Vincent Wajtyna, age 12, of Butler, Pennsylvania, for his question:
What is the difference between iron and steel?
Iron and steel have many different properties, and it may surprise you to learn that these differences are only a matter of refinement. Durable, crack resistant steel is actually a purer form of brittle iron.
The making of steel begins with the making of iron, and the basic ingredient is iron ores found in the ground. As you know, the element iron tends to oxidize in the air and crumble away in rusty red flakes of iron oxide. It is one of the earth's plen¬tiful elements but nature never leaves chunks of it lying around. We find it mixed with other elements in mineral compounds. Deposits of hematite and magnetite, limonite and several other mineral compounds are rich enough in iron to be worthwhile ores.
The next step is to separate the metallic iron from the other elements in the ore. This requires tremendous heat but if limestone is added to the mixture, the mixture will separate at lower temperatures. A furious blast furnace, maybe 90 feet tall, is heated by four seething stoves. Perhaps 20 carloads of iron ore, 10 of limestone and 10 of coke are fed into the seething giant. The coolest level at the top of the furnace reaches 400 degrees Fahrenheit while the bottom level reaches at least 3,000 degrees. Blasts of hot air are piped in to make things even hotter.
The heat triggers chemical changes in the ingredients. Some of the unwanted im¬purities are driven off as gases, while others float to the top of the molten brew. Because it is heaviest, the iron sinks to the bottom. The molten metal is drained off into troughs at the bottom of the blast furnace. When cool, the iron becomes a rough and tough metal, strong and unbending and rather prone to crack under stress. Its brit¬tle quality is caused by 4% to 5% of carbon and other impurities that the furious fur¬nace failed to remove. When these unwanted materials are reduced, we get a finer grained metal with the strength of iron plus a pliable quality that yields under stress. It is steel, more malleable, stronger than iron, less brittle and more likely to yield than crack.
Steel is made by removing most of the carbon and other unwanted ingredients from ordinary iron. This mammoth job is done by loading iron and scraps of steel into a super furnace and heating the mixture once again to furious temperatures. This produces ordinary carbon steel, so called because its carbon content is reduced to about 11. This metal is fine for a multitude of everyday duties. But steel man want steels with extra qualities for a variety of special duties. These super metals of the Machine Age are alloys of steel mixed with other metals.
Stainless steel alloys made to resist rust and corrosion contain chromium and per¬haps other metals. Traces of chromium also add extra hardness to steel alloys. Nickel added to the recipe provides extra toughness and makes the alloy more resistant to heat and acids. A trace of vanadium metal makes a more springy alloy. Manganese adds strength and durability and molybdenum adds strength and resistance to heat.