Revealing Kiln Test.

Nathan the Machinist said:
Yes, but it is easy to make a knife in D2 using "standard practices" that does both of those tasks poorly. And the rockwell numbers can be almost meaningless, so they are no guide.

For example, you can have two D2 knives with the same geometry that came out of the same bar of steel that were heat treated two slightly different ways (change the timing of a couple of steps) that both have the same rockwell hardness, and one can do a variety of tasks ranging from fine cutting to rough use well, and the other nearly identical twin does poorly at these same tasks.

My point here is, without actually testing the work, you wouldn't know if the process was working. And if you'd never compared the results with other known good work, you might mistakenly believe you were getting the "full potential" out of the steel by following the industry standard or using a reputable heat treater.

I have test blades like this here, and I can send them to you if you'd like to see what I'm talking about.
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I'm with you on this. I'm all about testing that's why this thread got to me a little. I'm all about testing when tested correctly. Ofcourse I have heat treated my blades (same bar, same grind, same edge angle, differant heat treat) and tested for performance. I love my D-2 some jobs call for cryo some don't. Some call for differant tempering cycles. All that being understood, to me this thread is really about quality. The industry standard is not always best for a skinning knife, but it's the best place to start. You can't achieve that standard without the right temps and tactics. How many makers do you know that check the hardness of there knives with a file and say " Oh yeah that's about 60 Rc. " I don't know the Q.C. people at Nicholson.:D
 
Nathan the Machinist said:
A)Commercial practice is generally not about fine edged cutting implements, and commercial heat treaters are largely focused on hitting Rockwell numbers without warping or cracking your work...
B)...But this begs the question, how does one determine if they're reaching the full potential of a steel if following the industry standard or sending out to a reputable heat treater isn't necessarily the gold standard?
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A) I'm certain that is generally true. And, with a few notable exceptions, most of us are using alloys that weren't specifically designed for skinning deer, opening your mail or building survival shelters. They were designed for things like injection-molding plastic, cutting hundreds of miles of paper, and blanking out thousands of parts without crumbling.
B) Skin deer, open envelopes and build survival shelters :)
 
james terrio said:
Fascinating conversation gentlemen, thank you. I've often been told to put blades in cold and let them heat up with the kiln, but I think I understand how that could be a problem, now. I'm not qualified to ask the complex questions, so I'll ask a simple (but multi-part) one:
A) after allowing the kiln itself to reach temp and stabilize, how long does it take for a room-temperature blade to reach the desired austenizing temp? If I understand this right, it's important to let the whole piece come up to temp, then time the "soak", yes? (FWIW I'm talking about deep-hardening, moderate-to-high-alloy steels, so I'm presuming this is fairly important)
B) Would preheating the steel to, say, 400F in a separate oven while the kiln ramps up and stabilizes help, or just be a waste of electricity?
C) Again, assuming we're dealing with a kiln that's as accurate and stable as we can get it, what effect does putting in 6 blades rather than 1 at a time have? Does the extra mass help keep things even, or would I get measurably different results on the blades closest to the walls/elements, compared to the one in the center of the kiln?

I have a 14" 110V Paragon, if that makes a difference.
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First question
My experience with blades of no greater thickness than 1/4 inch going into a fully preheated and equilibrated kiln took typically about 10 minutes to come up to temp on the surface, I typically add 5 minutes to ensure penetration. I did a test with an embedded thermocouple in a block that was 1/4 x 3 x 1 1-4 and it took 12 minutes.

Second question
Can't hurt but I cannot speak to any benefit, electricity is cheap

Third Question
I believe that in a small kiln with unshielded elements you will get proximity differentials in radiational heating between your outside blades and your central position ones, also the added thermal loading will take longer element cycle times to recover which will lead to more infrared exposure.

You want large thermal mass in the kiln in relation to the thermal load of your blades. My experience in Aerospace metallurgical testing backs up the OP results of a kiln coming up from cold to temp overheating objects with small thermal mass in relation to the mass of the kiln

-Page
 
I am glad that you posted this up, you reveal a common mistake by many.

When I temper my blades they only go to 388 f. I program my Paragon to go to 388 in one hour and place the blades in at room temp. Start the Paragon and in one hour it reaches 388 f. The Paragon will range a few degrees above and below 388 for two hours, then shut down and cool to room temp.


When I first started I was anxious and set it to go to 1,00 f. but stop at 388 f. to hurry the process a little. What I found immediately by testing my blades was that they had been overheated, I learned this lesson through testing the performance qualities of my blades.

Your documentation is well stated, thanks.
 
Thanks, Ed... this thread was intended to get folks thinking about the equipment they use... Electric kilns in particular. Of course, this could carry over to every piece of equipment in your shop. Know your tools and how they affect your workpiece is the bottom line here.

We are starting to drift off topic(partially my own fault)... I think I accomplished what I set out to do. Thanks for all the replies.

Rick
 
I re-opened this thread because I have received a lot of good questions/critiques of the experiment, which was the whole point of the time I spent on this.

I would like to avoid discussing particular HT'g practices and simply stick to learning about the equipment we use.

Thanks,
Rick
 
I have been curious for some time about putting a blade in the oven during the ramp cycle vs putting it in once Temp is reached. This might be a stupid question, but is it possible that taking steel that is sitting at room temp a suddenly exposing it to such high heat could cause internal stress and even cracking/warping? I would think allowing the steel to ride the ramp cycle, would allow it to adjust to higher temps more evenly, and setting the kiln to a lower temp and allowing to equalize before full temp could lessen the risk of overheating. I could be dead wrong of course.
 
Rick Marchand said:
Just for clarity guys...

Normally, I DO allow my kiln to equalize BEFORE I put in my blades. This test was set up to reflect the temperature spikes during ramp up proceedures and to validate the infrared/radiant heat scare that a few of us have been trying to get across to folks.

It is also important to note that the Tempilstiks can melt BEFORE the piece they sit on gets to temperature. I found this out while using the T-stiks to "calibrate my eye" when using an open forge. I was originally pre-marking the steel and gaging the temperature by when it melted.... that was the wrong way. I needed to apply the marker to the steel OUT OF THE HEAT SOURCE to get a true reading of the steel itself, rather than reading the forge.

The experiment in this thread was all about getting to know my own kiln than nailing the temperature for a good heat treat. If you have a kiln, I strongly urge you to do your own testing. Tempilstiks are easy to find online.

As for the Sugar Creek Kiln...

230 Volt
11 Amp
2530 Watt

I should be able to hit the stainless temps but admittedly, I'm somewhat afraid(however unjustified) of buring out an element. Perhaps someone who regularily hits these temps can try an experiment. Besides... my Tempilstiks only go to 1800F.
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Rick, I have the exact same kiln and I have treated s30v with no problem---set to 1950 wait till temp evens out then wait 15 more min.No hurry, make a new pot of coffee. Jerry
 
Good question Dave. I always took the conventional statement of "slowly heat the steel to critical temperature" to mean "evenly". Especially when using a heat source that runs hotter than your target temperature.... like a coal or gas forge would. I think you just want to avoid overheating the thinner sections while the piece comes to temp.

Skilldust.... thanks for chiming in..... good to know.
 
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