Mild steel and stainless steel are the two metals we fabricate, and the choice between them comes down to one thing above all: corrosion resistance. Mild steel is a low-carbon steel that is strong, easy to work and economical, but it rusts when exposed to moisture, so it is protected with primer, paint or galvanising and used mainly for structural frames, beams and columns. Stainless steel contains chromium, which forms a self-protecting layer that resists rust without any coating, so it costs more but suits exposed, external and corrosion-prone work such as balustrades and handrails. For most hidden structure, mild steel with a finish is the sensible choice; where the steel is seen or exposed to the elements, stainless earns its higher price.
Composition and corrosion resistance
The difference starts with what is in the metal. Mild steel is mostly iron with a low carbon content and no significant chromium, which is why it rusts: with nothing to protect it, the iron reacts with oxygen and moisture and corrodes. That is not a flaw, it simply means mild steel needs a protective finish to survive outdoors or in a damp environment.
Stainless steel contains a meaningful amount of chromium, typically at least around 10.5 per cent. The chromium reacts with oxygen to form a thin, invisible passive layer on the surface, and that layer repairs itself if it is scratched. The result is a metal that resists rust without any added coating, which is the whole reason to specify it.
So the headline is straightforward: mild steel relies on a coating to keep corrosion out, while stainless steel resists corrosion by its own composition.
Strength and weldability
On strength, neither metal is simply “stronger” than the other across the board, and strength is rarely the deciding factor between them. Structural mild steel is supplied to graded standards such as S275 and S355, and the engineer designs beams, columns and connections to those grade values, which is why mild steel is the standard for load-bearing steelwork. If you want the detail on those numbers, see our guide to structural steel grades, S275 vs S355.
Both metals weld well in skilled hands, but stainless behaves differently under heat: it conducts heat less readily and can distort or discolour if the process is not controlled, so it asks for the right technique, filler and care to keep its corrosion resistance intact across the weld. Our coded welders work in both metals, which matters because a poor stainless weld can become the one spot that corrodes.
Cost difference
Mild steel is the more economical of the two, and by a clear margin. It is widely stocked, easy to cut and weld, and it is the reason the bulk of structural fabrication is done in mild steel rather than stainless.
Stainless steel costs more, both for the raw material and often for the additional care in fabrication and finishing. The practical takeaway is the same one that runs through good steel buying: use stainless where its corrosion resistance or appearance genuinely earns its keep, and use coated mild steel everywhere else to keep the package economical. We give qualitative guidance like this on every job and put real figures into your written quote.
Finish and appearance
Appearance is the other reason stainless gets specified. Mild steel comes with a plain mill surface and is almost always coated, so its final look is the look of its finish: primer, paint or the matt grey of galvanising. That is perfectly good for structure that will be hidden or painted, but it is a surface that needs maintaining over time.
Stainless steel can be left bare and still look clean and modern, with finishes from a brushed satin to a bright polish. For anything that will be seen and handled, a balustrade, a handrail, a piece of feature metalwork, stainless gives a crisp finish that holds up without repainting, which is a large part of its appeal.
Typical uses: which metal for which job
The split in practice is clear.
Mild steel is the workhorse of structure. Beams, columns, portal and goalpost frames, lintels, brackets and the bulk of fabricated steelwork are made in mild steel and then protected with primer, galvanising or paint. It is strong, economical and ideal wherever the steel is hidden behind cladding or plasterboard, or where a coating will do the job of keeping corrosion out. This is the heart of our steel fabrication work.
Stainless steel comes into its own where corrosion or appearance leads. External and exposed balustrades and handrails, feature work that is meant to be seen, and anything in a corrosion-prone setting such as wash-down areas, coastal or chemically aggressive environments, are natural stainless jobs. Here the self-protecting surface and the clean unpainted finish are exactly what the project needs.
It is worth separating this choice from a different one buyers sometimes blur with it: mild and stainless is about composition and corrosion, whereas the difference between hot rolled and cold rolled steel is about the forming process. They are independent decisions.
How we help you pick
Because mild and stainless are the two metals we fabricate, we are not steering you toward one to suit a stock list, we are matching the metal to the job. We look at where the steel will live, whether it is hidden or on show, whether it faces weather, moisture or chemicals, and how much maintenance you want to sign up for over the years, then we recommend the metal that gives the best result for the budget.
Section sizes for any load-bearing member still come from a structural engineer’s calculation, and removing a load-bearing wall or fitting an RSJ also needs Building Control sign-off; we fabricate to those drawings and can carry out the survey and produce fabrication drawings if you do not have them yet. We design, cut, weld and finish in our own Banbury workshop and erect with our own team, so one fabricator takes the work from drawing to final fix in whichever metal is right. If you are unsure which your job needs, get in touch for a free quote and we will spec it with you.
Frequently asked questions
What is the main difference between mild steel and stainless steel?
The main difference is corrosion resistance, and it comes from chromium. Mild steel is a low-carbon steel with no significant chromium, so it rusts when exposed to moisture and needs a protective finish such as primer, paint or galvanising. Stainless steel contains at least around 10.5 per cent chromium, which forms a self-repairing passive layer that resists rust without any added coating. Mild steel is cheaper and the structural workhorse; stainless costs more and is chosen where corrosion or appearance matters.
Is stainless steel stronger than mild steel?
Not necessarily, and strength is not the reason to choose between them. Some stainless grades are comparable to or harder than mild steel, while structural mild steel graded to S275 or S355 is designed specifically for load-bearing work. For frames, beams and columns the engineer designs to the structural grade, so mild steel is the standard structural choice. Stainless is selected for corrosion resistance and finish rather than for raw strength.
When should I choose stainless steel over mild steel?
Choose stainless steel when the metal is exposed to weather, moisture, chemicals or wash-down, when it will be seen and left unpainted, or when ongoing maintenance needs to be minimal. External balustrades, handrails, feature work and corrosion-prone environments are typical cases. For hidden or coated structure such as beams, columns and frames, mild steel with a protective finish is usually the better-value choice.
Can you fabricate in both mild and stainless steel?
Yes. Mild steel and stainless steel are the two metals we fabricate, and our coded welders work in both. We design, cut, weld and finish in our own Banbury workshop and erect on site with our own team, so a single fabricator takes the job from drawing to final fix. If you are unsure which metal your project needs, send us the details and we will spec it with you.