[Tim Harris]

An old blade of mine, forged from 5160 spring equivalent, seems to have lost its temper entirely. (Yes, I know how that phrase reads).

It had seen at least two years of extensive use. After the last heavy bout, it started to take a set, verging on a bend, which didn't look good. On closer inspection, I discovered that even the forte could be bent by hand. It had originally been commercially hardened and tempered to 50 Rockwell C, and until that point, had performed well.

The question for any pros who might see this is: is this a rarity?

Thanks in advance.

____________________
Nonnumquam proctalgia

[Doug Lester]

The only thing that I know of that will remove the temper from a piece of steel is heat. Has this blade been exposed to high temperature, like greater than 500 degrees F. I would also want to know what you mean by bend. Does the steel come back on its own or does it take a set after you bend it? How are you applying the bending force? I have some 1X1/4" 9260, which is a very similar steel and it's not all that easy to bend in an annealed state, which is as about as soft as it gets. I'm wondering about stress fractures in the blade that are too small to see, for right now.

[Craig Johnson]

Hmmm

That does sound strange. Two years of excessive bending (lets say a truck spring under duress testing by the manufacture) might show some type of decrease in the spring of the material, but for a sword blade to exhibit this loss of spring over all is difficult to explain. As Doug stated heat could do it but we are talking temps that would discolor the metal. Was the blade forged or stock removal? Is it soft in the sense that it takes little effort to bend near the forte or does it still need to be flexed with intent to take a set? What is the thickness of the blade near the forte?

Best
Craig

[Bill Tsafa]

During a recent mat cutting event that I participated in, I was surprised to see a lot of swords bend. The event included a number of people with different brandname swords that included Albion, A-Trim, Gen 2 and Windlass. All the Type XVa's bent across the board regardless of who made them. They were all able to be bent back to their original form by hand. It seems to be in the nature of swords to bend. The Type XXIIIa swords with their wider blades seemed to be more resistant to bending.

[Fabrice Cognot]

Better an bendy sword, than a breaky.

[Tim Harris]

Craig,
The sword in question was forged, and it wasn't exposed to heat after completion.

It took a set in combat, which could be removed manually, but kept returning - as sets do once they get established. It looked quite severe, as though the blade had never been hardened and tempered

The thing that concerned me was that, as I mentioned, I found I could bend the forte in the middle ( 4mm thick, with a central fuller) by hand . This was with the sort of pressure you'd apply in testing the flex. It didn't spring back.

I'm starting to think I had a dodgy heat treat to start with, but then again, the sword seemed perefectly OK for some years of use, and I am still baffled as to why all the temper should disappear.

[Jean Thibodeau]

Could the blade have been surfaced hardened only so that it would have seemed hard enough to take a good edge and enough to have some spring it it initially but after being stressed for a while metal fatigue would have weakened the hardened surface and now the soft core is no longer " braced " by a harder outer layer ?

Bad heat threat if my theory is true but some swords could be done like this deliberately and have a soft core with a hard surface and edge.

[Doug Lester]

5160 should have good depth of hardening but if the steel was not allowed to soak for a few minutes once it had reached a non-magnetic state the middle of the blade might not have been completely austinized before the quench and failed to convert to enough martinsite for hardness. Another posibility is that the back of the blade had the temper drawn to remove hardness and increase toughness and too much of the hardness was removed. What one wants is a soft, relatively speaking, back, a springy middle section, and a hard edge.

[Tim Harris]

Thanks for the replies.

Jean, I think you might be close to the truth. The heat-treater wsn't a specialist by any means, and I always found it a matter of pot luck with them. It is a big industrial concern, and small jobs like mine may not have had the right attention.

I'll put it down to imperfect treatment and see what happens when I get it back after being re-treated.

[Doug Lester]

Looking over my reply last night I realized why I think that it's not a good idea to reply to anything after midnight. My reply was framed on the view of doing a back draw on a single edged blade. You can draw the temper on a double edged blade but the heat has to be applied to the middle of the blade and back a way from the tip. A hot rod can be used for this purpose and you still watch for the color change in to steel to judge the draw on the temper. This can vary in the due to the abient lighting, so it can be a little iffy. Tim I glad and a little supprised that you could find a professional heat treater that will treat an oil tempering steel and can handle something the length of a sword blade. A lot ot professional heat treaters seem to only want to handle air hardening steel.

[Kelly Powell]

if these are silly theories, feel free to shoot them down

1: you said heavy use....could fatigue have cause the loss of temper?

2: could the "commercial" temper have been faulty to begin with? Maybe it was a Friday afternoon job and they did the equivalent of case hardening?

[Doug Lester]

The only thing that I know that would cause a piece of steel to loose it's temper is exposure to heat. Use could cause cracks in the steel that are too small to see. It can occures in sections of "hard" steel where there is martinsite or retained austinite and then the crack stops where there is mostly ferite and pearlite, which are "tougher" but "softer", and stops. What you have left is "softer" steel that will bend and take a set.

