About Stainless Steel

About Stainless Steel Although commonly referred to as one material, stainless steels are in fact a group of fifty or more iron-based alloys each of which contain at least 10.5% chromium. Each of these stainless steels has a number of characteristics in common, most importantly of which is that they are NOT stainless.

There are a number of methods of categorizing stainless steels such as the Unified Numbering System developed jointly by the American Society for Testing and Materials (ASTM) and the Society of Automotive Engineers (SAE) and which applies to commercial metals and alloys. However, in the construction industry, the most commonly seen designation is the numbering system (200, 300 and 400) developed by the American Iron and Steel Institute (AISI).

The term austenitic is used to describe stainless steels containing chromium, nickel and manganese (200 Series) and chromium and nickel (300 Series). The terms ferritic (not hardenable by heat treatment] and martensitic (hardenable by heat treatment) are used to describe straight chromium stainless steels (400 Series).

There are variations and combinations of each of these. However, because of their appearance, good resistance to corrosion and their ability to be worked in a variety of manners, the most commonly used stainless steel in the swimming pool industry is the 300 Series.

There are many divisions within the 300 Series but the most widely used is the 304 stainless steel. It is also frequently referred to as 18-8 stainless reflecting its 18% chromium and 8% nickel composition. There are also variations of the 304 type (such as 304L (low carbon) and 304N (nitrogen) for special applications.