The "Workhorse" Metal Mild steel is the go-to material for everything from DIY garden gates to massive industrial skyscrapers. It’s cheap, incredibly easy to weld and drill, and highly recyclable. While it can rust if left bare, a quick coat of paint or galvanisation makes it nearly indestructible.
What’s in this guide
What exactly is mild steel?
Think of mild steel as the "all-rounder" of the metal world. Technically known as low-carbon steel, it contains about 0.16% to 0.29% carbon. This specific balance makes it soft enough to be shaped but strong enough to support a building.
Quick Facts:
- Magnetic? Yes (it’s ferromagnetic).
- Recyclable? 100%.
- Melting Point: A blistering 1450°C to 1520°C.
- Flexibility: Highly ductile (it bends before it breaks).
Mild steel is a ferrous metal made from iron and carbon. It is a low-cost material with properties suitable for most general engineering applications. Low-carbon mild steel has good magnetic properties due to its high iron content; it is therefore defined as being ‘ferromagnetic’.
Mild steel has a relatively high melting point of between 1450°C and 1520°C. Steels with a higher carbon content than mild steel have a lower melting temperature. This high melting temperature means that mild steel is more ductile when heated, making it particularly suitable for forging, cutting, drilling, and welding, and easy to fabricate.
Mild steel is not suitable for through hardening. It can be case-hardened by heating and adding a chemically reactive carbon source; the subsequent quench cycle will harden the surface layer. This outer layer, ‘the case’, will become hardened.
Mild steel, including galvanised products, is recyclable.
Mild steel does not have high corrosion resistance in its untreated form; however, corrosion resistance can be greatly improved by applying an appropriate surface protection product to the exposed parts of any project. There is a wide range of red oxide primers, metal paint, metal spray paint and zinc treatments available to enhance the appearance of mild steel and to protect it from rust and corrosion.
Mild steel can be cleaned by ‘pickling’. This is a chemical surface treatment that removes stains, contaminants, rust and scale. Surface rust can also be removed by mechanical grinding and then treated with a surface protector, such as red oxide primer, zinc primer, or metal paints and sprays.
Mild steel is graded according to its chemical composition, how it is produced, and its properties, so you can easily choose the best product for your project.
Can I weld it? (The short answer: yes, easily!)
If you are new to welding, mild steel is your best friend. It is much more forgiving than stainless steel or aluminium.
Pro-Tip: If you're welding mild steel to other metals, use this quick compatibility cheat sheet:
| Welding mild steel to | Use filler wire type |
|---|---|
| Itself | Rutile, 6013, lo hy, 7018 , 7024, sifsteel 11 |
| Corten | Lo hy, rutile, 6013, 7018, 7024, sifsteel 11 |
| Galvanised mild steel | Sifredicote 1, 6013, 7018, rutile, lo hy, 7024, sifsteel 11 |
| Brass | Sifbronze 8 |
| Copper | Sifbronze 8 |
| Stainless steel | Sifbronze 8, sifsteel 312 |
| Bronze | Sifbronze 8 |
| Cast iron | Sifbronze 2 |
| Aluminium | Pre-coat mild steel with sif silver solder 40 or 43, then weld using sifalumin 15 |
| Weldability | Value |
|---|---|
| Gas | Excellent |
| Arc | Excellent |
| Resistance | Very good |
| Brazability | Very good |
Will it rust? How to protect your projects
Because mild steel has high iron content, it will rust if exposed to rain or humidity. However, you have three easy ways to stop it:
- Painting: Start with a Red Oxide Primer followed by a metal-specific topcoat.
- Galvanising: This adds a protective layer of zinc. (metals4U stocks BS EN ISO 1461 standard).
- Pickling: A chemical bath that removes existing scale and rust to prep the surface for coating.
Standard strength specs
If you’re doing the math for a structural project, keep these average values in mind:
| Property | Average Value |
|---|---|
| Yield Strength | 275 - 400 N/mm² |
| Tensile Strength | 370 - 560 N/mm² |
| Thermal Conductivity | 50 W/m°k |
Common shapes and sizes
You don’t have to buy a massive slab and cut it down. Mild steel comes pre-formed in shapes that fit your project:
- Angle Iron: Great for frames and brackets.
- Box Section: Lightweight but strong for furniture or gates.
- RSJ (I-Beams): The heavy hitters for supporting walls and roofs.
- Sheet/Plate: For flooring, splashbacks, or custom cut-outs.
We supply mild steel in sheet and a wide range of profiles such as:
Choosing the right mild steel grade: which one do you need?
Not all mild steel is created equal. Here is a simplified breakdown of the most common grades:
- S275JR: The "Everyday Hero." Used for most general engineering and construction.
- EN3B: The "Machinist’s Choice." Better for light engineering where you need a cleaner finish.
- EN1A: The "Speed Demon." Best for high-speed turning on lathes (Leaded version is even easier to cut).
- Corten: The "Designer’s Choice." Naturally develops a "rusty" protective layer; popular for garden art and architecture.
- Rebar (500B): The "Muscle." Specifically designed to strengthen concrete.
Need a custom length? Remember, metals4U offers free custom cutting with no limits!
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