turning a blade into molten metal, and back again

[dethkruzer]

so I don't really have much in the understanding of metallurgy, so I thought I would ask: if you had a sword or other similar metal weapon, that you needed to melt down say for example in order to alloy the base metal, and then reforge it back into a weapon again, how would the process here work out? Asking for sake of research.

[Brother Oni]

so I don't really have much in the understanding of metallurgy, so I thought I would ask: if you had a sword or other similar metal weapon, that you needed to melt down say for example in order to alloy the base metal, and then reforge it back into a weapon again, how would the process here work out? Asking for sake of research.

Depends on the type of sword. Many of the higher quality swords consists of multiple grades of metal, with a softer core for the main strength and harder and a more brittle harder layer for the cutting edges (often with a number of intermediate layers between). There are also complex internal microstructures like those found in wootz steel, and additionally complex manufacturing techniques required for damascus or other pattern welded steel.

Melting a sword down will remove pretty much all the complex microstructures and layering, plus doing it properly will burn off all the intentionally added purities that give these swords their unique properties and superior performance (doing it incorrectly will give you poor quality steel riddled with impurities and weak spots). If you wanted to re-create the same quality blade again, you would have to do all the processing and manufacturing again from scratch; hopefully you have a blacksmith, sword sharpener and all the other craftsmen who know how it was originally created.

Even bronze swords are composed of multiple different bronze alloys - the Sword of Goujian comprises of 6 different alloys of bronze:

https://upload.wikimedia.org/wikipedia/commons/e/eb/Sword_of_Goujian%2C_Hubei_Provincial_Museum%2C_201 5-04-06_01-edit.jpg

While this sword is most probably a decorative weapon, excavations of bronze weapons used for combat typically reveal a composition of at least 2 different alloys.

Edit: Mass produced swords generally won't have this level of complexity so can be basically almost stamped out in large quantities (eg the standard issue swords of Imperial Japanese officers during WW2). While they're generally very consistent grade steel, they're not very good quality swords.

[dethkruzer]

lets say for sake of argument that the weapon in question did not possess this level of complexity to the internal structure, at most perhaps what is brought on by some very rudimentary differential heat treatment. Let's also say that the original material is fairly poor in terms of things like impurities and such in the metal. I.e generally poor material, fairly unremarkable craftsmanship, just that the material itself is to be reused because reasons.

That said, I'm not so much looking into all the intricaies like that, and more into how you would go turning a weapon or remnants-of-a-weapon back into molten metal and then worked back into something usable. I assume you'd probably cast the molten metal into an ingot or billet and go from there, or something like that?

[gomipile]

In general, small quantities of steel were not historically and are not now often handled in a molten state. When reusing small quantities of steel for bladesmithing, they'll be heated to red hot and forged back together.

If steel is being melted down and re-used, it's typically only for structural grade steel like A36.

For something close to what a bladesmith would actually do in a situation like that implied by your question, look at canister welding. Basically, you make a steel can, put all the scrap you want in the final product in the can, seal it up, heat it, and forge it all into one solid mass. This is often done for aesthetic reasons, to get a nice visual pattern on the surface of the steel.

If canister welding were being done for for more practical reasons, the bladesmith might, say, fold the resulting billet several times to smooth out the resulting product to avoid discontinuities which could weaken the final product.

The more general set of techniques here is are "pattern welding" and "forge welding."

[Lvl 2 Expert]

If we dial it back, and talk about a nice military knife or something to ignore the layers and such, a lot of the quality difference is going to depend on how well the reworking is done. If you just melt the blade and recast it you're going to end up with a lower carbon content (I think, right?), which means a more ductile blade. One of the ways to counteract this is to temper or harden the steel. Depending on how well the tempering and several similar post-production steps are handled and how well they were done last time you're probably still going to end up with something that feels a bit more like soft tool steel than the old blade did, but it's really not that much of a foregone conclusion. If the new guy has some serious skill he might be able to make something that's better than the first version. But that also depends on how good the first knife maker was. In general it'll be a pretty easy blade to sharpen, but will have some trouble holding an edge. And overly hardening it might just make it prone to breaking without improving the edge retention enough. (Making swords into plowshares would work pretty well though, a softer tough steel is often preferable for that kind of tool.)

