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View Full Version : This may sound like a stupid question but



A.W.Stovall
08-15-2010, 08:34 PM
what temp are you supposed to put the knife in the oven? do you put it in when you start heating up? do you put in at the 1400 deg point I really dont know.
Anthony

murphda2
08-15-2010, 09:11 PM
Very good question. I'm curious as well.

Justin King
08-15-2010, 09:29 PM
A lot of ovens will overshoot the set temperature when you first fire them up. There is also the radiant heat factor which can cause the blade to overshoot the temperature inside the oven due to radiant heat off of the element, if your oven does not have a baffle of some sort between the element and blade.
Mine being 110v, it takes a long time to ramp up from a pre-heat to a higher austenizing temp. I offset this by running the oven up to the higher austenizing temp first to let the insualtion soak up heat, then let it drop to the pre-heat temp. With A2, I run it up to 1775 for about a half hour, then set it to 1250, when it comes down to this temp, then I put the blade in. Equalize, then ramp up to equalize at 1450 or whatever it is, then back up to 1775 to austenize. This helps reduce temperature bounce and time beteween target temps.
I think it does not hurt with any steel to run up to 1250 or so and equalize before going up to your hardening temp, unless the specs say otherwise.

silver_pilate
08-15-2010, 09:40 PM
I turn my oven on and let it soak at temp for 20-30 minutes after it gets to temp. This gets the oven heat soaked which results in a more stable oven interior with less temperature swing and makes sure the full interior is as close to set temp as possible. After this, I put my knife in and let the oven stabilize. At 1450F or so, it takes a typical blade about 6-8 minutes to reach target temp in my oven. So I just add that to my desired soak time.

That's just how I do it. Also, once the oven is stable and heat soaked at temp, the coils are on much less duration than when the oven is working to raise the temp. The coils I'm familiar with typically reach 2300F-2400F when on, and the relay just cycles the coils on and off to stabilize the temp. If the coils are on for a longer period of time while the oven is heating, you *may* have some more surface decarb as the higher amounts of radiant heat attack the very outside surface of the steel. And the over-shoot of some ovens that Justin mentions is another good reason.

--nathan

BossDog
08-15-2010, 09:47 PM
I just throw them in cold and ramp it up. I tend to pause a few hundred degrees below austenizing temp for 10 minutes just to make sure everything is "caught up" so I can sneak up on my final temp.

silver_pilate
08-15-2010, 10:36 PM
I think the main thing is to recognize that you need to have a stable temperature, and the knife should be at target temp before you start timing your soak. Other than that, it doesn't matter too much. Get to know your equipment and how it responds to various scenarios, and act accordingly.

--Nathan

John Barker
08-17-2010, 08:51 AM
I do like like Tracy and let it equalize at the preheating temp for 10 minutes, then go on up to the austenitizing temp for the desired length of time. My steels have been coming out at the desired hardness each time.
-John

JDW
08-22-2010, 07:42 AM
I do like Tracy and John. Also most steel data sheets say to heat slowly.
Dale

Kevin R. Cashen
08-22-2010, 09:42 AM
We tend to take for granted how easy we really do have it considering how simple the shapes and cross sections are with most knives. Granted we also push hardness levels and other properties farther than other applications but a knife blade is a fairly simple flat shape. There is an awful lot written into heat treating recommendations and spec sheets with the assumption of much more intricate shapes than ours.

You will often see pre-soak temperatures, and often it will be for complex alloys that need it but often you will also see it with simpler steels where industry also has to worry about all the parts of a complex shape coming up to temp at the same time. Think of this and also consider how easy we have it in quenching as well:3:

I never worked much with ovens before making the jump up to other methods and equipment but I have learned a bit about thermal mass and temperature regulation/fluctuation. I bring everything up to temp and level it off exactly where I want it before introducing the workpiece. If I didn't do it this way I would do it the way others have described here with a short wait at 100F lower and then up to my final temp. I would not go straight to the temp. and struggle with the controller regulation. It is even more important to not go to temp and then introduce a cold blade into a oven that he controller has not fully leveled out and adjusted to yet, for then you would never really know what item was at the readout temperature, nor could you fully trust a controller that you pulled a mind scramble on when it was in the process of learning for the day.

A.W.Stovall
08-22-2010, 12:08 PM
Tracy say's he puts em in cold and ramps the temp up whats the down side to this it has to have one or else everyone would do it this way?