Graybeard said:
What is the metal he put in the middle of the ax? Why did he do that?
Graybeard
I don't know for sure on this, so this is mostly speculation.
Steel is normally a mix of primarily iron and carbon, as well as other elements such as chromium, titanium, etc. The powder he adds to the steel during the process is probably some mix of (C)arbon, (O)xygen, and probably (P)hosphorus , but the majority is probably carbon. Basically, the reason by carbon steel makes the steel "stronger" is that since Iron is a pretty big atom, and C,O, and P atoms are pretty small, the small atoms fill in the empty space left in the lattice by the big ones (imagine if you had a bunch of golf balls in a bucket, and then put a bunch of marbles in, you could fit a lot into the empty space.
Well, this process in metals is really slow, so when he is adding the powder as you see in the video, and then puts it into the fire, the diffusion of the small atoms (C,O,N) into the lattice of the Iron isn't very fast. In a couple of hours the atoms might have only diffused into the Iron lattice 1-3mm, depending on the temperature of the fire.
So, the punchline here, there are standards when trying to reach a high carbon content measure by weight% in different steel compositions. The main piece he started out with was probably "raw" Iron or a lower carbon content steel and the piece that he adds in was probably a high carbon content steel. It would make sense for him to buy a high carbon steel from somewhere else because of the tremendous cost for a private business owner to run his furnaces for weeks at a time to get a metal evenly elevated to a certain carbon content. So once he works that piece into the middle, the distribution of carbon content on the steel will be highest right in the middle, the cutting edge, but slightly weaker farther up the axe head to allow for the vibrations from the tip of the axe which is very rigid to the less rigid areas along the rest of the head which is a lower carbon content and is more free to move on an atomic level.
This was a lot of writing, and like I said, a lot of this is just me reasoning through what I think, I could be completely wrong, but it's what made some logical sense to me.
