Into the oven cold or no?

Signalprick

Signalprick

Jason Ritchie
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Ok, dumbass question of the day and it seems there is varying opinion on this depending on who you ask. I'll preface by saying my main steels that I use are A2, AEB-L, CPM154 and Magnacut. So here goes, when the HT recipes say "preheat" does that mean to put your parts into the oven cold and bring up to preheat temp or bring the oven up to preheat temp then insert your parts? If the concensus is the latter then my next question is how does it negatively affect the steel by going in cold?
 
It takes my Evenheat just under an hour to reach 1975F. Thats too long to be heating up in my opinion. Most all knowledgeable makers, notably Devin Thomas, say preheat the oven to austenitizing temp, and then insert the knife. Once the temp rebounds start your timer.

Preheat are mostly for large, thick, and/or complex shapes, none of which describe a knife
 
Keith Nix said:
It takes my Evenheat just under an hour to reach 1975F. Thats too long to be heating up in my opinion. Most all knowledgeable makers, notably Devin Thomas, say preheat the oven to austenitizing temp, and then insert the knife. Once the temp rebounds start your timer.

Preheat are mostly for large, thick, and/or complex shapes, none of which describe a knife
Click to expand...
That's an interesting take and one I haven't heard before. So your saying no "preheat, hold" just get straight to austenitizing and go on from there? Agreed also on the time to get up to temp. I'm about the same as far as time is concerned.
 
I think the regular preheat is not necessary. Usually when you look at steel producer recommendations you will find that the preheating information is used for parts with certain thickness.

Some makers prequench stainless steels, if I remeber right DevinT uses or used to prequench AEBL.

KSN has a good article on prequenching, it is easily accessible through Google.

Also check the following topic by Kevin McGovern:

Reheat treating AEB-L​

Seems like pasting links is completly prohibited since I can't even paste links from BF anymore.
 
Devin also said in that same AEB-L post that when he does preheat steels he uses two ovens. He also mentioned it would be better to go straight to austenitization temp than preheat and then wait for that same oven to heat up to aust. temp. If my memory serves. Most of us don't have access to two ovens.
 
Another good point Keith. I should mention for context that for me personally I'm mostly heat treating small folder parts, blade and spring. Occasionally a small fixed blade but nothing thicker than 1/8". Maybe Devin T will chime in with some insight. I appreciate the comments so far. Thanks!
 
I preheat my oven for an hour a little above aus temp, turn it off, put my blade in then turn it back on to the correct aus temp. The steel heats up so fast, I don't really see much point in keeping it hot for any longer than it takes to austenitize from room temp.
 
Signalprick said:
That's an interesting take and one I haven't heard before. So your saying no "preheat, hold" just get straight to austenitizing and go on from there? Agreed also on the time to get up to temp. I'm about the same as far as time is concerned.
Click to expand...
the preheat is for cross sections in tooling not knives.

Lorien said:
I preheat my oven for an hour a little above aus temp, turn it off, put my blade in then turn it back on to the correct aus temp. The steel heats up so fast, I don't really see much point in keeping it hot for any longer than it takes to austenitize from room temp.
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There is none scientifically. But it is okay for it to drop in temp actually, if you want less drop, heat soak the firebrick for a hour at the austenitizing temp...
What is listed in a datasheet is not necessarily ideal but I'd advise following that for now. *

Edit: Lorien Lorien , the way the PID is programmed from a computer standpoint, you are honestly working against it. I am assuming this is an evenheat not random PID. I learned this myself!
 
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FredyCro said:
I think the regular preheat is not necessary. Usually when you look at steel producer recommendations you will find that the preheating information is used for parts with certain thickness.

Some makers prequench stainless steels, if I remeber right DevinT uses or used to prequench AEBL.

KSN has a good article on prequenching, it is easily accessible through Google.

Also check the following topic by Kevin McGovern:

Reheat treating AEB-L​

Seems like pasting links is completly prohibited since I can't even paste links from BF anymore.
Click to expand...
Let's see if I can post a link to BF - is this the thread you're referring to?


