Mild Steel vs Stainless Steel: Key Differences

The main difference between mild steel and stainless steel is chromium. Stainless steel contains at least 10.5% chromium, which forms a thin, self-healing oxide layer that keeps it from rusting. Mild steel is plain low-carbon steel: cheaper, easier to weld and machine, and strongly magnetic, but it rusts unless it's coated. In strength they are closer than most people expect. Annealed 304 stainless has a similar yield strength to mild steel and a higher tensile strength.

Choose mild steel (MS) when cost matters most and the part will be painted, powder coated, or kept dry. Choose stainless steel (SS) when the part will be wet, outdoors, in contact with food, or left bare.

Mild Steel vs Stainless Steel at a Glance

Strength values are specification minimums or typical ranges. Material from a given mill run usually tests higher.

Composition and Properties

Mild steel, also known as low-carbon steel, is mostly iron with a small amount of carbon, typically less than 0.3%. That low carbon content gives mild steel its combination of strength and formability. At Fabworks, we offer two types of mild steel:

1. 1008 cold-rolled steel: known for its smooth surface finish and tight thickness tolerances.
2. A36 hot-rolled pickled and oiled (HRPO) steel: a balance of strength and workability.

We also stock G90 galvanized steel, which is carbon steel with a zinc coating for corrosion protection.

Stainless steel contains a minimum of 10.5% chromium, which forms a protective layer of chromium oxide on the surface. That layer gives stainless steel its corrosion resistance. At Fabworks, we provide 304-2B stainless steel, the most widely used grade. The 2B is a smooth, matte mill finish. Our comprehensive guide to stainless steel covers the other grades and families.

Corrosion Resistance

Corrosion resistance is the biggest difference between mild steel and stainless steel. Mild steel rusts when exposed to moisture and air, so it needs a protective coating or regular maintenance. Bare mild steel parts can show surface rust within days in a humid shop.

Stainless steel's chromium forms a self-healing protective layer that makes it highly resistant to corrosion and rust. If the surface is scratched, the layer re-forms. That makes stainless steel an excellent choice for harsh environments or where hygiene is crucial, such as food processing equipment and outdoor installations. It isn't completely rustproof: chlorides like salt spray and pool chemicals can pit 304, and contamination from carbon steel tools can leave rust spots on the surface.

To protect mild steel, use powder coating, paint, or G90 galvanized sheet. Our guide to preventing rust on laser cut parts compares the options.

Is Stainless Steel Stronger Than Mild Steel?

It depends on what you mean by stronger.

• Yield strength (when a part starts to bend permanently) is similar. Annealed 304 has a minimum yield of 30 ksi, A36 has a minimum of 36 ksi, and 1008 cold-rolled sheet is typically around 20–40 ksi.
• Tensile strength (the most stress before it breaks) is higher for stainless. 304 has a minimum of 75 ksi, compared with 58–80 ksi for A36 and around 40–50 ksi for 1008.
• Toughness and ductility favor stainless. 304 stretches 40% or more before breaking and stays tough at low temperatures.
• Hardness after forming goes up quickly in stainless, because it work-hardens. That's one reason it takes more force to bend and machine.
• Heat is where stainless pulls ahead. It keeps its strength and resists scaling at higher temperatures than mild steel.

For most sheet metal brackets and enclosures, the two are interchangeable on strength. The choice usually comes down to corrosion, cost, and fabrication. For definitions of these terms, see yield strength vs tensile strength.

Cost Considerations

Mild steel is less expensive than stainless steel, and it's the most cost-effective material we stock. That makes it the default for large projects and for parts where corrosion resistance isn't a primary concern. Consider long-term costs too, including coating, maintenance, and possible replacement.

Stainless steel costs more up front but often proves cost-effective in the long run thanks to its longevity and low maintenance, especially in challenging environments. It also skips the coating step entirely.

