Stainless Steel Grades and Finishes
What is Stainless Steel?
Stainless Steel is an alloy that contains at least 50% iron and 10% chromium. The chromium slows down the corrosion process and plays a key part in defining stainless steel. Generally the higher the chromium percentage the more corrosion resistance.
Stainless Steel alloys are groupled according to the structure of their crystals. Adding nickel creates the structure used in marine applications, called austenitic. Austenitic stainless steels are identified by their '300' series designation.
Grade '304' is a general purpose stainless and is the most common grade of stainless produced. It is made up of at least 18% chromium and 8% nickel offering good corrosion resistance. 304 stainless steel is best suited for indoor use and is inadequate for many marine applications.
Grade '316' offers the best corrosion resistance among standard stainless steel and is often refered to as "marine grade". 316 stainless is made up of at least 16% chromium and 10% nickel. 2% molybdenum is also added to 316 stainless to increase its corrosion resistance. Grade 316 is most suited to outdoor and marine applications.
There are several finishes of stainless available. Some of the most common finishes are:
No. 2B: Mill Finish. Cold rolled, annealed, pickled and passivated then pass-through highly polished rollers.
No. 4: Brushed Finish. Also refered to as Satin. Brushed stainless has a slight directional grain running though it. Common places brushed stainless can be seen are on house hold applicances such as fridges.
No. 8: Mirror Finish. Highly polished to have a mirror shine. Common places this can be seen are on handrails around shopping centres.