Glossary

	Glossary
	Here is a Glossary of some of the more important iron steel and sword related words and terms that come up a lot in the Hyperscript and are either not necessarily known to all and sundry or possibly known but open to misinterpretation. Far more keywords with links to their appearance in the text can be found in the index Words given in red italics here are words you also find in this glossary.

Atom

My heartfelt commiseration if you had to look that one up! Here you'll find first help - but you should definitely go and see a professional.

Alloy

A mixture of two or more metals with "sliding" concentrations in contrast to a compound with a fixed concentration.
Iron plus carbon in any concentration below about 4 % is an alloy called steel or cast iron.
If you mix 25 at% carbon with iron (about 6.7 wt%), you have the fixed values needed to form only Fe₃C and that is a compound called cementite and not an alloy. Cementite relates to iron just like water relates to oxygen or hydrogen or the IRS to service: not at all!
An alloy is typically called after the element that dominates. On occasion some alloys have a name of their own. Iron alloys are also known as "steel" or "cast iron".

Austenite

The name for face-centered cubic crystal phase of iron or steel, quite different from the body-centered cubic crystal phase called ferrite, the stuff you typically have at room temperature.
Austenite is named after the eminent scientist William Roberts-Austen. For pure iron and most simple steels it can only exist at high temperatures. Austenite at room temperature is only found in high-alloy "austenitic" steels containing large amounts of e.g. nickel.

Beer

You do know what that is. What you don't know is how important it was and is for the development of iron, steel and swords.

Blast furnace

An iron smelter that produces liquid (cast) iron or pig iron in contrast to a bloomery that produces solid iron / steel.
There is no basic difference between bloomeries and blast furnaces except that the latter can be huge and run continuously since there is no need to remove anything from the inside. Everything comes out as liquid.

Bloomery

An iron smelter, always small, that produced a bloom, i.e. a piece of solid iron / steel, in contast to a blast furnace that produced liquid iron.
There is no basic difference between bloomeries and blast furnaces except that the necessity if removing the solid bloom and compacting it by banging it with a hammer necessitated to keep bloomeries small.

Bloom

The more or less spongy mixture of iron / steel with inclusions of slag, charcoals and other dirt produced in a "bloomery", an old-fashioned smelting furnace.
The distinctive feature of a bloom is that its iron / steel was never liquid.

Brass

An alloy of copper and predominantly zinc. All other copper alloys are called bronze.

Bronze

The generic name for all copper alloys beside brass. Typically distinguished by prefixes like "phosphorous-bronze". Without prefix it is usually tin bronze.

Brittleness

The opposite of ductility. A brittle material cannot be given a new shape by deforming it, e.g. with a hammer. It breaks or fractures if deformation exceeds a certain typically small limit.
Look here for details.

Carbide

A somewhat imprecise name for simple carbon compounds like Fe₃C (cementite) SiC (silicon carbide) or many metal carbides like Mo₂C; W₂C, and VC. Carbides tend to be very hard and are part of many steels.

Carbon steel

In principle, you can alloy iron with all the elements of the periodic table. Modern steel does incorporate many elements, indeed.
Carbon as alloying element is very special. For millennia it was the major alloying element (with phosphorous coming second), and even today carbon steel is very prominent because the sum total of the resulting properties often provides for the best compromise between performance and price.
However, the modern term carbon steel always "forgets" that there are always sizeable concentrations of manganese and silicon in your carbon steel too.

Cast Iron

The name of all iron-carbon alloys with a carbon concentration larger than about 2%.

Casting

Producing a certain shape of some material by pouring the liquid material in a suitable form. Extremely simple in principle, one of the most complex Materials Science and Engineering process in reality. Here is a first entrance into the "why".

Cementite

The stuff that turns iron into carbon steel. Cementite is the name for the chemical compound Fe₃C; it is an and iron carbide. It forms as a new phase all by itself inside your carbon steel as soon as the mix gets colder than some specific temperature specified by the phase diagram

Charcoal

Rather clean and pure carbon produced by pyrolysis (= heating in an oxygen free / lean environment) of wood. The one and only reducing agent available for smelting for several millennia.
All about that here.

Coke

Rather clean and pure carbon produced by pyrolysis of (always very dirty) coal.
Used for smelting after charcoal became scarce because most available trees were already cut down.
All about that here.

