530.352 Materials Selection

1. 530.352 Materials Selection Lecture #35 Processing of: Steel and Aluminum Wednesday December 6th, 2005

2. Steel production: http://science.howstuffworks.com/iron3.htm • Iron ore -> Pig Iron • Fe2O3 + 3CO -> 3CO2 + 2Fe 2Fe really: 92% Fe, 3-4% C, .5-3% Si, .25-2.5% Mn, .04-2%P, trace S • Pig Iron -> Steel • 2Fe + Air (O2) -> Fe (purer) + slag • Finishing • Blooming, roughing, finishing mills (rolling).

3. Iron ore : • To make iron, you start with iron ore, a rock that contains a high concentration of iron. Common iron ores include: Hematite - Fe2O3 - 70 % iron Magnetite - Fe3O4 - 72 % iron Limonite - Fe2O3 + H2O - 50 to 66 % iron Siderite - FeCO3 - 48 % iron • Iron is plentiful -- 5 percent of the Earth's crust is iron, and in some areas it concentrates in ores that contain as much as 70 % iron. • One thing that gave certain countries an edge between the 15th and 20th centuries was the availability of iron ore deposits.

4. Iron ore to pig iron: • A blast furnace is charged with iron ore, coke (charcoal made from coal) and limestone (CaCO3). • Huge quantities of air blast in at the bottom of the furnace. • The calcium in the limestone combines with the silicates to form slag. • At the bottom of the blast furnace, liquid iron collects along with a layer of slag on top. • To create 1 ton of pig iron, you start with 2 tons of ore, 1 ton of coke and half-ton of limestone. The fire consumes 5 tons of air. The temperature reaches almost 3000 degrees F (about 1600 degrees C) at the core of the blast furnace! http://www.bbc.co.uk/history/games/blast/game_window.html

5. Pig iron to steel: Bessemer process: • The principle for the manufacture of steelfrom molten pig iron involves oxidation of the impurities in the iron by the oxygen of air that is blown through the molten iron. • As the air passes upward through the molten pig iron, impurities such as silicon, manganese, and carbon unite with the oxygen in the air to form oxides; the carbon monoxide burns off and the other impurities form slag. • The heat of oxidation raises the temperature of the mass and keeps it molten during operation. • Alloying elements are added to make alloy steels.

6. Pig iron to steel: Basic Oxygen Furnace • WHAT: A pear-shaped furnace, lined with refractory bricks, that refines molten iron from the blast furnace and scrap into steel • WHY: BOFs, which can refine a heat (batch) of steel in less than 45 minutes, replaced open-hearth furnaces in the 1950s, which required 5 to 6 hours to process the metal. • HOW: Scrap is dumped into the furnace vessel, followed by the hot metal from the blast furnace. A lance is lowered from above, through which blows a high-pressure stream of oxygen to cause chemical reactions that separate impurities as fumes or slag.

7. Making aluminum • Mining • Aluminum is one of the most plentiful metals in the earth's crust; it is naturally found in the form of bauxite, an ore containing aluminum oxide, or alumina and can be surface mined. • Refining • Smelting • Recycling

8. Making aluminum • Mining • Refining (Bayer process) • Bauxite ore is not used directly to make Al. It must first be refined into aluminum oxide, or alumina. To turn bauxite into alumina, grind the ore and mix it with lime and caustic soda, pump into high-pressure containers, and heat it. The aluminum oxide is dissolved by the caustic soda, then precipitated out of this solution, washed, and heated to drive off water. • Smelting • Recycling

9. Making aluminum • Mining • Refining • Smelting • Smelting is the process of extracting aluminum metal from aluminum oxide (alumina) through electrolytic reduction. During smelting, the aluminum oxide is placed in a electrolytic cell with molten cryolite. A carbon rod in the cell is charged and the reaction results in carbon monoxide, carbon dioxide and aluminum. The aluminum sinks to the bottom where it is removed from the tank and sent to a melting or holding furnace. Smelters typically operate hundreds of pots, linked electrically in configurations called potlines. Smelting requires large amounts of electricity!!! • Recycling

10. Making aluminum • Mining • Refining • Smelting • Recycling: • Every minute of every day, an average of 123,097 aluminum cans are recycled. The national average of aluminum can recycling is two out of every three cans. • Tossing away an aluminum can wastes as much energy as pouring out half of that can's volume of gasoline. • Making new aluminum cans from used cans takes 95 percent less energy and 20 recycled cans can be made with the energy needed to produce one can using virgin ore. • Recycling one aluminum can saves enough energy to keep a 100-watt bulb burning for almost four hours or run your television for three hours.