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Adam Simmonds




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PostPosted: Tue 12 Jun, 2007 1:45 pm    Post subject: does steel weaken with time/ use?         Reply with quote

hi there,

one of the many things i have learnt from this site, is the fact that flexing a blade, though they are designed to sustain such treatment, is nonetheless inherently damaging to the steel.

my question is - over time, if a sword were well used (as it was desgined to be) - would there be any lessening of the steel's spring, would it lose its rigidity and become floppier or what would be the noticable effects of the flexing it had undergone through regular use?

ie - extant historical pieces which saw a fair amount of use during their lives - would these likely be weaker and or less/ more flexible now then when they were made - as a result of this use?

what, if any, are the noticable effects on a blade of the weakening to its structure, which apparently happens through being flexed?

cheers, adam s.
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Bill Grandy
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PostPosted: Tue 12 Jun, 2007 2:18 pm    Post subject:         Reply with quote

Steel, just as with all physical objects, does indeed weaken with usage. The more stress it recieves, the more damage it develops. Usually the damage is in the form of microscopic fractures and stress points. In the long run, all swords have the potential to break.

That said, factors such as heat treatment, steel type, steel thickness, the type of maintenence it sees, and the type of stress it receives can affect just how long it takes for that potential breakage to occur. There are a number of swords I own that get used regularly, and I suspect that they will last my entire life. (crossing fingers, anyway...)

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Adam Simmonds




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PostPosted: Tue 12 Jun, 2007 3:03 pm    Post subject:         Reply with quote

thanks for the info Bill,

what i am particularly interested in is the noticable signs, effects of said weakening and damage.

for example - have you noticed any change in the rigidity etc of your blades since new?

also, do you think all bending is damaging? like, does one damage one's blade with every parry and every thrust which causes it to flex?

cheers, adam s
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Jim Mearkle




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PostPosted: Tue 12 Jun, 2007 4:18 pm    Post subject:         Reply with quote

Here's a basic explanation of metal fatigue.

http://en.wikipedia.org/wiki/Fatigue_(material)

Note this part:
Quote:
Some materials (e.g., some steel and titanium alloys) exhibit an endurance limit or fatigue limit, a limit below which repeated stress does not induce failure, theoretically, for an infinite number of cycles of load. Generally speaking, a steel or titanium component being cycled at stresses below their endurance limit will fail from some other mode before it fails from fatigue. Most other non-ferrous metals (e.g., aluminium and copper alloys) exhibit no such limit and even small stresses will eventually cause failure.

Jim
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Adam Simmonds




Location: Henley-on-Thames
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PostPosted: Tue 12 Jun, 2007 4:47 pm    Post subject:         Reply with quote

thanks very much, Jim

some great info on this subject!

cheers, adam s.
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Jim Mearkle




Location: Colonie, NY
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PostPosted: Sun 01 Jul, 2007 5:33 am    Post subject:         Reply with quote

I was in a bit of a hurry last time, so I didn't have time to answer one of your questions. You asked:

Quote:
also, do you think all bending is damaging? like, does one damage one's blade with every parry and every thrust which causes it to flex?


Just to get the terminology right, bending means the metal is permanently deformed - it does not come back to its original shape after the force is removed, so, yes, all bending is damaging.

Flexing is used to describe deflection to a point where permanent bending won't occur. Unless it is above the fatigue limit, it won't cause permanent damage to steel.

Jim
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Jean Thibodeau




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PostPosted: Sun 01 Jul, 2007 1:10 pm    Post subject:         Reply with quote

Oh, I don't think a blade will change over time just sitting there i.e. the temper or heat treatment getting old and wearing off. Eek! ( A 52 r.c. blade becoming a 45 r.c. blade after a few centuries or becoming 30 r.c. after a few thousand years ).

I wonder if this is what the original question was partly about ?

