This sword is forged from meteorite iron - but how is that any good?

Question

You know the common trope in fantasy. Meteorite iron is amazing.

My armor is made of sky iron, made for me. A bear's armor is his soul, just as your daemon is your soul. You might as well take him away" – indicating Pantalaimon – "and replace him with a doll full of sawdust. That is the difference. Now where is my armor?"

Iorek from The Golden Compass.

Cold iron is iron found in a pure state (either meteoric iron or an especially rich ore) and is forged at a lower temperature to preserve its delicate properties.

Probably from Volo's Guide to All Things Magical (ISBN-13: 978-0786904464), via this site.

And I won't even link to TVTropes.

And you probably know how it really is:

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What I'm asking here is how to make meteorite iron superior, in a medieval setting, without magic?. What changes to reality, especially star system, I need to make?

Point by point, what I want is:

1. An Earth-like planet with humans or humanoids indistinguishable from humans.
2. Meteors that could form in the solar system with an Earth-like planet, if there is a way to make them numerous enough.
   1. Meteors that actually fall on Earth are best.
   2. Could-be-meteors that don't really fall on Earth but are found or suspected in our Solar system are strong second best.
   3. Changing solar system is acceptable. Smaller changes are better.
3. By numerous enough above I think amount sufficient to equip heroes if the quality would be legendary, or small armies if it would be barely "very good".
4. Of course, it does not have to be pure iron. Or even to contain iron at all. Only similar enough that calling it "meteorite iron" or "star iron" would seem justified.
5. Qualities I seek are resistance to breaking, edge retention, resistance to chipping/notching, ability to forge it thinner, et cetera. Basically, anything that would make clearly superior swords or armors. Preferably both.
6. Last but not least, it must be possible to actually forge it using medieval techniques, and it must be impossible to forge something better or even similar using available technology and no meteorite iron. If tech required is sufficient to make modern alloys, it is no-go.

Note: Well described and proven impossibility of such meteorite iron also counts as an answer. One I hope I will not get, but one I can accept if that's the case.

Answer 1

Kamacite and Taenite

Kamacite and Taenite are both Iron-Nickel alloys found (on Earth) only in meteorites. Kamacite's composition is in the 90:10 to 95:5 Fe:Ni range. Taenite's composition is from 20% to 65% Nickel.

Kamacite, in particular, can form massive crystals. A kamacite crystal listed in table 1 here had dimensions of 0.92x0.54x0.23 meters, and a mass of 303 kg; plenty of material to make a whole batch of swords. Finding these crystals means that you have found a pre-mixed alloy. There is no longer any need to smelt to mix the alloy. The crystal can be directly worked into a sword via the normal methods. The melting point of both kamacite and taenite is not significantly different from iron, so normal, time-period appropriate methods of swordmaking would be valid.

Hardness

Hardness is the resistance of a blade to strain. That is, when a force is applied, how resistant is the material to deforming. A harder blade will cut through a softer one (or wood or bone) without getting blunted.

Both these alloys have a hardness advantage over regular iron. A study of 22 siderites (Iron-Nickel meteorites) reported on their hardness in Table 1 here. For a comparison, we can use this study of wrought iron sampled from 10 bridge built in Massachusetts in the 1800s.

The average Rockwell B hardness of 24 meterorite samples is 81; while the average from 53 bridge components is 58. The 95% upper limit for the bridge iron is 72; 92% of the meteorite samples had a hardness greater than this. For a comparison to more modern materials, matweb.com's database has information of 176 types of high carbon steel. The average Rockwell B hardness is 95.7 over the range 43-100.

Rockwell B is a hardness test for softer materials, so it doesn't scale well to harder materials. For example, the difference in theoretical hardness between 95 and 100 is much larger than the difference between 40 and 50 on the Rockwell scale. For a better high hardness test, the meteorite study includes the Brinell scale as well.

The average Brinell hardness is 169, but with an upper limit of 330. 9% of the samples have hardness over 230. This variance in hardness may be a result of the shocked vs. unshocked nature of the crystals. Unshocked crystals evidently have hardness about 50% higher, according to a Wikipedia statement that I cannot verify.

