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Paul Checa

Heat cycle, heat treatment, quench, temper

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Hi guys, so I was making a dagger and did 3 heat cycles at critical temp then quenched and tempered the blade for 3 hours at 350 F I was fitting the handle and guard and I twisted too Hard and the hilt snapped so I lost the blade. I'm attaching to show you my grain structure to see if it was properly treated (so I can learn something from this loss) I broke the blade in half so I could see the structure in the middle as well. Please comment below how you see the structure 20190426_103942.jpg

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The grain is quite large. How were you monitoring the temperature and which steel is it made of?

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Yes, that has been overheated and held at heat for a long time.  That is obscenely large grain.  Are you watching for decalescence?  

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I'm going to quote myself from another post, just because I'm pleased with the way I said this:

I have to agree with everything Joel said, but I'd charge more. ;)

Do break a test piece and look at your grain.  I  just taught a "knifemaking (mostly) unplugged" class for my local guild in which I taught the decalescence method and the benefits of normalizing/thermal cycling.   First I put my muffle pipe in the forge and let it warm up to what looked like a nice orange color, then asked them what temperature they thought they were seeing based on the common charts.  Everyone agreed it looked like the classic orange just above cherry red, or about 1500 degrees.  I put a thermocouple in it and it came out 1795 degrees F.  Moral:  Don't trust the color.

I also had some W1 forged to 1/4" square that I let soak at that heat for three minutes, quenched, and broke.    The grain was like table sugar.  I then did three thermal cycles (take it to critical judging by decalescence, let air cool to black, repeat) and quenched on the last heat and snapped another half-inch off the end.  The grain was like glass.  This showed them just how important temperature control is. and how easy it is to overshoot your target heat.  

The great thing about using decalescence is that it works for ALL the steels you can heat treat effectively in a typical home shop without a kiln.  Don't know the critical temperature for your steel? Don't worry about it, decalescence will show you.  1095 transforms at around 1450 degrees F.  5160 does it at 1525 F.  52100 does it at 1550 F.  But what about the magnet test?  Magnets are great, but not for heat treating.  All magnetic steels go non-magnetic at 1425 degrees.  That gets you close with most of the 10XX series steels, but not quite where you need to be.  with 5160, 52100, O1, etc, nonmagnetic is a subcritical anneal.    

So what is decalescence?  It is when the glowing steel stops emitting photons because the crystalline phase is changing from body-centered cubic to face-centered cubic, aka critical temperature.  In low light conditions it appears as a sort of swirling shadow inside the surface of the steel.  It starts at the thinner parts and creeps into the thicker as the heat evens out in the steel.  As soon as all the shadows are gone, the blade has fully transformed and is ready to quench or let air cool.  If you choose to air cool, you will see the opposite effect, recalescence.  This appears as a bright line that moves from the edge back into the spine, caused by the emission of photons when the crystalline phase shifts back.    These are quantum phenomena that can't be faked.  The class got a kick out of it once they saw it for themselves, and I told them they were now practicing quantum physics without a license.  

It sounds complicated, but it's really not.  You don't really need to know exactly what's happening at the subatomic level (although that's kinda cool if you're a big a geek as I am), all you need to know is to watch for the shadows on a rising heat and pull the blade when the shadows are gone.

Finally, the oil needs to be a little hotter.  130 degrees is the usual statement for canola or veterinary mineral oil.  That is the point at which those oils are the most effective at heat transfer, and for 1095 you really need the fastest heat transfer you can get short of cracking the blade, because with that alloy you have just under one second to drop the temperature from critical to 900 degrees or it's not gonna harden.  With 5160 or 80CrV2 you have around six seconds to do the same thing.  With O-1 you have around 30 seconds, which is why thin blades of O-1 will air harden.  

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On 4/26/2019 at 11:02 AM, Joël Mercier said:

The grain is quite large. How were you monitoring the temperature and which steel is it made of?

