Iron and Steel in the Dreamlands

Copyright (C) 2011 by Kevin L. O'Brien

Iron and Steel Making Technology in the Dreamlands

Iron and steel production is probably the best example of industrialized activity in the Dreamlands. "Industrialized" as used here must be taken with a grain of salt. The total output for the whole of the Dreamlands for an entire year would not equal the output of a modern Waking World industrialized nation for a single day. Even so, the output does exceed that for local needs only, with the access being used for commerce. What is perhaps even more amazing is that this activity is sustained using pre-sixteenth century power sources and technology, yet some of this was pretty extraordinary even in the Waking World.

Like most other metals, iron rarely exists in the native state; that is, as metallic iron rather than a compound like iron oxide or as part of a mineral ore. Native iron has only two sources: inclusions in basalt rocks found in the mountains of the Northern Lands and the Cold Waste, and meteorites. Another source of relatively pure iron is hematite, which is a mineralized form of iron(III) oxide. Bands of hematite can contain nodules of metallic iron, which can be separated with some difficulty from the mineral matrix. The only other forms of iron are other oxide, carbonate, and oxyhydroxide ores, but these are common in all the mountain ranges throughout the Dreamlands.

Metallic iron is malleable at ambient temperatures; this is known as cold forging or cold working. Metallic iron can also be hardened by plastic deformation; that is, the repeated hammering as it is worked into a specific shape can compress the iron crystals into a compact form that is stronger and more resistant to stress. Metallic iron has a relatively low melting point, making it possible to soften it using the heat obtained by charcoal or coke fires for easier working; this is known as hot working. This makes it amendable to forge welding, which is the joining of two pieces of metal by heating them and hammering them together. This technique can also be used to alloy two metals with different properties together without melting them. All this is of extreme advantage, because it allows iron to be worked into a wide variety of forms for a variety of uses.

If native iron is unavailable or of insufficient quantity, it must be smelted from ore. All iron ores contain some form of iron oxide, so the method is a simple one: reduce the oxide to metallic iron by driving off the compounded oxygen. The simplest method is simply to roast the crushed ore on a bed of charcoal or coke. This takes advantage of the fact that neither fuel burns completely, producing just water vapor and carbon dioxide; instead, a substantial amount of carbon monoxide is produced as well. This strips the oxygen off the iron oxide, creating metallic iron without melting it. The iron particles accumulate at the bottom of the fire, forming a spongy mass called a bloom. However, the mineral matrix tends to melt as well, forming a slag that encases and permeates the bloom, requiring that it be separated from this waste product before it can be used.

Though an open charcoal or coke fire is generally hot enough to smelt iron, it normally only results in a few ounces of poor-quality metal. To produce more of better quality, the temperature must be increased; this is done in two combined ways. The first is by creating a chimney structure; the second is to introduce pipes into the bottom of the structure to allow air to enter. The structure is called a bloomery, while the pipes are known as tuyeres. Not only does the bloomery contain the heat of the fire to concentrate it, the air flow increases the strength of the fire, thereby increasing the overall heat. Generally speaking, the higher the heat, the greater the efficiency of the smelting process, both in terms of quantity and quality, but care must be taken, because the higher the temperature, the more impurities such as carbon and silicone the iron can absorb. As well, if the temperature gets too high, the iron will melt, forming pig iron, which is too brittle to be worked. Increasing the temperature does, however, allow for increasingly larger bloomeries to be constructed.

A bloomery is operated by burning charcoal or coke at the bottom, pre-heating the structure, while the ore is being crushed. When it is hot enough, the crushed ore is mixed with more fuel and introduced into the bloomery at the top. The bloom then forms at the bottom, from where it is removed once the smelting process is finished. While a bloomery cannot be run continuously, once the ash, slag, and bloom have been cleaned out, new fuel and ore can be added to start the process over again. As well, the slag usually still contains large amounts of iron, so it can be crushed and added to the ore to recycle it. Bloomeries are so easy to set up and operate that they can be found throughout the Dreamlands, even in hamlets and small villages, the only restriction being the availability of ore and fuel. Wood is unsuitable, because it doesn't burn hot enough, whereas coal contains too many contaminants, such as sulfur. Charcoal and coke are ideal, but there may be problems obtaining either.

Bloomeries typically produce about two pounds of iron at a shot, though larger ones can produce as much as thirty pounds. Increasing the heat and size can up production to some 600 pounds. The best way to increase the heat is by increasing the air flow into the bloomery. This is usually done by using bellows. Human and animal-powered bellows are sufficient to increase production above thirty pounds, but water or air-powered systems are needed to produce amounts in excess of a hundred pounds. For the highest production levels, however, a trompe is needed. This is a device that uses falling water to compress air; the farther the water falls, the more the air is compressed and the faster it will blow when released. Since the conditions needed to create a continuous fall of water are rare, however, these devices are only used by a few smelters. Smelters with high production levels are known as Catalan forges.