Unworked iron has a Brinell hardness of 110-120. This is the base material from which a sword is made, so a kamacite alloy can start two or three times harder than pure iron.

The standard measure from blades is the Rockwell C test. The Rockwell C hardness for three Damascus steel blades from ~1750 are given as 23, 32, and 37. This chart converts those values as 240, 300 and 340 on the Brinell scale. A summary chart (Graph 1 here) shows average example blade hardness from 8 swords that convert to 130, 170, 180, 190, 210, 260, 400, and 440 on the Brinell scale.

For modern materials, cast iron has a Brinell hardness of 183-234 and high carbon steels from 163-600 with an average of 262 (over 207 different types). So it is possible to find a meteorite alloy that is harder than some modern high carbon steels and as hard as high quality Damascus steel blades. Perhaps 10% of the iron-nickel meteorites you find will be of the un-shocked high hardness variety. A modern tool steel forged into a Damascus type blade had hardness of over 700.

Strength

Strength is the ability to withstand deformation. The integral of strength over deformation distance is toughness. While a hard blade might not deform upon being struck against a stone wall, it might fracture. A tough blade will deform (getting notched, or bent slightly) but won't fracture. The data for stress-strain curves for meteorite samples is not available (to me, at least), so instead of toughness I am using strength at comparable strains.

The Gibeon iron-nickel meteorite was drawn into a rod with a tensile strength of 392 MPa and a compression strength of 373 MPa. For a sword blade, compression and tension strengths would be similar to each other. For a raw meteorite alloy, the kamacite meteorite found in Canyon Diablo had a compression yield strength of 424 MPa with 0.2% compression (that means it only deformed by 0.2% of its initial size); tensile strength should be similar.

The comparisons here are to modern cast iron, with a tensile strength of less than 276 MPa. High Carbon steels have a range of tensile strengths from 161-3200 MPa with an average of 1010 MPa over 219 types. The ratio of tensile to compression strength can vary by application.

Manually puddled wrought iron, made and reported in the 1920s, had tensile strengths around 165 MPa at 0.2% tension. The bridge samples averaged yield stres of 230 MPa; all samples yielded below 0.2% tension. An investigation of iron products made in a replica of a 10th century forge had yield stress from 300 to 500 MPa with yield elongations between 0.05% and 0.4%. Ancient Wootz steel swords were found to have yield strengths in the 800-1500 MPa ranges. Modern steels forged into layered Damascus steels were found to have yield strengths around 1200 MPa at 1.3% elongation.

Overall, we can see that the compression strengh of the meteor iron is lacking in comparison to modern materials or the finest Damascus steel, but competitive with medieval forge products.

Conclusion

The alloys found in iron-nickel meteorites had properties that would have made them competitive as blade making materials. For hardness, un-worked meteor crystals had hardness equal to the finest Damascus steel blades, close to the finest of any blades, and significantly higher than wrought or cast iron. This material is un-worked; the raw alloy has a hardness advantage of two or three times on un-worked iron. Presumably there is quenching and tempering process that can increase the raw material's hardness by another factor of two or three, just as ancient steel blades are up to four times harder than raw iron.

Toughness is greater than the iron products that would be common in everyday use, but not as great as the best steels available. Toughness is equivalent to iron sword products made with 10th century technology.

Overall, I think that you could reasonably expect a 'just right' Iron-Nickel alloy meteor to contain large, pre-alloyed crystals that could be forged into swords. This alloy, if annealed just right (through luck, the assistance of the Gods, or however the smith acquired the right knowledge) would make a blade strong enough to be usable, but harder than anything available until the 19th century.

Answer 2

Don't make space iron better. Make all other iron worse.

Read up on Low Background Steel. Have all of earth's iron contaminated with something, and less useful than we think of iron being.

At some time in the past, there was a cataclysmic event which contaminated all iron with something. Maybe the Elder Gods awoke, and their presence cause decay or corruption of all steel or iron.

Only meteorites that have landed since then remain free of this imperfection.

