Is Spring Temper the best??? Read this and tell me what you think.

A

anduin-de-smitty

Joined
Sep 30, 1999
Messages
18
Ive been talking with a friend of mine and he raised a very interesting point, and I'd like to see what the opinion of the group is.

the conversation with my friend was about the best method to create a useable blade, and he brought up the ABS.

He said that the ABS calls for a knife to be bent to 90 degrees with out
breaking, and the only way this test is passed is to make a blade that has been
edge quenched and tempered so the blade back remains completely soft, never having been hardened. These blades can be flexed to say 45 degrees, many times, and will always spring back to straight, and if this blade is bent to 90 degrees, it will not break. The blade will spring back somewhat but remain bent. At this point the blade is mostly unusable. The 90 degree bend
requires a certain force to accomplish, often times may even be DONE BY HAND. He says a thinner blade has a better chance of passing the 90 degree test.

The second scenario was hardening all of an identical blade. Temper the same way, but deeply draw the temper from the back of the blade with a torch, keeping then edge cool with water. Repeat for a total of 3 times. Lets call this the "Spring Temper". This blade will perform just as good as the ABS
blade in all cutting tests, but not the bend test. Like the ABS blade, this blade will flex to 45 degrees repeatedly and spring back to straight. On top of that, the Spring Temper blade will bend to 70 degrees with out breaking and return to straight, but when we bend it to 90 degrees it fails
by breaking. At this point the knife is unusable in any normal sense, just like the ABS blade. The AMOUNT OF FORCE required to bend this blade to the point of failure is MUCH GREATER than the force required
to bend the ABS blade to 90 degrees rendering it bent and unusable. In fact, it may require a piece of pipe or other long handle to be used to get the leverage necessary to bend the Spring Temper blade. It may well be impossible to bend it far enough toward 90 degrees to break it by hand alone. So how could it break with normal use? When it's possible that the ABS blade could break with normal use.

He is not arguing for one or the other approach as being right or wrong, even though it may seem like it. In
a fair fight I don't think you would ever know the difference. If you want
the closest thing you can get to an idiot proof knife for the person who
insists on using a knife as a crow bar, then the ABS type blade would be better for it would bend, but not break.
Perhaps for a purely utility knife where great strength is required and bending is possible, perhaps the Spring Temper blade is what should be used as it takes more to render it unusable.

As for my opinion, I can't say that I have one yet, because I have no experience in these fields, because I have not tested either of these methods.. and until I do, I dont think I should render my opinion. I do believe in testing theories and that whatevetr works for you is the right way. Those who have the experience, please lend your opinion, so that we can learn something from these very well thought out opinions.

Thankyou for your time
- Loren Patterson
 
Differentially tempering a blade as you describe is quite a common practice for large blades intended for chopping. The edge is hard to maintain its sharpness, but the spine is soft to absorb impact forces.

--JB

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e_utopia@hotmail.com
 
I think mostly this is right. But "spring temper" is not an exact term. 45 Rc and 50 Rc are well within range of having spring-like properties, but they will behave differently.
Then there is a matter of material. L-6 will flex more than O-1 at the same hardness.
 
I don't see the sense in having a blade be so much flexible if it lowers the strength that much you can deform it by hand - unless you need the dead soft spine for the increased shock resistance for combat reasons heavy blade on blade type impacts.

-Cliff
 
Actually many times the "spring tempered" blade will pass the 90 degree bend test. But not always. As Cliff said, there are a lot of variables.

The real point, however, is not that all blades should bend 90 degrees w/o breaking. It is a test devised by the ABS to test the smiths knowledge and control of heat treating. It is understood that it is a test to destruction, and is never recommended as a way treat a knife or to test your own at home. Unless, that is, you just want to destroy your knife.

If the smith cannot achieve this and still pass the cutting tests then he doesn't yet have control of heat treating carbon steels and won't be given his journeyman rating.

At least that is my take on the testing procedure.

Gary Bradburn www.toptexknives.com/bradburn.htm
 
GARY B, very good point, i didnt think of that. i bet its very common that after a student of the ABS passes his tests, he might choose to make his personal blades a different way. Can anyone attest to this?

- Loren
 
Gentlemen, that's an easy one:

Steel (carbon or low alloyed), as bought, is soft annealed, i.e. has a HRc of about 20 which also means an US of approx 110ksi.

When hardened and tempered to 58 HRc the US will be approx 310 ksi (and still somewhat brittle, not much bending!).

If "spring tempered" to about 45 HRc then the US will be 210 ksi and the steel "very tough" but no longer "much edge holding".
smile.gif


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D.T. UTZINGER
 
Lets set a couple of parameters, 5160 and a 10 camp knife. The kind made for the ABS tests. The variables edge quench 2/3rds of the width of the blade, or full quench and soft back draw to spring temper (lightblue). Which knife will take more abuse, in use. Bending 90d. is a good test but I can't remember the last time I needed to use a knife in that manner! Has anyone ever tried to bend one of those little flat spring wonderbars (nailbars)at 90d.

