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  #1  
Old 07-05-2017, 09:45 AM
WNC Goater WNC Goater is offline
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HT Oven questions

I'm not on the verge of buying anything and I know there is about an equal division between the Paragon and Evenheat. So my question isn't about that(Though I'm always interested in experience and why you chose THIS one over THAT one)

I currently use my burnout oven at work for HT, however it is limited as far as length. I have an order for a butcher knife of damascus steel that will be about 14" OAL per customer's request. I will have to heat/quench/harden using my propane forge as 14" won't fit in my oven. Which again, raises an interest in perhaps buying a blade oven.

Sorry, long winded, on to the specifics...

1. Does this oven need to be vented? My oven at work I have a kitchen stove fan/vent over the oven, vented to the outdoors. But we burn out wax and resins and the venting is to remove wax fumes. So does a knife oven need venting to remove heat or does that much heat exude forth?

2. How quick is the recovery DOWN from high heat? In other words, how long after heating a blade to the 1500? range does it take for it to stabilize at 425? for tempering? Is it feasible to expect to be able to do the first tempering in the oven I just quenched/hardened from?
My work oven takes a while so I go from the quenching oil into a 2 hour temper with a toaster oven. It takes that long for the oven to lose heat enough to stabilize @ 425? for the second temper and requires the door be left open as the walls retain a lot of heat and take time to cool.

I'm investigating the viability & convenience of having an oven at home but if there is no advantage or outside venting is necessary then there are a lot of other things to invest that amount of money in.


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Last edited by WNC Goater; 07-05-2017 at 09:47 AM.
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  #2  
Old 07-05-2017, 10:16 AM
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Ray Rogers Ray Rogers is offline
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1. No venting

2. Slow. Get a toaster oven for tempering or do cryo (because you can postpone the temper until after cryo)


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Old 07-05-2017, 10:43 AM
dtec1 dtec1 is offline
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I agree I have never needed to vent anything. I would think the smaller the oven the quicker it cools. Mine is 22in deep. So when I first got it I put a fan in front of it after it was off to try and cool it down quicker. I was quickly told that you can break the heating elements doing that. Even letting it cool with the door open can hurt the elements. 95% of the stuff I do is stainless so it goes into quench then into liquid nitrogen over night so that give me time for the oven to cool down. When I do use a carbon steel I end up tempering in the kitchen oven most of the time....Most of my heat treating I do toward the end of the day so it goes into oven then quench the liquid nitrogen over night BUT if I do it in the morning then I really only need to leave it in the liquid nitrogen for 2 hours wich usually cools the oven. When I do that I close the door after I take the blade out and let it cool for 30-45 mins with the door closed then open the door a bit to let it cool the rest of the way....I don't know the exact time it takes to cook but I will be heat treating a folder blade either tonight or in the morning....I will make it a point to see exactly how fast it cools and ill let you know tomorow
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Old 07-05-2017, 03:57 PM
KevBooth KevBooth is offline
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Ok... after reading this I have a question. Are you guys going straight from the oven and quenching right into the liquid nitrogen? Or are you quenching (air, plate, oil) whatever, and then going into the nitrogen?
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Old 07-05-2017, 04:37 PM
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Kev,

You quench by whatever method is appropriate and then - after the steel has cooled to where it is only warm to the touch - then it goes into the LN ...


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Old 07-05-2017, 06:57 PM
jimmontg jimmontg is offline
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You can accurately temper with your stove oven and an accurate thermometer. I have almost never used a HT oven for tempering except very high heats, above 500. A home oven will work once you figure out how it heats and how much, a gas oven is preferred by me as it's more even. Or as Ray said a toaster oven will work too. That way if there is no cryo you (like 1084) can quench and straight to the temper like your supposed too.


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Old 07-05-2017, 07:54 PM
WNC Goater WNC Goater is offline
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Quote:
Originally Posted by jimmontg View Post
You can accurately temper with your stove oven and an accurate thermometer. I have almost never used a HT oven for tempering except very high heats, above 500. A home oven will work once you figure out how it heats and how much, a gas oven is preferred by me as it's more even. Or as Ray said a toaster oven will work too. That way if there is no cryo you (like 1084) can quench and straight to the temper like your supposed too.
I'm aware of all that.

I was specifically seeking info about the characteristics of ovens designed for HT blades.


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Old 07-05-2017, 07:57 PM
WNC Goater WNC Goater is offline
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Kev,

You quench by whatever method is appropriate and then - after the steel has cooled to where it is only warm to the touch - then it goes into the LN ...

Something I have a difficult time wrapping my head around. That a blade after quenching, if not immediately started in the tempering cycle, can spontaneously crack if left lying in open air, yet putting it in LN while still warm from the HT doesn't cause complete shattering from the thermal shock.


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Old 07-05-2017, 08:17 PM
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Well, first you have to put a handle on what "warm from the HT" means and as I said just warm to the touch or about ambient temp BUT that doesn't mean you can leave it lay around for half the day. When it cools to that point then its into the LN right away.

The reason it doesn't crack when it goes into the LN is that you don't just dump it in there. It takes me at least 5 minutes to get it into the tank, can take longer depending on if the blade is entering the liquid or just in the gas above the liquid and how much mass is in the blade. A small blade suspended on a wire might hang in the gas if the tank is partly empty and if it is a large enough tank so that goes in pretty quick. If the blade has to enter the liquid then it has to be done slowly. I define slowly this way: the first half inch or so of the tip goes in the liquid and you can hear the liquid start to boil. Hold that position until the boiling stops, then drop another half to and inch depending on how violent the boiling sounds (experience will teach you this). When the blade is far enough into the tank that the wire holding it can be secured and the tank closed then that's far enough. When its time to pull the blade out, simply remove it from the tank and hang it on a nail until it reaches somewhere that's cool to the touch, then immediately into the tempering oven. Always temper after cryo. You can temper right after quench if you have the means to do so and then cryo but you'll need another temper after the cryo. All the cryo does is continue the transformation process that happened when you quenched the blade, simply forces it to go a little further.

