MARKINGS AND COMPOSITION OF STAINLESS STEEL

Stainless Steel Markings and Composition

At Shade Fittings we prefer marine grade stainless steel fittings which work particularly well on shade structures for strength and to withstand the test of time. Differing compositions of stainless steel will result in a product suitable for different applications and having different properties.

Austenitic stainless steel refers to the crystalline structure of stainless steel. Austenite steels make up over 70% of total stainless steel production.  An often used austenite steel is 304 stainless steel also known as 18/8 due to its composition of 18% chromium and 8% nickel. 304 may also be referred to as A2 stainless refers to austenitic steel, cold-worked, with minimum 700N/mm² tensile strength.

A more resistant austenite steel is the marine grade stainless 316 grade, referred to as A4 stainless or marine grade stainless and is used primarily for its increased resistance to corrosion. A typical composition is 18% chromium and 10% nickel. Chromium helps to form a protective oxide layer on the iron and higher chromium levels give longer protection.  A4 Grades of stainless steel are often used in caustic environments where improved resistance to pitting and corrosion is required such as in marine uses. Pitting occurs once chromium levels are exhausted following caustic attack. The effects are usually localised to the exposed areas. The pitting forms as the iron atoms become exposed to oxygen and oxidise to form rust. Rust is not desirable in shade structures. A4-70 indicates austenitic steel, high strength with minimum 700N/mm² tensile strength. 326 grade stainless steel is strong, offers rust protection and has a long life.

Shade structure hardware is typically 316 grade.

Online sources Wikipedia, Institute of Australian Engineers report on fasteners and online graphics. 2016