Now, would thousands of years or even millions of years of just sitting there change the heat treat characteristics of a blade if corrosion is factored out of the equation. ( corrosion being something that one would expect would destroy any blade eventually ).

So does heat treating change over time ? Any evidence that it does ? A spring under tension would lose strength over time but does it if not under any load.

You can easily give up your freedom. You have to fight hard to get it back!
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Jared Smith




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PostPosted: Sun 01 Jul, 2007 2:39 pm    Post subject:         Reply with quote

Adam Simmonds wrote:

what i am particularly interested in is the noticable signs, effects of said weakening and damage.
for example - have you noticed any change in the rigidity etc of your blades since new?
also, do you think all bending is damaging? like, does one damage one's blade with every parry and every thrust which causes it to flex?


Fatigue failures (failure from large numbers of impacts and bending) as well as corrosion-stress combinations tend to be pretty hard to detect. One would normally look for onset of the failure "on the surface" with dyes plus special lighting, high strength magnification, etc. Without these aids you probably won't detect the failure before it occurs.

Absence of evidence is not necessarily evidence of absence!
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Reinier van Noort





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PostPosted: Mon 02 Jul, 2007 3:04 am    Post subject:         Reply with quote

Jean,

In geology, mineral assemblages that formed deep underground at very high temperature and pressure are not in equilibrium at the earths surface, but because of the very low temperature here (relatively speaking of course), the processes required to metamorphose the minerals into different minerals that are in equilibrium are slowed down so much that effectively they don't occur, even over millions of years, and that is if they take place at all.

I am no metallurgist, but how I understand hardening is that you freeze the steel into a assemblage of crystals that are in equilibrium at high temperature but not at room temperature. Slow cooling allows the steel to turn back into an equilibrium assemblage, but rapid freezing does not. Presumably the steel, like rock, could change back into a softer equilibrium form with time, but I would think this would be a very slow process. Perhaps somebody more involved in metals could explain just how much slower.

If there is somebody like that here; I've understood that, in geology, the minerals that are not in equilibrium at the earth's surface are more likely to dissolve through processes like (chemical) weathering and similar things. Does that also mean that a hardened steel is more likely to rust (as it is not in equilibrium)?

School voor Historische Schermkunsten

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Lafayette C Curtis




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PostPosted: Mon 02 Jul, 2007 3:50 am    Post subject:         Reply with quote

Glad to hear that there's somebody else who has some mineralogical knowledge here. Wink

As far as the terms of this discussion go, I can't contribute much more than to add that steel is an alloy, so we have to consider not only the crystal configuration of the iron atoms but also the presence of impurities, both intentional (mostly carbon) and unintentional. We all know how the carbon turns iron into harder steel by filling the gaps/irregularities in the crystal structure and pinning them in place, but I'm not sure about the effect produced by the other elements--or whether they'd be able to undergo further change by undergoing, say, chemical or electrochemical reactions with the iron after the whole thing has cooled.

I don't think rusting has much to do with mineralogical equilibrium/disequilibrium, but I may be wrong since I don't know much about how different iron crystal configurations will affect the behavior of electrons and electrochemical reactions (or whether it would have any effect at all). Maybe it has some (indirect) relation with the tendency to chip and spall in use compared to soft iron, which tends to bend rather than shatter.
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Reinier van Noort





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PostPosted: Mon 02 Jul, 2007 7:32 am    Post subject:         Reply with quote

Well, the reason I asked about the rusting is that if the steel is hardened by freezing in a disequilibrium texture and/or crystal assemblage, then that should mean that at room temperature, the hardened steel must have stored a relatively large amount of energy (compared to non-hardened steel that is at equilibrium at RT), and then I'd think that that extra energy would increase the driving force for reactions such as oxidation and other electro-chemical processes. But again, I am not a metallurgist and this is not my area of expertise. (That would be fluid-rock interaction).

