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The Newbies Arena Are you new to knife making? Here is all the help you will need.

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  #1  
Old 05-03-2016, 10:38 PM
Sabrerider Sabrerider is offline
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Heat treat question

Sorry having search problem. Probably already answered this for someone before but anyway, I hear a lot about simple heat treatment of the 10xx steel and it's understood that pre warming the oil to 125-140 is the proper way. What is the outcome of using it at say room temperature. What does it do to the steel? Thanks for tolerating another newbie question.
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  #2  
Old 05-04-2016, 06:23 AM
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Crex Crex is offline
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The cooler oil will not drop the temperature of the steel at a fast enough rate to get a proper hardening.
May seem counter-intuitive, but there are certain thermal dynamics at play here that affect the viscosity of the oil and it's ability to adsorb heat from the steel quick enough.

Sure it's a lot more technically complicated than that, but that's a nutshell explanation. Understand that that temp range is general - optimum for any oil is more specific/exact for that given oil but that ball park figure will work. Post testing the quench results will tell you if you got it right. I would err to the lower side of that temp range, since the hot steel will immediately change things on the quench.

Bottom line is you are trying to "freeze" the carbide mix at it's most homogenous (sp) state, which will intern make the steel the hardest you can get it within the parameters of the technology you have on hand.


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  #3  
Old 05-06-2016, 10:04 AM
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Andrew Garrett Andrew Garrett is offline
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Taking that a bit further for a better 'mind's eye' view of what is going on:

Putting a hot blade into cold oil creates a wide temperature difference between the steel and the oil.
This will cause the oil/steel contact zone to react violently as the cold oil struggles to get up to temperature. That reaction manifests itself as rapidly sizzling oil all around the hot steel. This causes a 'vapor jacket' around the surface of the steel which prevents proper contact with the oil. Therefore, the steel cannot cool quickly enough to harden properly. Sounds weird, right?

Oil that is heated to a temperature cool enough to harden the steel, but hot enough to prevent the 'vapor jacket' is ideal. For the peanut oil I use, I find 120-140 to be the acceptable range (I prefer 120-125).

The way you move the blade through the volume of oil upon quenching is also relevant. Starting a one end of a warmed oil tank and 'slicing' through at medium speed keep the oil around the blade from heating too much and/or forming any vapor jacket. In essence, if the 120-140 degree oil is best, then keeping oil at that temp in contact with the steel through the entire quench cycle (a few seconds) is best to my way of thinking.

I get great results.

I hope this helps.
Do not 'paddle' the blade side to side or it will warp.


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Old 05-07-2016, 12:48 PM
Tai Google Tai Google is offline
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Andrew, peanut oil and the other vegetable oils don't exhibit any vapor jacket phase, like the petroleum based fluids. Therefore, agitation is not as critical and they work well with a still quench. The convective current usually takes care of it. Although agitation or circulation may aid somewhat in convection, it probably won't make a big difference with the vegetable oils. Still quenching seems more ideal for blades, because you'll tend to get less warping.

The bubbles you may be seeing with the peanut oil are not vapors, but rather smoke. To the best of my knowledge, these bubbles don't appear until after the steel is already around the pearlite nose.


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Last edited by Tai Google; 05-07-2016 at 12:55 PM.
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  #5  
Old 05-07-2016, 01:48 PM
Tai Google Tai Google is offline
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... What we really need to realize here is that about half of the quenching information and advise we get on the internet is geared towards petroleum based fluids, and the other half is based on over the counter vegetable oils, water, brine and a few other odds and ends. There?s a huge difference between them. Most exhibit three cooling mechanisms or phases,. The other only exhibits one.

It?s important to know the differences.

... Depending on variables,... agitation, heating the fluid etc., may or may not be necessary.

There is no one *quenching technique*,... medium type or temperature etc., that works best in all instances.

With 10xx you're looking at pretty much all of them.


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Last edited by Tai Google; 05-07-2016 at 02:22 PM.
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Old 05-07-2016, 03:39 PM
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Andrew Garrett Andrew Garrett is offline
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Good stuff Tai! I learned something today!
Thanks!

Point of clarity though...,
You are saying that by the time I see smoke (vapor) it has already hardened and developed into the pearlite structure. Correct?

That's pretty darn fast (even in warmed oil).


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Old 05-07-2016, 04:15 PM
Tai Google Tai Google is offline
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No not exactly. In most cases, by the time the vegetable oil starts to smoke (not vapor) it's already on it's way to becoming martensite (hard). It's already in the transformational stage. On very thin stock there normally isn't enough time for the smoke bubbles to even form. This should be a split second event. After it gets just below the *atmospheric* smoke point, which takes a little more time, I usually take it out and finish it in air.

