David Miller, age 13, of Concord, N.H., for his question:
WHEN WAS IRON FIRST USED TO MAKE IMPLEMENTS?
The exact date when people discovered the technique of smelting iron ore to produce usable metal is not known. But the earliest iron implements discovered by archeologists in Egypt date from about 3000 B.C. and iron ornaments were used even earlier.
The more advanced technique of hardening iron weapons by heat treatment was known to the Greeks about 1000 B.C.
The alloys produced by early iron workers, and all the iron alloys made until about the 14th century A.D., would be described today as wrought iron. They were made by heating a mass of iron ore and charcoal in a forge or furnace having a forced draft. Under this treatment the ore was reduced to a sponge of metallic iron filled with a slag composed of metallic impurities and charcoal ash.
This sponge of iron was removed from the furnace while still incandescent and beaten with heavy sledges to drive out the slag and to weld and consolidate the iron.
The iron produced under these conditions usually contained about three percent of slag particles and 0.1 percent of other impurities. Occasionally this technique of ironmaking produced by accident a true steel rather than wrought iron.
Steel in general is an alloy of iron and carbon. Ironworkers learned to make steel by heating wrought iron and charcoal in clay boxes for a period of several days. By this process the iron absorbed enough carbon to become a true steel.
After the 14th century the furnaces used in smelting were increased in size and increased draft was used to force the combustion gases through the "charge," the mixture of raw materials. The product of these furnaces was pig iron, an alloy that melts at a lower temperature than steel or wrought iron. Pig iron was later further refined to make steel.
Modern steelmaking employs blast furnaces. Pig iron received its name because it was usually cast in stubby, round ingots known as pigs. The basic materials used for the manufacture of pig iron are iron ore, coke and limestone. The coke is burned as a fuel to heat the furnace and in so doing gives off carbon monoxide, which combines with the iron oxides in the ore, reducing them to metallic iron.
Steel is marketed in a wide variety of sizes and shapes, such as rods, pipes, railroad rails, tees, channels and I beams. These shapes are produced at steel mills by rolling and otherwise forming heated ingots to the required shape.
The working of steel also improves the quality of the steel by refining its crystalline structure and making the metal tougher.
Modern manufacturing requirements call for a large amount of comparatively thin sheet steel and special continuous mills have been developed for rolling such strips and sheets in widths as great as eight feet.