Fail Of The Week: Bronze-Brazed Wrought Iron

[Will Stelter], a promising young blacksmith working out of Montana, had a terrific idea for a unique composite material for finishing off a knife build. This build is a collaboration between multiple blacksmiths, and as the youngster of the group, [Will] really wanted to pull out the stops and finally make a material he’d been contemplating for years to impress the elders. He knows that if you try to forge wrought iron at too low a temperature, it develops cracks and splits. Could you do this on purpose, and then fill these cracks with bronze? It would be quite the stunning material, with the bright bronze veins running through the dark iron. He had to try.

Unfortunately, our young experimenter ran into some problems that didn’t have enough time to overcome. First, getting the bronze to flow and fill the voids of the iron was a challenge, particularly when heating with a torch. Throwing the whole experiment into a forge resulted in the bronze leaking through the enclosure. The most promising attempt was a beefed-up box, set in an oven for about 20 minutes, with the temperature high enough to liquefy the bronze. It was looking great, until he cut into it and found too many air pockets for a workable billet.

The attempt was a failure, but we’re delighted that [Will] went ahead and put the video out there anyway. And if you know how to make this work, go drop a comment on his channel, and we’ll all look forward to a part two, where he finally nails the technique.

16 thoughts on “Fail Of The Week: Bronze-Brazed Wrought Iron

  1. I wonder if its excess flux from using braising rods is causing the bubbles – gets liquid and flows inside but doesn’t then escape when the centre gets hot enough it turns to gas with all the now molten bronze on top. Seems like that pour into the hot steel can molten bronze worked nearly perfectly on the first pour, so I think that is the style I’d try again without the flux, or without as much flux. So perhaps just keeping that metal combination at temperature longer so the gas bubble may manage to escape or heating up much more slowly so the centre and outsides have less temperature differential and the flux can burn out more fully before the metal really starts to flow.

    Spin casting I don’t think is actually required from what we are seeing, but I don’t see how it can hurt.

    Really no expert in this stuff at all though.

  2. I’m not a metallurgy expert by any means, but my feeling is, that this air pockets will remain as long as he’s trying to meld the stuff under air pressure. I don’t know if there’s some existing technology but my idea would be to do this under a vacuum. Should help removing the air pockets altogether.

    1. Could possibly use casting sand to prevent the bronze from flowing off. The part could be heated up until the bronze is liquid, then moved to a vacuum chamber while still inside the sand mold.

      Pump vacuum to pop bubbles, then release it to squeeze down whatever bubbles remain.

      1. That sounds plausible to me, though in a high pressure tank may be easier – what shop doesn’t have an air compressor, and it will do a pretty good job I’d think in smashing any gas pockets down enough to be invisible.

        1. 1.) you are not casting epoxy, this is molten metal, so oxidation might be a problem with metalurgy (and not sure about possible fire hazard?). vacuum on the other hand will prevent oxidation unless the metal oxidizes before the chamber is fully evacuated.
          2.) increased pressure will probably increase cooling effect of the air. i can imagine that in 8bar air pressure the part will cool down ~8 times faster due to increased heat capacity per volume of air. especialy when you blow the air inside the chamber just like you might blow on hot food. so vaccum might help you achieve better thermal efficiency and give the metal more time to flow.
          3.) depends what are you trying to achieve. when bubble is too small to be seen, it can still damage structural properties of the metal, so it’s better to not have it in the first place. probably does not matter if you just need to create cool-looking lump of metal.

        2. Perhaps you can put some combustible material into the pressure chamber which will burn at lower temperature than melting of the metals. That way you will remove all the oxygen from the equation. But that might produce soot or similar residue which would prevent the metal from fusing. On the other hand you might use something that burns cleanly (perhaps ethanol?). But then… do you really want to ignite alcohol in pressurized vessel with increased amount of oxygen? Sounds like pressure cooker bomb to me… But i guess there is probably some other way to safely capture oxygen…

    2. That depends on where the bubbles are coming from – if these pockets are from the flux as I suspected the vacuum can only at best increase the speed of the off gassing and increase the likelihood the bubbles expand to the outer surfaces and pop.

      It may treat the symptoms enough to work well but It won’t actually solve the root cause as it wasn’t trapped atmospheric air at all – if you look at his first pour of molten flux free offcut melted down out the crucible that seems to be very very close to void free, though with how much more open the iron bits were in that piece its hard to say if it is just letting the trapped air out easier or not got bubbles in it because it doesn’t have lots of flux turning to gas trapped inside.

  3. A simple thought…. How bout setting the whole hot box set up on a vibrating surface? Think in line of hooking whole forge up to one of the old belt vibrator\exerciser machine used to see in cartoons. Or preferably a vibrating surface with tunable frequencies? Maybe 10hz would work get bubbles to float out, or maybe a mHz or 2 would be better. I’m have no experience with any of this, but have a long history of removing bubbles from liquids and semi-solids; and my gut says it’s got a good chance. But if not, please let me know that I’m full of it.

  4. Funnily enough I tried this exact thing in college metalsmithing class. I tried packing steel scraps into a metal box with brazing rod and putting that in a furnace. It ended up snapping apart because the bronze and steel shrank at different enough rates that the bronze delaminated.

    Bronze/Iron composites are around, though. I have a keychain that was printed in sintered steel and then infiltrated with bronze to make the part solid. You can see an animation of what I think is the same process here – The infiltration may have to be done under a vacuum or it could just have a shielding gas. Not sure how liquid bronze is and how powerful the wicking action is, here.

    I can imagine a low tech home version where you get the steel chunks down to a size that would play well in CTE terms. That would also help prevent bubbles from getting trapped in the mix.

  5. If only aesthetics are what he’s trying to achieve with an iron/bronze matrix, then let soak for sufficient amount of time in a furnace under a reducing atmosphere, allow to cook slowly, repeat. Being sure to fire the billet in the same orientation each time, and mill off the top 1/5 or so of the billet. Or why not hammer forge the bubbles out of the billet?

    A homogenous iron/bronze blend is an alloy. Which is much more practical in regards to just about every physical property than a heterogenous matrix.

    Idk, I havnt watched the video and dont care to, so maybe I’m not understanding the point… Inflation has made my time too precious so I must be very selective with the content I watch and how it matters to me. (Tiny violin playing)

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