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  1. #1
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    teach me about metalurgy of bronze?

    I have been working with bronze tools on a boatbuilding project for 7 weeks and quite a few questions have been raised.

    There was some discusion in this thread http://www.britishblades.com/forums/...ghlight=bronze
    But we just had a guy come and cast some tools on site which raised more questions and I am hoping some folk here can give me answers or folk with better google fu can post links.

    What I want is a dummy's guide to the metalurgy of bronze. I forge my own steel tools and harden and temper and want to understand the basics of bronze.

    Clearly the mix of tin and copper and possibly various trace elements have an effect but what about the heat treatment? Neil Buridge cast some tools for us and he quenches in water, this he thought gave a more ductile tool. In use ductility seems to be the one thing I have noticed as a variable. Some you can cold hammer to shape easily whereas others crack and crumble.

    I'd be interested too to see some decent objective research on work hardening, everyone says bronze work hardens, I have not really been noticing it much in practice and our tools are still pretty soft after much hammering and use but they still work so long as you set up the edge profile well to cope with the softness.

    So what I want is a dummy's guide but backed up with some objective test info so I can believe what is being said. Does the crystaline structure change with heat treat and if so how and at what temps?

  2. #2
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    Re: teach me about metalurgy of bronze?

    If you watch E-bay and vintage book stores there is a series of books done by The Copper Development Association that are very informative about all copper alloys. I believe they may be available as a PDF as well.
    Whoever dies with the most tools wins.......Now accepting donations.
    I buy old folding and fixed blade knives of all kinds. Especially Case. PM Me.

  3. #3
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    Re: teach me about metalurgy of bronze?

    May be of use

    http://www.keytometals.com/Article71.htm

    This thread has some info
    http://www.britishblades.com/forums/...0-Bronze-knife

    The link to this description of hammering out an edge included some interesting jigs
    http://www.scythesupply.com/workshop.htm

    This link has some detail and pictures too

    http://www.aleacionesdeberilio.com/d...g&Strength.pdf
    Last edited by TB_London; 24-04-12 at 12:20 PM.

  4. #4
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    Re: teach me about metalurgy of bronze?

    Work hardening should be done prior to using the tool. Work harden the edge of a tool by hammering it until harder, then sharpen. Copper chisels for shaping stone were used as they were work hardened before use. You can't expect bronze to be at its hardest right from the cast. More work must be done. Play around with some scrap bronze and see how far you can push the material, before it gets too hard and brittle. Best of luck, and sounds like a great project.

  5. #5
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    Re: teach me about metalurgy of bronze?

    Heating bronze to a dull red then quenching it will actually soften the metal... steel is rather unique in it's reaction to being quenched from high temperatures, most metals get softer. The hardening of the bronze is done by work-hardening. Hammering is quickest but to my understanding filing/scraping/sanding will all have some effect on the hardness. It is possible to over-harden the metal, resulting in brittleness and cracks, to my understanding the bronze-age method was to cast the blade at the thickness where hammering the edge down would be enough to harden it without making it brittle.

    I have a friend who does quite a bit of this, if you want I'll send you his contact information.

  6. #6
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    Re: teach me about metalurgy of bronze?

    Quote Originally Posted by robin wood View Post
    everyone says bronze work hardens
    Work hardening really refers to putting strain energy into the material which is not recovered after the force is released. So 'work' is energy lost.
    It isn't really 'as I work with the tool, it gets harder'.

    Ductility in metal comes from irregularities in the crystal structure called dislocations which correspond to missing or extra atoms in the regular lattice. Metal bonds allow these irregularities to move when a stress is applied (the atoms don't move much, but the bonds move so the position of the irregularity moves). The moving of the dislocation caused the stress to be relieved a bit and the slight movement of the atoms results in deformation of the metal (it remains bent). The more dislocations that are free to move in this way, the more ductile the metal will be.
    When one moving dislocation meets another dislocation then it becomes much more difficult for either dislocations to move further. Stress can't be relieved by this dislocation any more, but also the atoms here won't move (so it won't bend).
    Heating metal introduces dislocations. Higher temps have more dislocations (the amount of which, statistical theory can predict quite well). Slow cooling will tend to settle the density of dislocations back at the equilibrium for the lower temperature. Fast cooling locks in the dislocations from a higher temperature. So heat and quench to soften and make bronze more ductile.
    Hardness is related to how easy dislocations can travel. If there are less dislocations, or the dislocations are locked together, then the material will be harder and more difficult to bend or dent or deform.

    That is an good model for understanding work hardening and annealing metals like copper. Bronze has the added complication of the different alloy elements.

  7. #7
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    Re: teach me about metalurgy of bronze?

    The final link I added gives some pics to help explain the dislocation of interstitials, whole article is a PDF so not easy to post in thread unfortunately

 

 

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