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Heat Treating and Metallurgy Discussion of heat treatment and metallurgy in knife making.

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  #1  
Old 12-28-2015, 04:54 PM
WNC Goater WNC Goater is offline
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Newb: Heat treating 1084

Okay, search function just doesn't quite work. I know there are probably a dozen hundred threads asking how to heat treat 1084 but I'm striking out with the search function. So...

I've got a couple blades ready to heat treat, 1084 from NJKB. Here's the plan gleaned from internet snooping:

Heat blades in kiln to 1500?, hold for no more than 10 minutes.
Quench in canola oil @ 125?-150? (yes I realize not optimal but it's what I have)
While blades are still warm, put into oven for temper @ 400? for 2 hours, allow to cool to room temp.
Then another 2 hours @ 400?

So from you experts and experienced, am I on the right track here?

Only other question is should I add the blades to a pre-heated oven or put them into a cold oven and bring it up to 1500??




I have also discovered there are a multitude of opinions as to heat temps and anneal temps and on and on. What I listed above seems to be somewhat of a consensus, if you will, or at least the most common process as I've been able to determine.
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  #2  
Old 12-28-2015, 07:04 PM
jmccustomknives jmccustomknives is offline
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Check out this thread that's currently running. it probably covers every question you have to ask. http://www.knifenetwork.com/forum/sh...ad.php?t=65716
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  #3  
Old 12-29-2015, 12:35 AM
Doug Lester Doug Lester is offline
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Don't put it into the tempering oven while the blade is still hot. You may not be giving the steel long enough to convert to martensite and you'll end up with elevated retained austenite. Wait until you can hold the blade in your bare hand without too much discomfort. The temperature of the kiln and the soak time are probably good as you need most of that time for the steel to come up to temperature.. I would back the tempering cycles down to 375? unless you are making a chopper. A slicing blade could use the extra hardness. I think that the consensus is that you put blades into a preheated oven.

Doug


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Old 12-29-2015, 06:01 AM
WNC Goater WNC Goater is offline
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Quote:
Originally Posted by jmccustomknives View Post
Check out this thread that's currently running. it probably covers every question you have to ask. http://www.knifenetwork.com/forum/sh...ad.php?t=65716
Thanks. Yes I'm aware of that thread and actually waded through the first 10 PAGES, and frankly saw nothing other than a mention of heat treating. Also I'm treating blades profiled by stock removal not forging or using a billet of damascus. After 10 pages I was tired... Hats off to your and Ray's patience though.

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Originally Posted by Doug Lester View Post
Don't put it into the tempering oven while the blade is still hot. You may not be giving the steel long enough to convert to martensite and you'll end up with elevated retained austenite. Wait until you can hold the blade in your bare hand without too much discomfort. The temperature of the kiln and the soak time are probably good as you need most of that time for the steel to come up to temperature.. I would back the tempering cycles down to 375? unless you are making a chopper. A slicing blade could use the extra hardness. I think that the consensus is that you put blades into a preheated oven.

Doug
Thanks Doug, that's what I was looking for. And yes, when I mentioned the temperature of the blade going into the tempering oven I meant cool enough to handle but still warm. Don't know if that is critical or room temperature is okay but most of what I've researched recommends just what you said.
I've seen tempering temps from 375 - 500. There seems to be a lot of opinions there. I'm making just a general purpose knife/hunting/camping. I'd like something that will hold a reasonably good edge after obtaining the initial edge, you know what I mean. So I'll back down the tempering cycles to 375 and perhaps sharpen one up before adding the scales. That way I suppose I could re-temper at slightly higher temp if I feel it's too hard.

Thanks for the help Doug!
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  #5  
Old 12-30-2015, 05:25 AM
jmccustomknives jmccustomknives is offline
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The nice thing about 1084 is it's forgiving. You should get good results, but you do need to test one. You can take a piece, do this method and break it strait out of the quench. Your looking for a clean break and fine grain structure.
With your blades, out of temper get a brass rod and clamp it in a vice. You'll take the edge and hold it a little steeper than the sharpening angle and press it into the rod. Your looking for the edge to deflect then return. Chipping indicates the blade is too hard, if the edge bends but doesn't return it's too soft.

That and comparative cutting test. Will help tell you how well your blades were done.
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  #6  
Old 12-31-2015, 09:08 AM
WNC Goater WNC Goater is offline
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Quote:
Originally Posted by jmccustomknives View Post
The nice thing about 1084 is it's forgiving. You should get good results, but you do need to test one. You can take a piece, do this method and break it strait out of the quench. Your looking for a clean break and fine grain structure.
With your blades, out of temper get a brass rod and clamp it in a vice. You'll take the edge and hold it a little steeper than the sharpening angle and press it into the rod. Your looking for the edge to deflect then return. Chipping indicates the blade is too hard, if the edge bends but doesn't return it's too soft.

That and comparative cutting test. Will help tell you how well your blades were done.

Okay, I ended up wading through all 23 pages of the thread you mentioned. (Whew) I see Ray's suggested process for heat treating 1084 etc. Okay, good info. But I have this nagging question that I haven't quite settled. That is, the need to break a blade.

