I have used a circular saw blade for this type of knife also. I used a well used (dull) high speed steel saw blade without and carbide tips. I drew the temper from the whole blade by heating it in a charcoal fire with a blower pipe in the center hooked to a small vacuum cleaner in the blow mode. I put a damper in a connection pipe so I could control the flow of air and therefore the temp of the fire. I heated the blade to a bright orange and then buried it in a bucket of old sandblast sand that we had not dumped yet. I put about 4" of sand in a plastic 5 gallon bucket and as soon as I dropped the hot blade in flat on the sand, I poured another 4" of sand on top of it and let it cool all night. Taking it out of the sand the next morning, I was able to easily file it and cut it with a hacksaw to shape. I filed my bevels on the edge and polished the blade before coating it with Dial soap as a paste to keep the surface from oxidizing. While the soap dried on the round knife I fired up the home made forge again and opened the 5 gallon bucket of waste oil. I covered the firebox of the forge with firebrick to make an oven like opening. I evenly heated the blade to a bright red through and through, I picked out the blade with a pair of vise grips with a welding glove covered hand. I Rapidly dunked the blade in the oil and kept it moving through the oil until it was no longer smoking when I lifted it out of the oil. I then left the blade in the oil until I could handle it comfortably with my bare hands. I cleaned the soap of the blade and shined it up until it was what I refer to as white bare metal. Taking a hand held propane torch, I started heating the handle end of the blade while holding it with the vise grips. You can watch the temper colors run ahead of the flame. I follow the dark almost black color into the actual blade and then sweep the torch back and forth on the back of the blade staying way from the outside points of the cutting edge. I look for a dark straw color starting to turn purple to hit the edge at the same time (that's the tricky part of this process) then dunk it into the oil again. This will give you a strong but flexible handle and back edge and a cutting edge that may be a little tough to sharpen but will hold an edge for quite a while. After removing the blade from the tempering oil an clean and polish again. Then I rivet two slabs of hardwood to the handle and shape that down with a belt sander until this is comfortable in the cutting positions. You might want to make more of these knives of different sizes and you may find one very handy in the kitchen too.

Good Luck

Lowell