[Dan Petersen]

Danny,

I do see a problem with the heat treat. You say "I take the forge to 1650 to give myself a little more heat than critical to compensate for the temp loss between the forge and the oil." Okay, that is not is correct. You do not want the blade to rise above the critical temperature. IT is not how hot the blade is right as it goes into the oil. It is how hot the blade got during that heat treat cycle. So, 1650 is just too hot for that steel and I would argue you are probably getting grain growth you do not need especially on the second or last quench. It is time and temperature and in this case the temperature is too high for this steel.

Here is another factor to consider. Harder does not necessarily equate to better edge holding. I would argue that a small blade (1084) at 60 RC gets better edge holding than the same blade at 65 RC. Abrasion resistance is what you are striving for and in certain mediums you cut through micro abrasions can be more frequent with a 65 than a 60 RC blade. Often we talk about a really fine sharp edge having a slight burr on the edge (too big a burr and it lies over and that affects sharpness). If the edge is too hard that burr chips off quickly. The result is dull. It is not chips you can necessarily see with your eyes, it is chips nonetheless.

Now this is all relative to the steel being used. Some steels will show the best edge holding at 64 and others maybe at 59/60. It all depends on alloys that inhabit that steel. My experience suggests that with 1084 you are too hard and I question your grain size. A smaller grain size will result in better strength and edge holding.

One last comment. I am not a proponent of testing the edge of a knife on aluminum cans or any other hard metal. If I want to cut metal the edge geometry will look more like a chisel than a knife blade. Even engraving tools have a sharp but chisel shape to them. I do not use a knife to cut aluminum or other metals. I use wire cutters or tin snips. Aluminum oxide is what they put on grinding belts and next to diamonds it is one of the hardest substances we have. Why would I try to test a blade on aluminum? Now the only value I see in aluminum cans for testing is whether the edge chips when I cut them from top to bottom in one slice using a knife big enough for that purpose. But that is not a test edge holding.

I hope that helps some.

[Lin Rhea]

This picture shows a burr curling off the hardened clip on a knife I recently finished.




The burr behaves in a particular way if you ever have opportunity to check it. In the above case, the burr was stiff but not brittle. That same behavior is appropriate for the blade edge on a different scale. The behavior of your blade is just not consistant with an edge that is hard enough and yet tough enough to be sevicable. You recognize that and that is a very good thing.

I agree with Dan. More is less when the "more" becomes too much. We want as hard an edge as possible till we start losing toughness. Testing behavior (in accoordance with the knife's intended use) is how we know where that tipping point is.

[ben seward]

Hey Danny, here's my suggestion. Make a 10 in. blade... nothing fancy just a good chopper. I think you will get a better idea of the cutting potential with this size. To me the grain structure looked too big... ideally it should closely resemble a brake in glass. Try this for a thermal cycle process...just above critical, then cool--just below critical, cool--dull red, then cool. I like to thermal cycle after the grind, just before heat treat, to relieve stresses caused by grinding. Test after heat treat with a new file...it should skate on the cutting edge. After tempering test with the file again...it should just grab. Thin the edge to thirty thousandths and roll at about 20 degrees to the cutting edge. Sharpen and test. I like to test on seasoned antler. Give it a good chop, if the edge geometry/heat treat holds up ,it should handle any reasonable cutting task. Watch for edge distortion, chipping, rolling etc. You may have to play with the geometry to get a properly supported edge. After this move on to cutting free swinging rope...this will test the edge geometry. Chop some 2x4's, if the blade has performed well so far, you should be able to wear yourself out on 'em...don't avoid the knots! Good luck, Ben

[ben seward]

An after thought. I'm not sure the five minute soak is necesary. I've been working with 1075 and no soak is necessary. Perhaps Lin Rhea could clarify this...I think he's been working with 1084. Another thing, in my opinion the closer to critical on the quench the better. I've been working with hamons and using a low critical quench for the pictoral effect of the hamon. This seems to result in a tougher blade, capable of thinner edge geometry. A low critical quench with 5160 seems to mirror those results. All the best, Ben