does steel weaken with time/ use? -- myArmoury.com

Adam Simmonds · Posted: Tue 12 Jun, 2007 1:45 pm Post subject: does steel weaken with time/ use?

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.

Bill Grandy · myArmoury Team

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...)

Adam Simmonds · Posted: Tue 12 Jun, 2007 3:03 pm Post subject:

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

Jim Mearkle · Posted: Tue 12 Jun, 2007 4:18 pm Post subject:

Here's a basic explanation of metal fatigue.

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

Note this part:

Adam Simmonds · Posted: Tue 12 Jun, 2007 4:47 pm Post subject:

thanks very much, Jim

some great info on this subject!

cheers, adam s.

Jim Mearkle · Posted: Sun 01 Jul, 2007 5:33 am Post subject:

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

Jean Thibodeau · Posted: Sun 01 Jul, 2007 1:10 pm Post subject:

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.

Jared Smith · Posted: Sun 01 Jul, 2007 2:39 pm Post subject:

Reinier van Noort · Posted: Mon 02 Jul, 2007 3:04 am Post subject:

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)?

Lafayette C Curtis · Posted: Mon 02 Jul, 2007 3:50 am Post subject:

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.

Reinier van Noort · Posted: Mon 02 Jul, 2007 7:32 am Post subject:

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

Angus Trim · Posted: Mon 02 Jul, 2007 8:07 pm Post subject:

Lafayette C Curtis · Posted: Mon 02 Jul, 2007 10:26 pm Post subject:

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...

Jared Smith

David McIntyre · Posted: Wed 04 Jul, 2007 12:05 pm Post subject:

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.

Nate C. · Posted: Wed 04 Jul, 2007 1:08 pm Post subject:

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.

Angus Trim · Posted: Wed 04 Jul, 2007 1:44 pm Post subject:

Adam Simmonds · Posted: Thu 05 Jul, 2007 8:36 am Post subject:

Angus Trim · Posted: Thu 05 Jul, 2007 8:52 am Post subject:

Jared Smith · Posted: Thu 05 Jul, 2007 1:52 pm Post subject:

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