10 Jul Steel – Mild, Galvanised, Stainless or Weathering?
Steel is an excellent material for signage & wayfinding structures, but it can be quite confusing deciding what to specify. Here’s a brief guide that might help you…
What is steel?
Steel is made from iron ore, which is smelted in blast furnaces to remove impurities and to add carbon. Other metals can be added to give it extra qualities as we will see.
This is most common type of steel with 0.05%-0.25% carbon by weight. It is economically priced and very versatile, being ductile, machineable and weldable. It can be Mild steel corrodes so external use requires a surface coating such as powder-coating, wet-spraying or galvanising for protection.
This is a mild steel which has been hot dipped in a zinc coating. The mottled silver finish is highly corrosion resistant although being a surface treatment it can eventually corrode.
Stainless steel (304/316)
Stainless steel has 15%-30% alloy by weight and has superior corrosion resistance.
There are two grades commonly used – 304 which contains 18% chromium and 8% nickel, and 316 which contain 16% chromium, 10% nickel and 2% molybdenum. The molybdenum gives added resistance to harsh environments and is especially suited to marine environments with a higher salt content.
This is sometimes known by a common brand name Cor-Ten. Weathering steel contains chromium, copper and nickel which corrode quickly to for a protective, maintenance free patina. This process can start in as little as 2 weeks and the patina will continue to darken over the years.
Weathering steel does require a wet/dry cycle for the patina to form so is not suitable for continually wet areas.
Staining can be a problem, especially onto porous stone facades or paving. This can be mitigated by using stand-offs to keep run-off away from the building and planted areas/or water features below.
Look at our Oldknow’s Legacy case study to see weathering steel in action! Click here to view full details.
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