Material Science

• Chemical Properties - are characteristics of the chemical composition of metals and their chemical reactions to other metals.
• Physical Properties – are characteristics of metals when they are not being acted upon by outside forces. Color, density, weight, and electrical and heat conductivity are physical properties.
• Mechanical Properties – are characteristics exhibited by metals when outside forces are applied to them.
• Hardness – means resistance to penetration by other materials. Hardness may be increased by cold working such as bending, hammering, or rolling at room temperature. Hardness may also be increased or decreased by treating the metal in different way with heat. Ex. Steel is much harder than lead or pure aluminum.
• Hardenability – is the property of a metal to harden uniformly and completely to its center. A metal with poor hardenability will harden on its surface only, while its center will be left relatively soft.
• Brittleness – refers to how easily a metal will break with little or no bending. Hardened tool steels and gray cast iron are brittle compared to unhardened steels.
• Ductility - is the property of metal to be bent, rolled, or otherwise changed in shape without breaking. Metal high in ductility include soft steel, copper, and aluminum. They can be drawn into fine wire and rolled into thin sheets without breaking.
• Malleability – permits a metal to be hammered or rolled into shape without breaking. refers to its ability to withstand sudden shock without breaking or fracturing. A metal high in toughness will usually bend or deform before fracturing. Special kind of heat treatment, called tempering, reduces hardness and increases toughness.
• Machinability – refers to the ease with which metals may be machined, or cut by a machine tool.
• AISI - stands for the American Iron and Steel Institute, a trade association of companies that sell or work with iron and steel. The AISI develops and sets ratings or standards for making, selling, and using different kinds of iron and steel.
• Fusibility - enables a metals, when in its liquid state, to join easily with another liquid metal. Metals high in fusibility are usually high in weldability.
• Strength - is the resistance of a metal to deformation. Tensile strength is resistance to being pulled apart. Compressive strength is resistance to being squeezed together. Shear strength is resistance to cutting or slicing forces. Torsional strength is resistance to twisting forces.
• Elasticity – is the ability of material to return to its original size and shape after the external force causing a change in shape has been removed. Elastic limit is the maximum load per square inch or square centimeter that can be applied to a material without forcing it to change shape permanently.

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• Fatigue is the characteristic that causes a metal to fracture (break) under a repeated load that is well below the tensile strength of the metal. Parts subjected to repeated bending or vibration sometimes break because of fatigue
• A pure metal is a single chemical element that is not combined with any other chemical element. It is generally too soft, low in strength, or low in some other desired property to be used in many commercial applications. Its use in the pure state is limited to laboratory experiments and a few construction applications.
• Pure metal or metal may be further classified as either ferrous or nonferrous metal. The word "ferrous" is derived from the Latin word "ferrum", which means iron. Thus, all steels are called ferrous metals.
• Examples of nonferrous metals are aluminum, copper, lead, tin, and zinc.
• Alloys are melting and mixing one or more other pure metals with it can change the properties of a pure metal.
• Iron - the most common and most useful metal; about 5% of the earth crust (by weight) is iron; the purest iron comes from the sky in the form of meteors. Pure iron does not rust in water; iron rusts because it contains impurities. It is seldom used in industry because it is too soft for most work. It is so soft that it can be scratched with fingernail.
• Iron is used in three forms, such as: Cast iron, Wrought iron, and Steel.
• Iron Ore - is not pure as it comes from mines. Low-grade ores, such as taconite (consisting of two iron compounds plus quartz) are enriched in processing plants near the mines.
• Pig Iron - is very hard and brittle; it is used in making cast iron, wrought iron, and steel. It contains about 93 % pure iron (by weight) and from 3% to 5% carbon; the remainder is silicon, sulfur, phosphorous, and manganese.
• Silicon is a chemical element found in clays, sand, and rocks; it gives hardness to iron.
• Sulfur is a yellow, flammable nonmetal; excess sulfur and phosphorous weaken iron and steel. Too much sulfur makes these metals weak and brittle, causing cracks.
• Phosphorous is a poisonous, active nonmetal; it causes brittleness and coarse grain in iron and steel.
• Manganese is a grayish white metal, hard and brittle; it resembles iron but not magnetic; it is used in making steel.
• Cast Iron - is a pig iron that has been re-melted and poured into mold; the iron cools in the shape of a useful machine part or article. An object made this way is called casting.
• Gray Cast Iron - is the cheapest kind of metal, it is used to make large pipes, steam radiators, water hydrants, frames for machines, and other machine parts; it is used for products or parts that must be large and heavy but in which impact strength is not very important. Gray cast iron can be machined easily. Gray cast iron is made by slowly cooling the molten metal. One basic type usually contains from 17% to 4.5 5 carbon. It melts at about 2200 °F.
• White Cast Iron - is so named because of its white, crystalline color at the fracture when broken; it is made by rapidly cooling the molten pig iron; the carbon content usually ranges from about 2% to 3.5%. Most of the carbon in white cast iron is in a chemically combined state. It forms a very hard substance called cementite, or iron carbide (Fe,C). White Cast Iron is so hard that it cannot be machined except by grinding. Its direct use is limited to castings requiring the surfaces to withstand abrasion and wear The major use of white cast iron is in making malleable cast iron.
• Wrought Iron is pig iron from which most the carbon has been removed; it contains only about 0.4 % carbon; it was the most important structural metal before the development of the Bessemer steelmaking process. The metal was tough, easily formed, and corrosion-resistant. It was widely used for fences, horseshoes, nails, lamps, and door hardware.
• Ductile Cast Iron is also known as nodular iron or spheroidal graphite iron
• The carbon in the grain structure of ductile iron is in the free state, in small, rounded lumps of carbon clusters called nodules
• Ductile Cast Iron is produced similarly to gray cast iron, with magnesium alloys and other elements added to the molten iron before casting
• Ductile Cast Iron has properties similar to malleable iron, being tough, machinable, and sharing characteristics with steel
• Ductile Cast Iron is used for making tough castings for automobiles, farm machinery, and various other types of machinery
• Gray Cast Iron - has a good compressive strength, hardness and excellent damping capacity. However, has lower tensile strength and ductility.
• White Cast Iron - very hard and brittle, high hardness and excellent wear resistance. Low toughness, ductility and impact resistance.
• Ductile Cast Iron - moderate to high in strength and malleable. It is used widely in industries. Common application are for plumbing and automotive.
• Wrought Iron - has much more tensile strength than cast iron. Suitable for horizontal beams
• Steel is iron that contains carbon in different amounts, from 0.05 % to about 1.7 % by weight. Its carbon content is between that of wrought iron and cast iron.