Understanding steel grades

Steel is one of the most commonly used metals in  engineering, construction, and manufacturing sectors. Its versatility and strength are influenced mainly by its grade, an indication of its composition, properties, and suitable applications. To achieve the required strength, durability, safety, and cost-effectiveness of a project, you must select the appropriate steel grade. This article examines the classification of steel grades, their properties, and how to choose a grade that meets specific project requirements.

Introduction to steel grades and classification

Steel grades are used to define the makeup, strength, and functional performance of different steel materials. The grade classifications enable manufacturers, engineers, and buyers to choose the right steel for the job.

Each grade of steel represents the specific combination of elements added during manufacture, these include manganese, carbon,  nickel, and chromium, as well as other trace elements.The balance of these elements affects strength, ductility, corrosion resistance, workability, and many other properties. A steel classification chart is often used to compare grades across different standards, such as the British Standard (BS), European Norm (EN), American Iron and Steel Institute (AISI), and others.

By standardising steel grades, industries can ensure consistent quality and performance across projects, making it easier to source, use, and trust the material.

Types of steel material - Carbon, alloy, stainless, and tool steel

There are four main types of steel, and each type has its own characteristics depending on its composition:

1. Carbon Steel

Carbon steel is made up of iron and carbon as its primary elements, with minimal alloying additions. Carbon steel is  sub-categorised into:

• Low carbon steel (mild steel) – ductile and easy to work with.

• Medium carbon steel – stronger and harder, often used in automotive parts.

• High carbon steel – very strong, but less ductile, commonly used in tools and springs.

Explore our Mild steel and Galvanised steel ranges for popular carbon steel products.

2. Alloy Steel

Alloy steel contains added elements such as chromium, molybdenum, nickel, or vanadium. Including these additional elements helps to improve the steel's strength, corrosion resistance, and heat resistance. This is why these alloys are a common choice of material in aerospace, automotive, defence, and structural applications.

3. Stainless Steel

Stainless steel is a corrosion-resistant alloy due to it containing at least 10.5% chromium.. Its clean appearance and durability make it a popular choice for use in medical devices, food production, and architecture. You can browse our full Stainless steel range online.

4. Tool Steel

Tool steel is specifically designed for manufacturing tools due to its  high hardness rating and superb abrasion resistance; these properties enable it to withstand high temperatures and pressures. Tool steels are ideal for applications such as the manufacture of cutting and machining tools, and moulds and dies.

Each type of steel material has specific steel grades that dictate its exact performance characteristics based on its steel composition.

Understanding stainless steel grades

Stainless steel grades indicate the specific alloying elements and structural composition of stainless steel. Stainless steel is manufactured by adding chromium at a minimum of 10.5% by weight which gives it its high resistance to corrosion and rust. These grades are classified into several series, with the most common being:

• 200 series: A high manganese grade, also often referred to as CrMn, or chrome manganese grade. The addition of manganese stabilises the austenitic structure. This grade is a more budget friendly option than the 300 series and has poorer corrosion resistance. 300 series: 304 and 316 are austenitic stainless steels known for excellent corrosion resistance and formability. 300 series uses nickel to stabilise the austenitic structure rather than the manganese used in the 200 series.

• 400 series: Ferritic and martensitic stainless steels like 410 and 430. have a higher carbon content which provides a higher strength and wear resistant metal, but with a lower corrosion resistance than the 300 series.

The 304 grade is the most commonly used due to its balance of cost, corrosion resistance, and workability. For marine or chemical environments, the 316 grade is preferred due to its added molybdenum content, which enhances corrosion resistance.

When choosing among grades of stainless steel, consider both environmental factors and mechanical performance. For more information, visit our in-depth guide on stainless steel and its various grades.

Steel grading systems and standards

Steel is graded according to regional and international standards to ensure consistency and performance:

• AISI/SAE (North America): Uses a four-digit code, e.g., 1018 for low carbon steel.

• EN (European Norm): Replaces older national standards (e.g., BS) with codes like S355 or 1.4301.

• BS (British Standards): Still used in some sectors, but increasingly harmonised with EN.

• ASTM: Defines material specifications and testing standards, widely used in structural and manufacturing industries.

A steel grades chart can help compare equivalent grades across these systems. This is especially important when sourcing steel internationally or working on multinational projects.

Factors influencing steel grade selection

When selecting a steel grade, there are several factors that should be considered to make any project a success.

• Application: Load-bearing parts may require higher-strength steel, while decorative components may prioritise the use of a steel grade with a more aesthetic appearance or higher  corrosion resistance.

• Environment: Exposure to moisture, chemicals, or high temperatures will impact grade choice.

• Machinability and weldability: Some grades are more appropriate  to cut, weld, or form than others.

• Cost and availability: Higher alloy grades tend to be more expensive, so budget constraints can influence the selection.

The right grade of steel ensures reliability, efficiency, and safety while meeting the practical demands of your project.

Comparing common steel grades - Properties and applications

The table below highlights some widely used steel grades, along with their typical characteristics and applications: To understand more about mild steels and their properties, refer to our in-depth blog on mild steel, which explains commonly used grades and applications.