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Tough, resistant and tenacious

12/05/2006

These are terms that could be used to describe the "hard man" in an action movie, but they appear here as some of the properties of the material most commonly used in building the structure of the Gran Telescopio CANARIAS: steel.

Steel is an alloy, a mixture of metals that normally contains iron and carbon. Other materials - known as alloying agents - can also be added to produce steels with different properties for different end uses.

This means that there are different types of steel. For example, the steel used in skates contains manganese, silicon and copper, whilst cars are made with an alloy containing carbon, manganese, silicon and copper. Space capsules, artificial bones and aircraft are made of stainless steel, which is produced by adding chrome and nickel. These are just a few of the uses of a material that is almost everywhere.

Steel is typically produced in blast furnaces, immense "pots" in which iron, coke and limestone are mixed. When coke - a fuel produced from coal - is burnt in the blast furnace, it heats up and gives off carbon monoxide. Limestone is used as a fluxing agent and it also gives off carbon monoxide, which combines with the iron oxide and reduces it to metallic iron. The mixture heats up progressively and the metals melt when it reaches a temperature of 1,400 ºC.

This burning compound is called "cast iron" and one of its alloying agents is oxygen. When large quantities of oxygen are injected into the liquid metal at high speed a chain reaction results, burning out impurities and turning the cast iron into steel.

If any impurities remain on the surface, they are then removed; once the steel is considered "ready" a mechanism is opened allowing it to fall into the receptacles that will shape it.

Next, heat treatments are applied to the solid steel to give it different qualities, like machinability (the ease with which it can be shaped when solid), toughness, resistance to wear and tenacity (this means that it is resistant to, or able to absorb, energy. Without this property the steel would fissure).

The various types of steel are grouped into five classes: carbon steel, alloy steel, high strength low alloy steel, stainless steel and tool stell. The GTC's mechanical structure is made of carbon steel, one of the most common: 90 percent of all steel is of this type: A type that is tough, resistant and tenacious.

Natalia R. Zelman

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