The iron produced by a bloomery typically has from as little as 0.05% to as much as 4% carbon, the amount depending upon temperature (the higher the temperature, the higher the carbon). Hence, a bloomery can produce wrought iron (0.05% to 0.25% carbon), carbon steel (0.25% to 2% carbon), or cast iron (2% to 4% carbon) depending upon conditions; it can also create pig iron (>4% carbon) if the iron melts. However, the purpose of the bloomery is to produce malleable iron; cast and pig iron are not malleable, and neither is high-carbon steel (>1.25% carbon). As such, bloomery operators will usually reduce the temperature as much as possible to produce low-carbon iron. However, since steel is a desirable product, many bloomeries are set up to create high-carbon steel or cast iron, which can be alloyed with low-carbon iron to make a workable steel.

Once the bloom is produced, it must be further processed to remove as much slag as possible. This is done by heating the iron until it softens and the slags melts, then working it in a forge to consolidate it into a solid mass. It may have to be reheated several times before it is finally formed into a bar. This tends to be quite time consuming and labor intensive. Not all of the slag is removed; some of it becomes trapped within the iron as inclusions known as stringers. These lend a certain strength to the iron and increase rust resistance. This process also reduces the carbon content, since some carbon is burned off with each heating. Iron created in this fashion is known as wrought iron, because it has been "wrought", or worked.

Wrought iron can also have extra carbon added to it by being carburized. This is when the bar is inserted into burning or heated charcoal to absorb carbon; it can then be folded and forge welded several times to distribute the carbon more or less evenly. This is the basis for creating the samurai sword. Finished objects can be case hardened the same way, by leaving the carbonized iron as a thin layer on the outside of the object. Simple steel swords are often created in this way, producing a hard shell that can hold an edge encasing a soft core that can absorb impact without breaking.

Wrought iron is by far the most common form of iron in use in the Dreamlands, but it has its limitations. However, creating steel from wrought iron is a difficult process. There are five basic methods commonly used: forging, faggoting, cementation, crucible, and alloying.

Forging, faggoting, and alloying take advantage of the fact that a bloomery can create iron with differing amounts of carbon. Forging begins by forge welding wrought iron and low-carbon, or mild, steel into sheets. Then high-carbon steel is layered on top, another low-carbon sheet added on top of that, and the whole sandwich forge welded together. It is forged into a thin sheet, then folded and forge welded. This last step is repeated a few or several times, depending upon the quality needed. Several sheets can then be welded together and forged into a bar. This gets rid of most of the remaining slag, but it also burns carbon with each welding, so it is important to start with a large amount of high-carbon steel.

Faggoting involves bundling rods of different forms of iron and forge welding them together. The final bar can then be broken up and refaggoted, or folded and forge welded a number of times to homogenize it as much as possible. Alloying involves melting wrought iron and adding varying amounts of cast iron or high-carbon steel to create mild steel.

Cementation involves carburization on a larger scale. Multiple bars of wrought iron are packed in charcoal in layers in a stone box and heated for as long as a week or more. Since the boxes are heated from below, the different layers absorb different amounts of carbon, less the farther away they are from the heat source. This creates what is known as blister steel, because the steel forms as blisters on the surface of the iron. These rods can then be faggoted to form sheet steel, or broken up and used as part of an alloy.

Crucible refers to the use of clay crucibles to heat mixtures of wrought iron, charcoal, and glass. The glass acts as a flux to absorb impurities, forming a slag, while the steel forms as buttons. This process can also be used to create steel directly from iron ore, or steel made from carburization can be used to produce homogenized steel that can be cast into ingots.

Despite the ubiquity of the bloomery process and the amount of iron it can produce, it cannot sustain a viable industry because of the amount of work needed to process the bloom after it has been created. What industrial iron-making capacity there is in the Dreamlands is sustained by blast furnaces and cast iron. These are not true blast furnaces but rather high-temperature Catalan forges, but in truth the only significant difference between a bloomery and a basic furnace is the temperature either can produce. In places like the Treadmill iron works in the Tanarian Hills outside of the town of Carsoon in Ooth-Nargai, and the city of Fonderia in the Six Kingdoms, facilities have been built consisting of multiple large-scale Catalan forges aerated by trompes based on waterfalls or dam spillways. These forges are designed to operate more or less continuously by feeding ore and coke, plus crushed limestone as a flux, into the top and drawing off molten iron and slag out the bottom. The iron contains from 4% to 5% carbon and is called pig iron. It is directed into sand molds where it forms ingots. When cooled, these can be stored until needed for further processing.

