What is stainless steel?
Stainless steel (also called inox) is a steel alloy with at least 10.5 per cent chromium. In Dutch it is abbreviated to RVS (roestvast staal). The chromium forms a wafer-thin, invisible layer of chromium oxide on the surface that protects the steel against rust. If the surface is damaged, that layer repairs itself as long as oxygen can reach it. The steel grades are laid down in the European standard EN 10088.
The two grades you meet most often
- Stainless steel 304 (A2, material number 1.4301): about 18 per cent chromium and 8 per cent nickel. Suitable indoors and for normal outdoor use inland: handrails, cooker hoods, screws and bolts.
- Stainless steel 316 (A4, material number 1.4401): also contains about 2 per cent molybdenum, which makes it much more resistant to chlorides. Choose this on the coast, around swimming pools, near road salt and for anything buried in the ground or cast into concrete.
The designations A2 and A4 are mainly seen on fixings such as screws, bolts and cavity wall ties.
Uses in construction
- Cavity wall ties and facade anchors, because they are inaccessible once the wall is built and must not rust through.
- Screws and bolts outdoors, especially in hardwoods such as oak, which contains tannic acids that turn ordinary steel black and attack it.
- Handrails, balustrades, drainage channels and kitchen worktops.
- Reinforcement and anchors in places where corrosion of ordinary reinforcing steel is unacceptable.
Common mistakes
- Mixing ordinary steel and stainless steel. Steel particles from an angle grinder or an ordinary wire brush on stainless steel will rust and leave brown spots. Use separate tools and discs for stainless steel.
- Using 304 by the sea or near a swimming pool. Pitting soon appears. Choose 316.
- Combining stainless steel with aluminium or galvanised steel in a wet environment. Without an insulating washer, galvanic corrosion can occur, attacking the less noble metal.
- Thinking stainless steel never rusts. In closed, oxygen-poor crevices or where there is a lot of chloride, stainless steel can corrode too.
Related terms
- Corrosion
- Corrosion class
- Corten steel
- Structural steel sections
- Aluminium in construction
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