The most dangerous mammal in North America kills over 130 people each year, and seriously injures another twenty-nine thousand. The most recycled material in North America was dumped in landfills until the late 1970s, but now, nearly 100 percent of that material contains recycled content.
The animal? The white-tailed deer. The material? Highway asphalt. Things that are very important are often common and overlooked.
Prior to the 1970s the question "What's the most recycled material?" had a very different, but just as surprising answer: Iron. Nearly 100 percent of all automotive iron and iron from construction debris, as well as over 80 percent of iron from consumer appliances is recycled. Iron doesn't have a memory. The girders and beams from the World Trade Center were sold to iron foundries, and will appear as buildings, refrigerators, and washing machines around the world. Over half of the iron used in the world comes from recycling.
In coming issues of the Grantville Gazette articles will discuss various problems facing the Grantvillers, including the "stainless steel problem," the replacement of the power plant, constructing boats and bridges and barges, making the steam engines to power those, reproducing the machine shops and building new machine tools, the chemicals industry, coke, medicines, surgery, anesthesia, clocks, navigation, and mapping. All of these face a common element in what the 1632 series authors and background researchers have come to call the "tools-to-make-tools" problem: iron.
In the early 1630s, just before the appearance of the Ring of Fire, the annual production of iron in the part of Europe that became the USE was about fifteen thousand tons. One hundred miles of main line railroad needs over twenty thousand tons of iron. The telegraph line from Grantville to Magdeburg needs almost fifteen thousand tons of iron. Small main line railroad steam engines need three to five tons of iron each, and "real" railroad engines run seventy-five tons. Barges, even small barges like the classic U.K. narrow boat, require six to ten tons of iron per barge. A fifty- by twelve-foot barge runs around thirty tons. Future articles in the Gazette will detail the rapid increase of iron and steel production in the USE. The projections resulting from the projects named in the 1632 books published by 2006 indicate that within two years of the Ring of Fire, European iron production will have to have increased by a factor of two to three, with a planned increase by a factor of ten by year five.
This leads to the question: what is so important about iron? Other materials like wood, copper, aluminum, plastics, and alloys including brass and bronze are all common. Why make such a big deal about iron? This article will attempt to place civilization's use of iron in context historically, and physically.
Iron is the fourth most abundant element in the earth's crust. The most abundant is oxygen, which isn't much good for building things. Next is silicon, which we use for computer chips, but not for bridges or boats. Third is aluminum. We do build with aluminum, but winning aluminum metal from the earth's crust turns out to be a very difficult prospect that requires the use of massive amounts of electricity. Most aluminum in the crust is bound up chemically in ways that make it very difficult to separate, even with twenty-first-century technology. Iron, on the other hand, comprises about 5 percent of the earth's crust, and can be separated from its ore with little more than fire and charcoal. Other metals used by civilization are very rare. Copper exists in the crust at sixty-eight parts per million. Lead is even more rare at ten parts per million. One driving force then that makes iron an important part of civilization is that it is common, and easy to produce.
Iron has some very neat properties. It is very strong. Pound for pound, iron was the strongest material available before the twentieth century. It is very workable. Iron can be cast, beaten, rolled and formed into almost any shape. Because it is strong, thin sheets of iron can substitute for thick, heavy layers of other substances. Iron can be flexible, and makes great swords and springs. Iron can be stiff and makes great cutting blades and hammers and tools. Iron melts at a very high temperature. Iron's melting point is more than twice the temperature of a normal open fire. Iron doesn't even soften in normal fires, so it can be used to contain fire and form stoves and pipes. Even when heated red-hot, iron retains much of its strength. No other single metal does all these things. Copper is ductile; it can be formed into all sorts of shapes, but it is soft. Bronze can be hard, but it is weak, and melts at a low temperature. Lead, gold, and silver are soft, and the latter two are so rare that we make money out of them. Iron is unique and has been the basis of civilization in Europe, Asia, and Africa for over three thousand years.
