Rob,
Yes, it is very laborious to forge and HT a blade this way. But then... "Anything worth having is worth waiting for" right? Before I started to forge I made knives via stock removal for 4 years. All of them were made without the use of power tools except for a small drill press and a homemade buffer. I thought that by learning to forge I could cut down on some of the hrs. that it took me to make a knife especially the big ones. What was I thinking?
But to be perfectly honest... If I could add a small fraction to the performance of my knives by doubling the amount of work that goes into them I would happily do it. I'm the type of person that is rarely satisfied. It is a personal motto of mine that "there is always one more thing that you can do". It's a real struggle some times for me having a motto like that but being inherently lazy. You should hear some of the arguments that I have with myself.
Anyway, I'm getting way off subject. To answer your questions:
Q - During the heat/quench cycle, do you have a feel for how hot "non magnetic" is for your process? How long do you hold the blade at non-magnetic?
A - I am definitely getting there but I will never give up the magnet, as far as I know it will never lie to me. I have never timed myself but I would guess I'm between 15-30 seconds at non-magnetic before the quench. It always takes about 15-20 minutes to get the blade evenly heated in my forge and as soon as it is evenly non-magnetic I put it back into the forge for about 10 seconds before it gets quenched.
Q - Have you ever tried a single quench?
A - Not yet. As soon as I get my ABS JS stamp out of the way I plan on doing a lot more experimenting. I really want to take a whole year to play around and see what works best for me before I start selling a lot of knives.
Q - Exactly how does one do a brass rod test? Brass rod in a vise? I assume you are bending knife's edge over? So you use two hands to hold the knife and bend knife edge, pulling across whole blade's edge? How far over are you bending the edge? 10 deg? 20 deg? 45 deg?
A - Yes, the brass or steel rod is firmly clamped horizontally in the jaws of the vise so that almost half of it's circumference is above the jaws. I then place the edge of the blade near the ricasso (at about the same angle that you would if you were sharpening it) onto the rod and try to press the edge into the rod, and then draw the blade back. The edge will deflect slightly at the point it makes contact with the rod. It takes some pretty good force to get it to deflect. I would guess that it deflects somewhere around 5 degrees??
Q - Any idea why the tempering temp drops by 5 degrees each time?
A - I wanted to make sure that I wasn't heating any higher than my first tempering temperature just to keep a handle on what was going on. This was an idea that I had a while before I started doing my own heat treating. Actually, I wanted to set my hardness with the first tempering cycle and then drop my temp by 10 degrees for the second and third tempering cycles. So if I tempered my blade at 330 degrees on the first cycle then the second and third would both ideally be at 320 degrees. My idea was confirmed when I recently read "Cryogenics" by William E. Bryson and he suggests a similar thing. If I remember correctly he suggested to drop each cycle by 10-15 degrees from the previous one.
Q - How often does edge chip and require that 4th temper?
A - I have been very fortunate and haven't had to re-temper any blades yet. I have a feeling that the one I'm working on now might be my first. I decided to temper it at 320 degrees on the first cycle. We'll see what happens.
Q - Ever leave out the cryo to see if it is really doing anything for retained austenite, and does it improve toughness?
A - Good question, I think you're reading my mind this time. The blade that I'm working on right now will not receive any cryo treatment prior to testing it for edge flex and cutting ability. When I have played with it for a while and am satisfied that I understand it's capabilities I'm going to cryo it in Liquid nitrogen and then temper it as close to the third tempering heat as I can. Without two nearly identical knives treated differently, hopefully this will give me some idea if there is a benefit to be had.
Mete, Thanks for your reply to my question a few pages ago. Actually, I got in a hurry when I asked the question and didn't word it properly. What I was wondering is this... When I edge quench a blade, the whole blade is at critical (non-magnetic) because I'm not using a torch to selectively heat the just the portion of the blade that will be quenched. Do you have any idea if the extra heat that is in the spine of the blade will have an effect on the martensite that is formed in the quenched part of the blade (help refine the grain in some way or produce a grain structure that consists of something other than just martensite and retained austenite?) I'm guessing, but I think it would take a lot longer to get all of the heat out of the blade during an edge quench than it would for a full quench. Is it possible that a triple edge quench would have a different grain structure (other than an obvious transition zone between the martensite and pearlite matrices) than a triple full quench (or single full quench for that matter)? All other variables being equal of course.
Thanks,
Rick
