Answers and Solutions

Answer

Iron to Steel

Fill a crucible with pig iron and carbon. Carbon can be made from charcoal or charred organic material such as bone or wood. The final carbon content of the steel is nearly impossible to predetermine, but filling the crucible three-quarters full with steel and the rest carbon is a good start.

Cap the crucible with broken glass. The glass acts as a seal when it melts and prevents air from reacting with the molten metal thus ruining the chemical reaction needed to make steel.

Place the crucible in the furnace and raise the temperature above 2,786 degrees Fahrenheit, the melting point of iron.

Keep the crucible at temperature for one to three hours so the carbon and iron can combine to form steel.

Cool the crucible by allowing the forge to burn down and the heat to naturally radiate away. Once cool, remove the contents of the crucible, which should look like a dark sponge.

Break the contents, called a bloom, into pieces and sort them. If the reaction was successful there should be chunks of steel intermixed with pieces of slag and other impurities.

Answer

• The Bessemer process was the first inexpensive industrial process for the mass-production of steel from molten pig iron prior to the open hearth furnace. The key principle is removal of impurities from the iron by oxidation with air being blown through the molten iron. The oxidation also raises the temperature of the iron mass and keeps it molten.
• The process is carried on in a large container called the Bessemer converter, which is made of steel and has a lining of silica and clay or of dolomite. The capacity is from 8 to 30 tons of molten iron; the usual charge is 15 or 18 tons. The converter is egg-shaped. At its narrow upper end it has an opening through which the iron to be treated is introduced and the finished product is poured out. The wide end, or bottom, has a number of perforations (tuyeres) through which the air is forced upward into the converter during operation. The container is set on pivots (trunnions) so that it can be tilted at an angle to receive the charge, turned upright during the "blow," and inclined for pouring the molten steel after the operation is complete. 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 with a blue flame and the other impurities form slag. Dolomite is used as the converter lining when the phosphorus content is high; the process is then called basic Bessemer. The silica and clay lining is used in the acid Bessemer, in which phosphorus is not removed. In order to provide the elements necessary to give the steel the desired properties, another substance (often spiegeleisen, an iron-carbon-manganese alloy) is usually added to the molten metal after the oxidation is completed. The converter is then emptied into ladles from which the steel is poured into molds; the slag is left behind. The whole process is completed in 15 to 20 min.