R

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Angus Trim




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PostPosted: Mon 02 Jul, 2007 8:07 pm    Post subject:         Reply with quote

Jean Thibodeau wrote:
Oh, I don't think a blade will change over time just sitting there i.e. the temper or heat treatment getting old and wearing off. Eek! ( A 52 r.c. blade becoming a 45 r.c. blade after a few centuries or becoming 30 r.c. after a few thousand years ).

I wonder if this is what the original question was partly about ?

Now, would thousands of years or even millions of years of just sitting there change the heat treat characteristics of a blade if corrosion is factored out of the equation. ( corrosion being something that one would expect would destroy any blade eventually ).

So does heat treating change over time ? Any evidence that it does ? A spring under tension would lose strength over time but does it if not under any load.


Boeing has some steel parts, on some of the earlier aircraft, that are time dated, ie they need to be changed after a certain amount of time......... Because the steel in question "ages", and loses strength and hardness over a measurable amount of time. I don't recall whether the time is five years or ten.............

But, with most simple steels, I think its safe to say it won't change appreciably in your lifetime. Over several hundred years maybe, particularly if a true temper wasn't done.......

One of the things a temper does, is make it so the steel's "temper" doesn't change much over time unless the temp of the temper is gone over. In other words, a sword blade tempered for two hours at 650F won't change much unless reheated over 650F..........

But many sword blades over the world today, don't get a real temper............

swords are fun
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Lafayette C Curtis




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PostPosted: Mon 02 Jul, 2007 10:26 pm    Post subject:         Reply with quote

Steel used in aircrafts has to take on a great deal more static and dynamic loading than a sword, so it's no surprise that they are expected to develop some sort of fatigue fairly soon. Not to mention all those vibrations from the engine, from drag, and from harmonic interactions within the airframe...
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Jared Smith




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PostPosted: Tue 03 Jul, 2007 8:49 pm    Post subject: Re: does steel weaken with time/ use?         Reply with quote

Adam Simmonds wrote:
hi there,

the fact that flexing a blade, though they are designed to sustain such treatment, is nonetheless inherently damaging to the steel.

my question is - over time, if a sword were well used (as it was desgined to be) - would there be any lessening of the steel's spring, would it lose its rigidity and become floppier or what would be the noticable effects of the flexing it had undergone through regular use?
.


The general mechanical properties of a nicely executed heat treat in steel should not be considered suspect.

Most of the maker's recommended on this site offer fairly premium grades of "spring steel." Some of the plain 1090 grade carbon spring steels and other spring steels are also used for automotive leaf and coil springs. These are tested by some manufacturers in test rigs that accumulate millions of cycles over a period of a few years prior to failure under conditions that produce deflections considered extreme (equivalent to driving over "pot holes" in roads) as well as 50,000 + miles of test driving on outdoor tracks with abusive obstacles (like running over square curbs, etc.) specifically designed to abuse the springs. The reality is that corrosion or an "accident" causing deflections beyond normal expectations usually gets the better of an automotive spring. In the case of a sword, the failure could very well propagate from a nicked edge, corrosion, or a weak area in the tang which was not evident during design and a couple of hundred test cuts.
How you protect the sword from corrosion, dress or avoid edge damage, and some aspects of the design will probably outweigh the mechanical properties of good quality spring tempered steel when it comes to failure.

Absence of evidence is not necessarily evidence of absence!
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David McIntyre





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PostPosted: Wed 04 Jul, 2007 12:05 pm    Post subject:         Reply with quote

Hello all

I've been looking around these forums for quite some time now so I thought it was high time I posted something. I'm a recent graduate in mechanical engineering with a focus in material science so this topic is right up my ally. Anyway, the basic idea behind fatigue and stress in ferrous materials has already been explained pretty well with that wiki article, but I could go into more detail if someone wanted to hear it. In response to the question about whether a lack of equilibrium would increase the corrosion rate, the answer is that it won't because the metal is in equilibrium at room temperature. In the heat treatment process the metal is first heated to a single phase field and then quenched to room temperature quickly enough to avoid diffusion into an equilibrium state. After quenching, the metal is heated again to an intermediate temperature which allows equilibrium structures to form. The metal is also aged at this time, and it is the aging time and temperature at this stage that controls the properties. This means that the instability created by the initial heating is used to form the granule structure that gives the metal its strength, so in the end there is no extra energy left over. If anyone wants more detail or clarification feel free to ask.

