Steel and Cast Iron
Steel and Cast iron are the most common ferrous metals in general use.
1. Steel
There are two general kinds of steel, carbon steel and alloy steel.
1.1 Carbon Steel
Carbon Steel are classified according to the percentage of carbon they contain.
a. Low carbon steel containing from 0.05 to 0.25 percent carbon. Steels in this class are tough, ductile, and easily machined, formed and welded. Low carbon steels are very soft and can be used for bolts and for machine parts that do not need strength.
b. Medium carbon steel containing from 0.25 to 0.6 percent carbon. They are strong and hard but can't be worked or welded as easily as low carbon steels.
c. High carbon steel containing from 0.6 to 1.7 percent carbon. High carbon steel may be hardened by heating it to a certain temperature and then quickly cooling in water. The more carbon the steel contains and the quicker the cooling is, the harder it becomes. Because of its high strength and hardness this grade of steel may be used for tools and working parts of machines.
But for some special uses, for example, for gears, bearings, springs, shafts and wire, carbon steels can't be always used because they have no properties needed for these parts. Some special alloy steels should be used for such parts because the alloying elements make them tougher, stronger, or harder than carbon steels.
1.2 Alloy Steel
Alloy steel contains some other "alloying elements" such as nickel, chromium, manganese, molybdenum, tungsten, vanadium, etc. Alloy steel have special properties determined by the mixture and the amount of other metals added. Some alloying elements cause steels to resist rusting (corrosion), and such steels are called stainless steels. Stainless steels contain a high percentage of chromium, Chromium also makes steel harder. Nickel is used in steel to increase strength and toughness. Some alloying elements (such as chromium and tungsten) make the grain of steel finer, thus increasing the hardness and strength of steel, because the finer the grain is, the stronger the steel becomes.
2. Cast iron
Cast iron is used for the heavy parts. Cast iron is low in cost and wears well. It is vey brittle, however, and can't be hammered or formed. the basic kinds of cast iron are white iron, gray iron, nodular iron and malleable iron.
White cast iron is the hardest type of cast iron. It is unweldable.
The most common type of cast iron is gray cast iron. Gray cast iron has little ductility, and can sustain high compressive loads.
Nodular iron is a variation of gray cast iron, and has a microscopic structure that overcomes most of the limitations of gray cast iron. Nodular iron likewise contains graphite, but the iron is inoculated with a small amount of magnesium while being poured into the ladle. As a result, the graphite becomes nodular or approximately spherical. The result is a cast iron with excellent ductility and tensile strength. Nodular iron is a kind of cast iron that is even better for withstranding shocks, blows and jerks.
Malleable iron is a paticular kind of cast iron, made more malleable by an annealing procedure. Malleable-iron casting are not so brittle or hard. They can strand a great deal of hammering. Many plumbing fixtures are made of malleable iron.
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