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It is better to bear the rebuke of a wise man than to enjoy the flattery of fools.
 
Mike :

Which knife will take more abuse, in use.
Click to expand...

The spring tempered blade will be stronger, the annealed spine one will be more ductile and tougher. Personally I would go with spring temper as the other I could deform by hand. If the nonhardened spine blade is strong enough for you (you don't want to pry) then it would be the directly better choice.

-Cliff
 
Cliff Stamp, thankyou for providing the first most relevant answer to my question.

(which method do you think is better and why?)

e_utopia, i agree that the spring temper should be used on large blades, i see that as a very smart move on a knifemakers part, because large blades are much more likely to bend.

And in reply to tallwingedgoat's post, I agree that "Spring Temper" is not an exact term, but please understand it is being used for convenience because it describes a way to heat treat that will yeild a blade with "spring like" characteristics. I don't claim to make knives that are actual springs, I only use the term so people might better understand the theory.

mikeS, i'm on your side. but i think people get wrapped up in the fact that the ABS bends their knives to 90 degrees. I dont think they call a knife with a 90 degree bend a good utility blade, what i believe they are doing is bending to 90 degrees and saying, wow, he sure knows how to control his heat-treat. I'm sure that most people would want a blade that is very tough to bend, and if they do manage to bend it, it will come back. I think the only use for a blade that will easily bend 90 degrees and not break is to show how well you are in control of the heat treating process. It is a wonderful accomplishment to make a blade that will cut so superiorly and bend so far without breaking, but i don't think i would want my personal utility knife to be made that way. i would prefer the Spring Temper as well, because my knifes are much more likely to bend a little bit rather than a full 90 degrees since I dont use my knives as a crow bar. This is along the lines of what i think GARY B was trying to say.

This is some good stuff, id love to hear more opinions from more people!

thanx for your time
- Loren Patterson
 
Well, as for terminology, that type of tempering is called 'differential temper.' If you use that term, people should know what you mean (or you have a chance to enlighten someone, which is always good).

--JB

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e_utopia@hotmail.com
 
I think leaving a body extremely soft is good for the likes of axes and certain trail knives where they must resist termendous shock, but their extreme thickness will prevent them from flexing at all.

[This message has been edited by tallwingedgoat (edited 04-18-2000).]
 
ok! from now on, it's called differentially tempered. that does make it easier.

tallwingedgoat, that's a VERY good point, and i agree with you. Axes, huge chopping knives, and maybe that's all, i cant think of anything else.

so is this everyones comclusion? what about small knives with blades around 6 inches? how would you want that heat treated?

or is it only the long chopping blades that everyone wants differentially tempered?

- Loren

[This message has been edited by anduin-de-smitty (edited 04-19-2000).]
 
"Differential tempering" is usually not applicable to small blades. It is not necessarily any less usefull here, just can't do it on a small blade. "edge quench" can be done to fairly small blades. I don't think most makers who do Differential tempering or edge quench on bigger blades bother on small blades. "Hunting knives" and skinners and such that are to be used exclusively on flesh with edge holding as the ONLY criteria of quality are usually not differentially tempered or edge quenched. It simply is not needed. It is on the big knives that have chopping potential, the rough use "survival" knife, and on the all purpose "working knife" that the differential temper and edge quench really shine. The differences discussed in this thread are between a "spring temper" back and a "Ductile" back blade. the cutting edge is the same.
 
I edge quench my hunters as added insurance for the guy that decides its also an axe and a crowbar, when dressing deer. Fox, you are right, we were talking about differential heat treat. ductile back vs. springy.

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It is better to bear the rebuke of a wise man than to enjoy the flattery of fools.
 
an abs master smith no name mention said to pass the bending test rc42 was where you needed to be whitchwould not be any good for using knife


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All that is not Given Is Lost
 
I think the point of the ABS test may be misunderstood in most circles. The way it was explained to me by a higher up in the ABS was.....
IMHO From what was said "The point of the ABS TEST is to prove that you can make a knife blade that bends 90 degrees. This shows that you know how to heat treat. The soft back is just to prove that you know how to make the steel do what they want". This is what I was told.
Is it a good test.. Well thats not the question . I have the same questions you have. I feel that the soft back was not my idea of a good solid blade.
As for the diff tempered blades.. YES the spring backed blade is better on big knives IMHO from the tests I have done. Diff tempering is one of those unique parts of life that is explainable to a degree.. but then again not.
I dont have a lab set up with the equiptment to prove it. I have found in my cutting tests that a diff tempered blade wins hands down in abuse tests like chopping cinder blocks, tip twisting, ect in some steels. The shock resistance is much better than SOME I SAID SOME full hardened blades IMHO.
And let me add this disclamier. This is my opinion. I only know what is real in the tests I do. NOT everything that is in writting or paperwork is real life fact.
Science does not explain everything.
I feel that science is a starting point only.
After explaining the process of diff tempering a blade to a heat treater metalurgist ( hes been heat treating since 1958 also not tainted by the knife industries guru's) friend his thoughts were that the blade was thin at the edge and the hardness on a diff tempered blade became softer and softer as it went towards the spine of the knife IF DONE PROPERLY. The trick is to have the right steel and make the back springy 42-48 rc and the towards the edge get harder and harder edge to the optimum
hardness of the manufacturer.. OR whatever works best for the maker.
This would create a buffer or cushion for the hard edge so to speak making the edge more flexible. We cut a blade in half and did the etch test. HE was right..according to the etch test. (this is not science here)
Good bladesmiths know how the other half of diff tempering process is done (spring back hard edge) This comes from experience and heat treating useing this process. They can get the blade to have a spring back and a hard edge.