In that thread at post #14 I give a fairly detailed HT info I collected from DevinT (Hoss).
 
Pääru Stash said:
the preheat is for cross sections in tooling not knives.


There is none scientifically. But it is okay for it to drop in temp actually, if you want less drop, heat soak the firebrick for a hour at the austenitizing temp...
What is listed in a datasheet is not necessarily ideal but I'd advise following that for now. *

Edit: Lorien Lorien , the way the PID is programmed from a computer standpoint, you are honestly working against it. I am assuming this is an evenheat not random PID. I learned this myself!
Click to expand...
would you explain? I don't understand.
 
Thanks for the link Ken. So I'm gathering that of all the steels I named besides AEB-L which probably requires the extra pre-quench step I should be going into the oven hot and not cold. Can anyone tell me why? Also K Ken H> I assume with the AEB-L it needs to be foil wrapped for both the pre-quench and the austenitizing cycles correct?
 
I'll try. We've established that it takes the typical evenheat about an hour to heat up to AEBL temp. That whole time the elements are wide ass open trying to get there. That's a lot of radiant energy, hot spots, and time for decarb and scale even if foil wrapped. Maybe Larrin or Devin can ring in on what might happen to microstructure. Time AND temperature are important, so we cannot assume that nothing bad happens to the steel for that hour.
I'm on the fence about prequenching. I think the benefits are minimal in AEBL
 
Signalprick said:
Thanks for the link Ken. So I'm gathering that of all the steels I named besides AEB-L which probably requires the extra pre-quench step I should be going into the oven hot and not cold. Can anyone tell me why? Also K Ken H> I assume with the AEB-L it needs to be foil wrapped for both the pre-quench and the austenitizing cycles correct?
Click to expand...
What I've heard (read) from Hoss (DevinT) and his son Larrin that the least amount of time in oven is best for several reasons. With the blade foil wrapped there's not much (if any) scale being formed, but still better for blade to be at temp least amount of time possible. The time is of course depending on soak time required. Some steels don't really require "soak" time, just enough time to reach spec'd temp evenly thru out the blade, while other steels require soaking for a certain time at temp for best results.

That's one reason to allow oven to "soak" at temp for at least 30 minutes or so before putting blade in. I find the temp drops less, and recovers to temp faster if the oven has had time to soak prior to actually placing blade(s) in oven.
 
Bare steel in the kiln on its way to 2k° for an hour?

I guess it really depends on if you like decarb or not...

I mean that's a great way to burn a lot of carbon out, so if you want to get the carbon in your steel, maybe that is what you want to do...
 
I foil wrap everything. It goes into the oven close to the preheat temp. I've consistently hit my expected marks with the exception of AEB-L which I am using for the first time currently. I have personally tested every steel I have used so far and no real issues. So this is all just out of curiosity. I have seen Lorin put packets in rhe oven at AUS temp and it got me wondering why can't they go in cold. I'm curious as to the "why" both ways. Honestly I never heard before this thread that it's OK to skip preheat.
 
Have you looked at the HT recipes in Larrin Larrin 's book?

I don't recall there being any of them that call for a pre-heat.

Honestly though, I haven't looked very heavily at complex steels. I really only mess with simple carbon steels.
 
Personally, I'm not a know it all or at least I know what I don't know. So being a new maker using new steels and since I make slip joints I'm not looking for the steel to perform better one way or the other so I tend to follow the recommended HT recipie from the data sheet which calls for a pre heat. I've yet to see a data sheet that says "if your a knife maker you can skip preheat" lol. That being said I don't yet own a copy and I haven't read Lorin's book. :)
 
You should really get a copy, it's not that expensive and boy, it's just chock full of good info.

And if you don't live at the ends of the earth like me, you can have it in a couple days! (Amazon Prime takes up to two weeks to deliver to me down here on the border, it's ridiculous.)
 
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