Semper Fi. Carry on.
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Nate C.




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PostPosted: Wed 04 Jul, 2007 1:08 pm    Post subject:         Reply with quote

When I read this topic what came to mind for me was fencing weapons (i.e. foil, epee, saber). I have seen people with well maintained foil blades that were well over 10 years old and still perfectly safe for use. I have seen some abused ones that were unsafe after 2-3 years because of care and the popularity of "flicking" that requires a floppy blade. Keep in mind that these blades are designed to flex much farther than actual swords are.

Frankly, if you maintain your equipment well and there shouldn't be any reason that you couldn't get several generations of use out of the same blade. I mean, it's a matter of historical record that many older blades (by centuries even?) were re-hilted in the fashion of the time for continued service. It is also true that some swords broke and were re-hilted for use as daggers, dirks, and catsbalgers. These I think were probably broken in battle or from poor heat treatment, not from overuse.

Just my $.02.

Nate C.

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Angus Trim




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PostPosted: Wed 04 Jul, 2007 1:44 pm    Post subject:         Reply with quote

David McIntyre wrote:
Hello all

I've been looking around these forums for quite some time now so I thought it was high time I posted something. I'm a recent graduate in mechanical engineering with a focus in material science so this topic is right up my ally. Anyway, the basic idea behind fatigue and stress in ferrous materials has already been explained pretty well with that wiki article, but I could go into more detail if someone wanted to hear it. In response to the question about whether a lack of equilibrium would increase the corrosion rate, the answer is that it won't because the metal is in equilibrium at room temperature. In the heat treatment process the metal is first heated to a single phase field and then quenched to room temperature quickly enough to avoid diffusion into an equilibrium state. After quenching, the metal is heated again to an intermediate temperature which allows equilibrium structures to form. The metal is also aged at this time, and it is the aging time and temperature at this stage that controls the properties. This means that the instability created by the initial heating is used to form the granule structure that gives the metal its strength, so in the end there is no extra energy left over. If anyone wants more detail or clarification feel free to ask.


Well, that works like that in a situation where you have a true, complete quench, then a tempering process.......

Not all sword blades in the world today are made made that way. A few years ago, there were a few smiths who really didn't harden and temper their blades the way many of us discuss it today, more of a 'forge hardening" than a true harden, quench, temper. One smith used 5160, and the blades came put fairly tough and springy this way.

There's another method that has several names, one being "slack quench", which is basically run the blade up to the austenizing temp, then partially quench, pulling it out of the quench before it reached the quenching medium's temperature....... From here, let air cool to room temp.........

This last can give a fairly tough blade, and on the plus side, has less tendency to warp, than, say run up to 1550F and quench in 300F oil........ But its not as stable as a true tempered blade is...........

In fact, considering all the sword blades made in the world today, I'd almost bet that the "austenize, quench, temper" way of heat treating is in the minority today.............

swords are fun
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Adam Simmonds




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PostPosted: Thu 05 Jul, 2007 8:36 am    Post subject:         Reply with quote

Angus Trim wrote:



There's another method that has several names, one being "slack quench", which is basically run the blade up to the austenizing temp, then partially quench, pulling it out of the quench before it reached the quenching medium's temperature....... From here, let air cool to room temp.........

This last can give a fairly tough blade, and on the plus side, has less tendency to warp, than, say run up to 1550F and quench in 300F oil........ But its not as stable as a true tempered blade is...........

