Tempering

M

MikeS

Active Member
Good morning guys,
I have another very simple question this morning. I am trying figure out my tempering routine. I currently am using my wife's oven with an out board thermometer( digital ) from thermo works. the thermometer works well. The problem is the temp in the oven swing as much as 50 degrees when the heating elements turning on and off. I am attempting to come up with something that does not vary that much in temp. Any thoughts? I had wondered about letting my heat treating oven (Evenheat) cool down and set it at my tempering temp and put the blades back in. It takes it several hours to cool down enough for tempering. Do you think think that would harm the blade to wait a few hours to temper it? I'm working with both O-1 and 1084 steel.
Thanks guys
Mike
 
In my opinion alone, I would say your best option would be to wait and use your HT oven. A fifty degree swing in temps is more than enough to effect your temper. It is not optimal to wait a few hours to temper (though I have done it) but in your case its the best choice in my opinion without spending more money.
 
Yup. Use the Evenheat. Ever tried opening the door and using a small fan to blow on it? Helps a bunch.
 
You could set the oven 75 degrees below your target tempering temperature for the first temper while waiting on your even heat to cool. Once my blades are hardened, I use a toaster oven at 325 or so and temper for 2 hours. Once my kiln is cooled down, I temper another 2 rounds at my target temperature.
 
Hello Mike,

As some have pointed out, adding some thermal mass to the oven will help even it out. As will waiting for the oven to fully equalize and come to a hold before introducing you blades. But if you have an actual heat treat oven, that would be the thing to use. What I might do in your situation is set you kitchen oven from 50°F to 75° lower than your desired temp, ideally around 300°F and then do what is called "snap tempering" while your heat treat oven settles to the temperature you want, Then do the actual temper in there.

The snap temper is enough to take some of the internal strain effects to a safe level until you can get the full temper done. Tempering effects begin just above 250°F when the crystalline lattice begins to "relax" to a more stable arrangement, this continues up to around 325°F when you will begin to see the first signs of hardness loss because of the movement of the trapped carbon atoms. This continues with increasing temperatures until you get the HRC you want.
 
Kevin R. Cashen said:
Tempering effects begin just above 250°F when the crystalline lattice begins to "relax" to a more stable arrangement, this continues up to around 325°F when you will begin to see the first signs of hardness loss because of the movement of the trapped carbon atoms. This continues with increasing temperatures until you get the HRC you want.
Click to expand...
First time I'd seen those numbers for snap tempering. Thank you for sharing - I'll be putting that in my HT'ing notes so I don't lose it.
 
Thanks for all the input. I got curious and I called Evenheat and spoke with Tech support and I asked if opening the door and let the oven cool would damage it.
Here is what they said:
It would not damage the oven, but they recommended that let it cool to 800 degrees with the door half open when it is below 800 degrees open the door completely. at 200-300 degrees the blow a small fan in it. However, be careful when closing it up and watch the temp go up and it can exceed the tempering temp because the firebrick has absorbed heat previously.
Another option is to start the oven from dead cold and increase the temp at 150 degrees per hour until at tempering temp. This gives it enough time to heat the firebrick and not overshoot the temp.
Mike
PS the guys at Evenheat were real nice
 
Kevin,
snap tempering I've heard the term but this first time I've had a explanation of it
Thanks
Mike
 
I took a large Toaster oven took out the controls and replaced it with a PID, Relay and Thermocouple. Then insulated the inside bottom and back with 1" KAO-WOOL. Took off the outer jacket and put a layer of 1" KAO-WOOL in there too! I can hold temp plus or minus 4 Degrees. With a better PID probably better!
 
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