As with low background steel, you could argue that items already forged into steel were safe from this corruption, making meteorites and ancestral relic swords both viable, but anything forged new is poor.

Answer 3

Some meteoric iron can make for very nice weapons, you can go buy some now. In the medieval period most places couldn't actually make great weapon steel. Many swords (where the quality of the steel and the style of manufacture is more important than in an axe head or spear point) came from just a few places/forges, or at least the metal was sourced from a few areas that could produce quality sword steel. So not any old blacksmith could hammer out a quality sword even if they had the right base metal.

So for you, the area the heroes are in simply doesn't have good quality iron ore stores and no one really knows how to refine what they do have (look at crucible steel, Japanese pattern welding, and Damascus steel for examples of very technique specific/location specific steel sword manufacture). So meteoric iron from a few meteors with the right metallic components could very well be the only source of quality sword steel.

To source most of your iron from meteors would be problematic, it would mean that the tectonic activity of the planet itself, as well as it's construction, is substantially different from Earth, and lots of falling meteors depositing metals tends to not make for an environment suitable for advanced civilization (or any civilization, really). Obviously you can handwave this with magic (maybe a high metallic content moon was shredded in an ancient war and rained down on the planet?) or with just ignore it completely. In your world, or at least the area the story is set in, ground deposits of iron are very scarce so meteoric lodes are actively searched for and fought over.

Of course in this area swords probably wouldn't be particularly popular and other weapons would be more prevalent (which was generally true for most of the historic medieval period anyway), swords that were around would be cherished heirlooms and the sword fighting techniques would be restricted to those nobles with access to swords in the first place.

It is also worth noting that the origins of "cold iron" supernatural properties probably start well before the iron age, when meteoric iron, even poor quality, was probably superior to the bronze metal used by everyone else. There is little to suggest that meteoric iron would be superior to what a medieval smith could produce from a good sword smith shop that had access to good terrestrial iron.

Answer 4

Iridium iron: Chengdeite.

http://www.galleries.com/Chengdeite

Chengdeite in fact is only beat out by minerals that are more enriched in iridium and/or osmium; specifically the minerals iridium, osmium and iridosmine, an iridium/osmium alloy. Iridium, at a calculated density of 22.65 grams per cubic centimeter, is probably the densest element known to man.

Iridium is more common in meteorites than it is in earth's crust, probably because it is so freaking dense any iridium on the planet is in a lump in the center of the core. The high iridium content of the geologic layer at the end of the Cretaceous is what gave a hint that a meteoric impact might be involved. Iridium is three times more dense than iron and three times as hard. It is so hard that it is very difficult to process; to my understanding the main use of iridium alloys is for dies which do not wear away as they process huge amounts of steel wire.

Your sword of iridium iron would be like Odysseus' bow or Thor's hammer - three times heavier than it appears to be and so requiring preternatural strength to wield. The extreme hardness would mean extreme sharpness, and I suspect sharpening stones adequate for terrestrial weapons would not sharpen this celestial sword - you would need garnet or maybe sapphire.

Your meteorite sword would be very heavy, very sharp and nearly unbluntable.

Answer 5

@kingledion has the best base reality answer. There was a scy phy Beowulf crossover I saw. Where the crashed space traveler forged part of the hull of its ship to destroy the alien monster (Grendal) that escaped from the crashed ship. A crashing space ship could easily be seen as a falling star. And depending upon the space ship design, its hull could be superior to standard iron/steel.

http://www.imdb.com/title/tt0462465/

Note This is most likely an aluminum alloy or titanium based on current earth space tech. However I haven't been able to find the specific alloys used in the Space shuttle.

Answer 6

the main advantage of meteorite iron is it is far purer than the vast majority of earthly sources, and removing impurities is the single biggest limitation is the strength of early steel. It is really hard to make quality steel when you don't know what is in the iron to begin with, especially things like silica, oxides, and carbon, the things iron rich meteorites have very little of. The forging is still the same (maybe a bit easier since you don't have to do excessive folding) but it is the turning of ore into usable metal that is much easier. Better raw material often translates into a better finished product, the steel has the same properties throughout, not mixed mess full of weak points.