Composite

Something made from at least two different materials / phases on a macroscopic scale (visible without microscope). Examples.
pattern welded swords (2 kinds of steel).
Concrete (stones and cement).
Steel enforced concrete (concrete and steel).
Carbon or glass fiber enforced epoxy (CFC, GFC)

Composition

The quantitative listing of what is inside
Example: Some high-speed steel with a composition of 1 % C, 0.4 % Si, 0.4 % Mn, 4 % Cr, 6 % Mo, 6 % W, 2 % V, and 5 % Co.
This describes an alloy since percentages are "sliding", i.e could have other values, and there can be no compound with that exact composition.

Compound

Anything that can be also described as a molecule with a fixed composition. H₂O is a compound of 2 hydrogen and 1 oxygen atom called "water", C₂H₄OH is a compound of 2 carbon, 5 hydrogens and 1 oxygen atom called (ethyl) alcohol, and a mixture of water (51%) and alcohol (49 %) is an alloy called wodka.

Concentration

How much of something is contained in something else. There are many ways to attach numbers to concentrations, and that leads to a certain amount of confusion. Prominent are

Percent [%]. If not qualified it always means weight percent [wt%].
Atom percent [at%].
Parts per million [ppm]. Always relative to atoms or molecules.
1 ppm = 0.0001 %

Crucible

A typically small ceramic container that allows to melt metals or to smelt metal ores inside it without dissolving, melting or breaking.
Normal ceramics do not make good crucibles; "refractory" materials had to be developed for serious melting / smelting of iron and many other materials.

Crucible steel

Steel produced in ancient times (maybe 400 AD - 1800 AD) in the "East" (India, Sri Lanka, Iran, ...) by processing bloomery iron together with a carbon source in a small crucible that could resist very high temperatures. If all goes well the product is a ultra-high carbon steel that was liquid once and thus is free from solid inclusion, in contrast to bloomery steel.

Crystal

Any regular arrangement of atoms or molecules in space.

Damascene
Technology

A highly confusing misnomer that should not be used. Its usual meaning (especially in German) is the forging of a steel composite.

Defects

Any locally occurring deviation from the regular arrangement of atoms / molecules in a crystal.

Diffusion

The random movement of atoms inside some ensemble of many atoms. Easy to conceive for a gas, inconceivable inside a solid for centuries.
Diffusion in solids like iron nevertheless occurs, helped by defects like vacancies and interstitials, and provides the key to most if not all of material processing and technology.
I give you a science super link for this

Dislocations

Defects inside the otherwise perfectly periodic arrangement of atoms called crystal. The deviation from perfection happens along a (virtual) line that runs throught the crystal.
Dislocations are responsible for much of the material properties that are important for swords (or just about all metal products), in particular hardness and ductility.

Ductility

The opposite of brittleness. A ductile material can be formed into a new shape with a hammer before it finally will crack or break. It will undergo plastic deformation
Look here for details

Elastic deformation

Any deformation induced by applying forces (a better word is stress) to some objects that is reversible, meaning that the object assumes its initial shape again after the forces / stress is released.
Plastic deformation, on contrast is irreversible; there is a permanent shape change after the deforming stress is released

Elasticity

A dangerous word since it typically mixes up two different things:
1Young's modulus, a measure of how much force is needed to elastically elongate a standard sized piece of material a certain amount, and
2. how much force is needed to bend something like a sword blade a certain amount.
In the second case what you get depends on Young's modulus and the exact size and geometry of the blade. Materials with a large Young's modulus we call stiff; the opposite is resilient.
Look here for details

Etching

Generally the dissolution of something in a corrosive liquid.
Here the conditioning of a polished surface by dissolving a little bit in a structure sensitive way ("defect etching"), revealing the structure

Ferrite

The body-centered cubic crystal phase of iron or steel found at room temperature, quite different from the face-centered cubic crystal phase of austenite, the stuff you have at high temperature.

Fire welding

See "Forge welding"

Forge welding

Joining two pieces of iron / steel in the forge so it becomes one piece with a hardly noticeable boundary and with both pieces always being solid. This is in pronounced contrast to liquid welding, the "usual" type of welding today.
This is one of the many ways of welding, also known as "hammer" or "fire" welding. Essential are rather high temperatures and a kind of "flux", sprinkled on the hot surfaces before they are welded together by banging with the hammer. Every decent smith can do it; science has not yet quite understood how it works.