Marquenching (interupted quenching),bainite tempering, and others are other heat treating processes that work well on SOME steels . Each steel has its place for different applications and the heat treat is different for each. STEEL selection and HEAT TREATING process should be part of a BUYERS purchasing requirments .
I do not feel there is a wonder steel that fits all the needs of every knife. There are extremes both ways. There are also applications that fit those extremes.

For some background on this process... my company at the time.. diff tempered the blades for a fig bar cutting machine some years back. The blades were chipping out after 2,000,000 bars. The rate after diff tempering (same edge hardness) went to 4,000,000 bars. The Blade was carbon steel. This most likly does not apply here but it is a fact. Guesing.. we felt that stress build up from the full hard blade #1 and the edge being more flexible as the blade got thicker from the diff temper #2 was the reason for the improvment. These blades were 3/16 thick with a one sided flat grind about 2 inches high.
Another fact.. Why do the parts on a bud beer lid canning machine wear out in 60 days with a harder material? 13 points harder rc... thats a big jump.
We replaced the parts (4150 58 rc wearing out direct from the machine manufacturer) with 17-4-ph stainless parts that we build to the new part specs. There was no corrosion involved. This is just one of those times when you feel like the 4150 at 58 rc should have done the job BUT the softer steel 17-4 at 45 rc lasted 3 years in its place compared to 60 days of the 58 rc 4150. There was no breakage involved either . It was just wear properties and flexibility.
This kind of reminds me of the talonite stellite blades.. 45 rc or 58 rc stainless or carbon ... Depends on what the end use is of the blade....

Now do me a favor. If you want to quote what I said here USE THE WHOLE POST. I feel that the others reading this cannot get the WHOLE TRUTH AND CONCEPT about what was said here by cutting it in little sections like the gossip rag type news papers do. They only print what they want you to think was said or done to make you read them. People love dirt eh!
rolleyes.gif

Diff tempering to me is like trying to explain how to touch love. You know its there but you cant touch it. The etch test somewhat proved what was going on But is still not book science.

Thanks
PS. My cutting tests are based on several different grades of carbon and stainless steel blades with a thickness of 3/16 inches aprox at the spine, full flat grinds. Lengths vary from 6 inches of blade to 12 inches of blade and around .02 edge thickness at sharpening I use a slight convex (appleseed) grind on the edge. These knife blades are normalized and sub annealled before grinding then heat treated. The heat treating process may vary with the steel of choice. I cannot relate these findings to short straight knives.....these comment may or may not reflect the comments of those living or dead ... so on and so on...

Keep cuttin :]

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Web Site At www.infinet.com/~browzer/bldesmth.html
New Web at www.darrelralph.com



[This message has been edited by Darrel Ralph (edited 04-23-2000).]
 
Darrel Ralph,

something you said was

"I have found in my cutting tests that a diff tempered blade wins hands down in abuse tests like chopping cinder blocks, tip twisting, ect in some steels. The shock resistance is much better than SOME I SAID SOME full hardened blades IMHO."

I'm a little bit confused as to your terminology. When you say "full hardened blades" do you mean that the blade has the same Rc throughout the entire blade, including the spine? where as the differentially tempered blades have a spine that started fully hardened, but was tempered much softer than the edge?

I understand what you mean about clipping small parts of your post and referring to them, but i would hope people would read each post in its entirerty and then move onto the next one below it, so if i was to take a small quote, it would be to help point out the general area of your response i am referring to.

one more thing, if your choice for big blades is what you call "spring backed" blades, what would you use for small blades? Is "spring backed" the same as differentially tempered according to your terminology?

thankyou for your time, I hope i dont seem rude, i'm just the type of person that needs things explained out to the maximum so i'm sure i'm understanding it right.

- Loren Patterson
 
ok, everyone is giving me the opinion that yes, use differential tempering on large blades, but noone is saying what they do to their small blades. blades that would mostly do push cutting (as in rope or wood) those types of blades are bent a little because of force exerted, but enough to justify a
fully hardened blade and selective temper? or maybe just fully hardened and uniformly tempered to the same temp? (no differential tempering).
is selective hardening good enough for small blades? or should you do fully hardened and selective temper just to be safe?
what do you guys think?
- Loren
 
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