Exploring metal especially as used in martial arts.
While chemistry might define a metal as an element that readily forms positive ions (cations) and has metallic bonds, the martial arts are more concerned with metallurgy (the field of materials science and engineering that studies the physical and chemical behavior of metallic elements, their intermetallic compounds, and their alloys or mixtures) for the improvement of arms and armor.
In the American Iron and Steel Institute (AISI) steel grades, the first 2 digits indicate the alloy composition and the following digits or letters indicated variants. The Unified Numbering System (UNS) is an alloy designation system consisting of a letter (for the alloy) and 5 digits (the first 3 of which match older numbering systems like AISI). There are other organizations that have also named different alloys such as the Society of Automotive Engineers (SAE).
Here are the Mohs hardness ratings of common items:
Fingernail or gold 2.5
Copper penny 3.5
A knife blade 5.5
Window glass 6.5
A hardened steel file 7.5
Copper (Cu, Z=29, SG=8.96, melting point=1084 C, Mohs hardness=3.0) was probably the first metal used in blades. UNS: C00001 to C99999, covers bronze and brass too.
Bronze improved on copper by alloying it with Tin (Sn, Z=50, SG=5.77, melting point=232 C, Mohs hardness=1.5). Although the Bronze Ages occurred before the Iron Ages, bronze was actually superior to old iron (not steel) almost every use. The transition from bronze to iron occurred more because of trade issues since tin ore is not commonly found with copper ore. The limitations of early metals kept swords short and wide --good for hacking and thrusting.
Brass is copper alloyed with Zinc (Zn, Z=30, SG=7.14, melting point=419 C, Mohs hardness=2.5).
Iron (Fe, Z=26, SG=7.86, melting point=1538 C, Mohs hardness=4.0) is harder than copper and its alloys but also more brittle. Copper and its alloys were used throughout the Iron Ages, but as iron got better and cheaper, iron overtook copper and its alloys in the Middle Ages.
Pig iron is raw iron fresh from smelting iron ore with coke and limestone. With around 3.5% C, it is very brittle and is not used for much except for making better iron and steel.
Cast iron has carbon greater than 2.1%. Brittle. UNS: F00001 to F99999.
Ductile cast iron or nodular cast iron is less brittle than cast iron because the carbon forms spherical nodules in the crystal structure instead of flakes.
Steel is an alloy of iron with carbon between 0.05 and 2%. UNS: G00001 to G99999 (except for tool steels).
Plain carbon steel has no significant quantities of other elements besides iron and carbon. Generally speaking lower carbon is more ductile while higher carbon is harder.
Ultra high carbon steel has carbon between 1 and 2%.
High carbon steel has carbon between 0.6 and .99%.
Medium carbon steel has carbon between 0.3 and 0.59%.
Mild carbon steel has carbon between 0.16 and 0.29%. Probably the most common steel with a good balance of ductility and hardness.
Low carbon steel has carbon between 0.05 and 0.15%.
Alloy steel is steel that has iron, carbon, and significant quantities of other elements.
Tool steel. A typical composition: 1.0% C, 0.3% MN, 0.25% SI, 0.04% S, 0.04% P. Known for toughness, especially for maintaining shape at high temperatures. UNS: T00001 to T99999.
HSLA steel or high strength low alloy. A typical composition: 0.15% carbon, 1.65% manganese.
Spring steel. A low alloy (mostly silicon) and medium-to-high carbon steel with very high yield strength.
Wrought iron has 0.035% carbon or less and is considered quite soft. Also has slag. Used since the Romans, but by the 1960s it was cheaper to make mild steel than wrought iron.
Commercially pure iron has less than 0.008% carbon.
Damascus steel is not a particular alloy of steel but a method of folding and layering iron to produce a distinctive blade which recent studies suggest had nanutubes.
Stainless steel or Corrosion Resistant Steel (CRES) is steel alloyed with at least 10% Cr. Stainless is non-magnetic and much more rust, stain, and corrosion resistant due to passivation, but does re-sharpen easily. UNS: S00001 to S99999.
S304xx or 18/8 steel is the most common steel.
S316xx is the second most common steel.
S409xx is the cheapest steel.
S420xx is surgical steel.
S440xx is cutlery steel, aka razor blade steel.
S44004. Aka AISI 440C. SG=7.63, 1% C, 17% Cr, 1% Mn, 0.7 Mo) is one of the most common steels for blades.
Aluminum (Al, Z=13, SG=2.70, melting point=660 C, Mohs hardness=2.75) is less dense than iron but is cheaper and is commonly used for non-sharpened practice weapons. UNS: A00001 to A99999.
There are many process that affect the properties of a blade.
Casting melts and pours material into shapes.
Machining shapes material by removing material from it by processes like drilling, sawing, milling, turning, grinding, punching, and stamping.
Forging shapes material by plastic deformation (a non-reversible change in shape).
Hammer and anvil, although modern forges also use presses and powered hammers.
Extrusion or cold drawing shapes material by pushing it through a shape called a die.
Drawing pulls on a material to lengthen it.
Rolling passes a material between rolls to flatten it.
Layering is done by hammering two pieces or folding one piece and hammering it back into itself.
Heat treatment or tempering alters materials via heat. More than merely softening, tempering frequently involves carefully playing with phase changes with time and temperature.
Quenching is rapid cooling. This "tenses" stress within metal making it harder. Grains re-crystallize into plates or lenses.
Annealing is slow cooling. This "relaxes" stress within metal making it softer. Small grains gradually re-crystallize to form larger grains.
Full annealing cools in the furnace.
Normalizing annealing cools at room temperature.
Case hardening or surface hardening hardens the surface by having one substance seep onto the surface of the target material at the right temperature.
Bluing is a passivation process that enables steel to resist rust better and it may or may not involve heat. Bluing oxidizes the surface of steel to form magnetite (Fe3O4), a black-blue oxide of iron which takes the same volume a regular iron and holds fast. In contrast, rust (Fe2O3), a red oxide of iron, does not take the same volume and does not hold fast. Bluing does not make an piece invulnerable to rust and should still be oiled.
Precipitation hardening or precipitation strengthening or age hardening or dispersion hardening adjusts the temperature so that an alloy becomes supersaturated with certain items which then precipitate or fall out within the material.
Differential hardening or differential tempering is where different parts of the piece are tempered differently to achieve different properties. The most famous example are the Japanese katana where the true edge is cooled more rapidly than the false edge (or spine) resulting in a harder (and more brittle) cutting edge, while retaining an overall flexible blade. The difference between the two is the wavy hamon line.
Lead (Pb, Z=82, SG=11.34, melting point=327 C, Mohs hardness1.5) is very dense, fairly soft and malleable, has a low melting point, is very corrosion resistant, and is a poisonous neurotoxin. Lead in the martial realm is best known for its use in guns as the bullet itself. Lead is the only metal that has a zero Thompson effect, i.e. no gradation in temperature when conduction electicity.
Uranium (U, Z=92, SG=19.1, melting point=1,132 C, Mohs hardness=6.0) is very dense, has a high melting point and hardness, and is radioactive. Uranium along with plutonium are fissile and are used in nuclear fission weapons. Depleted uranium is also used in high level armor and armor piercing.
Gold (Au, Z=79, SG=19.3, melting point=1,064 C, Mohs hardness=2.5) is very dense, fairly soft and malleable. Gold is often fought over.