METALLURGY IN MIDDLE-EARTH

James Owen: 325 S. Cloverdale Ave #105, Los Angeles CA 90036-3439, USA (jhgowen@earthlink.net)

©1994 James Owen; first published in Other Hands 4.

The materials sections in the 'Moria' and 'Lórien' supplements are riddled with inaccuracies which I will not waste time going into here. It would instead be better to start again and produce some scientifically-accurate material. Also some metals are named, without giving any of their properties.

First a brief explanation of materials science, then a list of useful metals and alloys, and finally some metal-shaping processes.

Metal atoms cluster together into a crystal. A large piece of metal which is all one crystal can be made for particular applications, but this is very expensive and is not generally beneficial. A more typical piece of metal will contain millions of small crystals, known as grains, each c.1-10µm in diameter. This crystalline structure is the cause of all the physical properties of metals. Because the metallic nature of an element is dependent upon its electrons, not the nucleus, it is very easy for one metal to dissolve in another, and so alloys are easily formed. Other non-metallic elements, such as carbon, oxygen, phosphorus and sulfur, can also be dissolved in metals due to their small size. One fundamental fact about metallurgy is that the properties of an alloy are not the sum of its constituent properties, so that the addition of an element to a metal will not have predictable results.

When a piece of metal is stretched, it will first stretch elastically, and when the stress is removed, it will return to its original length. If it is pulled too hard, it will pass its elastic limit, and deform permanently. There are basically two mechanisms by which a metal deforms. Line defects, 'mistakes' in the crystal, are called dislocations. Under an applied stress, these will move through the crystal, and so the shape of the crystal will change, producing a plastic strain in the crystal which is permanent. If the pull is too hard, a weak point in the metal will stretch more than surrounding areas, and this so-called 'neck' will eventually cause the piece of metal to break in half. The second way for a crystal to deform is more catastrophic. At the tip of a small crack, or hole in the metal, the stress will be concentrated and so the crack will lengthen. The crack will grow slowly for a while, then at a certain point, the piece of metal will suddenly fail, in an explosive manner. This is called brittle fracture.

What determines whether a metal is brittle or tough is the difference between the stress needed to cause dislocation flow, and the stress needed to cause brittle fracture at some pre-existing crack. If the dislocation flow stress is lower, the metal is tough, if the brittle fracture stress is lower, the metal is brittle.

Some of the useful properties are:

Metals

I will first list the pure metals given in Moria and Lórien, in the terms given above.

We are asked to believe that metal is made into a wire form by drawing from the melt, like nylon. Later, we are told that dwarves hammer metal for weapons 'to compress the basic fabric of the metal'. Let us have some real science here. First, a more accurate analogy for wire-drawing would be squeezing toothpaste from a tube, this shearing process gives the wire high strength in the longitudinal direction. Secondly, sword blades were historically hammered and folded because back when iron could not be melted, the only way to remove the carbon from the metal to stop it being brittle, was to hammer it flat so that the carbon rose to the surface, then fold and hammer again. This creates a laminate of strong, brittle, carbon-rich particles in a matrix of softer, tougher iron. In the same way that fiberglass is stronger than either glass or plastic, this process makes an extremely strong and tough sword. In Moria, we are told, the dwarves are able to melt iron, and so would not need to do this. Cycles of hammering and heating would be necessary to reduce the grain size of the metal, which increases both strength and toughness, which are not the same thing. There are many other examples, which I will not go into here where the science is confused.

The author of 'Moria' seems to think that a metal that will stretch like rubber makes a good bowstring. Bowstrings are designed not to stretch, so that the bow itself is forced to bend into a curve and to store the effort of the bowman's arm as elastic energy, which is released as the arrow's motion when it is loosed.

Good steel requires that care be taken at every stage: in choosing the right ore, smelting under proper conditions in order to remove impurities, in adding alloying metal in the right amounts, cooling down at the right rate, in rolling or forging to the right degree and at the right temperature, in quenching at the right speed so as not to crack it, and in tempering—after quenching, whatever the Rolemaster Alchemy Companion might say—at the right temperature in order to obtain the correct strength and toughness. Care means that high-quality and high-price steel is produced; carelessness means that it is brittle and therefore useless.