1095 steel, just guided myself by color (bright yellow) quenched in 200º motor oil 

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On 4/26/2019 at 12:18 PM, Alan Longmire said:

Yes, that has been overheated and held at heat for a long time.  That is obscenely large grain.  Are you watching for decalescence?  

How can I watch for that?? 

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On 4/26/2019 at 12:57 PM, Alan Longmire said:

I'm going to quote myself from another post, just because I'm pleased with the way I said this:

I have to agree with everything Joel said, but I'd charge more. ;)

Do break a test piece and look at your grain.  I  just taught a "knifemaking (mostly) unplugged" class for my local guild in which I taught the decalescence method and the benefits of normalizing/thermal cycling.   First I put my muffle pipe in the forge and let it warm up to what looked like a nice orange color, then asked them what temperature they thought they were seeing based on the common charts.  Everyone agreed it looked like the classic orange just above cherry red, or about 1500 degrees.  I put a thermocouple in it and it came out 1795 degrees F.  Moral:  Don't trust the color.

I also had some W1 forged to 1/4" square that I let soak at that heat for three minutes, quenched, and broke.    The grain was like table sugar.  I then did three thermal cycles (take it to critical judging by decalescence, let air cool to black, repeat) and quenched on the last heat and snapped another half-inch off the end.  The grain was like glass.  This showed them just how important temperature control is. and how easy it is to overshoot your target heat.  

The great thing about using decalescence is that it works for ALL the steels you can heat treat effectively in a typical home shop without a kiln.  Don't know the critical temperature for your steel? Don't worry about it, decalescence will show you.  1095 transforms at around 1450 degrees F.  5160 does it at 1525 F.  52100 does it at 1550 F.  But what about the magnet test?  Magnets are great, but not for heat treating.  All magnetic steels go non-magnetic at 1425 degrees.  That gets you close with most of the 10XX series steels, but not quite where you need to be.  with 5160, 52100, O1, etc, nonmagnetic is a subcritical anneal.    

So what is decalescence?  It is when the glowing steel stops emitting photons because the crystalline phase is changing from body-centered cubic to face-centered cubic, aka critical temperature.  In low light conditions it appears as a sort of swirling shadow inside the surface of the steel.  It starts at the thinner parts and creeps into the thicker as the heat evens out in the steel.  As soon as all the shadows are gone, the blade has fully transformed and is ready to quench or let air cool.  If you choose to air cool, you will see the opposite effect, recalescence.  This appears as a bright line that moves from the edge back into the spine, caused by the emission of photons when the crystalline phase shifts back.    These are quantum phenomena that can't be faked.  The class got a kick out of it once they saw it for themselves, and I told them they were now practicing quantum physics without a license.  

It sounds complicated, but it's really not.  You don't really need to know exactly what's happening at the subatomic level (although that's kinda cool if you're a big a geek as I am), all you need to know is to watch for the shadows on a rising heat and pull the blade when the shadows are gone.

Finally, the oil needs to be a little hotter.  130 degrees is the usual statement for canola or veterinary mineral oil.  That is the point at which those oils are the most effective at heat transfer, and for 1095 you really need the fastest heat transfer you can get short of cracking the blade, because with that alloy you have just under one second to drop the temperature from critical to 900 degrees or it's not gonna harden.  With 5160 or 80CrV2 you have around six seconds to do the same thing.  With O-1 you have around 30 seconds, which is why thin blades of O-1 will air harden.  

You are a master!

I did absolutely over heat my blade then, hahaha which proves I am over eager and like to over do everything. I will take this into account and will not over heat my steel next time... Is there a color I should be aiming for so I don't repeat my mistake? 

Should I use a pipe and put my blade in to evenly heat it?

During my forging should I stay in what color so I don't over heat as well? 

Do you have a link to the knife making unplugged class I'd love to see it! 

