|Making a Katana: The First Fold
||[Aug. 12th, 2011|01:48 am]
So, I got a start on a project I've been looking forward to for a long time. I made some steel, got it all welded together, and made the first fold.
Photos and commentary behind the cut. Once again the video didn't come out very well, but I'll see if I can edit out some decent shots, though that may take me a while.
I decided to repack the blister steel into a retort and see if I could get some more carbon in there. The steel that had before had a worryingly low level of carbon in it is now all blistery, and parts had half-melted and partly welded together.
Some test forging showed that I'm right on the edge of forgeability in terms of carbon -- which is where I want to be for this project.
Both retorts were destroyed in the process of removing the blister steel, as pieces had stuck to the sides and had to be chiseled out. The retorts had both oxidized in the furnace almost all the way through, their outsides covered in thick jackets of hard, brittle iron oxide. It started breaking off in big scabrous chunks during the extraction process, the rest I hammered off while trying to extract the last few bits of steel.
Another view of the steel. The round stock up at the top is the wrought, from an 18th century bridge, that I'll process and turn in to the soft iron core of the sword. Just below it to the left is a rectangular stick of a previous batch of blister steel I worked up as a proof of concept a few years ago, that will also be going into the sword.
All together I made 2.41kg of blister steel, or 5lb 5.2oz.
I took about half the steel, 1055g, cut it up into smaller pieces, and assembled it into the preliminary stack. I tack welded the pieces of the stack together so it would hold together long enough to get all the bits welded together and firmly stuck together.
Sadly, the video camera cut out before I actually started the welding portion, which I didn't discover until after I'd finished the first consolidation weld and fold, and was just drawing out as much of the billet as I could.
That first weld is always the hardest -- you don't have to close all the gaps, just get it all to not fall apart long enough to start fusing together. You do have to deal with pieces deciding they want to fall off, scale that will cheerfully show up later as in inclusion, fluxing enough to keep scale down but not so much that it too becomes and inclusion. Get the whole billet to a welding heat, but not so hot it burns or melts. Into the yellow-hot areas areas inside the forge, back to the white, flip, rotate, all with fire jetting out, soaking through the felted kevlar glove in uncomfortably warm pulses on the tong hand, and shrinking the leather of the lighter hammer-hand glove, noticible as a gentle pressure followed by heat.
The first hit on a weld is always the hardest: is the billet hot enough? Will it hold together? Does it need more flux? Is there too much flux? Should I start here, where it's hottest, or there, where it looks more likely to not fall apart? Will it actually weld, or have I overheated it and it is just burn and crumbly like cheese? Finally, it has to be right: out of the forge, onto the anvil: hammer in hand, just sort of push it down, very light taps, just trying to get the pieces to stick, and in sticking fuse, and in fusing become one piece of steel. It doesn't quite get there.
Back in the forge, stopping only to re-flux, and keep it moving in there, rotate and flip, get it back up to welding heat, flux bubbling and white fumes rising out of the steel. Out and on the anvil, this time with harder hits, and on the other side. There's visible gaps, but it's sticking. There are also cracks starting to form, and a few pieces haven't quite welded yet -- you can see from the way they cool faster than the main piece. It doesn't feel like hammering steel, but more like some sort of dense clay, absorbing all the energy from the hammer while not actually moving all that much, no ring to it, not quite solid.
Back in the forge, fluxing en route. Out, but this time wire-brush off the white-hot flux and scale, trying to avoid splatting anything flammable, like the carpeted area or my feet. I mostly succeed. Over to the power hammer, and using the lightest taps the machine can give just get it welded. Flip and repet. Forge, Hammer, forge, hammer, forge, hammer. I've lost count of the trips back and forth.
It's now about half again it's original length, half the thickness, and about the same width. There are gaps, there are cracks, including one that threatens to break the billet in two. It still feels soft and squishy for steel, but it's firmer than before, air gaps and pockets space being squeezed shut. I use a hot-cut to finish what the crack has started, clean off the mating surfaces, flux lightly, and stack them up in the forge. After reheating, a few taps has them solidly welded together. A few more trips to the hammer, and it's as drawn out as I'm going to get it tonight.
I'm starting a clock on this project. I've put in a good 4 hours so far on preparing the steel, and about $20 in supplies. Tonight, I spent from 8pm until 11pm in the forge doing prep and forge welding.
Initial number of layers: 6
Current number of layers: 12
Staring weight: 1055g
Finish weight: 845g
% loss: 20%