Evenheat Kiln -heat treating frustrations- HELP!!!

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Okay so I've had my evenheat kiln for about 3 or four months now and I'm finding I get very mixed results with the heat treat.

I finally thought I was beginning to dial in on my process and get all issues worked out and just went to do a couple of simple product tests and BOOM! Broke the tip off of two! Now before I destroy the others I would like some insight on how I can redo the HT and get the results I'm looking for.

Here's what I've been doing...

Using 01 tool, 3/16" thick, I grind out my blanks, drill pin/lanyard holes, and flat grind bevels down to around .02-.03" at the edge.

-Apply Brownells antiscale coating
-Place in the evenheat at 1300 degrees soaking for 20 min.
-Remove and allow to air cool to handling temp
-remove residual antiscale and reapply fresh coat
-Return to kiln and ramp at full speed again to 1300 and soak for 10 minutes.
-Ramp at 75% speed to 1490 and soak for 15 minutes
-Remove and quench in 130-150 degree preheated canola oil ensuring blade goes into the oil straight with edge facing down and applying slight agitation in an up-down motion only.
-remove and hang up to further cool while the kiln cools to around 200 degrees.
-once kiln has cooled, place blades back in and run a temper cycle at 400 degrees for 2 hours.
-remove blades and hang to cool in still air.
-repeat 2 hour temper cycle at 400 degrees.

I always test the blade tips by stabbing into pine and trying to pry out a piece of wood... Not deep, maybe .25" or so. And on average about 50% are snapping, and it's pissing me off like crazy!

Am I just grinding my tips too thin or what? I just feel like they should be bending more before snapping like that. Please help!

Also, for the ones I have already treated, should I anneal them and re-do the heat treat?
 
My only changes would be:
Use the oil at 120-130F
Don't stab the tip in wood and bend it unless you really get off on breaking the tip. The tip is most likely too thin as well.
There is no need to air cool slowly between and after tempers. Just cool off in running water and put back in the oven.
The quench is best done straight in point first and agitated with an up and down motion and a slicing motion combination.

Questions:
Are you using enough oil? It should take one to three gallons to properly cool a blade.
Have you tried a 425F or 450F temper?
 
Stacy E. Apelt - Bladesmith said:
My only changes would be:
Use the oil at 120-130F
Don't stab the tip in wood and bend it unless you really get off on breaking the tip. The tip is most likely too thin as well.
There is no need to air cool slowly between and after tempers. Just cool off in running water and put back in the oven.
The quench is best done straight in point first and agitated with an up and down motion and a slicing motion combination.

Questions:
Are you using enough oil? It should take one to three gallons to properly cool a blade.
Have you tried a 425F or 450F temper?
Click to expand...

Thanks for the reply. I haven't tried the higher temp temper cycle, as I'm trying to keep it around 60-61 Hrc, but I can give it a shot. I'm using a good size ammo can for my oil container with about 1.5 gal of oil and the quench method of tip down is how I do it.

As far as not testing the tip like that, is there a better way? I feel like as the most vulnerable part of the knife it should be tested. I really don't want to sell it and have an unhappy customer when it breaks. And I feel like I've seen plenty of makers successfully test their tips like this. As a general purpose/woods knife it should be able to handle this.

Here's a pic of the knife I'm making. Again, it's 3/16" 01 tool with a 5" blade and 10.5" overall.

f756f12da914cffd84baac8f124e14d6.jpg
 
Also you might want to try taking O1 to 59c instead of 60-61
 
I find that evenheats are hotter towards the back were the coils run across the back wall. Harder to handle but try putting it in handle first.

Hoss
 
That could be it. I typically put the blade in just beyond the thermocouple probe that hangs from center. I've thought about flipping it but I feel like the handling of it after to quench would be risky.
 
The tip should be tested for its use. The temper should be done for the use. The knife you show is for a filed/camp/hunting use. These don't need or want to be of high edge hardness.

O-1 is a tough steel, but not the best for higher hardness. It should be in the Rc-58-59 range for best toughness vs edge retention. The thin tips will easily break at Rc61 but will be dozens of times tougher at Rc 59.

For some reason the idea has been spread that at a 400F temper steel becomes soft. A quick perusal of the temper charts for most of the popular knife steels shows that they are still above RC60 at 400F, and usually still at or above Rc 58 at 450F. A 350F temper is just going to remove a little brittleness, but do no toughening at all in most cases.