How do you produce iron then? First, select a rock with lots of iron in it. The iron will be bound up with oxygen. The best iron ores are nearly pure rust. They are little more than iron and oxygen. Most iron ore isn't of this quality, and contains varying amounts of silicon, sulfur, manganese, and phosphorus. Oxygen combines with carbon more strongly than it binds with iron. If you powder iron ore and charcoal or coke, and heat the mixed powders, the iron gives up a bit of its oxygen. The oxygen binds with the carbon to make carbon dioxide. In the simplest smelting process, crushed iron ore, crushed charcoal, and a little limestone or sea shells are heated together until they are red-hot. As this spongy mass, called a bloom, cools, pure pieces of iron are intermingled with leftover charcoal and the other chemicals left behind. The parts that aren't iron are called slag. The bloom would be hammered and turned and hammered and turned, and the slag would be squeezed out, and the bits of iron would come together to form wrought iron. Wrought means "hammered" or "worked." In the seventeenth century, there were hundreds of hammer mills scattered throughout Europe wherever a seam of iron ore coexisted with a stream capable of turning a wheel and powering a hammer. All the iron available in Europe in the seventeenth century started life as wrought iron. Wrought iron has a carbon content of around 0.02 to 0.08 percent by weight. This is important because the factor that is the most important in describing the strength and brittleness of iron is the carbon percentage. A very small difference in carbon results in a huge difference in the properties of the iron. Consider the next type of iron to be smelted.
If you take iron and carbon and heat it above red-hot (to about 1,200 degrees Celsius) something interesting happens. The iron begins to absorb the carbon, and starts to melt. The iron-carbon mixture has a melting temperature far below the melting temperature of pure iron (which is around 1,500 degrees C). If you make a tall chimneylike structure, and layer charcoal, flux, and iron ore in it, and pump air with a bellows through it so that it gets above the critical temperature, molten iron would run out of the blast furnace. The cast iron produced has 3 to 5 percent carbon in it. Cast iron is very different from wrought iron. It is hard and brittle. If you hit it with a hammer, it will crack or shatter. Microscopically, cast iron is a mat of fibers of iron crystals, iron carbide crystals, and graphite. It is very rigid and very tough. It doesn't soften much before it melts, and it cannot be worked by hammer and anvil into a shape like a knife, a sword, or a gun as wrought iron can. Cast iron was known in Europe in the Middle Ages, but was not used much beyond pots, pans, cannon, cannon balls, and bells. Casting iron was called founding and so businesses that cast iron are called foundries. Cast iron is perfect for making things that need to be very rigid.
Cast iron is not very expensive. Generally, items made out of cast iron are cast in sand. A wooden copy of the item is made, and sand is formed around the master. The master is removed, and molten iron is poured in. After cooling, the sand is shaken off and reused. Grantville will use far more cast iron than the Europeans were using before they arrived. They know neat things to make from it, like Franklin stoves, frying pans, and the Eiffel Tower. But for all its strength, cast iron is brittle. Guns made from cast iron fail because they are not elastic. They can't expand with the explosion of the powder and then spring back to shape. If they are not made very thick to withstand the pressure, cast iron guns explode after a few uses, so they have to be very heavy for their power.
Beginning in the Middle Ages, iron makers learned to transform cast iron into wrought iron by burning the carbon out. They would use a fining furnace, where they would break the cast iron into small lumps and heat the lumps with a stream of very hot air. The iron would melt, and carbon would burn out and the decarburized iron droplets would sink to form a bloom below the hot zone. Then, they would forge the bloom just like they would in a hammer mill. Wrought iron made this way was more expensive than iron made directly from the ore, but the two-step process could be done with some iron ores that the one-step process was not effective for. This was expensive.
In the late 1700s, an Englishman, Henry Cort, developed another technique for transforming cast iron into wrought iron. Molten cast iron was poured into a stone basin in a reverberatory furnace and exhaust gases from a hot fire were run over the top of the basin. A worker with a long rake stirred the surface of the puddle of iron, and carbon monoxide in the gases would combine with carbon in the iron. The resulting pure iron melted at a higher temperature than the cast iron it was suspended in, so it would form semisolid bits of wrought iron. At first, these puddlers would gather these into a single mass that would be wrought like any wrought iron. Later puddlers would keep mixing the mass of iron, as it became more and more viscous. Skilled workers would recognize when the hot iron had "jelled" enough to have had enough of the carbon burned out of it.
