At Carver Engineering, we’re specialists in large-scale steel fabrication. With projects spanning footbridges, highway infrastructure, marine structures (and more!), we’ve spent decades working alongside some of the world’s most trusted contractors to create steel structures that stand strong in demanding environments. And the type of steel you use plays a huge role in the longevity of your project.
Understanding the differences between steel types is key to building safe, cost-effective and long-lasting structures. We’ve created this go-to guide to help project leads and engineers make informed material decisions. We’ll walk you through the main categories of steel used in fabrication, dive into specialised grades that solve complex engineering problems, and share real-world case studies that show just how important choosing the right type of steel really is.
The 4 primary types of steel
Carbon steel
The vast majority of the steel we work with at Carver is carbon steel. This versatile material is used across a range of industries for things like structural components for buildings and bridges, machinery parts and cutting tools.
Carbon steel is defined by its carbon content:
- Low‑carbon (Mild) Steel (≤ 0.30% C)
Highly ductile and very weldable. A go-to for structural I-beams, brackets, columns and general-purpose steelwork. Ideal for bridges and frame assemblies as it’s easy to form and cost-effective.
- Medium‑carbon Steel (0.31–0.60% C)
Balances strength and ductility. Commonly used for machinery parts and gears. Less common in heavy structural fabrication, more an engineering-grade steel.
- High‑carbon Steel (≥ 0.60% C)
Hard and strong, with trade-offs in ductility. Found in springs, cutting tools, and wear-plates, but not something we work with in our infrastructure projects.
Alloy steel
Not something that’s directly relevant to our standard structural fabrication scope, alloy steel is often blended with other elements like chromium or nickel for strength and toughness. Most of our projects don’t require its complex heat-treatment or higher costs, unless the spec unusually demands it.
Stainless steel
Corrosion-resistant and hygienic. We only use it sparingly – usually 316-grade stainless, for applications like drain covers on footbridges. Beyond that, stainless steel welding and finishing aren’t core to our offering.
Tool steel
Precision-engineered and extremely hard, as its name suggests, this type of steel is used for cutting tools, dies and punches. Again, it’s not a type of steel that’s suited to infrastructure fabrication and we wouldn’t recommend it for that kind of project.
Specialised engineering steel types examples
For certain projects, standard carbon steel doesn’t cut it. We’ve been commissioned to fabricate structures using specialised grades of steel that offer enhanced properties, including…
Abrasion-resistant (AR) steels
High-carbon, quenched and tempered plates designed to resist wear. Ideal for mining liners, chutes, hoppers and aggregate handling systems.
We have experience using:
- AR 450
- Hardox 400 / Hardox 450
These grades are similar in abrasion resistance and toughness and are used in applications where high wear and abrasion resistance are key.
High‑strength structural grades
When structural components must carry higher loads or endure impact, we’ve worked on projects that required the following types of high-strength structural steel:
- S355K2
- S355NL
- S460
These European grades deliver superior strength and toughness compared to mild steel, making them perfect for long-span footbridges or highway beams where weight and rigidity are critical.
How is steel classified?
Steel isn’t defined by one property alone. Multiple classification systems help engineers, designers, and fabricators select the right material for the job:
Composition: This refers to what the steel is made of. Most common classifications include carbon steels, alloy steels, stainless steels, and abrasion-resistant (AR) steels. Each has different properties based on its elemental makeup—such as carbon, manganese, chromium, or nickel.
Finishing method: How the steel is finished after it’s rolled plays a huge role in surface quality and tolerances.
Hot rolled steel is processed at high temperatures, making it easier to shape and form. It’s less precise dimensionally but ideal for structural applications.
Notably, 99.9% of the steel we process is hot rolled, which delivers consistent mechanical properties, structural integrity and cost-effectiveness for large-scale infrastructure fabrication.
Cold rolled or cold finished steel is processed at or near room temperature, offering a smoother finish and tighter dimensional tolerances, which are not typically needed for our heavy fabrication work.
Production method: Steel can be produced via different manufacturing routes:
- Electric arc furnace (EAF) steel is made from recycled scrap and is energy-efficient
- Basic oxygen furnace (BOF) steel is made from raw iron ore
Continuous casting provides consistent, high-quality billets and slabs. This method is standard for structural steels.
Microstructure: The arrangement of steel’s internal structure impacts performance:
- Ferritic steels are magnetic and have good ductility
- Pearlitic steels strike a balance of strength and toughness
- Martensitic steels are extremely hard and used in wear-resistant applications
Strength levels: Steel is categorised by yield and tensile strength, usually denoted by codes like S235, S275, S355 and S460 in the EN system. The higher the number, the greater the strength. For example, S355 is commonly used in bridges because it offers a strong balance between strength and workability.