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Posted (edited)

bright yellow is probably much too hot.  smiths often suggest "cherry red" is more like it, though my critical temps usually look more orange.

if you are not that experienced, i highly recommend using a forge with even heat distribution and a thermocouple so that you can monitor temps reliably.  doing it by eye is "cool" and traditional, but can be a steep learning curve.  you need to learn the proper color first with reliable monitoring of temperatures. 

also, don't try to gauge the proper color in a well-lit space (like they always do on Forged in Fire).  that's asking for trouble.

Edited by joe pierre
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25 minutes ago, Paul Checa said:

all you need to know is to watch for the shadows on a rising heat and pull the blade when the shadows are gone.

This

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also search thermocycling aka normalization here.  you should not be doing that at critical during each cycle, but doing it at successively lowers temps.

as for forging temps, don't worry about that.  the point of normalization after you're done forging is to decrease the grain size.  

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50 minutes ago, Paul Checa said:

You are a master!

I did absolutely over heat my blade then, hahaha which proves I am over eager and like to over do everything. I will take this into account and will not over heat my steel next time... Is there a color I should be aiming for so I don't repeat my mistake? 

Should I use a pipe and put my blade in to evenly heat it?

During my forging should I stay in what color so I don't over heat as well? 

Do you have a link to the knife making unplugged class I'd love to see it! 

Not a master, just been doing this for 21 years.  B)

Forging heat can be anything from bright red up to almost welding, steel moves better when hotter and you refine the grain while hammering.  You then use the normalization cycles to refine the grain.  

Absolutely use a pipe with  one end welded shut.  If you leave it open on both ends it acts like a chimney and you won't get even heat.  Do not use galvanized pipe, it both makes poisonous gasses when heated above 700 degrees and will coat your blade with zinc oxide.  Put a lump of charcoal in the pipe when it is up to heat, this will scavenge all the oxygen and prevent scale from forming.

Try quenching in cooking oil, it is more reliable than motor oil and smells better too.  It's also easier to clean off  the blade.

And sorry, no link, it was an in-person event over the last few monthly meetings.

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6 hours ago, joe pierre said:

bright yellow is probably much too hot.  smiths often suggest "cherry red" is more like it, though my critical temps usually look more orange.

if you are not that experienced, i highly recommend using a forge with even heat distribution and a thermocouple so that you can monitor temps reliably.  doing it by eye is "cool" and traditional, but can be a steep learning curve.  you need to learn the proper color first with reliable monitoring of temperatures. 

also, don't try to gauge the proper color in a well-lit space (like they always do on Forged in Fire).  that's asking for trouble.

I will wait for night and do it then cause my shop is very well lit! And will aim for cherry red or dark orange. Thanks a million! 

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Posted (edited)
5 hours ago, Alan Longmire said:

Not a master, just been doing this for 21 years.  B)

Forging heat can be anything from bright red up to almost welding, steel moves better when hotter and you refine the grain while hammering.  You then use the normalization cycles to refine the grain.  

Absolutely use a pipe with  one end welded shut.  If you leave it open on both ends it acts like a chimney and you won't get even heat.  Do not use galvanized pipe, it both makes poisonous gasses when heated above 700 degrees and will coat your blade with zinc oxide.  Put a lump of charcoal in the pipe when it is up to heat, this will scavenge all the oxygen and prevent scale from forming.

Try quenching in cooking oil, it is more reliable than motor oil and smells better too.  It's also easier to clean off  the blade.

And sorry, no link, it was an in-person event over the last few monthly meetings.

How's this one in the pic? I'll weld it shut on the other end. Or is a thicker one better? 

Wood charcoal or mineral charcoal? 

I'll swap it for cooking oil then (also heated to 200º F?) 

One last thing... Should I wait for the pipe to be up to temp and then put in the blade cold and let it heat up or let it all come to temp together from the getgo? 

And it's too bad you don't have that unplugged recorded it would have been like taking a semester of forging college... I would have payed for it! And probably many more people. 

