Memory in Steel? Dealing with Blade Warp

Rick Marchand said:
Interesting thoughts Greg.
All we can be certain of is that there are no absolutes. We can however, do the best with the knowledge we have, now. The understanding we had of steel was made more complex with alloying... but never the less, it can be made predictable and controlable, as well. I think we are doing an injustice to the advancement of knowledge to assert opinions as facts, before they are validated by current standards. Opinions and propositions are the seeds of discovery but when they are based in apprehension and assumption rather than proof or reason they can corrupt truth. When discussing groundbreaking science like quantum and string theory, the experts avoid absolutes. There are however, theories, concepts and laws that have withstood challenge and scrutiny to the point that they become fact. The basic principles of metallurgy are among these truths. We know what happens when you heat steel. I think the challenges we face in heat treatment lie more in control(temperature, atmosphere, etc...) and measurement(hardness, strength, etc...) than new breakthroughs metallurgical science... the information is already there for our interpretation.

... or I could be wrong.:D
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FWIW, I totally agree, and am not suggesting otherwise. At the root, I'm just saying let's not be overly confident of the knowledge we have today (and its source).
 
tryppyr said:
FWIW, I totally agree, and am not suggesting otherwise. At the root, I'm just saying let's not be overly confident of the knowledge we have today (and its source).
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I somewhat disagree but I think it is more of a semantics thing. I believe you can be very confident in the knowledge you posess as long as you are open to criticism and the possibility of being proven wrong. So if your definition of "overly confident" is being "absolute" then we be cool, bro.
 
parbajtor said:
You've never seen a blade rust? That's the start of the transformation process.

As a former fencer I have seen many blades take on an "unnatural" set where they bend the wrong way. In order to get the weapon to work correctly, they are usually straightened and overset to reduce that wrong way bending. If they are subjected to the same wrong way bending forces in a short period of time (usually within a month of 3 nights a week training), the unnatural bend returns and is generally very difficult to straighten out. If it manages to last a month without bending the wrong way, they usually "forget" the bend and perform jiust like any other blade.
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As a fellow fencer (although I suspect in a much different discipline) the initial set is cold plastic deformation, the subsequent correction is also cold plastic deformation. What happens is the initial strike is taking the blade (or often a portion of the blade) beyond it's elastic limits into the plastic range, by counterbending it you are taking it into the plastic range in the other direction and putting additional stresses into the blade (not to mention potentially work hardening it)
I typically will take a brand new foil or epee blade and gently "train" it into a continuous curve with aproximately 1 inch or so total offset toward the bottom so that overthrusts will follow the initial direction of training rather than potentially inducing deformation along a new axis, I have been able to extend the service life of foil and epee blades from months or weeks to years by doing this as well as decreasing the potential of excessive force transmitted to my opponent (or worse broken blades)

The memory we are discussing is memory that "remembers" all work done to the metal, and is not erased at normalization, annealing, or Austentizing temperatures, which has been posited by some knifemakers, but does not make metallurgical sense

-Page
 
parbajtor said:
You've never seen a blade rust? That's the start of the transformation process.

As a former fencer I have seen many blades take on an "unnatural" set where they bend the wrong way. In order to get the weapon to work correctly, they are usually straightened and overset to reduce that wrong way bending. If they are subjected to the same wrong way bending forces in a short period of time (usually within a month of 3 nights a week training), the unnatural bend returns and is generally very difficult to straighten out. If it manages to last a month without bending the wrong way, they usually "forget" the bend and perform jiust like any other blade.
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So you are saying that if the blade stays straight for an expended period of time it gets amnesia? Why not straighten it and put it in the corner until it's ready to play nice?... lol... just messin'. I think what you are experiencing has more to do with the variables that govern elasticity and deformation than the effects of time and memory. It gets confusing because we insert familiar words to help form an understanding of certain concepts and it begins to snowball. Pretty soon steel developes human emotions and the right to vote!(again, I'm playing) I just started into Young's Modulus of Elasticity. Things I experienced while testing my blades but couldn't explain, now have names, meaning and purpose... it's so cool gettin' edjumicated!!