It would seem per your suggestion above, let me rephrase, I don't know what I would learn from breaking a blade out of the quench before the temper. Yes, I could look at grain structure but it seems to me the quality of the blade would be judged at the end of the whole heat treating process which would include the temper. I would expect a blade at the end of the quench to be brittle and bend very little before breaking. Seems after tempering and THEN breaking a blade could tell me something maybe.

But...

If the rod/blade deflection test is successful, i.e. the sharpened edge visibly deflects and returns without bending or chipping, I would think the heat treating was successful. But I suppose it also makes sense that the edge could pass that test but the blade overall be too brittle or soft, but I don't know that to be true. But still, it seems only after the temper process would that be clearly evident. As stated above, I would expect it to be brittle after the quench but before the temper.

So I'm not questioning, just trying to learn, and not quite understanding.

Seems also that 1084, being "forgiving" would be less critical to subject to such stringent testing. I understand different batches can differ slightly with alloys used etc, but by "forgiving" I would think that to mean some temperature variations/fluctuations can be present and still achieve good results.

Perhaps I better understand the break test if using a forge to heat treat (non-temperature controlled) where there are unknown temperatures vs a controlled oven with known temperatures.
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  #7  
Old 12-31-2015, 05:14 PM
jmccustomknives jmccustomknives is offline
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Steel with a course grain structure is usually hard but weaker than steel with a fine grain structure. You wouldn't necessarily need to break a blade, just do a piece of that steel exactly as you do the knife.
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Old 01-01-2016, 09:16 AM
WNC Goater WNC Goater is offline
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Quote:
Originally Posted by jmccustomknives View Post
Steel with a course grain structure is usually hard but weaker than steel with a fine grain structure. You wouldn't necessarily need to break a blade, just do a piece of that steel exactly as you do the knife.
That makes perfectly good sense. However, what would that course grain indicate as far as fault in the heat treat? Coarse grain = too hot temp of heat treat or too cool? And depending on that, what increment of temperature correction should be used to re-test?
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  #9  
Old 01-01-2016, 09:30 AM
jmccustomknives jmccustomknives is offline
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The grain grows when you get past the austinitic state (too hot). There's a point where the carbon atoms start moving within the iron. At this point the carbon moves into the iron molecules, when quenched they get locked in causing the steel to harden. If the steel doesn't reach the heat needed to allow the carbon to move in solution then it will never harden properly. When you go past that magic point the molecules start clumping together growing the grain. It's a fine line to walk.
Steel is predictable but testing is the only way to make sure everything went as expected.
As far as the temper goes, if the edge deflection test shows chipping then you may do another cycle adding 25 deg. It's easy to take a little hardness out, getting it back is another story.
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Old 01-01-2016, 07:20 PM
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Quote:
Originally Posted by jmccustomknives View Post
The grain grows when you get past the austinitic state (too hot). There's a point where the carbon atoms start moving within the iron. At this point the carbon moves into the iron molecules, when quenched they get locked in causing the steel to harden. If the steel doesn't reach the heat needed to allow the carbon to move in solution then it will never harden properly. When you go past that magic point the molecules start clumping together growing the grain. It's a fine line to walk.
Steel is predictable but testing is the only way to make sure everything went as expected.
As far as the temper goes, if the edge deflection test shows chipping then you may do another cycle adding 25 deg. It's easy to take a little hardness out, getting it back is another story.
So regarding the conventional wisdom which states "1084 is more forgiving", does that mean there is a lot of temperature latitude for the steel to be at the austinitic state without the grain growth? If so, what type of latitude are we talking about? 25?? 50?? 100??

And likewise does the statement, "1095 is less forgiving" mean that latitude is smaller and thus making the testing more critical?

I'm gonna take a guess here and say there is a fairly broad latitude to get reasonably good results with 1084 but for OPTIMUM results one would want to test and thus narrow down that optimum temperature for each batch of steel. Is that a fair assessment?
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  #11  
Old 01-01-2016, 07:33 PM
jmccustomknives jmccustomknives is offline
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1084 just needs to reach austinitic state, the carbon goes into solution and it can be quenched. 1095 requires a "soak" time for it's carbon to completely go into solution. While 1095 will harden if heat treated like 1084 it can't reach its full potential without a soak.
As far as temps go, you've probably got 100F over and your still ok with 1084.
The last statement is very true. Different steel runs can vary in alloy content. The difference is minuscule but can change how the steel acts.
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  #12  
Old 01-01-2016, 11:33 PM
Doug Lester Doug Lester is offline
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The 1084 from TNJSB comes with a little vanadium in it. It's not the older alloy that went by that designation. That will put a little drag on the growth of the iron crystals, not molecules, which is referred to as grain. With 1084 all you have to do is get the steel up to just a little above non-magnetic and hold it just long enough to make sure that it's heated all the way through before the quench. You don't have to worry about getting too much carbon into solution because there is not enough carbon in the alloy to overload the austenite. Something like 1095, besides not having much besides the aluminum used to kill (deoxidize) to put a drag on grain growth. It also has plenty of carbon in it to give problems if you dissolve too much of it into the austenite and preventing the face centered cube of the austenite into a body centered tetrahedron of martensite. So the temperature of austinization is reduced to around 1450? and the soak time in increased to about 10 minutes at temperature to assure good carbon solution without grain growth.

Doug


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