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There are a number of structures in iron that are simply impossible to achieve on earth - for example, the Widmanstätten pattern of large, interlocking iron crystals that can only be found in meteorites that have cooled extremely slowly.

Hypothetically, suppose a culture had access to a form of magic that would allow them to nanoconstruct materials, placing every atom in exactly the correct place. What would be the optimal structure to create steel for, say, a sword?

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    $\begingroup$ What kind of properties should the steel have? It usually lies on a spectrum between rather soft / elastic and hard / brittle. In Japanese (Samurai) swords there are different areas in which the steel has different properties. Mixing all of that together to an average hardness would be inferior to the traditional sword. $\endgroup$ – Elmy Jan 8 at 17:40
  • $\begingroup$ Steel is an alloy. There is no single ideal version of steel. You might want to look at this Wikipedia page : List of blade materials. Note that there are also different types of swords and knifes and ideally these would have a careful blend of materials to make them suited to the particular purpose. $\endgroup$ – StephenG Jan 8 at 19:39
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    $\begingroup$ There are many kinds of swords. Some are intended for stabbing, some are intended for cutting, some are intended for hitting and crushing. Some are long, some are short. Some are expensive, some are cheap. You want different kinds of steel for different kinds of swords. And in the end, a scrawny guy with a cheap pistol, or a small woman with a crossbow, will still kill the best swordsman with the best sword. $\endgroup$ – AlexP Jan 9 at 3:05
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There is no perfect material in general, it depends on the application.

When you use a material to make a sword, you are looking for different properties in different places of the sword.

For the outer part you want to have high hardness, to withstand impacts, while for the core you want to have resilience to dissipate the energy of the impacts.

You cannot achieve both with a single material, this is why swords-makers had to come with all the techniques to differentiate the content of carbon in the iron matrix, since carbon is the main responsible for the different behavior of the steel.

Long story short, a single type of alloy sword would be inferior to a properly made sword: either too brittle or too soft.

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  • $\begingroup$ The outer part is hard in order to have a sharp cutting edge, not to withstand impacts. The rest is fine. $\endgroup$ – Santiago Jan 8 at 17:56
  • $\begingroup$ @Santiago, that's the same: if you want to keep the profile sharp, it has to be though, else it dents $\endgroup$ – L.Dutch Jan 8 at 18:07
  • $\begingroup$ a solid steel sword of a single uniform allow is still superior to a wooden one in most respects, it's unavoidable that there are generally superior compounds. indeed if a macromolecular sword could be formed in such a way as the questioner suggests it would potentially be superior 'from the get go' to a traditional forging... I say potentially only to be 'polite,' if it worked it would be better in every conceivable way, except perhaps ease of repair. $\endgroup$ – Giu Piete Jan 8 at 18:24
  • $\begingroup$ Who says steel is only iron and carbon? $\endgroup$ – WhatRoughBeast Jan 9 at 3:50
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    $\begingroup$ @WhatRoughBeast, I used "main", not "only" $\endgroup$ – L.Dutch Jan 9 at 3:55
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If you can perfectly place every atom, you can make a perfect metal crystal in the shape of a sword. I do not mean the single-crystals that we currently use in turbine blades and such, where there are NO grain boundaries, but some dislocations (such metals have excellent high temperature properties, but their cold temperature properties can be exceeded by alloys and polycrystalline grainlocking type methods). A perfect crystal would have NO dislocations, and no grain boundaries in the metal.

This would be extremely hard. I'm not even sure if modern materials science has a way to think of such things on the macroscale. You might need to break every atomic bond across the sword simultaneously to damage it. If you CAN break a few atomic bonds at once, it is possible the damn thing would just cold-weld itself together as the atoms are perfectly aligned.

Perfect crystal swords. Totally outside of current measurements, and very hard. I guess the edge would chip (on the atomic level) over time, and I'm not sure how that would impact the sword. Maybe the magic user just patches it up again with some spare metal atoms?

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    $\begingroup$ Actually, perfect crystals are not better in all respects than micrograined materials. The grain structure can absorb energy of deformation which would otherwise cause fractures, and fracture propagation will often stop when it hits a grain boundary. A diamond is much harder than carbon fiber, but must less useful when you want tensile strength. Material science is hard because material properties are complicated. $\endgroup$ – Mark Olson Jan 9 at 18:35

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