Blast furnaces produced bulk cast iron efficiently, but the puddling furnace was a major bottleneck. The process was slow. It required huge amounts of fuel. Only very strong men could stand the heat, and work the thick, heavy liquid metal and tell when it was ripe to be withdrawn. Many attempts were made in the 1800s to mechanize the process, but they all failed.
So far we've talked about two types of iron. Cast iron, with carbon content over 2 percent, and wrought iron, with very little carbon at all, less than 0.1 percent. What about iron in the middle of the range? We know that wrought iron is flexible, and can be forged into all sorts of shapes. We know that cast iron is rigid and brittle. It should come as no great surprise that iron between 0.1 percent carbon and 2 percent carbon is intermediate in its properties. It is stiffer than wrought iron, but less stiff and brittle than cast iron. It has a higher melting point than cast iron, but less than wrought iron. Clearly, this is what we want to use to make stuff. Iron intermediate in carbon between wrought and cast is called steel.
Even today, the basic chemistry of iron is such that it is difficult to move directly from iron ore to steel. In 1632, we have to come at it from one end or the other. We can take wrought iron and add carbon to it, or we can take cast iron and reduce its carbon. Several techniques were developed in antiquity that resulted in steels of different carbon content and different microstructure. One common element is that all these were small batch processes that were labor intensive. Steel was very expensive.
The oldest known steels were produced by cementation. Sheets of wrought iron were packed with charcoal or other carbon sources in a closed ceramic container and heated red-hot (1,000 to 1,100 degrees C) for five to seven days. The carbon would be absorbed into the iron in the solid state. The process was very slow since the iron is solid, and the carbon atoms have to move into the spaces in the solid iron crystals. The resulting sheets of blister steel had very high carbon content on the outside, and very low carbon content at the center. The sheets would be forged and folded together to distribute the carbon more evenly in very fine layers. This process of heating and folding and heating and folding was very labor intensive. The result could be a blade that combined the best of both wrought iron and cast iron, with very rigid hard bits to hold the shape well, and very flexible bits to allow the weapon to flex. But it was difficult to impossible to make large forms like guns and cannon this way. In the 1740s Benjamin Huntsman developed a way to take the blister steel from the cementation process and melt it in a closed crucible with a special flux that grabbed up fine bits of slag to make a very pure crucible steel, but crucible steel is very, very expensive.
Smiths in India developed a different method of heating wrought iron pellets with organic material in sealed containers for long periods at high enough temperatures to get the iron to melt and the carbon to mix with the iron in liquid phase. This wootz process resulted in ultrahigh carbon steels (nearly 2 percent) with microstructures that mixed the pure iron and the iron-carbon complexes at a much smaller scale than could be achieved by the folding and forging process above. The resulting blades called "Damascus" steel had a combination of strength and flexibility that was unmatched until the twentieth century, but the process produced only small ingots suitable for knives and swords. The material could only be forged at low temperatures or the whole thing would literally fall apart as the steel turned into cast iron. This still didn't produce a steel capable of being formed in bulk.
The other way to produce steel is to reduce the carbon in cast iron. Smiths in China mixed bundles of cast and wrought iron together and forged and heated them to diffuse them in a manner similar to the cementation process describe above. Puddling furnaces can be run without removing the wrought iron pieces from the molten iron, mixing the result over and over until it is of a thickness and carbon content wanted. This was the first process that could produce bulk steel. The amount of steel that you could produce was dependent on the strength of the puddler and the reach of his rake.
Still, technological civilization needs cheap bulk steel. The first railroads ran on wrought iron rails. The passing trains bent and deformed the rails, and wore the edges so fast that on some busy stretches the rail had to be replaced every other month. What the world needed at the dawn of the railroad period, and what Grantville and the USE needs in 1632 and beyond, is cheap steel that can be cast into rail and cannon and other forms.
