Carbon Steel is a metal, a combination of two elements, iron and carbon, where other elements are present in quantities too small to affect the properties. With a low carbon content it has the same properties as iron, soft but easily formed. As carbon content rises the metal becomes harder and stronger but less ductile.

 

Cast iron usually refers to grey cast iron, but can mean any of a group of iron-based alloys containing more than 2% carbon (alloys with less carbon are carbon steel by definition). It is made by remelting pig iron, often along with substantial quantities of scrap iron and scrap steel, and taking various steps to remove undesirable contaminants such as phousphorus and sulfer, which weaken the material. Carbon and silicon content are reduced to the desired levels, which may be anywhere from 2% to 3.5% for carbon and 1% to 3% for silicon depending on the application. Other elements are then added to the melt before the final form is produced by casting.

 

Mild steel is the most common form of steel as its price is relatively low while it provides material properties that are acceptable for many applications. Mild steel has medium carbon contents (up to 0.8%) and is therefore neither extremely brittle nor ductile. It is also often used where large amounts of steel need to be formed, for example as structural steel. Another popular use is in steel wire mesh.MILD STEEL:With it's higher and greater strength mild steel has superiority over wrought iron in it's strength and consistency which it gives a much wider range of it's application, it also can be  hardened by heat treatment. Mild steel has just about replaced wrought iron in the last century. Mild steel does tend to corrode

 

steel, alloy of iron, carbon, and small proportions of other elements. Iron contains impurities in the form of silicon, phosphorus, sulfur, and manganese; steelmaking involves the removal of these impurities, known as slag, and the addition of desirable alloying elements.

steel industry, the business of processing iron ore into steel, which in its simplest form is an iron-carbon alloy, and in some cases, turning that metal into partially finished products or recycling scrap metal into steel. The steel industry grew out of the need for stronger and more easily produced metals. Technological advances in steelmaking during the last half of the 19th cent. played a key role in creating modern economies dependent on rails, automobiles, girders, bridges, and a variety of other steel products.

Iron working can be traced as far back as 3,500 B.C. in Armenia. The Bessamer process, created independently by Henry Bessemer in England and William Kelly in the United States during the 1850s, allowed the mass production of low-cost steel; the open-hearth process, first introduced in the United States in 1888, made it easier to use domestic iron ores. By the 1880s, the growing demand for steel rails made the United States the world's largest producer. The open-hearth process dominated the steel industry between 1910 and 1960, when it converted to the basic-oxygen process, which produces steel faster, and the electric-arc furnace process, which makes it easier to produce alloys such as stainless steel and to recycle scrap steel.

After World War II, the U.S. steel industry faced increased competition from Japanese and European producers, who rebuilt and modernized their industries. Later, many Third World countries, such as Brazil, built their own steel industries, and large U.S. steelmakers faced increased competition from smaller, nonunion mills (“mini-mills”) that recycle scrap steel. The U.S. produced about half of the world's steel in 1945; in 1999 it was the second largest producer, with 12% of the world market, behind China and ahead of Japan and Russia.

Since the 1970s, growing competition and the increasing availability of alternative materials, such as plastic, slowed steel industry growth; employment in the U.S. steel industry dropped from 2.5 million in 1974 to to less than a million in 1998. Global production stood at 773 million tons in 1997, down from 786 million tons in 1988. U.S. steel production has remained constant since the 1970s at about 100 million tons, but 50% of that total is now produced by mini-mill companies. An increase in U.S. demand during the 1990s was largely met by imports, which now account for from about a fifth to a quarter of all steel used annually in the United States. The old-line U.S. steelmakers, losing market share and with higher wage, health, and retirement costs, experienced a string of bankruptcies beginning in the late 1990s, leading to industry and union pressure for protective tariffs, which were imposed by President George W. Bush in 2002 on most steel from non-NAFTA industrialized nations. Later reduced, the tariffs were found in 2003 to be illegal under World Trade Organization rules, and President Bush reversed the tariffs.

Aluminum: Aluminium is a soft and lightweight metal with a dull silver-gray appearance.  Aluminium is about one-third as dense as steel or copper is malleable ductile, and easily machined and cast; and has excellent corrosion resistance and durability due to the protective oxide layer. It is also nonmagnetic and nonsparking and is the second most malleable metal (most being gold) and the sixth most ductile.Whether measured in terms of quantity or value, the use of aluminium exceeds that of any other metal except iron and it is important in virtually all segments of the world economy.Aluminium alloys form vital components of aircrafts and rockets as a result of their high strength to weight ratio. Aluminium was selected as the material to be used for the apex of the Washinton Monument, at a time when one ounce cost twice the daily wages of a labourer.

Aluminium was, when it was first discovered, extremely difficult to separate from the rocks it was part of. Since the whole of Earth's aluminium was bound up in the form of compounds, it was the most difficult metal on earth to get, despite the fact that it is one of the planet's most common. The reason is that aluminium is oxidized very rapidly and that its oxide is an extremely stable compound that, unlike rust on steel, does not flake off. The very reason for which aluminium is used in many applications is why it is so hard to produce.Recovery of this metal from scrap (via recycling) has become an important component of the aluminium industry. Recycling involves simply melting the metal, which is far less expensive than creating it from ore. Refining aluminium requires enormous amounts of electricity; recycling it requires only 5% of the energy to produce it. A common practice since the early 1900's, aluminium recycling is not new. It was, however, a low-profile activity until the late 1960's when the exploding popularity of aluminium beverage can finally placed recycling into the public consciousness.

Electric power represents about 20 to 40% of the cost of producing aluminium, depending on the location of the aluminium smelter. Smelters tend to be located where electric power is plentiful and inexpensive, China is currently (2004) the top world producer of aluminium.