However, sword steel is not really further removed from the ideal pre-cast sword steel than raw ore is. You can just take the whole thing back a few steps in the production chain, clean it off impurities, add the right carbon content, even make different steels if you want to do layers. You're going to lose a little material, but in principle there's nothing stopping you from melting a good sword back into a good sword. It's just a lot of work, you're doing the work of a steel mill, but at a very small scale, as well as the work or a sword smith. But you're much less limited in what you can do with the material. You should even be able to re-separate most alloys.

[factotum]

The real question is, though, why would you go to all that effort? There has to be a reason why you're melting down a sword and re-using its metal rather than just forging a brand new one. In Game of Thrones they do this with Valyrian steel because they don't know how to make it, so their only choice is to re-use what they already have.

[Bohandas]

The real question is, though, why would you go to all that effort? There has to be a reason why you're melting down a sword and re-using its metal rather than just forging a brand new one. In Game of Thrones they do this with Valyrian steel because they don't know how to make it, so their only choice is to re-use what they already have.

Perhaps it's broken. Like into more pieces than is reasonable to patch or weld.

[Bohandas]

Would it make a difference if it was dissolved in aqua regia and then percipitated rather than melted?

[Knaight]

Would it make a difference if it was dissolved in aqua regia and then percipitated rather than melted?

Either way you lose all the microstructures and the general shape. You're effectively starting over with a chunk of steel.

[halfeye]

Does this have any relation to the legends or stories of broken swords that were remade at least as good as new?

[gomipile]

Perhaps it's broken. Like into more pieces than is reasonable to patch or weld.
Canister welding is often done with steel filings in the mix. Thus, there are often millions of pieces of steel welded together to make a patterned blade if one counts each particle of steel dust and filings.

Even when filings aren't used, ball bearings and pieces of twisted steel cable are often used. A typical canister weld like this will have at least dozens of individual pieces of steel in it.

Given that, how many pieces would it take to be "more pieces than is reasonable" to weld?

[Brother Oni]

If you just melt the blade and recast it you're going to end up with a lower carbon content (I think, right?), which means a more ductile blade.

Yep, but melting iron requires significant temperatures (>1000C). An easier way of getting a lower carbon content steel was to keep it red hot (~700C) for several days and let the carbon react away with atmospheric oxygen to make carbon dioxide.

I'll have to check, but canister welding and other forge welding techniques doesn't significantly change the structure of most of the blade, only the heated parts around the joins as that's where you're focusing the heat and pressure.


Either way you lose all the microstructures and the general shape. You're effectively starting over with a chunk of steel.

Assuming that precipitation or iron is even possible with aqua regia (I'm very dubious, as iron sulphate is typically used to precipitate out other metals dissolved in aqua regia), you'll end up with a lump of iron, rather than steel, which involves even more work.


Given that, how many pieces would it take to be "more pieces than is reasonable" to weld?

It might also depend on the size of the pieces and how the blade is broken - a large blade broken into three evenly sized fragments would be easier to repair than a blade with three separate breaks at the hilt.

Narsil from The Lord of the Rings was broken into 2 pieces (6 in the movie) and it was reforged then.
The Valaryian steel blades from A Song of Ice and Fire underwent a more dramatic reworking as a single great sword was remade into two smaller blades. I suspect that a bit of fantasy suspension of disbelief is required here, as I can't think of a metal that would survive this sort of re-forging and still keep its original properties without basically re-making the blade from scratch.

[snowblizz]

(Making swords into plowshares would work pretty well though, a softer tough steel is often preferable for that kind of tool.)

So it's much easier to melt swords into plowshares than to go the other way back? That gives the saying a lot more gravitas really.

[warty goblin]

Depends on the type of sword. Many of the higher quality swords consists of multiple grades of metal, with a softer core for the main strength and harder and a more brittle harder layer for the cutting edges (often with a number of intermediate layers between). There are also complex internal microstructures like those found in wootz steel, and additionally complex manufacturing techniques required for damascus or other pattern welded steel.

Melting a sword down will remove pretty much all the complex microstructures and layering, plus doing it properly will burn off all the intentionally added purities that give these swords their unique properties and superior performance (doing it incorrectly will give you poor quality steel riddled with impurities and weak spots). If you wanted to re-create the same quality blade again, you would have to do all the processing and manufacturing again from scratch; hopefully you have a blacksmith, sword sharpener and all the other craftsmen who know how it was originally created.

Even bronze swords are composed of multiple different bronze alloys - the Sword of Goujian comprises of 6 different alloys of bronze:

https://upload.wikimedia.org/wikipedia/commons/e/eb/Sword_of_Goujian%2C_Hubei_Provincial_Museum%2C_201 5-04-06_01-edit.jpg

While this sword is most probably a decorative weapon, excavations of bronze weapons used for combat typically reveal a composition of at least 2 different alloys.