20190427_151128.jpg

Edited by Paul Checa

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15 minutes ago, Paul Checa said:

I will wait for night and do it then cause my shop is very well lit! And will aim for cherry red or dark orange. Thanks a million! 

i meant to suggest that it's very hard to go by color alone, especially if you are a relative beginner.  know your steel (what are you using?) and the proper temp for critical.  listen to what alan and the guys are saying about decalescence. 

do several rounds of proper normalization before you HT. 

and what's your forge set up?  can you leave the steel in there for an even heat, or are you doing the "move it back and forth" method?

 

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That pipe will work for a while, anyway.  Wood charcoal.  Preheat the pipe to get an even heat.  Have your oil at 130 degrees.

 

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On 4/27/2019 at 7:51 PM, joe pierre said:

i meant to suggest that it's very hard to go by color alone, especially if you are a relative beginner.  know your steel (what are you using?) and the proper temp for critical.  listen to what alan and the guys are saying about decalescence. 

do several rounds of proper normalization before you HT. 

and what's your forge set up?  can you leave the steel in there for an even heat, or are you doing the "move it back and forth" method?

 

Yes I normally do 3 heat cycles to critical temp and cooling in air temp in sand... But I guess I did heat it too much as well. (I don't have another way to do it that is not by color) I use 1095 steel i leave it for a even heat but I'm gonna do the pipe for a More even heat usin wood coal to withdraw any oxigen. 

17 hours ago, Alan Longmire said:

That pipe will work for a while, anyway.  Wood charcoal.  Preheat the pipe to get an even heat.  Have your oil at 130 degrees.

 

Perfect will do that. Thank very much. Cherry red right? 

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your normalization cycles should be at decreasing temperatures, not just critical each time.

like the guys said, look for the decalescence more than the color.  it's easy to overshoot or undershoot based on color alone.  make sure you're at least past magnetic if you don't have a thermocouple.  

good luck.

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This has been a valuable lesson.   Thanks Alann and Joe.  Good luck with your next blade Paul 

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8 hours ago, Paul Checa said:

Yes I normally do 3 heat cycles to critical temp and cooling in air temp in sand... 

Now, I’m far far far from an expert, but you don’t normalize your blade in sand or any other insulating material, that’s more of a rough ‘anneal’. Normalizing in still air should give you better results. Maybe one of these guys will verify what I’m saying, but I’m pretty sure I’m right.

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7 minutes ago, Eric Morgan said:

Now, I’m far far far from an expert, but you don’t normalize your blade in sand or any other insulating material, that’s more of a rough ‘anneal’. Normalizing in still air should give you better results. Maybe one of these guys will verify what I’m saying, but I’m pretty sure I’m right.

yup.

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10 hours ago, joe pierre said:

your normalization cycles should be at decreasing temperatures, not just critical each time.

like the guys said, look for the decalescence more than the color.  it's easy to overshoot or undershoot based on color alone.  make sure you're at least past magnetic if you don't have a thermocouple.  

good luck.

I do pass magnetic... The thing is I thing I overshoot every time... I'm overheating that's what we deducted on previous posts cause I go for bright yellow instead of cherry read or orange.

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I have to use the smallest flame possible in my propane forge in order to maintain the required temps for heat treating. Try lowering the heat in your forge. 

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Yeah, even if it takes a couple minutes for the blade to come up to temp, that’s still a very low price to pay to avoid overheating the blade. Plus, I’d imagine you’re less likely to develop warps heating more gradually. (I don’t know that for sure, but it seems logical to me)

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Yes.  You want the forge only a little hotter than the blade needs to be, and do not cool in sand.  Just hold it in still air until it loses all color.  

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Posted (edited)

If you heat your steel up past decalesence and then cool it slowly in an insulating material you are doing a critical anneal, or at least close to it, and than can give you problems with the carbides forming into plates. That will give problems with grinding and drilling. 

Doug

Edited by Doug Lester

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