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