Enter Henry Bessemer.
In the first half of the 1800s, steam engines had become common, and it was possible to produce pumps that could move huge amounts of air at high pressures. Prior to this, smiths had been restricted to the air that they could move with bellows. Some of the bellows were very large, and operated by water wheels, but the pressure was limited and the flow intermittent. By the 1850s engineers had developed pumps that could be driven by steam engines and blow air continuously at high pressure. These were first used to increase the size and output of blast furnaces and resulted in a drop in the price of cast iron.
In 1856, Bessemer designed what he called a converter. It was a large, pear-shaped vessel with holes at the bottom that the new pumps could blow compressed air into. Bessemer filled the converter with molten cast iron and then blew air into the bottom, causing it to bubble up through the molten metal. The resulting reaction was very violent. The oxygen combined with the silicon and the carbon in the cast iron, and burned off into the air in just minutes. As the oxygen in the air combined with the carbon, the reaction gave off heat, and instead of freezing up from the cold air, the metal became even hotter. Bessemer converters are large. Small converters take charges of five tons of molten iron. This means that very large quantities of steel can be produced very rapidly.
Historically, it took twenty years to perfect the Bessemer process to deal with all the chemical intricacies of iron ore. Bessemer himself cheated by using pig iron from special phosphorus-free ore bodies in Sweden. But by 1876, the basic Bessemer process could handle most anything that was thrown at it, and vast quantities of molten steel could be produced. Finally, with the Bessemer process we have the ability to produce cast steel items in bulk like railroad rail, cannon, and beams.
The Grantvillers can cheat too. They already know about things like lining the bottom of the converter with limestone to scavenge the phosphorus from the iron. With the books and knowledge brought down-time, the Grantvillers should be able to skip over two hundred years of technical development and jump into the age of rail.
Iron production is very scalable. In the U.S., in 1847 460,000 tons of wrought iron railroad rail was sold at a price of $83 a ton, and 2,000 tons of steel rail at $170 a ton. By 1884, wrought iron rails were no longer made at all, and 1,500,000 tons of cast steel rail were made at a cost of $32 a ton. By 1900 the cost of steel rail was down to $14 a ton. Participants in Baen's Bar in the 1632 Tech conference have been following this process for several years as a team of Barflies lead by John Leggett have documented the growth of USE Steel in a series of monthly reports.
Informed readers will note that this discussion skipped over the Siemans open hearth furnace, which largely replaced the Bessemer process by 1900. The consensus of the iron folks in Baen's Bar has been that the Grantvillers do not have the details of the designs, or the material, especially structural firebricks and other refractories, to successfully build and operate open hearth furnaces.
The Grantvillers will have several techniques to make steel in a variety of carbon contents from very low to nearly cast iron. However, to get the most use out of steel it is necessary not only to create it with the right chemistry, but to treat it to the right temperature conditions.
Consider the following recipe: Take two cups of flour, two eggs, one-third cup of oil, three teaspoons of baking powder, one teaspoon of salt, and one-third cup of buttermilk. This recipe can produce pretty decent biscuits, or pancakes, or waffles (if you separate the egg yolk from the white and beat in sufficient air). On the other hand, overmixed, dumped into a pan, and placed into a 450-degree oven, you'll get an inedible lump. Similarly, the same iron/carbon ratio can produce a wide range of steel products.
The room temperature normal form of iron is called ferrite. If you have ever studied crystals, you may want to know that it's a body-centered cubic crystal. If not, what's important is that ferrite has few gaps. It's a "tight" crystal that can hold only a few hundredths of a percent of carbon. If you heat iron above 906 degrees Celsius it switches to a face-centered-cubic structure called austenite. Austenite is a roomier crystal that can hold up to 1.7 percent of carbon. But you can't hold your tool above 900 degrees Celsius forever. As the temperature falls, the iron atoms try to rearrange themselves into a ferrite structure, and the carbons get squeezed out and diffuse to carbon-rich zones. Eventually, as the temperature reaches 723 degrees Celsius, the austenite crystals are as rearranged as they will get, and the carbon stops moving. What's left is crystals of ferrite, interspersed with fine layers of iron carbide (FeC3) This layered material is called pearlite and is the basis for high-strength steel wire and rope. The more carbon steel has, the more pearlite is formed, and the harder the steel is.
