Differential Heat Treat?

G L Drew

G L Drew

Knifemaker / Craftsman / Service Provider
Joined
Feb 3, 2005
Messages
4,809
I am a stock removal guy working mostly with ATS34. However, I just made my first knife from 1095 and thought about doing a differential quench on it out of the furnace. Couldn't bring myself to do it. I am not being a smart ass but what is the purpose of this treatment? I am using a steel with spring properties so it should stand up to excessive bending. Along with other tests, I did put the knife in a vice and bent it about 5 degrees with a nice spring back. I didn't put a pipe over the handle and apply 250 pounds of force (can you imagine the sharp steel flying around the shop if that came loose?) And why would someone want to do that with a knife anyway????
 
Well, to tell the truth, you probably differentially hardened it without realizing it as only the thinner sections of this steel will harden reliably all the way through. It's doubtful in my mind that the thicker back (depending on how thick your steel was of course) could be cooled quickly enough. If you etch the blade I imagine you will find a transition line between the thinner martensite areas and the thicker pearlite areas, but it may not stand out clearly as a certain amount of "skin" can be expected to harden up the sides of the blade as well. You know, I think I'd expect any blade regardless of heat treatment to handle a 5 degree flex without problems.

But, you have hit on the crux of a matter that is controversial in knifemaking circles. Whether to make knives as fully hardened as possible or whether to deliberately make knives with soft pearlite backs. With the simple 10XX steels fully hardening isn't always an option due to the aformentioned problem with cooling, even if the blade appears to have hardened, behind the skin in the thicker area you would expect to find a pearlite core extending down towards the edge. Most moderately rich alloys like 5160 and 01 can easily be transformed to a fully hardened martensitic state however.
 
G L Drew said:
I am a stock removal guy working mostly with ATS34. However, I just made my first knife from 1095 and thought about doing a differential quench on it out of the furnace. Couldn't bring myself to do it. I am not being a smart ass but what is the purpose of this treatment? I am using a steel with spring properties so it should stand up to excessive bending. Along with other tests, I did put the knife in a vice and bent it about 5 degrees with a nice spring back. I didn't put a pipe over the handle and apply 250 pounds of force (can you imagine the sharp steel flying around the shop if that came loose?) And why would someone want to do that with a knife anyway????
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Yes, your steel has "spring properties" but ONLY if tempered that way! Once you take a steel to full hard, it's just that - HARD! Now, to take advantage of the "spring properties" you need to draw it back/temper it accordingly.
One of the best known spring steels is 5160. Bring it up to austenizing temp and quench it in brine! Full hard! It'll shatter like glass. Yet, you might say, "I thought it had "spring properties!" True, but "spring" qualities come from high tempering temperatures AFTER martensite formation.
That's when you get a "REAL" spring.
If you hardened your 1095, you DON'T have a spring anymore. You'll need to draw back the spine to get some "spring properties".
The differential heat treatment would be recommended for a large knife that may end up getting camp-type abuse of cutting saplings for firewood. You may want the blade to "give" a little over its long length before it would break.
This treatment can be accomplished in numerous ways.
In some arenas, this is proof that the maker can selectively control the hardening of his blade, thus showing experience and knowledge.
 
Call me simple, but in my experience lots of people just like to look at the hardening line. It's visually nice, and it's something you can't get on a factory knife.

For whatever that's worth!

Mike
 
I full quench harden my 52100 blades ..after full tempering but maintaining a Rc 60 hardness,with additional leverage using a pole, they will flex to 45 degrees and return like a spring.......what more do I need?
 
G L Drew said:
I am a stock removal guy working mostly with ATS34. However, I just made my first knife from 1095 and thought about doing a differential quench on it out of the furnace. Couldn't bring myself to do it. I am not being a smart ass but what is the purpose of this treatment? I am using a steel with spring properties so it should stand up to excessive bending. Along with other tests, I did put the knife in a vice and bent it about 5 degrees with a nice spring back. I didn't put a pipe over the handle and apply 250 pounds of force (can you imagine the sharp steel flying around the shop if that came loose?) And why would someone want to do that with a knife anyway????
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Amen! The fact that you couldn't bring yourself to do it meant that something about it challenged a line of logic that you who stock remove seem to come by more easily. Bladesmiths are more sensationalistic and prefer to ecnourage abuse of blades instead of asking your simple question of "why would someone want to do that with a knife anyway?".

Mike is correct hat the best part of differential hardening is the easthetics, a well done hamon is very beautiful to look at and should add a good amount of value to the knife. Karl also contributes his usual very good points with mentioning that full hardness with an approrpiate temper makes a good spring, but it needs to be reiterated again and again that the strength of a spring is determined by it thickness, not by its heat treatment. Do truck springs bend or break when pushed too far? When you need to handle heavier loads with your truck do you have your springs re-heat treated or do you add thickness to the stack? Well…? Folks need to really consider this one because it is a common sense way for anybody to get grasp on the reality of stiffness and strength in steel (look mete, no fancy words needed;) ) . How many prybars have you owned that would easily flex from the force of you arm? How many prybars have you owned that would easily bend??

