Stainless steel is specified when it isn’t required and mild steel is used when there may be problems down the road. Understand which makes sense for your job.
The basic difference
Mild steel can be used in almost any application as it is cheap and easy to work with. The only major drawback is that it can rust if left unprotected. Stainless steel, on the other hand, costs around three to four times more and, while it can be more difficult to cut and weld, it does not rust. That is the short version.
When mild steel is sufficient
Mild steel can be used for anything that is structural and is going to be inside a building. Most of the mild steel used in construction is going to be used for frameworks, supports, brackets, and gates (that will be painted). It is even used to create railings as well as do a lot of other construction and fabrication work. It is less damaging to your tools, simpler to weld, and the cost differential means that there is more leverage to work with to surface paint or galvanize the steel if it will be needed.
It is common for farmers to use mild steel for the agricultural construction work that they do. A little bit of surface rust doesn’t usually bother farmers and stream mild steel weathering the elements is perfectly fine.
Mild steel is not suited for use everywhere.
Using mild steel near the sea is not an option. Salt air will coat and eat away at the exposed steel. Marine fabrications seaboards and coastal properties all require a stainless steel construction.
Stainless steel needs to be used in food processing due to the health regulations in place. Food factories, commercial kitchens, breweries, and stainless 304 all cross over. This also rings true for the medical and pharmaceutical industries.
For any construction around water, also use stainless steel. Every coating of mild steel that is used will eventually rust.
Stainless steel comes in different grades.
304 is a standard and is good for most applications. It is not the best but that is why 316 exists. 316 is a bit more expensive but out in the salt water and even in the winter 316 becomes worth it.
Other grades exist, but those cover most of the useful applications.
Working with stainless
Cuts more slowly than mild steel, which means you’ll go through consumables more quickly. Different settings are needed for welding, and it has to be stainless wire or rods. Some fabricators charge more for stainless because it takes longer, and the consumables are more expensive. Fair enough.
Just watch where you’re welding stainless and mild steel. If you’re welding stainless and mild steel together, cover the stainless, or you’ll get spatter on it that rusts. It looks bad and defeats the purpose of the stainless.
Galvanised steels as a middle ground
Sometimes galvanised mild steel is the sensible choice. You get reasonable corrosion resistance for a far lower price than stainless with hot-dip galvanizing. For external steelwork, railings, and outdoor structures, galvanised steel can last 20-30 years or more.
There’s a catch to using galvanized steel, though. You can’t paint and weld it and then galvanize it after. It needs to go to the galvanisers before the last assembly. It requires a little planning but is often the most cost-effective solution.
Making the decision\n\nYou should ask yourself the following: will it rust, does that matter, and can I prevent it another way? If the answer is yes, yes, and no, then you probably need stainless. If it is no, or yes but I can paint/galvanise it, mild steel is fine.\n\nWhen in doubt, just give us a call. We can usually figure out what will do the job based on what other like customers have done. When you have supplied steel for a number of years you pick up a reasonable amount of knowledge on what is durable and what is not.
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