Forging

The mechanical shaping of something into the desired form by plastically deforming it with a hammer (or modern stuff like roller mills). Forging includes techniques like "hammer" or "fire" welding.
Until about 1850 the only way to process iron and steel since the stuff could not be cast (in contrast to most other metals in use by then).

Fracture

You know the general meaning of the term "fracture". What you may not know is that fracture occurs right after (always small) elastic deformation for brittle materials and after a more or less pronounced regime of plastic deformation for ductile materials.
Fracture is sensitive to very small defects in the material.

Fracture Toughness

Simplified, this is just a measure of how much energy is needed to fracture a standard size piece of something. It is easy to measure.
Not simplified, trying to understand fracture toughness is a nightmare.

Hammer welding

See "Forge welding"

Hardness

Simplified, hardness is defined (and measured) as the extent to which a given force can press a very hard object (like a pointy diamond) into the material to be characterized.
Not simplified, it measures at what level of mechanical stress (the yield stress) plastic deformation will occur in metals. Rather complex but well understood.

Interstitial

An atom of any kind that is located in the interstices of a crystal structure, i.e. wedged in between the regular atoms. Interstitials are comparatively mobile inside a crystal i.e.. the can diffuse easily.
Carbon atoms are interstitials in an iron crystal and that goes a long way for understanding the properties of carbon steel.

Liquid Welding

The "normal" welding where the two pieces to be welded are turned liquid at the seams and the gap filled with liquid metal, too.
In sharp contrast to all solid-state welding (also known as sintering or bonding) and in particular hammer welding
One of the most complex processes in Material Science and Engineering; here is why.

Malleability

A material that allows to change its shape with a mallet or hammer (= malleus in Latin ) is malleable or has a high malleability.
Same thing as ductility.

Martensite

One of the several possible manifestations (or "phases") of crystalline iron with a little bit of carbon in it (= steel). "Manifestation" means the specific way the atoms are arranged in space.
Martensite is not a particularly "good" way to arrange iron atoms; it only occurs if the steel is not capable to produce its preferred arrangement because you do not give it enough time by cooling it very rapidly ("quenching"). Martensite is much harder than the other phases of iron but also quite brittle.

Melting

The simple phase change from solid to liquid for a material with just one atom / molecule, e.g. iron. Always occurs at a fixed and sharply defined temperature, the melting point.
Not so simple if you have more than one atom / molecule, e.g. the binary system iron / carbon. That's what phase diagrams are about.
Don't confuse with smelting.

Nucleation

What needs to happen at the very beginning of a phase change. Things don't melt (or freeze) all over all of a sudden, but the new phase spreads from tiny nuclei that must "somehow" form first.
Nucleation is typically difficult, helped by defects, responsible for much that goes wrong, and a powerful tool in the tool box for making superior steel and other materials - if you know what you are doing.
I give you a science super link for clarifying the "somehow" above.

Ore

Any compound you find in nature that contains the element wanted, typically as oxide (e.g. hematite; Fe₂O₃) but also as carbonates (e.g. siderite Fe₂CO₃) or sulfides (e.g. pyrite, FeS₂). Ores are rarely pure compounds, but mixes of all kinds of stuff plus "dirt", called gangue.
Unfortunately, rocks that contain traces of pure gold or platinum and not their compounds are also called ore

Pattern
Welding

Forge welding (also known as hammer or fire welding) at least two different grades of iron / steel in such a way as to produce a pleasing pattern on the etched blade. It is such an especially complex way of piling.
Often (and wrongly) referred to as "damascening", in particular in Germany.

Periodic table

A way of arranging all 92 or so elements that brings out similarities and relations between the elements.
Elements with similar behavior are always found in the columns of the periodic table; elements with just one proton more or less in the nucleus are next to each other in the rows of the table.
Here it is.

Phase

A word with many meanings. Here it means exclusively a region of space where all physical properties of a material (e.g. density, hardness, chemical composition) are essentially uniform.
A clearly defined piece of some specific material in other words.
Graphite and diamond are just two different phases of the material carbon (C), as are water and ice relative to H₂O.