Edit: Mass produced swords generally won't have this level of complexity so can be basically almost stamped out in large quantities (eg the standard issue swords of Imperial Japanese officers during WW2). While they're generally very consistent grade steel, they're not very good quality swords.

I don't think that's the case with Mediterranean/northern European bronze weapons. They have hammered edges to work harden the material, but I've never seen any documentation or evidence of a composite alloy blade. In which case you very much could melt it down and recast it into a new weapon or weapons. The only microstructure you'd lose is the work hardened edges, but you can just redo that.

[gomipile]

I don't think that's the case with Mediterranean/northern European bronze weapons. They have hammered edges to work harden the material, but I've never seen any documentation or evidence of a composite alloy blade. In which case you very much could melt it down and recast it into a new weapon or weapons. The only microstructure you'd lose is the work hardened edges, but you can just redo that.

Good point. The OP didn't specify steel.

With bronze, yeah, one melts it down and casts a new blade. The important thing is just to make sure not much oxygen touches the melt so that tin doesn't burn out of the mixture.

[Brother Oni]

I don't think that's the case with Mediterranean/northern European bronze weapons. They have hammered edges to work harden the material, but I've never seen any documentation or evidence of a composite alloy blade. In which case you very much could melt it down and recast it into a new weapon or weapons. The only microstructure you'd lose is the work hardened edges, but you can just redo that.

I was fairly sure that some of the higher end bronze weapons found in the Mediterranean region had such different alloys of bronze layered together in a single blade, but I'll defer to you on this subject as the only bronze weapons I really know about are Chinese ones, which did have such alloys; metallurgical analysis of arrow bundles found with the Terracotta Army indicated higher tin content in the arrow head for a harder edge with a softer, more durable bronze for the tangs (link (https://www.ai-journal.com/articles/10.5334/ai.1316/)).

I believe one analysis found something similar for the other weapons found with the rest of the army, but I'm failing to find a reference at the moment.

[Bohandas]

Canister welding is often done with steel filings in the mix. Thus, there are often millions of pieces of steel welded together to make a patterned blade if one counts each particle of steel dust and filings.

Even when filings aren't used, ball bearings and pieces of twisted steel cable are often used. A typical canister weld like this will have at least dozens of individual pieces of steel in it.

Given that, how many pieces would it take to be "more pieces than is reasonable" to weld?

Enough that it isn't clear at a glance whether or not you have all of them

[gomipile]

Enough that it isn't clear at a glance whether or not you have all of them

Why would that matter? The applicationof forge welding I'm talking about isn't for reattaching the old pieces like glue. It's for making a new piece of steel stock out of steel that is known to be of good quality.

[wumpus]

I've heard that most naginata (Japanese halberds) were made from broken swords. Thanks to differences in the carbon content between the edge and the "structual bits" you really weren't going to get results by trying to weld the pieces together for anything but to put the result on the end of a pole.

As mentioned, you don't melt steel/iron (to molten states) to nearly victorian times (I might be wrong about true Damascus steel, I've heard it described as 'crucible steel' which might indeed be molten). Modern recycling simply wasn't a thing.

I'd expect only the most primitive metal weapons to be considered for this method. Presumably iron weapons would work, along with primitive bronze stuff (although expect late bronze work to involve pattern welding: that stuff was expensive and labor was relatively cheap to craft a nobleman a fancy weapon). Once you get into the steel (or fancy bronze) material, expect the materials to be expensive enough that nobody is bothering with uniform types of steel throughout.

On the other hand, I've heard that the big strike against viking swords was the inability of norse smiths to manufacture consistent quality. I suspect that a final test of "hitting something solid" was needed and more than a few swords failed (and unlike swords broken in battle, there was no reason to weld them together at all). I'd assume that such steel was simply heated up and hammered into pattern welding strips, and the use was determined by how it broke (no idea if they tried to alter carbon content in such situations).

[factotum]

I've heard that most naginata (Japanese halberds) were made from broken swords. Thanks to differences in the carbon content between the edge and the "structual bits" you really weren't going to get results by trying to weld the pieces together for anything but to put the result on the end of a pole.

Well, there's also the issue that Japanese steel really wasn't all that good--they weren't able to get their furnaces hot enough to properly distribute the carbon through the iron, so they essentially had to make loads of steel and then pick out the bits that looked suitable for weaponsmithing and discard the rest. That made weapons-grade steel pretty rare, so I can see why they'd choose to make weapons from broken bits of old ones!