It's gonna be so boring after I become all-knowing.
 
I was a fencer too ! Back in the 60s and 70s the blades were very dirty and often broke - right at a large inclusion ! As a coach I often stopped a session to explain safety. All too often the cause of a bent or broken blade was due to not following safety rules . The instant your tip touches you should relax your arm ! The other common problem was that fencers were far too close ! Ever see a sharp broken blade go right through a jacket !

Brian , it's symantics to call it bent or warped ! The point is that the steel you get has a history that you don't know ! But the 1200 F stress relief isn't going to harm the structure .In fact if the structure has pealite it may help get it into spheroidized [sub-critical anneal].
 
Rick Marchand said:
I have read articles that suggested that the "damage" of warping is irreversible.

They even go as far as to suggest that ALL mechanical and thermal events are forever recorded within the steel.[/B]

Though, I have not seen any data to back that up.

So I ask...

Do you believe that steel has a memory of every mechanical and thermal event it's been subjected to?
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In my opinion it's utter hogwash.

At it's very basis, that memory theory fails to take into account the fact that not all steel is from virgin ore.

Steel can be recycled again and again since the iron age, over the last 3 thousand years.



It's a similar pathetic fallacy in attributing a soul to a knife.

It is somewhat poetic and may sell articles, but when I want real, reliable, repeatable, reputable info poetry just won't cut it.
 
Rich, did you catch this in Mete's first response?

mete said:
If you straighten with heat at tempering temperatures then changes would tend to be permanent as the crystal structure has changed.
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You've basically given the blade NEW memory. A new occurrence has taken place and that's how straightening by clamping and tempering works.
Just do it on the second cycle, after the first stress relief has taken place.
My percentage of fixing slightly warped blades this way is VERY high - like 99%? I've been doing it that way for over 10 years and have had no KNOWN "defectors".
 
Karl B. Andersen said:
Rich, did you catch this in Mete's first response?



You've basically given the blade NEW memory. A new occurrence has taken place and that's how straightening by clamping and tempering works.
Just do it on the second cycle, after the first stress relief has taken place.
My percentage of fixing slightly warped blades this way is VERY high - like 99%? I've been doing it that way for over 10 years and have had no KNOWN "defectors".
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Yup, I caught that.... and it is exactly what i wanted to verify. I remember you saying that you had been doing that for years which also helped validate it's effectivenes. I appreciate the input, O-Row Dude!
 
I continue to be utterly flummoxed as to why people who make knives with alloys designed for tool-and-die makers, hardcore industrial use, jet-engine-turbine blades and whatnot, so often throw decades worth of very expensive and real-world-proven experience out the window.

And that is all I have to say about that.
 
I had a blade warp on me and tried Ricks straightening method as posted couple months ago... didn't work for me..

can I just temper it again and try straightening by hand??

will I have to HT it again or is it going to be ok??

thanks
 
Odd, that it didn't work.... what type of steel and how severe a warp? Did you just clamp it straight or put a bit of an over-bend to it with shims? What are you tempering at?
 
ahhh shims!!!! is that what you did?? I knew I probably should have dug up that thread before I did anything else..

I just clamped it straight to some 5160.. the bent steel was 1095.. the warp was pretty substantial and easily noticeable..
 
Shim it up, brudda! I have to shim problem blades sometimes.

One thing I do now, is after the warp is fixed, I run it though one more cycle by itself(unsupported by jigs). I don't know if it is redundant but it makes me feel better when that blade comes out straight again.

Rick
 
Rick, have you tried taking one after straightening and just flexing it back and forth in a vice to see if it wants to favor the warp, or take a set back in that direction? I usually straighten out of an interrupted quench and haven't noticed any memory yet.
 