I suspect if you thickened the tip and do the temper for a Rc59 target ( 450F temper) the tips will do well and the overall knife will be better.
 
:thumbup:

My conjecture: Tempering at 400F-450F produces a very well balanced (strength & toughness) where hardened steels matrix contains more than 10% of plate martensite. I suspect majority of ht O1 has high % of plate martensite in the microstructure. In my view - plate martensite mostly is product of overly saturated carbon in aust matrix, driven in conjunction with level of high dislocation. It's a density of carbon, of which can be global and or aggregated/local in certain places (commonly near grain boundaries).

btw for me - I try whatever I can to keep plate martensite below 5%. Consequentially, allowing a wider temper temperature range - mostly at the low end.

Stacy E. Apelt - Bladesmith said:
The tip should be tested for its use. The temper should be done for the use. The knife you show is for a filed/camp/hunting use. These don't need or want to be of high edge hardness.

O-1 is a tough steel, but not the best for higher hardness. It should be in the Rc-58-59 range for best toughness vs edge retention. The thin tips will easily break at Rc61 but will be dozens of times tougher at Rc 59.

For some reason the idea has been spread that at a 400F temper steel becomes soft. A quick perusal of the temper charts for most of the popular knife steels shows that they are still above RC60 at 400F, and usually still at or above Rc 58 at 450F. A 350F temper is just going to remove a little brittleness, but do no toughening at all in most cases.



I suspect if you thickened the tip and do the temper for a Rc59 target ( 450F temper) the tips will do well and the overall knife will be better.
Click to expand...
 
According to My charts O1 can stil be 62-63rc at a 400° temper.
I can understand wanting to push the hardness so you have the edge retention but me personally would rather have a knife slightly softer and much tougher. O1 is not a super steel so no mater what your going have to sharpen more often then some of the heavy hitters out there. Only exception for me is that I have to a CPM 10v folder and love it. It's 63RC and I would NEVER pry anything with any part of it. I treat it as a slicer at that hardness and it works great. Now back to O1, maybe make just a few blade tips and try different tapering temp and see what you like. Remember a tougher easier to sharpen knife is a lot more useful then a broken one.
 
My recollection is that the 370-400F temper for O-1 was what people do who do not have kilns, could not soak at temp, were relying on multiple brief excursions above critical temperature, and generally not getting full hardness on quench.
 
A little update here, I have settled on 465 for my temper set point and I'm very happy with those results. The color of the steel was a perfect straw color and Edge retention was great cutting cardboard and leather during my tests.
 
Evenheat's KH418 knife oven has dimensions 6.5" W x 4.25" H x 18" D. It's the 120 volt model. I assume this is the one?

Just ordered one.... Really hoping those dimensions don't place my knives too close to the coils! Would be a bummer, since they market this one specifically to knife makers.
 
I don't think the Evenheat always does so great with perfectly even heat, but I think I have a work-around.

I've been pampered with a good industrial heat treat oven from my tool and die work that would have been hard to justify making a few knives. But it's too short for longer pieces so I use an Evenheat for long stuff. The Evenheat has more heat loss because of thin insulation and they also have exposed coils. Due to the heat loss, the coils are on a lot. And due to the exposed coils there is more undiffused IR heat. I think these two things, plus the coils on the back but not in the door can lead to differences in the temperature of your work piece along its length. A 25 degree difference during soak is a problem.

If it were glass or pottery and you were using a very slow ramp up, it would probably be moot. But for knives we want to get to temp quickly and this exacerbates the problem.

My work around for this problem is to soak the oven empty at 100-150 degrees hotter than you plan to soak your knife. Let it soak a while and build up some heat throughout the thickness of the firebrick. Then turn it off and stick your knife in cold and close the door. Turn it back on and set the next program which is the soak temp you want and a 500/hr ramp rate. With a bit of practice I have it where it's within a few degrees of my target temp when it starts to reheat so there is very little ramp time with the coils blazing for extended period. This reduces excessive heat accumulation in spots. With the knife itself cold there is little risk overheating a spot while the oven sorts itself out.

The other thing I do is an extra layer of loose stainless foil around the normal foil pack. This shields some of the IR. I roll the edges and break it into an E shape so it doesn't distort a lot. The shield can be used again and again.

Try not to put anything closer to a coil than necessary.
 
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