Fabrication and Welding

Both mild steel and stainless steel can be fabricated and welded, but there are differences to plan for.

• Welding: Mild steel is easier to weld. Stainless takes more skill. It conducts heat about a third as well as mild steel and expands more when heated, so heat stays concentrated near the weld and the part is more likely to warp. With proper technique, stainless welds are strong and corrosion resistant. Fabworks welds single bent parts in both, and the sheet metal welding design guide covers corner setups and weld types.
• Bending: Both bend well. Stainless needs more press force and springs back more, so it's overbent to hit the finished angle. Our sheet metal bending service handles both, along with G90 galvanized.
• Machining, tapping, and drilling: Mild steel cuts easily. Stainless work-hardens, so it needs sharp tools and steady feeds.
• Finishing: Mild steel parts need a coating for most uses. Stainless steel is usually left bare.

At Fabworks, our laser cutting service cuts both mild steel and stainless steel to a standard tolerance of +/-0.005", regardless of the material you choose.

Applications

Mild steel is used for:

• Construction and structural components
• Automotive parts and brackets
• General machinery and equipment
• Furniture and fixtures
• Enclosures and parts that will be powder coated or painted
• Magnetic mounts and parts that need to be magnetic

Stainless steel is used for:

• Food processing equipment
• Medical devices
• Marine applications
• Architectural features
• Chemical processing equipment
• Outdoor and washdown parts left uncoated

How to Tell Mild Steel From Stainless Steel

• Magnet test: Mild steel grabs a magnet hard. 304 stainless is essentially non-magnetic, though it can be slightly magnetic where it has been bent or cold worked.
• Appearance: Stainless keeps a clean silver or matte gray finish. Bare mild steel is darker and shows rust spots once it's been exposed to moisture.
• Labeling: Sheet and plate from a mill is usually marked with the grade. When in doubt, ask for a mill certificate.

How to Choose the Right Material for Your Project

Choosing between mild steel and stainless steel depends on your project's requirements, budget, and environment. Ask yourself:

1. Will the part be exposed to moisture, salt, chemicals, or washdowns?
2. Will it be painted or powder coated anyway?
3. Is strength, weight, or stiffness the main concern?
4. What is your budget for both initial cost and long-term maintenance?
5. Are there industry regulations or standards to meet, such as food contact?

If the answer to the first question is yes and the part won't be coated, choose stainless steel. If the part will be coated or stays indoors and dry, mild steel will usually do the same job for less. If you're also weighing aluminum, see aluminum vs steel.

Frequently Asked Questions

What is the difference between MS and SS?

MS is mild steel, a low-carbon steel that's cheap, easy to weld, and rusts without a coating. SS is stainless steel, which adds at least 10.5% chromium to resist rust. Stainless costs more and is harder to weld and machine.

Is mild steel stronger than stainless steel?

Not usually. Mild steel and annealed 304 stainless have similar yield strengths, and stainless has a higher tensile strength. A36 has a slightly higher minimum yield than annealed 304, while 304 is tougher and more ductile.

Does mild steel rust easily?

Yes. Bare mild steel rusts quickly in moist air, often within days in humid conditions. Powder coating, paint, or galvanizing prevents it.

Is stainless steel mild steel?

No. Both are mostly iron, but stainless steel contains at least 10.5% chromium, and 304 adds about 8% nickel. Mild steel has neither.

Can you weld mild steel to stainless steel?

Yes, with a filler made for dissimilar joints, commonly 309 stainless. The mild steel side will still rust unless it's protected.

Which is cheaper, mild steel or stainless steel?

Mild steel. Stainless steel costs more per pound and takes more time to weld and machine, though it doesn't need a coating.

Order Mild Steel and Stainless Steel Parts

Fabworks laser cuts and bends steel and stainless steel sheet, along with aluminum, and can powder coat, tap, and insert hardware in the same order. Upload a STEP or DXF file to get an instant quote in either material and compare prices side by side.