From the Petronas Twin Towers in Kuala Lumpur to the Chrysler Building in New York, stainless steel has been widely used throughout the architectural world. Highly regarded for its durability and extensive resistance to corrosion, stainless steel is being used not only in exterior surfaces, but is also finding its way slowly but steadily into interior applications.
What makes it so steely?
Stainless steel is the name for a group of iron-based alloys containing a minimum of 10.5% chromium. Ordinary carbon steel corrodes and gets converted into rust when exposed to water and air. Adding enough chromium to steel transforms the oxide on the surface. Stainless steel achieves its superior corrosion-resistant properties due to the presence of an invisible layer of chromium-rich oxide that forms on its surface in reaction to the oxygen in the air.
Steeling beauty: The Lloyds Bank building in London.
In order to further improve its corrosion resistance, heat-resisting properties and formability, other alloy elements such as nickel, molybdenum, titanium and copper are added, and the chromium content increased. In addition, non-metallic substances such as carbon and nitrogen are also used.
Which kind of stainless?
Stainless steel has different grades and is available in different finishes. Mill and polished finishes are the most common, but nowadays there are numerous special finishes such as plating, embossing and selective etching that are used for architectural applications.
Stainless steel is also categorized according to its microstructural features:
• Martensitic stainless steels are alloys of chromium and carbon that can be hardened by heat treatment, but are less resistant to corrosion than other categories.
• Austenitic stainless steels, which are tough, are made using nitrogen, nickel and manganese.
• Ferritic stainless steels have a chromium content of less than 30%. They have good ductility and formability, but their toughness can be limited in low temperatures.
• Duplex stainless steels are tensile but less tough than austenitic stainless steels.
• Precipitation hardening stainless steels may be either martensitic or austenitic in the annealed condition.
Where and why should I use it?
In architectural spaces, stainless steel is used for cladding, handrails, door and window fittings, structural sections, lighting columns and masonry supports.
Resistance to corrosion is a given, of course; but additional mechanical or physical properties may also need to be considered to achieve the overall service performance requirements. Other factors to keep in mind are surface finish, magnetic properties, and strength in cryogenic and elevated temperature conditions.
One of the best features of this material, besides low maintenance, is its high recyclability. Stainless steel, particularly the alloys that are high in nickel, can be recycled without losing any of its qualities. In fact, most stainless steel today is made using scrap stainless steel.