Stainless steel is steel which has chromium added to it. This gives the steel corrosion resistance properties, and these properties give the steel certain advantages. There are many different types of steels, and they are used for various applications such as sinks or basins and steel cutlery to name just a few. Steels are graded according to their properties. Some may be very 'hard' and difficult to machine/fabricated (milling & turning etc.) whilst others may be relatively 'soft' and fairly easy to machine. Tough ones will reduce the life of the cutting tool whilst relatively softer steels will machine more easily and the life of the tool will be prolonged. Duplex stainless steels are very resistant to corrosion and also have a high resistance to intergranular corrosion. They exhibit very high resistance even in sulphide and chloride environments, and have a high resistance to stress corrosion cracking. Super duplex grades exhibit even higher resistance to corrosion. Due to the high content of chromium in them, temperatures of over 300 degrees centigrade can cause embrittlement, however at lower temperatures the steel has better ductility than ferritic and martensitic grades. Duplex grades of stainless steels can be readily used down to at least -50 degrees centigrade. When machining or fabricating any types of steels, only tools dedicated to stainless materials should be used. Work and tooling surfaces should be clean to avoid any cross contamination by easily corroded metals that may discolour the surface of the machined product. They do not harden if heat treated but it can be work hardened. Annealing (a softening up process) may be carried out by rapid cooling after heating to about 1100 degrees centigrade. Due to the properties of duplex steels machining can be quite difficult, but the machining may be enhanced by using the following procedures; o Dull edges cause work hardening so keep cutting tools sharp o Light cuts should be taken but deep enough to prevent skimming the surface o Use adequate amounts of coolants and cutting fluids Some typical applications for duplex steels can include chemical processing, marine environments, oil and gas refining and pulp and paper manufacturing.
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