Stainless steel is used in a wide variety of structural, engineering and cosmetic applications. The alloy offers excellent durability and low maintenance needs when correctly specified and processed. It also delivers high temperature tolerance, resistance to vibration fatigue and corrosion resistance for piping, valve gear, vessels and structural components. Stainless steels are typically available in many different grades, with each class defining specific properties and environments of use. These are determined by the composition of the alloy, with chromium and nickel lending corrosion resistance whilst other metals enhance hardness, malleability, ductility, strength and tensile and shear strength.
Austenitic stainless steels are the most commonly used grade and offer good corrosion resistance in a wide range of conditions. These have a minimum of 10.5% chromium, which creates a chromium oxide film that is self-healing and effectively protects against oxidation. The alloys include a mix of other metals such as nickel, manganese, molybdenum and nitrogen.
They are easy to work with, and can be formed into shapes with relative ease. They are non-magnetic in the annealed state, but can become slightly magnetic depending on the composition and processing.
304 grade is the most widely used austenitic type, primarily due to its good formability and corrosion resistance. It is generally regarded as a general purpose grade, with applications in industrial and domestic equipment and construction.
316 grade is commonly known as marine grade, but it also finds its way into a wide variety of other applications. It has superior corrosion resistance to 304 grade when exposed to chlorides, particularly in marine environments. This is largely because of the addition of 2% molybdenum.
Duplex stainless steels combine the best of both austenitic and ferritic types, offering improved corrosion resistance than the more pure austenitic grades with better ductility and toughness than the more basic ferritic types. They are also resistant to stress corrosion cracking.
Martensitic stainless steels are stronger and harder than austenitic and ferritic grades but have lower corrosion resistance. They have a higher chromium content, often with nickel and molybdenum additions.
Precipitation hardening stainless steels are extremely tough and durable, with great corrosion resistance, especially to oxidizing acids. They have a high chromium content, and may have additional elements such as titanium and niobium to improve machinability.