| Given its importance in infrastructure and | | | | methods used air rather than pure oxygen, but |
| manufacturing-worldwide demand for it keeps | | | | this didn't allow for the same precision-air is, after |
| increasing-steel is a crucial part of everyday life. | | | | all, a compound, in which elements like nitrogen |
| (For example: A given car will be sixty-six percent | | | | mix with oxygen.) Other chemical cleaning agents |
| steel. The industry itself, as well as the | | | | are introduced later to create slag, a material that |
| scrap-metal recycling industry it in turn gives rise | | | | forms on the surface of the molten steel to |
| to, is a major employer, and one of the engines | | | | absorb chemical impurities. Slag is good-it drains |
| of economic development the world over. It | | | | impurities from the rest of the steel. |
| accounts for up to sixty-five percent of the | | | | At this point the furnace may be emptied |
| typical household appliance.) Yet many don't realize | | | | (tapped) into a giant ladle, where it is further |
| that there are, in fact, several kinds of steel, each | | | | refined-and this is where the different varieties of |
| having its own particular molecular | | | | steel may be produced. Here it is |
| arrangements-and hence its own particular qualities | | | | alloyed-mixed-with other materials, each of which |
| and strengths. | | | | creates a different molecular arrangement with |
| Steel has been made for at least three thousand | | | | the steel and, thus, creates different properties in |
| years-bits of it dating from 1400 BCE, or | | | | the steel itself. |
| thereabouts, have been found in East African | | | | Most modern steel tends to be carbon steel, |
| sites. Chemically speaking, it's an alloy-a material | | | | made wholly from iron and carbon. Once in a |
| made up from two or more elements (materials | | | | while, though, to create a somewhat stronger |
| made up of only one kind of atom), one of which | | | | steel, manganese (or other elements) may be |
| elements has to be, in this case, iron. The | | | | added. This kind of steel-high strength low alloy |
| temperatures needed to actuate the steel making | | | | steel-is more expensive but, as stated, stronger. |
| process are pretty high-in excess of 1370 | | | | Stainless steel-named not because it is stainless |
| degrees Celsius-but methods for reaching these | | | | but because it stains less than other sorts of |
| temperatures have existed for, it seems, more | | | | steel-is created by introducing chromium and |
| than six thousand years. What makes steelmaking | | | | sometimes a bit of nickel. (Officially, this |
| a more subtle art is the fact that the processes | | | | corrosion-resistant metal must be made of at |
| by which it's manufactured have an influence over | | | | least eleven-and-a-half-percent chromium.) |
| which elements mix-and to what degree-with | | | | Or let's say a steel tool that is heat-resistant is |
| steel as it's being made, and the smallest changes | | | | needed-even to temperatures beyond those at |
| in manufacturing method can thus lead to a steel | | | | which steel typically melts. For that, steel leavened |
| with a very different molecular shape-and very | | | | with cobalt or tungsten may be necessary, which |
| different physical properties-than others. | | | | creates a tough steel called tool steel. The |
| Today, steel may be made via a process called | | | | implements in a basement workshop are most |
| oxygen steelmaking. It involves molten iron being | | | | likely made from tool steel; it's often used in drills, |
| poured into a heatproofed container called a ladle, | | | | axes, and anything else that needs a cutting edge |
| then dumped into a furnace, in which a precise | | | | that won't dull. |
| ratio of old scrap steel is already inserted (to | | | | There are many other ways to alloy steel-these |
| maintain certain chemical balances that catalyze | | | | are just some of the more common. In any case, |
| the reactions desired). Nearly-pure oxygen is | | | | steel isn't the name for just one kind of thing-it's |
| blown into the steel and iron, which (a) raises the | | | | an umbrella term for many kinds of iron-based |
| temperature inside the furnace, (b) burns away | | | | alloys that see every imaginable kind of use. |
| the carbon and (c) purifies the steel. (Earlier | | | | |