Stainless Steel Me

Nickel’s resistance to corrosion is one of its most valuable properties. The estimated annual cost of corrosion in the U.S.A. alone is $300 billion — equivalent to 4% of gross national product. Far and away the largest use of nickel alloys is in the area of corrosion prevention.

Two-thirds of all nickel produced goes into stainless steel, to promote a stable, ductile, austenitic structure as well as contribute to corrosion resistance. The most common austenitic grades used are Type 304, which contains 18% chromium and 8% nickel, and the more corrosion-resistant Type 316 (18% Cr, 10% Ni, 2% Mo). The combination of corrosion resistance, clean ability, ease of fabrication, appearance and availability means that these steels are the materials of choice for many hygienic applications in food processing, beverage production and medicine. They are also increasingly popular among manufacturers of domestic kitchen equipment and utensils. These stainless steels are commonly found in many architectural applications (Figure 2) and are widely used in the transport, chemical processing and energy industries. The stability and toughness of the austenitic structure also allows these stainless steels to be used for cryogenic applications. Stainless steels are highly cost-effective when all costs, including maintenance and repair, are taken into consideration over the whole life of a product. This is partly why the use of stainless steels continues to grow. For example, some highway authorities are now considering selective use of stainless steel reinforcing bars in concrete bridges to avoid the corrosion problems caused by de-icing salt.

Further additions of alloying elements to the standard austenitic stainless steels, particularly nickel, chromium, molybdenum and nitrogen, result in a series of steel grades with higher resistance to general corrosion, as well as pitting, crevice and stress corrosion. These grades are suitable for the more aggressive environments encountered in certain marine applications, and in the oil, gas, power and chemical industries. Increasingly, these industries are also using duplex stainless steels, (which typically contain 5-7% nickel) and in which the mixed ferrite/austenite structure provides a combination of high strength and resistance to corrosion (particularly stress corrosion).