This whole process is shown on my Shop Chef video ...


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Old 07-05-2017, 10:20 PM
jimmontg jimmontg is offline
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I read some spec sheets about cryoing a blade and it definitely talked about Ray's slow intro to LN. I used dry ice as well and a slow intro is called for there. Dry ice is best for a metal like AEB-l which calls for it, but it will work some toughness into other steels if that's all you have.

Heat treating is such a fascinating subject and I have learned much from many contributors here.


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Old 07-06-2017, 06:18 AM
dtec1 dtec1 is offline
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yeh I don't think it would work out if you droped it in there I drop it in slow as well. SOME steel will say to do it after quench some will say after quench OR temeper so some steels can be tempered first then cryo then as ray said always another temper.....Hey I don't know the real science behind it but I can tell you it works
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Old 07-06-2017, 09:03 AM
WNC Goater WNC Goater is offline
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Still, putting it at warm, cool, room temperature or whatever, and very, very slowly into LN is still thermal shock. Okay, I get it can take it. And maybe that doesn't qualify as thermal shock. Maybe it's like the frog and boiling pot analogy!

My point however, is that it can take that without breaking and yet if it is just left at room temperature without tempering after quenching it can spontaneous break. Supposedly anyway. I've never experienced that, I just know that's what "they" say and so I've gone from warm to the touch from the quenching oil into the tempering oven. I've read of people deciding to leave blades "until tomorrow" to temper and find them broken the next day. That's a pretty extreme reaction for steel in my mind. Everything I've read or heard says go from the quench immediately into the temper, do not leave them lying.

Forget the physics behind it or the why...That you can NOT safely leave them lying for a time at room temperature before tempering but CAN put them into LN blows my mind.

Anyway, back to the oven questions. It would be handy to have one at home. As far as cooling down the HT oven, I suppose the experience would be just like my burnout oven. And I figured that was the answer. The thing heats up and the kiln lining absorbs and holds heat for a time. It will be that way with any oven but particularly one designed to heat up to 2000?. By necessity they must hold the heat inside to even be able to heat to those levels.
Maybe if I get flush with cash (ha, ha!) I'll consider buying one for home. As it is, everything I've made to date can be put into the oven at work and tempered with the toaster oven. Longer forged knives can be made with hidden tang so the OAL of the blade doesn't exceed my current oven's capacity.

This butcher knife I have an order for isn't typical, it is a full tang, and will be made using Alabama Damascus, which can be HT in a forge.

Thanks for the HT oven info.


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Last edited by WNC Goater; 07-06-2017 at 09:05 AM.
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Old 07-06-2017, 10:18 AM
dtec1 dtec1 is offline
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WNC GOATER...like I said not big into the science behind it. Someone once tried to explain this to me as far as bringing the tempeture down that low actually "freeze's" a lot of the steel not letting it have a catastrophic failure. And if you think about it ANY material you have at room temp the molecules are actually vibrating even tho we cant see down to that level... And what is heat? energy What is cold...just a lack of that energy....so ever thing slows down inside the steel as it has less energy.....That is just general science on any material ......But a VERY simple way of looking at it......say you had 2 nice steaks one you leave on the kitchen counter the other you put in the freezer....Now say you come back a week later wich one are you going to eat?
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Old 07-06-2017, 12:55 PM
WNC Goater WNC Goater is offline
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Quote:
Originally Posted by dtec1 View Post
WNC GOATER...like I said not big into the science behind it. Someone once tried to explain this to me as far as bringing the tempeture down that low actually "freeze's" a lot of the steel not letting it have a catastrophic failure. And if you think about it ANY material you have at room temp the molecules are actually vibrating even tho we cant see down to that level... And what is heat? energy What is cold...just a lack of that energy....so ever thing slows down inside the steel as it has less energy.....That is just general science on any material ......But a VERY simple way of looking at it......say you had 2 nice steaks one you leave on the kitchen counter the other you put in the freezer....Now say you come back a week later wich one are you going to eat?
HaHa! Having a difficult time equating that rotten steak analogy to a frozen knife!
Anyway, what you say makes sense I suppose. That's about as far into the science of it all I want to go. I have a tendency in my older age not to question so much the why, but just accept that it is. On the other hand, sometimes I do wonder, "well why does it do that"?

I understand a knife blade breaking under the stress of sudden hardening in a quench. I don't understand it spontaneously breaking AFTER it is quenched, with it just sitting there. But I can live life just knowing to go ahead a put it in the tempering oven and I won't have to know the "why".

Guys on here are much more tolerant. On a blacksmithng forum I recently asked about the difference between coke and coal. Coal, as you burn it to forge, converts to coke and THAT is what you actually forge with. Okay, we all know that basic truth. But I became aware there is industrial coke you can use for forging. I was trying to ask clarification between coke converted from coal in the forge, and this industrial coke. One particularly "cheery" fellow cut and pasted something off of Wikipedia then blasted me for asking for clarification. Never can understand those who participate in forum discussions yet are self-righteously indignant when someone asks questions. Always thought of forums like a bunch of guys chatting around a campfire. Some on forums, the way they respond, would get them thrown INTO that campfire!

And boy has this thread drifted...


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Old 07-06-2017, 01:05 PM
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Can't really say why it works the way it does. Possibly, it may have something to do with the fact that the steel is contracting as it goes into the LN whereas it is free to expand unevenly over time due to the grind of the blade and the different types of crystalline structure the blade now contains after quenching ...


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