... Just to clarify, vapors and smoke are not the same things, and I'm talking strictly about vegetable oils now. Most of my experience is with canola, though I've tried others.

So,... there is no vapor phase with vegetable oils, but there is a mysterious latter smoke phase that little is known about and is probably inconsequential,... other than being a possible temperature indicator.

In any case, with 10xx steels, after the first second of the quench, agitation could possibly do more harm than good by speeding up transformation and creating unnecessary stresses.


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Last edited by Tai Google; 05-07-2016 at 05:33 PM.
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Old 05-08-2016, 04:28 AM
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*****After it gets just below the *atmospheric* smoke point, which takes a little more time, I usually take it out and finish it in air.*****

This is where quench plates in a post vice really shine on thinner kitchen and fillet blades. Soon as it reaches this point I go from the quench straight into the plates to clamp and finish cooling. No problem with potential warping and takes care of any that does occurs during quench. Sweet thing about post vice's is the speed of the coarse screw.....quick 1/4 turn to close. No fiddling around.


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Last edited by Crex; 05-08-2016 at 04:30 AM.
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  #9  
Old 05-08-2016, 07:41 AM
Tai Google Tai Google is offline
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In the case of accelerated petroleum based fluids like Parks #50, keep in mind that they have additives in them designed to shorten the duration vapor jacket phase. So, whether or not the quench needs to be further accelerated by agitation/circulation (or preheating), really depends on exactly what's being quenched. Agitation may or may not be beneficial.

Besides speeding up the quench, there is one other thing to consider with agitation. It can be helpful in dislodging trapped bubbles and improve uniformity. However, on most blades there aren't any places for bubbles to get trapped. If there are pockets or undercuts in the blades or any places where bubbles can get trapped, then agitation could help,... but it maybe as simple as just going vertical instead of horizontal, or rotating the blade from side to side a few times.

To sum it up, if you are heating your oil and/or using agitation, or a "slicing motion", just because you heard the "experts" say to,... you really should investigate it further before making it standard procedure.


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Last edited by Tai Google; 05-08-2016 at 12:50 PM.
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  #10  
Old 05-08-2016, 08:51 AM
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Andrew Garrett Andrew Garrett is offline
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It never ceases to amaze me how many times in my 11 years of knifemaking I've had an occasion where, at least for a moment, I question if I even know what I'm doing.

You offer some interesting revelations Tai, and I thank you for them.

After studying any number of books and videos on knifemaking and considering the many opinions of 'experts' as you say on forums such as this, I have come to think that there are either many correct paths or that the best path has not yet been found. This must be even more frustrating for newbies who are just seeking a linear procedure. I suppose one should expect a certain amount of gray area in a pursuit where art meets science.

Yet, I can't discount my own experiences and testing results:
Most of my knives are stock removal, 10xx series steels, less than 1/8" thick at the widest part of the tapered spine, hollow ground, and clay backed for a differential HT with Satanite.

I bring it up to non-magnetic in a small atmospheric forge, check against a hanging magnet all along the areas to be hardened, and quench edge-down at a 45* angle in a 20MM ammo can filled with peanut oil warmed to 120ish. I 'slice' from one end of the can to the other slowly and back again leaving the blade submerged for around 30 seconds.

I then remove the Satanite with an old putty knife, wipe it down with a paper towel and file test it all alone the edge and verify the existence of a proper hamon. If I want more info on edge hardness and the *geometry allows, I let it cool to room temperature and put it on my Rockwell hardness tester to get a number (low to mid 60s).

I secure the blade edge up in a C-clamp, put it on a cookie sheet and put it in the center of an oven pre-heated to 400* and leave it for an hour. These times and temps can be adjusted for the intended purpose of the knife.

I can't recall how long its been since I warped a knife at any stage.

Finish grinding is slow with many dunks in the water bucket.

These knives perform well.

However, only a fool ignores the sage advice of a recognized master who was generous enough to share the benefits of his experience, so I will do some more testing to tweak or verify my process for better knives. I will report my findings here. My forthcoming retirement from tattooing should free up more time for knives. Thank you again.

*Rockwell hardness testing can be difficult on hollow ground and differentially heat treated blades due to the geometry of the flat anvils of my Rams Rockford tester.


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  #11  
Old 05-08-2016, 09:26 AM
Tai Google Tai Google is offline
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