De-oxidation process:
- Killed steel is fully deoxidized to remove oxygen, preventing gas porosity. It produces a more uniform structure and is common in structural applications.
- Semi-killed steel is partially deoxidized and may still contain small gas pockets, but it’s generally not used in critical load-bearing structures.
Heat treatment condition:
- As-rolled steel is used directly after hot rolling
- Annealed steel is softened for improved machinability
- Tempered steel is heat-treated for enhanced strength and toughness; it’s used in high-performance applications
Quality grade:
- Commercial quality steel is suitable for general purposes
- Pressure vessel quality is built to withstand internal pressure
- Drawing quality steel is designed for deep forming operations
What are the steel grading systems used in the UK & Europe?
Steel grades in the UK and Europe follow well-established naming conventions to ensure standardisation, performance and safety across structural applications. Understanding these systems helps engineers and fabricators match material performance to the demands of their project.
We work with several classification systems:
- BS (British Standard)
- EN / EN‑ISO (European and international norms)
Common structural grade examples
- S235: Minimum yield strength of 235 MPa. Suitable for light structural use but not common in high-load infrastructure.
- S275: 275 MPa yield strength. More strength than S235, but generally superseded in structural work by S355.
- S355: The most widely used structural grade in our line of work. With a 355 MPa minimum yield strength, it strikes the right balance between performance and cost. It’s ideal for footbridges, highway beams and industrial steel frames.
Weathering steel grades
Corten A / Corten B (also known as S355JOW and S355J2W) – designed to form a stable, rust-like appearance after weather exposure. These steels are atmospheric corrosion-resistant and ideal for bridges in exposed environments. We’ve used them successfully in several aesthetic bridge projects.
Key fabrication considerations by types of steel
Carbon (mild) steel
- Cutting: easy to cut, saw, plasma or flame.
- Welding: forgiving and widely supported.
- Cost: most economical.
- Suitability: perfect for I beams, plates, tubulars etc.
Alloy steel
Even though we use it sparingly:
- May need pre‐heat or post‐weld heat treatment.
- Requires accurate welding parameters.
- More complex and costly.
Stainless Steel (316)
- Welding needs cleanliness, purge gas.
- More expensive.
Abrasion‑resistant steel (AR)
- Hardness: significantly higher. Cutting may require specialist saw blades.
- Welding: qualifies for higher consumables, preheat and controlled interpass temps to avoid cracking.
- Ideal where hardness matters, like mining liners and material handling surfaces.
What’s the best type of steel for structural fabrication?
Mild / Carbon steel (S235-S355)
The most commonly used type of steel for infrastructure projects.
- Structures like footbridges, highway beams and columns all rely on this grade.
- Easy fabrication, abundant supply, well-understood engineering properties.
- Acceptable in most non-corrosive environments with protective coatings.
High‑strength steels (S355, S460)
This steel type is used when:
- Span length increases.
- Weight savings are critical.
- Impact tolerance or seismic requirements drive up demands.
AR grades of steel
Abrasion-resistant steel grades are perfect for:
- Mining equipment
- Chute linings
- Port and bulk handling
Weathering (Corten) steel
Ideal for ecologically sensitive projects or aesthetic, low-maintenance structures. The steel rusts uniformly and protects itself (which means there’s no need for paint).
We’ve built footbridges that require zero future painting, keeping maintenance to a minimum without compromising the look or integrity of the structure.
Our projects: real-world applications of specialised steel types
The Port of Tilbury Hopper (AR 450)
In collaboration with the Spencer Group, we supported the delivery of a hopper designed to offload up to 4,000 tonnes of granite stone per hour. The hopper’s interior was lined with AR 450 grade steel, chosen for its exceptional hardness and impact resistance.
We fully fabricated and trial-assembled the hopper at our state-of-the-art Doncaster facility, allowing us to refine the design ahead of on-site installation – making for fast, efficient assembly that reduced disruption and downtime at the port.
Installation of the hopper was completed as planned in December 2023, with all structural components smoothly integrated into the port’s existing conveyor system.
Chapel Street Road Bridge (weathering steel)
As part of a contract with Severfield UK, we worked closely with their project team to deliver a 350 structure in just 8 weeks. Not only was the structure a complex one, it was manufactured in weathering steel.
Weathering steel was chosen as it is durable, needs no maintenance or painting, is cost-effective and is a similar colour and texture to the existing listed structures that surround the bridge.
Start your steel fabrication project with Carver Engineering
Looking for an experienced team of structural steel fabricators who understand the ins and outs of your project requirements? We’ve got decades of experience working with a range of steel types. Get in touch to kick your project off, or take a look at our recent projects to see our capabilities in action.