Compared to modern steel meteorite iron is crap, but you need industrialization and advanced chemistry to make modern steel. Compared to the bog iron and bloom steel of the time it is wonderful and until advanced smelting techniques (crucible steel, ~8th century) and high quality ores are discovered it is the best raw material available. So up until around the 6-8th century meteorite iron would have been better than anything and would stay better than most for quite a while afterwards.

Answer 7

Metallurgy and biology to the rescue: your characters' usual enemies are severely allergic to nickel (or have some other really bad biological reaction to it).

Meteoric iron, despite the name, is actually an iron/nickel alloy. Even in the real world, people with nickel allergies often have trouble wearing alloys of nickel as well. If your enemies have particularly terrible reactions to nickel, then meteoric iron (to say nothing of pure nickel) would essentially be poisonous to them. The more realistic skin allergy might still be present in some people, and even arouse suspicion.

If your culture mirrors medieval Europe, then they likely do not have the technology to melt or smelt nickel: the temperatures required are simply too high. They might not even understand that nickel is a distinct metal. But the effect of meteoric iron on an enemy poisoned by nickel would be all too apparent, and may give rise to meteoric iron's reputation as a mighty enemy-killer, even as the relatively low level of technological advancement prevents them from making their own.

Answer 8

Set your civilization in the bronze age. Iron (or steel) doesn't exist except for what falls from the sky.

No one even knows what "iron" is, that it can come from the earth or how to extract it from the earth (hematite and magnetite)

Answer 9

Metallic meteorites are made of iron nickel alloys. Iron has been made from terrestrial ores for a few thousand years but nickel is pretty hard to get. We didn't isolate it here until the 1750s. Meteoric iron has average 10% nickel but can be 25% or more in some cases. Cobalt is the main other constituent at about 0.5%.

Nickel steels have several desirable properties. You can make low C steel with a few percent nickel content that has significantly higher elastic and fracture strains than unalloyed steel. Meanwhile it doesn't change the Young's modulus, so the material ends up having higher strength and toughness. It would also somewhat resist corrosion. The extreme example if this is called maraging steel, containing 15-25% nickel (but cobalt than almost all meteorites) which can be made to have remarkable strength at high toughness for aerospace applications. Sport fencing foils are also made of matching steel for its fracture resistance.

If you use a really high nickel steel it can be made stainless. It'll be reasonably soft so not blade material, but you can plate a sword with it and make it mostly corrosion resistant. It would stay bright and sharp even in humid environments. This would be pretty amazing to medieval people.

If you're willing do slightly stretch astrophysics then somewhat higher Co content in meteorites is plausible. With the help of a sufficiently wise wizard (metallurgist) the production of this material may be plausible with medieval infrastructure. Heat treatment and controlling impurities will be the important knowledge. You can frame meteorites as a starting material for maraging steel.

This would be a superior sword core steel with remarkable strength and toughness. It's low in carbon so it's not very hardenable so the edge should be high carbon steel forge welded on. This would be especially valuable in a context where high carbon steel is hard to make (which is true in most medieval societies.)

This stuff is fine for swords but it would be amazing for armour. Especially plate armour where buckling resistance is sought. That's exactly what it's used for in missiles and aircraft.

I think a cool concept is to apply people with modern knowledge (wizards) to a low tech medievalish society and see what they can do.

Answer 10

Some good answers here already, but how about this:

There is no other iron on the planet.

So meteorite iron is the only iron, from which skilled smiths can make steel, which obviously beats the crap out of the bronze weapons otherwise available. In a world where steel doesn't otherwise exist, its strength, hardness and resilience would seem pretty magical.

Answer 11

Most meteoric iron also contains some varying amount of nickel. Iron-Nickel alloys are stainless steels with varying levels of corrosion resistance, and are typically less brittle then straight steel.

Several other trace metals can be added to further increase varying degrees of corrosion resistance, anti-rusting, or toughness.

One way to make such weapons desirable would be the setting that your swords are used. Do the enemies have corrosive blood? Maybe meteoric blades don't dissolve into nothing after a killing (bloody) strike.