Heat treating is what will make or break a blade, sometimes literally. To harden a piece of steel, it has to be heated up until it is in a crystal form that is refered to as austinite. The hot steel is then quickly plunged into a coolant bath that will freeze some of these crystals in the austinite form and trap carbon molecules in other crystals as they reform back into ferite, these are known are martinsite. These are both abnormal states at normal temperatures and stresses the crytiline structure of the steel and make the steel harder but brittle. While in this state it can shatter if it is dropped. The steel has to be then tempered by soaking at around 400-450 degrees to remove some of this hardness by allowing some of the crystals to go into a more normal state.

The things that can go wrong in the heat treatment is, 1) the steel is not allowed to heat up enough through it's entire thickness to transform from ferite, pearlite, and cementite into austinite. If the steel is not transformed into it's austinetic form before it is plunged into the coolant, it cannot harden. What you can end up with hardening on the edges and the surface of the thicker middle where the heat had converted the crystiline state of the steel into austinite. The steel in the middle that did not have enough time to absorb enough heat to convert to austinite will remain ferite, pearlite, and cementite (iron carbides which are not as hard, relatively).

2) The quinchant could be too warm and only be able to cool the edges and the surface of the blade into martinsite and retained austinite. The middle section of the blade, although adiquately heated to form austinite, cools too slowly to prevent the austinite from converting back into ferite, pearlite, and cementite.

3) After proper cooling in the quenchant, if the blade is tempored at too high of a temerature and too much of the retained austinite and martinsite is allowed to convert back into the softer crystaline forms. In this case, the blade would have never have been able to hold a good edge or been very springy. This can also be caused by the blade being removed from the quenchant too soon and retained heat in the steel over tempers the steel.

This is just a short thumbnail sketch of what goes on in heat treating. Alloying elements and special heat treating techniques can alter this. Reheat treating will not mend microfractures, or big ones for that matter. Reforging at forge welding temperatures might.

[Tim Harris]

Kelly:

I was hoping to find out if stress can indeed cause a general loss of temper. In a tough spring steel, I suspect this would be unlikely, so I am inclined to believe it was a bad heat-treat.

Doug:

Thanks for the overview of the process .
Heat -treaters here are a mixed bag. The one who did the blade in question is used by quite a few local knifemakers, but I have no idea of how they deal with swords. Some of my experiences with them suggest "not well". I once had a batch of smallswords come back like spaghetti.

In commercial operations, jobs like mine end up as things done at the end of the day, after the large industrial ones. It becomes something of a lottery as to the result you might get. I have now found an outfit that is interested in what I do, and is prepared to take care.

That said, I have just bought a long forge, which should allow me to get an even heat on a blade, so I'm looking forward to at least trying to do my own treating by traditional means. I'll post the results when I get them.

_________________
Nonnumquam proctalgia

[Doug Lester]

Tim, if you want to start doing your own heat treating try getting some good reference material. I don't know if you can get it in Australia, if not Amazon.com will probably ship anywhere, but "Steel Metallurgy for the Non-metallurgist" by John Verhoeven is a good text. It's only 212 pages including appendicies and not too difficult to study. I'm still having a bit of trouble with the grafs but they're not essential for understanding the general principles of that goes on in heat treating and about the characteristics of iron and steel. Look on it as kind of a "Metalurgy for Dummies" type book. It doesn't have all the answeres but has enough information to give a good grounding in the subject.

[Doug Lester]

Tim, one other thing if you are considering doing your own heat treating, which is not as tricky as some people, like me, can make it sound. Try going to one of the knifemaking forums. The people there can give you a lot of good advise. Many make swords there too. Try Bladesmith's Forum; it's run by Don Fogg who is one of our custom makers of swords and knives. He has even traveled to England to give sword making workshops. The Knive Network also has a lot of makers.

[Luka Tic]

Perhaps you should heat treat it all over again.
I'm not an expert but I think that should work.

[Tim Harris]

Doug,

I haven't looked at Don Fogg's site for a while, but I have gathered some quality information from it in the past. I was left wondering how he finds time to do his excellent work when running a site as packed with detail as that.

Thanks again for the info. Coincidentally, I have just been sent a link to something from Project Gutenberg which covers the subject, but you can never have too much information for things like this. Some deeper understanding of the micro-processes would be good.

My plan, such as it is, was to try the way it was done for generations: get the blade to an even red, quench, clean up, heat to temper colour, quench again. Getting an even heat was always the problem.

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Nonnumquam proctalgia

[J.D. Crawford]

[Doug Lester]

J.D., cutting water bottles shows good blade geometry and good cutting technique. If you go to cut a bottle full of water and you knock it into the next yard, something is deffinantly wrong. You either have poor blade geometry or your technique is off. That is why the water bottle cut is used in some knife cutting competitions, it's a test of the knifemaker's manufacturing and cutting skills.

[Jean Thibodeau]