As a way to test my knowledge of process, I made a large test blade from an old spring harrow tooth a while back. All I knew of this steel was that it had been a spring harrow tooth of unknown, but old origin and that the gentleman who had used the harrow (who donated the teeth) had personally seen them go almost completely straight being caught on a root and then snap back to shape. In the interest of adding my $.02 to this thread, I'll relate from my experience rather than directly answer Kevin's questions. I think that I can provide more useful information this way. It's just a more effective method of communication for me. Here's how I did it:
- I forged the curved tooth into a flat bar
- I cut off a small piece, heated it to a bright orange and quenched in cold water. (This is useless other than I have found it is a reliable way to tell if something will harden at all.)
- I then clamped this piece in a vise and whacked it with a hammer. It snapped cleanly. Good sign #1.
- I then examined the fracture to see what the grain looked like after a violent quench from an overly high temp. If the grain hasn't grown terribly, I take this as a sign that the steel might contain some alloy to help retard grain growth such as Vanadium. Not terribly scientific, but we're not discussing pure science here... In this particular case, the grain was pretty large.
- At this point I forged out the blade. I knew I had something to work with, just wasn't certain exactly what it was.
- After forging, I brought the blade to a little above non-magnetic and allowed it to cool in still air. This was repeated for a total of 3 cycles. During this, I looked for (and found!) something very important. I was able to observe decalescence/recalescence. This is something that I'm surprised I haven't seen mentioned in this thread so far. The transition point was very obvious with this particular steel and I made certain to make a mental note of the color of the steel at the point of decalescence.
- I then heated the blade as evenly as possible to the color I made a note of before. Then I went just a TOUCH higher.
- I quenched in Parks #50. I used this oil for a few reasons. One, I had it available. Two, water had not caused the steel to ping before, so I knew a fast quench was a safe bet.
- File test time. Yes, I know this teaches us little, but it's a habit I picked up from my early teachers. It has told me on a few occasions when a quench did not work, so I keep doing it.
- I tempered initially at 400F, twice for 60 minutes each.
- I "blued" the tang, ricasso, and spine with a MAPP torch 3 times.
- Finished the blade out roughly. It was just a test knife, so I made it comfy, not good looking. I took it as an opportunity to test the quality of my standard hidden tang construction. The knife was assembled with no epoxy, only the pin to hold it all together.
I then proceeded to use this knife for everything around the yard. I hacked through trees and bushes that needed trimming rather than using a pruner. I observed the edge condition regularly, resharpened as necessary, and slightly reground the profile as I continued to learn about blade geometry. I hacked through 2x4s in the shop, I used it as a small spade to plant some mint in the yard, in rocky soil, etc, etc, etc. I learned something from every test. The handle loosened up a good bit, but the knife was still quite usable.
The last time I visited J. Neilson's shop, I figured it was about time to test this knife all the way. First, I made a few attempts at cutting a free hanging rope. From this, I learned that I need practice cutting rope
Had I had some more practice, I'm certain that I wouldn't have left that last piece hanging by a thread. Second, we grabbed a 4x4 hardwood barn beam and I proceeded to hack that to bits. It ALMOST shaved hair after that. I felt confident that had I been chopping 2x4s it still would have. Then we went to the vise. J. was just about to open his mouth to tell me I'd hit 90 degrees when the blade finally snapped. The rest of the blade only took about a 15 degree set.
