uscra112
Frequent Elocutionist
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Location: Switzerland of Ohio
Joined: May 7 th, 2007
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Re: So, What is the failure mechanism for a Ballard?
Reply #16 - Jan 10th, 2016 at 3:57am
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Soft, brittle steel is a bit of an oxymoron. Steel is either one or the other. Civil War Ballards are indeed malleable iron. Says so right in the patent documentation. And in fact that's the only way they could have been made economically, prior to the Bessemer revolution of the 1870s. (They could have been cast of crucible steel, but at a shocking price.) Malleable iron is "white" cast iron that has been heat treated for days at 1500 degrees or so, packed in an oxidizing material. Crushed iron ore was a common material. The oxygen combined with the carbon and gassed off as carbon monoxide, pulling a lot of the flake graphite out of the metal, and converting most of the remaining flake into spheroids that don't take up so much space in the crystal matrix, leaving almost pure iron for the remainder. (That's a very crude description of what the annealing process does.) That's why the big hole under the barrel spigot. The annealing process could only go so deep. Because it took so long in the furnace to accomplish the annealing, the process burned an awful lot of fuel, to say the least, but it was the only practical way to make a cast ferrous part that would stand any shock. One thing about malleable iron parts. They can be case hardened, but the process converts some of the annealed crystal structure back to plain old cast iron. If a malleable iron frame were repeatedly case hardened, it will be significantly weaker. Food for thought. Now, I'm still more than a little convinced that, by the time Marlin took up making the Ballard, that it would have been possible to cast the actions of fluid steel. That would have been much cheaper in that, not needing that long annealing period, the fuel cost would be much lower. It would be fairly easy to tell in a microscopical metallurgy lab, and I've got an rough old #3 frame that I'd donate. Anyone know someone with the requisite facilities? I've been trying to rig up to do this myself, but I can't find nitric acid for sale in less than gallon size lots. Phil
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