Another heat treat question

S

Steve Beckwith

Joined
May 29, 2004
Messages
393
It has been posted here recently by Stacy I believe that a kiln should be heated to about 1200F prior to putting blades in so that the kiln temperature has a chance to stabilize, then ramp up to your target temperature. I have a small kiln that I built for another purpose some years ago, made of 1", 2000 degree kiln board and powered by an oven broiler element. I had never gone above 1000 degrees until yesterday when I set my controller and ran it up to 1475. I went from 80 to 1475 in a little under 25 minutes. If I load the cold kiln with blades and then slam the power to it, is that too fast, will I damage the blades in some way on the heat up? Maybe I am being lazy but I am trying to avoid dealing with the heat from this kiln as much as possible. It is a top loader and it is a bit punishing to get in and out of it so I would prefer to only go into the kiln once to remove the blades instead of having to deal with the heat twice. Any feedback would be appreciated, thanx, Steve B
 
Steve, you are good to go, brother. I always set my kiln for 1475F (being a 120V glass kiln it takes almost an hour to get there), and once it reads 1475F I wait about 15 minutes or so to make sure the atmosphere inside is indeed 1475F. Then I put the blade it, and the temperature will drop. Usually maybe 10 or 15 degrees for a smaller blade. Up to maybe 30 degrees on a large blade. Once the readout has rebounded to 1475F, I then begin my soak timer.

You can certainly do what you have heard, put the blades in at 1200. Industry heat treats will often recommend a 1200F stabilizing, but after speaking with Kevin about it, the 1200 pre soak is more for intricate designs with lots of stress risers and funny looking parts. A knife is pretty simple shape object, so the 1200F thing really isn't needed.

As long as the kiln has stabilized at your austenitizing temperature, that is what matters most.
 
What I really want to do is put the blade in at room temperature and slam the heat to it. That really is my question, will I cause damage (warp) to the blade...I guess I'll find out!
 
Rapid heating of the blade isn't too much of a problem, and can help in some instances. However, if the blade is close to one of the heating elements, there can be some uneven heating, and just maybe get hotter in that spot than the rest, just due to the proximity of the element trying to heat that fairly large enclosed area. A muffle of some sort can help control direct exposure to the heating elements.
 
Putting the blade in when you start the kiln will not cause it to warp. Me2 hinted that rapid heating can help, and I do believe rapid heating produces a better heat treat. The glass kiln I have is top loading, and the elements are in the lid. I HATED placing/retrieving blades from inside that thing, and originally settled on putting the blade in first, then turning the kiln on. I got over that in a hurry, and actually modified my kiln so I can load a blade thru the side, and not the top lid. You might consider that yourself. My kiln is made of the soft fire brick, and a thin metal sheet exterior. EASILY cut with a hacksaw. So I cut a small "slit" in the side, about .375" wide by about 2.5" tall, right underneath the "peek hole". Now I leave the lid closed at all times. Turn kiln on and ramp to 1475F as fast as it will go, slide blade in, slide blade out!
 
Remember that anything you do to a steel blade at 1200 F or under will not cause any decarb or any transformation problems .It's then often a good idea to preheat at 1200 F then go on with the rest of HT.
 
I built this kiln with the element on the bottom and I would probably not be able to modify it. Fortunately it is only 4" deep so I am not having to reach into the depths of a hot top loader. Thanks to all who responded, Steve B
 
You must log in or register to reply here.
Back
Top