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Material selection for a mechanical or structural application requires some important considerations, including how easily the material can be shaped into a finished part and how its properties can be either intentionally or inadvertently altered in the process.

Depending on the end of use, metals can be simply cast into the finished part or cast into an intermediate form, such as an ingot, then worked, wrought by rolling, or processed by forging, extruding or another deformation process. Although the same operations are used with ferrous as well as non-ferrous metals and alloys, the reaction of nonferrous metals to these forming processes is often more severe. Consequently, properties may differ considerably between the cast and wrought forms of the same metal or alloy. To shape both non-ferrous and ferrous metals, designers use processes that range from casting and sintered powder metallurgy (P/M) to hot and cold working. Each forming method imparts unique physical and mechanical characteristics to the final component. As the more abundant of all commercial metals, alloys of iron and steel continue to cover a broad range of structural applications. Iron ore is readily available, constituting about 5% of the earth's crust and is easy to convert to a useful form. Iron s obtained by fusing the ore to drive off oxygen, sulfur and other impurities. The ore is melted in a furnace in direct contact with the fuel using limestone as a flux. The limestone combines with impurities and forms a slag, which is easily removed. Adding carbon in small amounts reduces the melting point of iron. All commersial forms of iron and steel contain carbon, which is an integral part of the metallurgy of iron and steel.

Manipulation of atom-to-atom relationships between iron, carbon and various alloying elements establishes the specific properties of ferrous metals. As atoms transform from one specific arrangement, or crystallic lattice, to another, strength, toughness, impact resistance, hardness, ductility and other properties are altered.


Idemat 2003