Phase Change
Phase
Transition

What happens at certain temperatures for materials. One phase of the same material then changes into one or more different phases.
Example 1: ice (solid H₂O) melts and becomes water (liquid H₂O),
Example 2: water evaporates and becomes steam (H₂O gas)
Example 3: ferrite (solid pure iron) changes to austenite (solid pure iron).
Example 4: Austenite plus 0,5 % carbon (one phase) changes into ferrite plus 0.01 % carbon and cementite (mix of two phases called steel).

Phase
diagrams

Maps in temperature - composition "space" that tell you exactly what you will find at some composition (e.g. iron with 1 % carbon) and some temperature (e.g. room temperature).
The phase diagram also tells you what happens if you go from one point (e.g. iron with 1 % carbon, room temperature) to another one (e.g. iron with 2 % carbon, 1000 ^oC). i.e. what kind of phase changes will occur at which temperature.

Photon

The "particle of light whenever light is represented by the particle avatar

Pig iron

The stuff produced by old blast furnaces. It is essentially cast iron with plenty of dirt.

Piling

Making a large piece of iron / steel by forge welding some single pieces with defined composition and geometry but without the goal to make a pattern as in pattern welding.
Details here

Plastic deformation

A permanent change of shape possible without cracking or fracture for ductile materials after sufficiently large forces (or better stresses) have acted on the object.
What a metal does after being struck by a hammer.
By definition impossible for brittle materials

Precipitates

Small particles of one substance or phase (like iron carbides; Fe₃C or silicon dioxide, Si₂O) embedded in a matrix of something else (like iron (Fe) or silicon (Si), respectively).

Quenching

Rapidly cooling something, e.g. by throwing red-hot steel in cold water. How fast the cooling occurs depends on size. Throwing a hot potato in cold water will cool down the skin within seconds but the inside of a large potato is still quite hot after minutes. There is nothing you can do about that.

Reduction

Here the opposite of oxidation. Oxidizing a metal produces a metal oxide ("MeO") or some kind of ore. Reducing the oxide, typically by the gas carbon monoxide (CO) produced be burning carbon (in the form of charcoal or coke), produces the metal and something else now oxidized, typically carbon dioxide (CO₂)
MO + CO --> Me + CO₂ in chemical shorthand.

Resilience

A vague term that is the opposite of stiff. A steel wire or a rubber band with the same cross section both deform elastically for forces not too large. But the steel is rather stiff compared to the resilient rubber; it gives far less than the rubber for the same applied force.
Stiff = large Young's modulus,
Resilient = small Young's modulus.

Second Law

Basic law of physics, subdivision thermodynamics, that states what kind of ("equilibrium") structure a large bunch of atoms present in some given form (for example a piece of steel, a beer, a cubic meter water, you) would assume at some temperature if given enough time.
It's a law that comes in equations so it gives you precise and unambiguous answers (provided you know what the question is and how to do the math).
Your equilibrium structure, by the way, consists primarily of water, some simple gases, and compost.

Segregation

There are many meanings, here I mean exclusively the separation of defects or impurities in a solid or during freezing by diffusion.
Segregation is what makes casting or any freezing process for something a bit "dirty" incredibly complex. Good for much fun and nightmares in Material ´Science and Engineering.
I give you a science super link for this.

Slag

Liquefied by-products of smelting, typically mixtures of oxides, that are not only almost unavoidable but absolutely essential to the smelting of metals.
Here is why.

Smelter

Any contraption that produces carbon monoxide by burning carbon that reduces the ore it is fed with (typically metal oxides, sulfides or carbonates) to metal and carbon dioxide (or other oxides).
Running a smelter - a bloomery or blast furnace, for example - involves to feed it (more or less continuously) with the ore, carbon (coke or charcoal) plus stuff for forming good slag at the top, to blow in a precisely determined and always large amount of air at the right position around the bottom, and setting the whole thing on fire.
What is going on inside a smelter is rather complicated.

Smelting

The process of reducing metal ore to the metal; typically done in a smelter.
Don't confuse with melting.

