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multiple quenches while forging...bad?


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I have a habit that I do alot when I'm forging, and it has occured to me it may be a bad one...

 

I forge and harden in a gas forge, so I'm bringing the whole blade up to heat. What usually happens is the point gets hot alot faster than everything else. So my habit is, I quench the point in oil halfway through the heat to let the rest of the blade catch up. I do this when I'm forging, and when I'm hardening blades. I try to do it when the point reaches critical temp, but not religiously...I go by eye when I do this.

 

Is this bad? Am I damaging the steel? Do I need to come up with a better way to keep the point from over-heating?

 

Thanks guys.

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Is this bad? Am I damaging the steel? Do I need to come up with a better way to keep the point from over-heating?

 

By quenching one half of the blade and not the other, multiple times, you are probably creating a blade with two different grain sizes. Finer in the portion that is quenched multiple times and not so fine in the rest. The portion with the finer grain will probably lose some hardenability as well. Hard to say for certain without testing the blades in question. If it is not possible to simply heat the blade with the tip pushed a bit out of the far side, you could try heating the tang end first and then flipping the blade around. Another option is to remove the blade when the thinner areas reach temperature and simply hold in still air until the thinner parts have reached the same color as the rest of the blade before putting it back in. Several cycles of this will get the whole blade up to temp. without overheating the thin parts. A combination of the above is useful as well. I hope this helps you.

 

Bruce

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Thank you for the reply, Mr Norris.

 

I have tested these blades in an unscientific manner, and I'm sure the point is hardening, with fine grain evident when broken. I etch alot of my blades, and the difference in grain is not visable. I do 2 normalising cycles after forging, then another right before hardening. Perhaps 2 or 3 'sub-quenches' afterwards isn't enough to reduce the hardenability to the point my quench isn't fast enough?

 

If this is all I'm running the risk of, I can live with it. I tested some of my early blades a long time ago and was not pleased with the grain size in the point area, so I admit I became a bit obsessed with keeping the point from over-heating. I should note that I work mainly with 1095, W1, W2, 5160, and L6, with a bit of O1 and 52100 thrown in for good measure... I think the reduced hardenability would be most noticeable with the 1095?

 

I've considered building a forge specifically for heat-treating, my main forge doesn't like to run cool enough (which, I suppose, is the reason I'm having this conversation in the first place). I've tried some of the methods you describe, but either didn't get the results I was wanting, or was too impatient to wait on it to air cool, with the oil sitting right there, preheated and ready... :lol:

 

Is reduced hardenability the only thing at risk here?

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Thank you for the reply, Mr Norris.

 

I have tested these blades in an unscientific manner, and I'm sure the point is hardening, with fine grain evident when broken. I etch alot of my blades, and the difference in grain is not visable. I do 2 normalising cycles after forging, then another right before hardening. Perhaps 2 or 3 'sub-quenches' afterwards isn't enough to reduce the hardenability to the point my quench isn't fast enough?

 

If this is all I'm running the risk of, I can live with it. I tested some of my early blades a long time ago and was not pleased with the grain size in the point area, so I admit I became a bit obsessed with keeping the point from over-heating. I should note that I work mainly with 1095, W1, W2, 5160, and L6, with a bit of O1 and 52100 thrown in for good measure... I think the reduced hardenability would be most noticeable with the 1095?

 

I've considered building a forge specifically for heat-treating, my main forge doesn't like to run cool enough (which, I suppose, is the reason I'm having this conversation in the first place). I've tried some of the methods you describe, but either didn't get the results I was wanting, or was too impatient to wait on it to air cool, with the oil sitting right there, preheated and ready... :lol:

 

Is reduced hardenability the only thing at risk here?

Id certainly consider building a Fogg style furnace ,I've just started using mine and having a controlled heat is a big advantage over the in and out of an over hot forge (its gotta improve the quality and controlability of the whole process).

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Thank you for the reply, Mr Norris.

 

I have tested these blades in an unscientific manner, and I'm sure the point is hardening, with fine grain evident when broken. I etch alot of my blades, and the difference in grain is not visable. I do 2 normalising cycles after forging, then another right before hardening. Perhaps 2 or 3 'sub-quenches' afterwards isn't enough to reduce the hardenability to the point my quench isn't fast enough?

I do the same thing you do on those occasions when I can't be bothered with the salt tank. I suspect they were doing the exact same thing for hundreds of years. Like you, I've never had a point fail to harden doing this in over fifteen years- and if the tip area turns out a bit tougher, as far as I can see that's a bonus, considering the dumb things some folks do with the tips of their blades and the thinness of the metal there, assuming it's not an "armour-piercer" style thick tip.

If it works for you keep doing it. Gods know I will...

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I don't think you need to worry. If the point hardens, you are in good shape. After three cycles above and below critical, unless you go hot enough to dissolve all the carbides, the grain won't grow much if at all. That requires one or two things. Really, really hot, for amoderate amount of time, or pretty hot for quite a while. Time at temperature. Real hot, short time, still no problem. Real hot, little longer time, then you will see grain growth again. Even if the austenitizing temperature is "uncontrolled" and gets quite hot, the steel will not have significant austenite grain growth if there are carbide particles to "pin" the grain boundaries if the time at temperature is short. The time at temperature is the thing in grain growth.

 

With all of the alloys I have played with and like, three cycles is enough to ensure fine grain in almost all conditions.

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I don't think you need to worry. If the point hardens, you are in good shape. After three cycles above and below critical, unless you go hot enough to dissolve all the carbides, the grain won't grow much if at all. That requires one or two things. Really, really hot, for amoderate amount of time, or pretty hot for quite a while. Time at temperature. Real hot, short time, still no problem. Real hot, little longer time, then you will see grain growth again. Even if the austenitizing temperature is "uncontrolled" and gets quite hot, the steel will not have significant austenite grain growth if there are carbide particles to "pin" the grain boundaries if the time at temperature is short. The time at temperature is the thing in grain growth.

 

With all of the alloys I have played with and like, three cycles is enough to ensure fine grain in almost all conditions.

 

Thank you Howard. Good information to know. What does it take for the hardenability to be reduced?

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I use a scrap piece of insulwool and put it over the tip as a heat condom of sorts. That slows down the tip heating and any decarb. The tip gets the heat by conduction from the rest of the blade which so far for me has been right at the perfect speed. You can flick the wool off with a gloved finger just before quenching.

 

This knife has a very thick cross section and the risk of overheating the tip was much higher. By using insulwool I was able to keep the heating even. The dark is just quench oil that I have not cleaned off yet.

 

survival24-web.jpg

Edited by B Finnigan
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Id certainly consider building a Fogg style furnace ,I've just started using mine and having a controlled heat is a big advantage over the in and out of an over hot forge (its gotta improve the quality and controlability of the whole process).

 

 

One of these drum furnaces has to be next on my list... the forge temps are just too erratic. Owen, did you equip yours with a thermocouple so that you can monitor actual temps, and what kind of a burner did you use?

 

It was good to meet you at Ashokan this year, although we got such little chance to talk!

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http://www.dfoggknives.com/photogallery/Dr...S/DrumForge.htm

 

Drum lined with 1" ceramic fiber insulation, small burner, either venturi or blown. The burner should be so small that it will not exceed 1550F running wide open and is adjustable.

 

The idea for this came from Jimmy Fikes. He built one using a piece of large diameter pipe. The concept is instead of trying to create and even heat over long length in a small space, make a larger space and let the heat even itself out. Works very well and is inexpensive to build.

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Thank you all for the very informative replys. Good to know I'm not hurting anything (I hate to think of how many blades I've done this way).

 

A new forge is on the drawing board...

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