In fact, considering all the sword blades made in the world today, I'd almost bet that the "austenize, quench, temper" way of heat treating is in the minority today.............


this is interesting, and calls to my mind the question: how can one discern a blade which has a "true" temper? and also, what is this stability which is refered to above?

would this type of temper be evident in the way the blade flexes and behaves in use? ie the degree of 'spring' a blade exhibits when restraightening after a thrust which causes it to flex - that is to say, the vigour with which a blade leaps back into line after being flexed? are there other telltale signs to look for which indicate the quality of a blades temper?

i suspect that eyes which have seen various different blades and tempers would discern the 'true' tempers much quicker then my own, yet am interested to know what qualities a "true" temper exhibits to eyes which have not been privileged to a large variety of blades and tempers.

cheers, adan
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Angus Trim




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PostPosted: Thu 05 Jul, 2007 8:52 am    Post subject:         Reply with quote

Adam Simmonds wrote:
Angus Trim wrote:



There's another method that has several names, one being "slack quench", which is basically run the blade up to the austenizing temp, then partially quench, pulling it out of the quench before it reached the quenching medium's temperature....... From here, let air cool to room temp.........

This last can give a fairly tough blade, and on the plus side, has less tendency to warp, than, say run up to 1550F and quench in 300F oil........ But its not as stable as a true tempered blade is...........

In fact, considering all the sword blades made in the world today, I'd almost bet that the "austenize, quench, temper" way of heat treating is in the minority today.............


this is interesting, and calls to my mind the question: how can one discern a blade which has a "true" temper? and also, what is this stability which is refered to above?

would this type of temper be evident in the way the blade flexes and behaves in use? ie the degree of 'spring' a blade exhibits when restraightening after a thrust which causes it to flex - that is to say, the vigour with which a blade leaps back into line after being flexed? are there other telltale signs to look for which indicate the quality of a blades temper?

i suspect that eyes which have seen various different blades and tempers would discern the 'true' tempers much quicker then my own, yet am interested to know what qualities a "true" temper exhibits to eyes which have not been privileged to a large variety of blades and tempers.

cheers, adan


Hi Adam

I don't think most people would know the difference. Frankly you can make a reasonable sword this way....yes, I'd love to make this a "sales' thread by telling you what a wonderful job of heat treating AT blades exhibit, but truth to tell, I believe that dynamic and harmonic balance, blade geometry and edge geometry are more important for a finished sword than having the best heat treat.........

You've read how careful you need to be sharpening a sword with a belt grinder to not overheat? A blade tempered like mine, that's not that much of a concern. Tempered at 575F "stabilizes" it such that you have to exceed 575F by a bit with the grinder to modify the temper. Warming it {the blade} enough to make it uncomfortable holding it, won't affect the temper appreciably. You'd really, really have to work at it........

A blade not tempered conventionally, might lose some appreciable hardness if its heated a bit. In other words, it takes more care grinding that a conventionally tempered blade.........

Truth to tell, if done well, and a blade is not pushed to its limits, you're not going to be able to tell the difference. Even a well tempered blade will fail under abuse........

Yes, there's more differences, but I don't have time to write a book right now..... and you're not going to be able to tell, untell there's a failure of some kind.........

swords are fun
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Jared Smith




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PostPosted: Thu 05 Jul, 2007 1:52 pm    Post subject:         Reply with quote

I wish to add to what Angus stated, some of these methods such as slack quench, are not necessarily new short cuts. The use of quench fluids other than water (urine, flesh of animals, sea water, etc.) and interrupted short quenches goes pretty far back. The Oakshott web site discusses them as possible methods but does not contemplate the percent popularity with which they might have been eployed.

The JUSTOR article link (need subscription to read full article) discusses short interrupted quenches being practiced as early as 4th century AD / CE.

http://links.jstor.org/sici?sici=0021-6682(20...0.CO%3B2-5

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