[Brother Oni]

Well, there's also the issue that Japanese steel really wasn't all that good--they weren't able to get their furnaces hot enough to properly distribute the carbon through the iron, so they essentially had to make loads of steel and then pick out the bits that looked suitable for weaponsmithing and discard the rest. That made weapons-grade steel pretty rare, so I can see why they'd choose to make weapons from broken bits of old ones!

It's more that native Japanese iron ore deposits are found in the form of iron sands with a ~2% ferric content, thus required a lot more processing and working to get usable steel of a decent quality. European ores tend to range from 20-60% ferric content, depending on the source (iron bog ores were especially rich).

[snowblizz]

It's more that native Japanese iron ore deposits are found in the form of iron sands with a ~2% ferric content, thus required a lot more processing and working to get usable steel of a decent quality. European ores tend to range from 20-60% ferric content, depending on the source (iron bog ores were especially rich).

It also matters what types of stuff is attached to the iron. Most iron ore has sulphur which is really hard to get rid of pre modern times. IIRC the Japanese sources had this problem.
Sweden happened to be lucky iron ore-wise and was thus an important producer of pigiron through the medieval and pre-modern eras.

[Maelstrom]

You're also going to lose a lot of material due to oxidation through the heating and forging process. In the end, the blade you end up with, as well as have a more homogenized mineral content, will be significantly smaller

[Brother Oni]

You're also going to lose a lot of material due to oxidation through the heating and forging process. In the end, the blade you end up with, as well as have a more homogenized mineral content, will be significantly smaller

From what I've read on other sword forums, loss through forging is minimal (mostly through scale, ie rust, every time you fold the metal). The greatest loss in mass is during smelting, where you're reacting off the impurities, forming slag and other byproducts - since we're starting off with presumably decent quality steel, we don't need to smelt.

[warty goblin]

From what I've read on other sword forums, loss through forging is minimal (mostly through scale, ie rust, every time you fold the metal). The greatest loss in mass is during smelting, where you're reacting off the impurities, forming slag and other byproducts - since we're starting off with presumably decent quality steel, we don't need to smelt.

There's also all the loss from re-grinding, polishing and sharpening the finished blade. This can be substantially reduced if you have a good smith who doesn't leave giant hammer marks in the piece during forging and/or don't care if there's some forge marks in the finished product.

[Brother Oni]

There's also all the loss from re-grinding, polishing and sharpening the finished blade. This can be substantially reduced if you have a good smith who doesn't leave giant hammer marks in the piece during forging and/or don't care if there's some forge marks in the finished product.

True, I forgot about after the blade is finished. I suppose if you were bored enough, you could work out the theoretical weight of material loss, based on the differences in blade geometry and surface finish grades before and after finishing, but it's probably simpler to just weigh the thing before and after. :smalltongue:

[SpoonR]

Old thread, but I'm fascinated with smithing.

TLDR find a couple episodes of Forged in Fire (https://en.wikipedia.org/wiki/Forged_in_Fire_(TV_series)). Reality show, but they have basically the whole process on camera. One episode was "take these bad blades and turn them into a goodun".

So, usually you very much don't want to melt the metal. That separates out any good or bad additives, gets rid of what little chemical control you have, and turns your 'weapons-grade steel' into 'wrought iron'. Same with dissolving the steel. If you know stuff, melting lets you adjust carbon & oxygen content, which does .... something beyond my knowledge.

For reforging Narsil, or turning good steel from broken armor (or steel from various parts of a car) into a weapon...
You have good metal to start from, so you want it hot enough to work, but not so hot you start getting chemical changes. Easiest way to go is the can method, or stacking the pieces to make a billet. Alloying is beyond my knowledge, but just layering the weapon steel with the other material is easily doable. If you have a big enough chunk of steel, you just heat it up and reshape it. In this case the critical step ends up being tempering - heat it to the right temperature for long enough, then sudden cool to control the iron crystal structure. Starting from good metal, good temper gets it just the right hardness for weapon. Bad temper can shatter the weapon during cooloff, or give it a weak structure (brittle, or bends too easy).

For those playing along at home, you can experiment with tempering using melted chocolate. Cool it one way and it's dry and chalky, cool it right and it is luscious.

Any material you lose from cleaning & polishing is still good steel. Shopvac it up and use the shavings to make another weapon.