Stainless Steel
Stainless steel is usually defined as an iron-chromium alloy containing at least of 11% chromium. Today, stainless steels often contain elements such as manganese, nickel, molybdenum, titanium and niobium. They are the most widely used corrosion resistant engineering materials and find applications in aggressive environments and at elevated temperatures. They are normally categorised in four main groups, and each group is further sub-divided into specific alloys. The main groups are ferritic, martensitic, austenitic, and duplex. Duplex may be divided into duplex and super-duplex. Austenitic stainless steels are the most widely used group, accounting for around 70% of all stainless steels fabricated. They are also the most expensive as they contain nickel. They are used in applications such as chemical plants, pharmaceuticals, food and brewing, and liquid gas storage vessels. The weldability of these grades is extremely good. Ferritic stainless steels are not as corrosion resistant or as weldable as austenitic stainless steels. They are cheaper, have high strength and good high temperature properties. They are used for exhausts and silencers, catalytic converters, air ducting systems, and storage hoppers. Martensitic stainless steels are high strength and difficult to weld but are the least costly of the stainless steels. They are used for coach and vehicle chassis, railway wagons, mineral handling equipment and paper and pulping equipment. Duplex stainless steels combine the high strength of ferritic steels and the corrosion resistance of austenitic steels. They find use in corrosive environments such as offshore and petrochemical plants, where the integrity of the welded material is critical. They do require careful control of welding parameters. All arc welding and power beam processes can be used to weld stainless steels, but care must be taken with some grades to ensure sound welds retaining good corrosion properties. Gas welding may be used but is used less frequently now than in the past.
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