Thursday, February 22, 2007

Chromite - Alloy for a better IRON

Coffee potSteel is a mixture of iron with a small amount of carbon - around 1 percent. Such mixtures of metals are called alloys. Iron, in its pure form, can be heated and then bent, hammered or "wrought" into many forms. Iron objects produced this way are only moderately hard, and they can bend in use. Melting iron and pouring it into molds produces "cast iron" products that are brittle once they cool. But adding carbon to iron changes its microstructure and properties. When this mixture is heated it reaches an extremely ductile stage and can be formed easily. As steel cools it gains strength and rigidity, becoming stronger than iron. This process is called tempering. Different amounts of carbon and the rate of cooling determine the final properties of steel.

Adding chromium to this mixture produces a harder steel by delaying the transformation that occurs as steel is cooled, and steels with 3 to 5 percent chromium were produced beginning in 1865. It was not until the early 1900s that the corrosion resistant-properties of steels containing percentages of chromium higher than 5 percent were noticed. At higher percentages, chromium makes steel highly resistant to many corrosive agents and environments. These "stainless" steels have many applications in materials requiring high strength and resistance to corrosion. Perhaps the most well known uses of stainless steel are in cutlery and cookware. The stamp "18-8" for example indicates that the steel contains 18 percent chromium (for strength) and 8 percent nickel (for sheen). Today the use of chromium in the production of stainless steel accounts for 60 percent of chromium consumption. Stainless steel utensils and cutlery are found in kitchens throughout the United States. Read more...

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