DONT TRUST your heat treat oven

JTknives

JTknives

Blade Heat Treating www.jarodtodd.com
Knifemaker / Craftsman / Service Provider
Joined
Jun 11, 2006
Messages
8,633
After my last post and realizing my 15n20 was coming out a touch soft compared to what others get that bought the same 15n20 from me. So I decided it was time to really break down and test this steel at different heats with extended soak times. My standby heat treat I have been using on 15n20 is 1500° for a soak for 3min.

My plan is to use 5 coupons of the same size and from the same strip of steel. I marked them 1-5 so I could keep track of them through the heat treating. I would give them 15min from the time I shut the oven door. This was to assure at least a 10min soak at temp. I started at 1490°, 1480°, 1470°, 1460 and 1450°.
Each coupon was quench in 70-80° parks 50

I think lots of us including me trust our equipment becaus we have no reasion to not trust it. Most things can be proven and tested but a heat treat oven can be tricky to accurately test and proof. I had just assumed after testing tha my oven was reading good and showing me the correct numbers. After this I'm still not sure if what I'm seeing is true on the display but it's proved one thing. You need to test the steel your using and really ring out the heat treat and just use the numbers the oven shows you as a starting point. Don't get me wrong I'm not doubting my oven, it has never let me down befor. I just think if your looking to squeeze out every last drop of performance then it's worth really digging deep and doing the work.

After running all 5 coupons through heat treating and doing RC testing this is what I came up with.
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The numbers don't mean anything on the display. The real results come from not reading a recipe, but from dialling in your numbers in your shop. To have a 20-50 degree variance in these ovens at 1500f isn't really that bad, considering our ovens are just fire bricks and a heating element.
 
How do these numbers look compared to what your getting?
 
Your 1450 numbers look like the numbers I get between 1465 and 1480. Consistent 66 and change. I think I saw one 67. I always wonder about tester error when I get 67+, except with W2.

I've mentioned the idea of testing more times than I can count. A number of people went to 1460 after I posted my test results with W2. That number is only really relevant with my kiln, into DT-48. Others can be best at whatever temp their kiln is calibrated at.
 
Looking at all the recent posts about the variable temps within the different zones of our ovens , you would have to take that into account too . I do my 15N20 at 1470F and it is pretty close to the readings you are getting. Having a Rockwell tester in my shop is one of the best things I have ever invested in. Just think though that up until recently everyone just judged it by eye.
 
I think one big contribution to this variance we are seeing is the length of the thermocouple that is exposed inside. I have noticed with my oven that the very tip of the TC is a shade darker then any heated steel in the oven even after soaking the oven for 1hr. Then as you fallow it back to the oven wall the TC gets darker and darker. This does not matter becaus inlet the tip is what measures the temp. But what I'm thinking is happening is the heat is flowing down the Thick TC Rods and cooling the tip just a titch. My TC is only sticking out of the wall by about an inch. So I'm going to do a test by extending the TC tip into the oven much further. This would normally be a problem becaus I do t want the TC sticking out so far it impends inserting a knife. So my thought is this. Nothing says the TC had to be stright. I will heat and forum the TC so one leg goes left and the other goes right then swoops back around and comes back togather where the top is. This will alow much more of the TC to be in the oven with out taking up more space.
 
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