What happens if instead of letting the steel cool slowly, we plunge the red-hot newly forged tool into cold water, or brine, or a mixture of water and oil? There isn't sufficient time for the carbon to diffuse and form carbon-rich zones. The iron may "want" to switch to the ferrite form, but the carbon is in the way. The crystal lattice becomes very distorted. If you look at the resulting crystals under a microscope, the steel has a distinctive structure with interlocking needles of crystals. There wasn't time to form big crystals, and anyway, the lattice is so distorted that the big crystals wouldn't work. This series of interlocking needles was named after its discoverer, Adolf Martens, and is called Martensite. Martensite is very rigid, so martensitic steel is very hard, but stiff.
It is possible to just convert some of the pearlite in a steel into martensite by heating and then quenching just the working end of a chisel or drill bit. The technique of rapidly cooling a steel blade to make it harder has been known since ancient times. Swords in particular have many myths about the proper solutions, temperatures, and procedures for quenching. Once a piece has been quenched, it may be useful to increase its strength and flexibility by reheating it and holding it at an elevated temperature long enough to allow some of the microstructures to realign. This is called tempering. A temper is followed by a quench, or rapid cooling to make sure the outside of the tool is hard. Tempering is an art and science all its own in addition to the chemistry of the steel. With a clever combination of heating, quenching, and tempering, it is possible to make tool steels that can be used in lathes and cutters and drills to cut steels of the same chemistry that have not been "hardened." Tempering in lead baths, hot oil baths, sand, and tempering ovens are all treatments that will be available down-time.
So far, we've just discussed iron and carbon. It is possible to mix iron with other metals. In particular, in 1912 Harry Brearley produced the first stainless steels. Stainless steels are low carbon steels with 10.5 percent or more chromium added. They are resistant to rust compared to steel without chromium. They stain "less" than plain iron. Chromium atoms combine with oxygen to form hard, stable clear layers of chromium (III) oxide (Cr2O3) on the surface of the metal. Chromium atoms and chromium-oxide have compatible geometries, so the oxide packs neatly on the surface of the metal and stays attached well. On the other hand, iron oxide (Fe2O3)(rust) has a geometry that does not pack well against iron atoms, and so it flakes, or falls off the surface, exposing more fresh iron to the oxygen. In chrome rich steels, if the chrome-oxide layer on the surface is scratched or disturbed, it quickly forms a new layer of chrome oxide, and protects the bulk of the metal underneath. That is why stainless steel is stainless. It's self-protecting, sort of. Note that the protection requires having oxygen available to form the protective layer. In oxygen-poor environments, or in low-circulation situations, stainless steel doesn't resist corrosion any better than plain steel. Also, in seawater, or in other situations where chlorine is available, the chloride ion attacks and destroys the chromium oxide layer faster than it can be formed.
The addition of nickel to the mix of iron and chromium can have even more interesting effects. Specifically, adding sufficient nickel results in the steel retaining its austenite structure at all temperatures. Among other things, chrome-nickel austenitic steels can be nonmagnetic.
Stainless steel, and its corrosion resistant companions will form the center of a full article in a future issue of the Gazette. For now, recognize that the Grantvillers know of only one source for chromium they can reach, it is going to be extremely difficult to mine, and lies near the arctic circle. Modern stainless steels may also contain nickel, manganese, niobium, tungsten, and titanium, none of which the Grantvillers will be producing anytime soon.
Iron, and more precisely steel, is central to the industrial expansion of modern technology. Few choke points in the development of modern civilization are pressing on Grantville harder than the shortage of steel. The expansion of iron and steel production will stress every resource: transportation, mining, construction, chemistry, lights, power, water, and manpower. It is a challenge they have little choice but to meet. Meanwhile, stranded up-time, I'm going to attempt to avoid hitting a deer while driving on an asphalt road in my steel car.