I recently finished (well almost) building a heat treatment oven I had been working on for a couple of months, and now that I have it done I can finally get to doing the HT on those knives I've been waiting to do. My oven measures 18'' deep, 6'' wide and 4.25'' tall,there is 3.5 '' of firebrick insulating the chamber. My elements are 14 gauge kanthal, and they put out about 4500 watts. Yes it heats up ridiculously fast. Here are some pics of the oven in action, some mods will be made, mostly concerning the control panel layout, but its mostly done
20161125_130835 by velferd, on Flickr
And a view inside, sorry about the ghetto blade mount obstructing view, I was doing thermal cycles on the test piece inside.
20161125_130922 by velferd, on Flickr
Although it worked great, one problem I found is that the front is cooler than the back of the kiln. I'm going to try raising the back end and sealing the door better to avoid this. I actually tightened the door more for later tests, but as the pieces got smaller (breaking into smaller pieces for hardening) it became less of an issue. This also seemed to be less of a problem once the kiln got warmed up, so I guess Ill have to let it equilize before doing any heat treating in the future.
I also did some testing to try and find an optimal austenizing temperature with respect to hardness. My methods were as follows.
Normalize a 1x1/4''x1x4 piece of W1 at 870, 815, 790, and 760 degrees celcius, with 10 minute soak times. the pieces were air cooled until they were black/grey and attracted a magnet, and started the next cycle. I broke the piece at the 790 and 760 degree cycles, to gauge grain size. Nothing changed between cycles. Sorry no pics of grain.
The pieces (now 1/4x1x1) were austenized at 770, 780, 790 or 800 degrees and quenched in #50 oil at room temp. Interestingly there were no huge differences between the hardness of each piece. The hardest pieces seemed to be the 790 and 800 degree samples, but not by a large margin. tThe comparison was done by sharpening a 90 degree corner on each piece and scratching the others. So the 790 and 800 scratched the 770 and 780, but could not scratch each other. To put it simply this is my ranking of hardness by austenizing temperature:
800=~790>708=~770
Yes, its simply a relative comparison, but does show that the higher temps. resulted in higher hardness than the lower temps. Better yet, these temps (790 and 800) correspond to about 1450 and 1475 farenheight. I know many people here use that range of temps to austenize similar steels like W2, so it seems I am in the ballpark.
Im going to do more tests, starting with re normalizing the pieces and then austenizing at 790, 800, 810, and 820. Maybe ill do another piece at 830 too. I'm hoping to see a drop off in relative hardness at the high temp range, but that may be wishful thinking. I will break the pieces after the final round to gauge grain size, and go from there. After that ill hopefully be confident enough to quench these and a few hunters! Any suggestions to improve my results/methods, general thoughts and comments? Thanks!
20161127_104008[1] by velferd, on Flickr
20161125_130835 by velferd, on FlickrAnd a view inside, sorry about the ghetto blade mount obstructing view, I was doing thermal cycles on the test piece inside.
20161125_130922 by velferd, on FlickrAlthough it worked great, one problem I found is that the front is cooler than the back of the kiln. I'm going to try raising the back end and sealing the door better to avoid this. I actually tightened the door more for later tests, but as the pieces got smaller (breaking into smaller pieces for hardening) it became less of an issue. This also seemed to be less of a problem once the kiln got warmed up, so I guess Ill have to let it equilize before doing any heat treating in the future.
I also did some testing to try and find an optimal austenizing temperature with respect to hardness. My methods were as follows.
Normalize a 1x1/4''x1x4 piece of W1 at 870, 815, 790, and 760 degrees celcius, with 10 minute soak times. the pieces were air cooled until they were black/grey and attracted a magnet, and started the next cycle. I broke the piece at the 790 and 760 degree cycles, to gauge grain size. Nothing changed between cycles. Sorry no pics of grain.
The pieces (now 1/4x1x1) were austenized at 770, 780, 790 or 800 degrees and quenched in #50 oil at room temp. Interestingly there were no huge differences between the hardness of each piece. The hardest pieces seemed to be the 790 and 800 degree samples, but not by a large margin. tThe comparison was done by sharpening a 90 degree corner on each piece and scratching the others. So the 790 and 800 scratched the 770 and 780, but could not scratch each other. To put it simply this is my ranking of hardness by austenizing temperature:
800=~790>708=~770
Yes, its simply a relative comparison, but does show that the higher temps. resulted in higher hardness than the lower temps. Better yet, these temps (790 and 800) correspond to about 1450 and 1475 farenheight. I know many people here use that range of temps to austenize similar steels like W2, so it seems I am in the ballpark.
Im going to do more tests, starting with re normalizing the pieces and then austenizing at 790, 800, 810, and 820. Maybe ill do another piece at 830 too. I'm hoping to see a drop off in relative hardness at the high temp range, but that may be wishful thinking. I will break the pieces after the final round to gauge grain size, and go from there. After that ill hopefully be confident enough to quench these and a few hunters! Any suggestions to improve my results/methods, general thoughts and comments? Thanks!
20161127_104008[1] by velferd, on Flickr