Stainless steel is a term that is thrown around quite a lot these days, but very few people actually understand the commonly used metal. We see it used in a variety of places and objects such as our knives and forks, our taps and on our staircases, pool enclosures and balustrades.
Unknown to many, there is a lot that goes into stainless steel and quite a lot of variables such as quality, grade selection and surface finish. As there seems to be quite a bit of confusion regarding stainless steel, especially for non technical individuals, we’ve run through what stainless steel is made up of, the grade selection process and surface finish selection process below.
Just what is stainless steel?
Stainless steel is an alloy of iron (FE) and chromium (Cr), with a controlled amount of carbon (C). They are a family of steels containing a minimum of 11{19cc6dfde2095820d75378ef5ea2a7429af84c4e3caa3f1811d59515c3bb9677} chromium, whose primary property is that of corrosion resistance. If 11{19cc6dfde2095820d75378ef5ea2a7429af84c4e3caa3f1811d59515c3bb9677} of more chromium is added, a protective, passive film will form. The higher the chromium content, the stronger the passive film, and the more resistant the stainless steel is. Stainless steels rely on a very thin surface passive film for their corrosion resistance. It is vital to maintain and preserve the integrity of the passive film with regular maintenance. Well-maintained stainless steel has an almost endless lifespan.
What is grade selection?
In architectural applications, the austenitic grades of stainless steel are most common with grades 304 and 316 most prevalent. When selecting the grade, the corrosive atmosphere is the most important factor with 316 being selected close to the ocean and aggressive atmospheric conditions close to factories or plants which emit pollutants, and grade 304 for other inland areas. Be certain that your appointed balustrade, staircase or pool enclosure contractor is using the correct grade of stainless steel for your application and insist on material certificates as proof.
How do I select the correct surface finish?
The selection of surface finishes is made by considering the specifier’s requirements, corrosive environment and availability. Plate is available in thicknesses from 4.5mm upwards and is normally finished in a No1 mill finish. Sheet is commonly available in thicknesses ranging from 0.5mm to 3mm and mill finishes include 2B, BA (Bright Annealed) and No4 finish which is a satin-brushed finish.
Aftermarket finishes such as media blasted (glass bead or shot), ring polished or engine turned, maidenhair or pattern rolled are also available. Tube is commonly available in DOM (Direct off Mill), 180 Grit satin circumferentially brushed on polished to 800 grit. When selecting a surface finish, the corrosive conditions must always be taken into consideration. The more extreme the environment, the smoother the surface finish should be, i.e.: external coastal applications require the use of grade 316 mirror polished finishes, whilst indoors, inland, grade 304 with a 180 grit finish is more than adequate.
The coarser the surface finish, the higher the risks of chlorides and salts gathering causing crevice corrosion or pitting. Brushed finishes should be installed vertically as far as possible to allow for natural cleaning by rainwater on external applications. Always ensure that the finish of the stainless steel is uniform and that brushing directions are vertical wherever possible to aid in natural water run-off.
By understanding the basics of stainless steel, you can ensure that you get the most appropriate stainless steel for your project’s needs.