Cooling down the oven?

dbalfa

dbalfa

Joined
Jun 23, 2008
Messages
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How do you fellas cool down your HT oven priot to tempering? Mine would take a few hours if left on it's own. I've tried blowing a fan into it but that still took 20 mins and when I turned it off, the temp rose 100 deg from radiating heat from the bricks. I didn't like waiting that long to temper anyway....any suggestions?
 
No don't force cool your HT oven, it will stress the refractory brick, causing it to break down over time. Same thing for the heating elements if it's electric.

After you are done with heat treating, close the oven door, and let it cool down slowly overnight. My Paragon oven is about 20 years old, in great shape. I only had to replace the elements once.

Use a separate oven for temper. For large blades I use the kitchen oven and smaller ones I use a good toaster oven. Avoid the cheap toaster ovens as they do not hold an even temperature.
 
I just got to where I heat treat one day and temper the next. Impossible to regulate the temperature after heat treating.

SDS
 
Even a cheap toaster oven works great if you put a pair of fire bricks in it to normalize the temperature between element cycles, and get a good oven thermometer to sit inside it, don't ever trust the dial setting on even a good toaster oven =D
 
Yep, it is electric - and I thought about the possibility of breakage..... I was sure hoping I could use this thing for temper, I have just finished making it and the 1 deg temp variation control gets me excited!

Just how bad for the blade is setting in the plates or warm oil for a few hours prior to tempering?
 
You can and should use your heat treat oven for tempering - and it is true that even leaving the door open to cool will reduce element life.

Put your blades in another oven at a lower temperature (~100 degrees less) for a 'flash temper'. Toaster ovens and even your kitchen oven are notoriously inaccurate, but at 100 degrees less you should be safe. The flash temper will take the stress of quenching off and you can do them accurately, with you heat treat oven, the next day at the proper temperatures.

Rob!
 
I'm just going off what I've been told, but maybe this is a good time to try your own cryo treatment. Leaving your blades in dry ice/kerosene for a few hours after your quenching process would give your oven time to ramp down.
 
Like Rob said, a 15 min snap temper in a preheated kitchen oven at 350 deg has always worked for me in the past.

The steel I work with the most has proven to work best without a snap temper, but cryo as part of the quench. So this gives me a few hours, and my oven time to cool back off. I do leave the door open (I'm going to hell, I know). I close the door and let it stablize a while before turing it back on.

So, I use my HT oven for temper, but I have trouble with overshoot down at tempering temps.

It is a fairly nice Lindbergh Blue industrial heat treat oven that heats quick, and holds one degree up at austenitizing temp. But low and behold it isn't too good down at tempering temps. I have to aim 25 degrees lower than I want, then it overshoots that by about 20 deg. Once it has settled in I bump it up 20. Then five. PITA.

So beware...
 
Well then, snap temper it is.
...luckily, when I have tested it, my oven will hold <5 deg variation at temp ranges - once it cools and stabilizes.

Cryo was spoken of - I am picturing dry ice in a cooler/bag with some acetone/ kerosene?(wouldn'tve thought of that) and the blade stuck down in there....is that right? Keep it there for a couple hours?
 
Definitly do not leave your door open,or blow a fan at it! i'm surprised your elements hav'nt fried yet. just keep it closed until its cool enough to temper!i generally heatreat at 5:30am ,so i have plenty of time left in the day!
 
dbalfa said:
Cryo was spoken of - I am picturing dry ice in a cooler/bag with some acetone/ kerosene?(wouldn'tve thought of that) and the blade stuck down in there....is that right? Keep it there for a couple hours?
Click to expand...

Pretty much, yeah. Here's the thread where I asked the same questions a while ago and got good answers. Enjoy!
 
I use alcohol and dry ice in a small cooler with some insulation board around it on all sides.

Mete has yapped about snap tempering before. I didn't find it in a google search. Its 300F to 325F. At 350F the austenite stabilizes and a cryo treatment won't convert it. I'm not remembering the recommended time for a snap temper. I think 30 minutes will do but it might be 60min.

A toaster oven is a great tool to temper in, snap temper or otherwise. As said, they just need a heat sink to flatten out the swing and a good oven thermometer. A person can wrap them in fiberglass insulation too, but it isn't necessary.

The way I'm going to deal with slow cooling of the kiln is snap temper blades until I've got a load then temper all at the same time... in theory, that is.

I can't help but put up this link. I found it again as I was looking for Mete's snap temper threads. There is a snap temper connection but not much to this thread's question. It's a "blast from the past"... a really nice one... good 'ol rlinger. I'll warn you that it doesn't finish... mores the shame.

Mike

http://www.bladeforums.com/forums/showthread.php?t=295483&highlight=stabilize
 
I have often thought about getting a second Paragon HT oven to use for tempering. Its true that toaster and regular ovens are not very accurate. Since I went through the expense of buying and using an oven specifically designed for accurate heat treatment of steel, perhaps it would be wise to do both stages of heat treat with the proper heat treating equipment. Perhaps some of you do this anyways.
 
Yep, I do what Rob says: Initial temper in a toaster oven then final tempers in my HT over. Using oven thermometers I know that my toaster oven is wrong on the low side: given that I temper A2 at 500, I let the toaster oven get to about 400 for the initial temper.
 
dbalfa said:
Thanks SO MUCH gentlemen! Any particular cooler size/type work best?
Click to expand...

I've got one of the small, lunch box coolers... found it at the dump without it's top. Maximum blade w/ tang of 12" across the corner flat on the bottom. A shallow rectangular pan would work and so would a tube with bottom in it. An insulating enclosure made of 2" blue board glued up around anything that will hold the alcohol/kerosene/acetone and dry ice should be fine.
----------------------------------------------------------------------

One of the things I've never found information on is the length of time needed to finish converting the austenite to martensite. I've assumed it was simply a matter of having the steel reach the temperature needed for conversion... that it was not a time based thing. But most of the folks who use the dry ice method seem to soak for amounts of time from 2-12 hours. I'd like to know the truth of the matter if anyone knows.

I've also just looked for and not found a thread on steels cryo can advantage and steels cryo either does not advantage or disadvantages. Mete was involved in the thread... maybe he'll see this and re-comment. If I'm remembering right, for 10xx steels and similar there were down-sides to the cryo effect with the dry ice method (-100F range).

Mike
 
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