The ease with which iron can be smelted and collected makes the furnace much more efficient than a bloomery; however, the resulting very high-carbon iron is virtually useless as it is. It needs to be decarburized first, and this can be a difficult process. There are two main methods for removing excess carbon from molten pig iron, the osmond process and the finery process. Both, however, use essentially the same technique: using air to oxidize the carbon to carbon dioxide and blowing it off.

The osmond process exposes a stream of melted pig iron to a blast of air. This reduces it to droplets that are caught by a spinning staff. This forms a ball of mild steel or wrought iron, which can be remelted and subjected to the process again.

The finery process mixes a vat of melted pig iron with air. This can be done in one of two ways. The most basic is simply to stir or agitate molten pig iron while exposing it to the air, either ambient air or a blast of air. This is the basis for a finery forge or a puddling furnace, both of which create wrought iron blooms, though the latter can be stopped before complete decarburization to produce carbon steel or cast iron. The other is to direct an air flow through the molten pig iron. In an open hearth furnace or an ad hoc Bessemer converter, the iron remains molten as the impurities are driven off by the stream of air. It can then be poured off to form ingots. Both of these processes can be halted before complete decarburization to form cast iron or carbon steel, as well as allowed to continue to completion to form wrought iron, but this is easier with a converter.

It should be kept in mind that for all these processes of adding or removing carbon, only the broadest of estimates as to carbon content can be made. This is why iron tends to be divided into five basic types: wrought iron, mild steel, high-carbon steel, cast iron, and pig iron. Which type a batch of iron is assigned to is based on physical properties and how it was produced, not an analysis of its carbon content. This analysis can be done, but even using magic the result is fairly crude, and is used mostly to resolve disputes over which physical properties are more important.

Wrought iron is malleable, ductile, and easily welded, but also tough, meaning it resists fractures. It has good tensile strength, meaning it can stretch and bend without deforming, but is not as strong in compression; that is, crushing. As a structural material, this makes it similar to wood, except much stronger as well as fireproof, so it can substitute in any structure that would use wood. It can also be work hardened, making it stronger even than carbon steel in certain circumstances: work hardened iron sheets do not bend as easily as steel sheets. Its high ductility means that it will tear and rupture under extreme pressure rather than fragment, thereby preventing explosions. Otherwise, wrought iron can be used to make any kind of implement, tool, or object that does not require good crush strength. However, such items need to be work forged by hand, which increases their cost considerably. Wrought iron can be cast, but there is no advantage to it, and in fact casting can weaken it.

Cast iron, on the other hand, is decidedly not malleable, ductile, or easily welded, and it is brittle; it can crack if hit by a hammer. It will deform and break before wrought iron if stretched or bent, but it has high crush strength. As a structural material, this makes it similar to masonry, except it is much stronger, so it can substitute in any structure that would use masonry, especially arches. It cannot be work hardened; in fact, it cannot be forge worked at all, even when hot. However, it can be quench hardened in water, though this is rarely necessary. Its brittle nature means that if it fails under pressure, it will fragment rather than rupture, causing an explosion. However, it does have a relatively low melting point with good fluidity and castability, making it easy to work with, and repairs are very simple: simply melt the object down and recast it.

Casting is easier and therefore cheaper than forging an item by hand. Solid cast iron is also resistant to deformation and wear, and it has excellent machinability and heat-retention. It is also more resistant to destruction and weakening by rust. Cast iron can be used to create any implement, tool, or object that does not need to be flexible or hold an edge. Widespread examples include cookware, muzzle-loading cannons, pipes, and machine parts, especially cylinder heads and blocks. Cast iron columns allow for the construction of tall buildings without enormously thick masonry walls or pillars. It can also be used to create decorative elements for facades instead of using carved stone. However, care must taken when using it for support beams that it not be subjected to too heavy a load, due to its inability to stand stretching and bending stress. Also, it can weaken if subjected to extreme heat, as in a building fire.

Pig iron is far too brittle to be of use for anything except as a source for making cast iron or carbon steel. However, it can be used wherever weight is needed, such as ballast or to hold lighter objects in place.

Carbon steel can replace iron in nearly every practical use. Mild steel is just as malleable and tough as wrought iron, but tends to be stronger and it can be quench hardened, whereas high-carbon steel is stronger than cast iron but not as brittle. However, whereas the properties of wrought and cast iron are very distinct, they are less so for mild and high-carbon steel, making it more difficult to distinguish between the two.