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I will relate something that I saw and that really surprised me. Although when I sat down and considered the matter it made perfect sense. We were told at the University of Idaho where I studied Civil Engineering that steel does not really and truly have the same strength in all directions. A material that displays strength directionality is termed either an orthotropic material or an anisotropic material. Wood is a very good example of an anisotropic material. Pull it parallel to the direction of the grain and it is a LOT stronger than if you tension it perpendicular the grain. Reinforced concrete is another obvious example. A NORMAL person (someone who is not and engineer) pretty much believes that steel is perfectly isotropic (same strength in all directions). And, by George, it IS! Mostly. But when you REALLY NEED to get down close and personal. When the fly shit has got to be picked out of the pepper. Then steel is not isotropic. It is orthotropic. Simple, Civil Engineers like me don't have to worry about the orthotropicity or the anisotropicity (I don't know if those are spelled right but they seems to make sense to me) of steel. We just have to get close and that, usually, is good enough. Well, to make a long story even longer, I once worked for an electrical substation manufacturer down in Alabama. All of the steel that I specified had to be Galvanized.

The Galvanize process requires that the host steel be immersed in liquid zinc. The temperature of the zinc bath goes to about 787 degrees F. If you are a knifemaker you already know that 787 puts the steel well into the plastic (tempering as we call it) range. Well guess what? That steel that had been straightened at the mill wangoed (that a technical term that is too sophisticated to explain here) back to the exact shape it was in when it came out of the rollers. It looked HORRIBLE!!!. All those lengths of 6" and 8" "W" and "C" shapes that I had calculated and specified now looked like gigantic pubic hairs!!!

The Galvanize plant engineer looked at my startled face and comforted me with this statement: "Aww hell, that don't matter. We run them members through our straightening shed and you won't never know the difference."

So. you roll out a 6" W section at the steel mill and it comes out curled. You would expect this if you gave it some thought. The mill guys don't have time to worry about the delicate feelings of civil engineers so they run those sections through a straightening process that cold springs those curled members into the nice, straight lengths that everyone is so fond of. But when they see that 787 degree bath they go right back to where they started from.

I don't know for an absolute, lead pipe fact but it seems reasonable to me that when you apply the Rick Marchand process to a warped length of very thin steel you pretty much take the heat imposed stresses out. The trick is keeping it at temperature for a long enough time to allow the stresses to relieve themselves. The method that I described above is used for mild steel. It really doesn't "mind" being cold bent. Roll it hot at the mill and it will curl just like the Christmas ribbon that your momma zipped across the back of her cizzers. Bend it back straight cold and it remembers where it was hot. Heat it to the plastic range and it will allow those cold stresses to be relieved.

Rick's process involves very sleight deflections and very low heat. It is my opinion that the Marchand method simply induces counter stresses and allows the deflected shape to creep to a relieved shape over time at low temperature.

That is my opinion. Beat it to death. See if it survives. I detest weak philosophy and shallow ideas.

Oh. And one more thing. Anyone who replies to foolish posts is himself a fool. Your momma taught you all how to act. Though it has never been one of my strengths to suffer fools gladly, I do have the ability to recognize foolish commentary. If the Moderator caint take care of fools then he needs to be replaced. It ain't yer job to police up the fools. It is your job to recognize foolish comments and keep yer mouth shut.

Nicholas Jasper
 
Nicholas.... so in a nutshell, you are speculating that if I took one of these straightened blades up to a higher heat, the warp would reappear? That sounds like an experiment I can do. Thanks.
 
Rick, when you put in shims for the overbend, do you overbend the same amount as the previous warp or just past straight? I have missed seeing a warp after hardening and tempering and not seen it until I was working on scales, then tried the overbend with shims but without heating. It works but you need to go as far the other way (if not farther) in order to straighten. I can only assume that I am inducing stress rather than relieving it when doing it this way. Does anyone temper with the blade clamped between something to reduce the chance of warp while tempering?
 
Stacy sometimes clamps his blades in between aluminum plates after an interupted quench. That sounds like a great idea to me and I've been meaning to make a set up like it with free-floating plates to accomodate distal tapers. Most of the time I can guage how much overbend to put into it by how much it moved with the straight clamp. I rarely overbend on the first try.
 
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