Steel

Before very roughly 1800+ steel was the word for an iron alloy with a carbon (or phosphorous) content between about 0.2% and 2.1% by weight.
In our modern world steel is a generic word for a wide range of alloys that always contain iron as the main component and many other elements (typically Mn, Si, Ni, Cr, V, ...); sometimes in in relatively large concentrations.
Steel is always a micro composite, consisting of different materials just on a microscopic scale.
I gave you a super module for the various kinds of modern steel

	Stiffness		Another word besides elasticity that needs to be considered with care. Stiff is the opposite of resilient and means "had to deform elastically". That may denote a specific material property expressed by Young's modulus as a number (stiff then means a "large" number), or the property of an object like a sword blade that can also be expressed as a mix (in a rather complex way) of Young's modulus and the precise dimensions / geometry of the object. A "thick" blade is always stfifer than a thin one made from the same steel, for example So beware!

Strain

What is caused by stress. In one dimension strain is simply the elongation of a an object expressed in fractions of the total length and therefore without a formal dimension.
A strain of 1 is a length change of 0.01 %.
Look here for details.

Stress

What causes strain. It is simply the force applied to a surface divided by the surface area. The (stupid) unit is Newton per square meter called 1 Pascal (Pa)
If you hang me from a rope with 1 cm² cross-sections, you have a stress of about 10 MPa.
Equal stresses cause equal strain in the same material - no matter what its dimensions.
Look here for details.

Structure

The arrangement of the various building blocks of a piece of material. For a simple crystal the structure describes the kind of periodic arrangement of the one kind of atoms encountered (austenite or ferrite?) plus the kind, distribution and concentration of the defects that live in that arrangement.
In a slightly more complex material like carbon steel it is all of that but separately for the different phases encountered plus the geometry and distribution of these phases
If you want it simple: The structure is what you "see" in a microscope after etching.
Here is an example. Now describe it in words.

Tempering

Nowadays it only means to keep some material at some elevated temperature for a while, typically to render the structure a bit less complicated by "annealing" some defects.
Tempered steel was and is steel that has been first quenched, producing extreme hardness coupled with brittleness and then is tempered, decreasing hardness somewhat but brittleness a lot.
In ancient times it meant predominantly the opposite, i.e. more or less rapid cooling by immersion into more less effective and disgusting liquids.

Temperature

You think you know what that is. You are most likely wrong.
Here is why.

True damascene

Describes the pattern on wootz swords as opposed to patten welded or piled swords.
Not a useful term; here is why.

Vacancy

A missing atom in a crystal, easy to conceive. Not easy to conceive is that the second law forces all crystals in the universe to produce a precisely determined amount of vancancies under all conditions; with rapidly increasing concentration if the temperature goes up. Even more difficult to conceive is that all material technology depends on these vacancies.
Start to find out why here.

Weldability

The ability to joing two metal pieces by liquird welding without suffering intolerable degradation of key properties.

Welding

The term welding without a prefix (e.g. hammer welding) always refers to liquid welding.
Weldabiltiy is a key property for many applications and at the same time an extremely complex property wth regard to composition and structure.

Wootz

There is no unambiguous definition of "wootz" or wootz" steel". Here I use the name "wootz" for ancient crucible steel that allows to produce swords with a "nice" water pattern consisting of bands of carbide (Fe₃C) precipitates.

Wootz swords

Swords showing a "nice" watered silk pattern. Here are details, including the meaning of "nice".

Watered (silk)
pattern;
Watered steel

Wootz swords with a specific pattern reminiscent of a water surface. Sometimes called "true damascene".
Always associated with wootz steel as the material used for making the sword.

Wrought iron

Originally meant as "worked iron", the stuff you get after consolidating a (carbon-lean) bloom.
Later the term describes iron rather low in carbon and not yet quite a steel that is easy to work with.

Yield stress
Yield strength

The particular stress (or the strain caused by it) that marks the onset of plastic deformation. A rule of thumb is: Stress below the yield stress produces only elastic deformation.
For metals the yield stress is the same as hardness, just given in different units.

Young's modulus

A simple number that relates stress and strain in the elastic region of deformation.
A material with a large Young's modulus (like diamond, tungsten or steel) is sometimes called stiff, a material with a small Young's modulus (like rubber or styrofoam) is sometimes called resilient.
Young's modulus has nothing to do with hardness.
Young's modulus of composite materials is essentially a (weighted) average of the two individual numbers.
Iron and all low alloy steels have pretty much the same Young's modulus. Piling or pattern welding thus does not change the elastic behavior of a blade.

With frame