I continue beating this dead horse because progress is being made!:thumbup: Last weekend at the Badger show I had so many conversations with folks who actually get it now that I feel there really is a chance of victory of common sense over marketing. The natural competitive instinct drives men to go to extremes in any direction they spin off in, those who want to cut things with steel will get the best steel to do it and then heat treat it to its highest potential to accomplish it, those who focus solely on easy bending there is a two word answer to their dreams- “mild steel”, but only if they are stuck thinking in the box about their metals, because any number of non-ferrous alloys will bend back and forth until your arm gets tired, heck lead can’t even work harden because it can recrystallize at room temp! But then there is that cutting thing isn’t there… embed glass in the edge!:D
 
I Thinks that as long as the ABS mandates it as a "test" of proper heat treat, this will always be a topic of dicussion.
 
Kevin, you have no idea how hard I am laughing! I didn't know the "mild steel" comment would come up that fast after speaking with you at the Badger Show!

I am wondering though, if there would be another test or series of tests that could prove that a smith has the ability to properly heat treat. The problem is, what one person cosiders "proper" another may not. There are a lot of variables to be considered, not to mention the actual real science involved. -Matt-
 
grease-man said:
Kevin, you have no idea how hard I am laughing! I didn't know the "mild steel" comment would come up that fast after speaking with you at the Badger Show!
Matt-
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That's cracking me up, too, Matt! You, me...I wonder how many times Kevin heard that term last weekend come up in this context?
 
S.Knowles said:
I Thinks that as long as the ABS mandates it as a "test" of proper heat treat, this will always be a topic of dicussion.
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That test will not be changing anytime soon, but as an ABS smith (however, not a board member, mind you), I can say that I never viewed, nor got the impression, that the test was intended to indicate proper heat treatment in a knife blade. I have used the analogy of katas in testing at self defense schools, going into a rigid horse stance when getting mugged will only result in a sound thrashing, yet it has immense value in determining the students skill level and control over technique. The differentially heat treated blade is an excellent way to show a wide array of techniques and skills in one package, what it doesn’t show about real world use it makes up for in showing us what kind of control a smith has over heat.
 
S.Knowles said:
I Thinks that as long as the ABS mandates it as a "test" of proper heat treat, this will always be a topic of dicussion.
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No, no, no.
In all fairness to the ABS, it is not stated that it is "proper" heat treatment. They just want to know that a fellow CAN do it.
Personally, I take mine to full hard.
I can thank Kevin for that.
 
grease-man said:
Kevin, you have no idea how hard I am laughing! I didn't know the "mild steel" comment would come up that fast after speaking with you at the Badger Show!

I am wondering though, if there would be another test or series of tests that could prove that a smith has the ability to properly heat treat. The problem is, what one person cosiders "proper" another may not. There are a lot of variables to be considered, not to mention the actual real science involved. -Matt-
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Hey there was an opening:) I had to use it before you did;).

I think they are doing the best with what they got. Thorough analysis under lab type conditions would be impossible for test blades. Even in much of my testing there is destruction, that is after all the idea- destroy one item so you know the limits for the rest in the series. The secret however is destruction in a way that tells you at least something about how the tool will be used. Imagine if I marketed my knives on a test where I subjected the knife to a plasma blast and measured the melting point of the whole thing? Normal knives will fail you at 2800F, but my knives will handle 2850F! When you life depends on a knife don't you want the one that can handle that extra 50F?:rolleyes:

But that is if the knife is being measured, in the test being discussed the knife is no different than an answer sheet for a test, it is all about the person taking the test. The last final exam I took is hardly the standard in paper or printing, it could have been on paper towel with a crayon as long as my answers revealed I had the knowledged covered.
 
I saw you change that, Karl! :eek: Had my boots on, though, so I was ok. :D
 
kbaknife said:
No, no, no.
In all fairness to the ABS, it is not stated that it is "proper" heat treatment. They just want to know that a fellow CAN do it.
Personally, I take mine to full hard.
I can thank Kevin for that.
Click to expand...

Point taken Karl. Perhaps it is what other people derive from the meaning of the test that clouds the issue so much. It may not be stated that it is "proper" heat treatment, but unfortunately by all too many people ("sheeple" might be more of an appropriate term) it has become the "standard" by which ALL knives should be judged. I can't agree with it. -Matt-
 
So, as I understand, a differential heat treat is like a tapered tang. Nice to look at, helps sell the knife, proves you can do it but doesn' t really add anything to the knife that a few discreet holes inder the scales wouldn't do.
 
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