Can a steel staircase be used outdoors?

Yes. A straight steel staircase works very well as an outdoor access to an upper floor, and for rain and frost we make it with a paint system over a zinc primer and grating treads that let water and snow fall through. The treads have a slip-resistant surface, and you can order the railing hot-dip galvanised. Mention in your quotation request that the stairs will be outdoors and the quotation states the finish. Read the exterior stair and railing guide.