I have posted about this before in a couple of threads on SFI, but I'd like to get the opinions of experienced swordsmiths about this.

I'm an archaeology student, and the archaeology department of our Museum of Science has done quite a lot of research on the viking swords in their collection. They did a lot of different tests, of whichI know very little, and cooperated with a very experienced engineer and smith called Kasper Andresen. mr. Andresen has experimented a lot with the museum in trying to find out the methods the swords were forged by, how the inscriptions and decorating were done, etc.

now, I was looking at the post about the windlass damascus swords, about them beeing only able to flex a few inches before taking a set due to bad heat treat. Is heat treat the main factor when it comes to the flexibility of a sword blade? I'm asking this, because Kasper says their studies revealed that a lot of the swords in the collection werent hardened by quenching. He says that instead, the edges have been cold forged, which work-hardens them to some degree (although not as much as a quench would) and gives the sword a lot of flexibility, so that is the way he forges his viking swords.

I saw one of the students pic up one of Kaspers swords, and he bent it 90 degrees and it returned true. He also told me that he has seen Kasper bend that sword until the tip met the pommel, and it still returned true. i know this guy very well, and I trust he is telling the truth. I dont know how much distal taper he puts in, but the sword in question starts at about 5mm thick at the cross, and feels very light and well balanced.

So has any other smiths here experience with cold forging, and how do you believe it effects the blade, if at all?

Thanks

Einar

Very interesting! I hope we get some good discussion on this.

Alexi

As soon as I hear someone saying a sword is bent from tip to pommel I get very careful in my continued reading...
This is not generally a sign of superior flexibility or superior heat treat, but rather a sign of a very strange blade. It would take a *very* thin blade to do this. Such a blade would not be efficient in battle.

That apart, cold working can be a method to increase flexibility. It can be done and it was certainly done at times. I am not sure this was the main method though.

When examining ancient blades there are a number of aspects to be aware of.
The steel used was normally of rather low caron content. A fine grain structure is desirable. Low carbon content and fine grain means low hardenability. That is the same as saying: you will not get martensite (hardened structure) very deep into the blade. Only a thin layer of the blade and some more along the edges are going to be hardened, the core is going to show structuires of unhardened and "semi hardened" (bainitic) structures.
If the blade is rather rusted, the thin layer of martensite will be eaten away. What you have left is a blde that seems to have been only rather badly heat treated, not being cooled quickly enough to form martensite.

Cold working leaves tell tell signs i the structure, though. If this has been found, then there should be some proof of that. I have not heard about that from any other source regarding viking swords than this Norwegian project. It can indeed be true, but I have not seen any articles about this myself. Untill I do, I will keep an open mind on the subject.

We must also realise that patternwelded blades of the viking age is made up of more alloy that what we call steel, The edges were usually of a steel with about 0,5-0,8 % carbon (to my knowldedge). The core was made up from wrough iron (no carbon-not hardeneable), low carbon steel (on the border of being hardeneable) and phosphorous iron. Phosphorous iron resopnds very well to cold working. It will perhaps reach something like "spring temper". Phosphorous iron is also a barrier against carbon migration, meaning that despite high tempreature during forge welding, the already rather low carbon ontent of the steely parts will not loose that prescious carbon to low carbon nwighbours as a result of carbon migration, if there is a layer of phosphorous iron in between.
If you are nervous about getting tto much harness andbrittleness fron quenching it can be a very good idea to have a core made up of material that will not respond to a quench while the edges will, Afterwards you can work the springiness by cold working.

And lastly: yes, the heat treat is paramount in the degree of flexibility you can expect in a blade. Cross section is also impportant: a thinner wider blade will flex more than a narrow thick blade.
A blade that is typical for a viking sword will need to have a certain flexibility to function, or they will bend on impact if the cut is not perfectly aligned.

Thanks for the reply, Peter.

Now, this is slightly embarrassing *cough*. I just talked to Raymond on the phone, and it turns out my memory is not what it once was. He has never seen Kasper bend a sword that far, but, like he showed me, he has seen him bend it about 90 degrees. He too thought he had heard someone claiming that Kaspers swords can be bent that far though, but, again, has never seen it himself.

So, sorry to post misinformation. I never intended it to be.

About thin blades. I believe kaspers Viking blades start out at about 5mm thick at the cross.

To the best of my knowledge, swords at the heyday of European weaponsmithing - to me that's around 7th c. - could _indeed_ be bent from tip to pommel -- and return true. This is described as typical sword test in period sources. And these swords were of course used in combat, and must have been very successful or they wouldn't have been made that way.

Again, this is part of the fabled damast story, secrets of swordsmithing that were lost over a thousand years ago. History became legend, legend became myth... ;)

Note: rapiers may also have been capable of that feat. I've been told so, though I don't see why anyone would want a piercing weapon flexing like that. Either way, they had their own special edge geometry.

Peter;

Well as an exercise in pushing the limits of shock resistance it might be interesting assuming that this high degree of flexibility equals an indestructable sword not a wiggly wagelly wet noodle of a sword in desparate need of a shot of viagra.

Well, I couldn't resist the VIAGRA joke and I don't want to insult anybody with a sword with these qualities who might be offended. as you said what use is this kind of flexibility and how good or bad would it be as real fighting sword.

Might be a good cutter depending on the media, but how good a thruster it would be against a hard target?

Now a sword with the same metallurgical heat threat qualities but thick enough that bending it like this would take hundreds of pound of force to do, but would survive this extreme amount of stress without failing or accumulating metal fatigue if repeated: Now that sounds like UNOBTANIUM ! Now add diamond hard at the same time .......... LOL.

Kirk, a little more descriptive info on your example, please. the blade has grabbed my curiosity in passing (the piece when not coiled around itself, i mean)

Chris, with nothing but due respect, if the swords used for these demonstrations are used repeatedly for this purpose, i might be looking for a little cover too. . . i've heard enough horror stories from folks wiser and more experienced than myself about failures nowhere near ninety degrees that i guess. . . well. . . um. . . yeah. . . may fortune favor your sword and all that look upon it.

i believe it was put best that severe (one could argue "destructive") flex tests like this are well and good for spot checking production and heat treat consistency, and beyond this, less is more :)

Jonathan, thanks for your concern. For safety reasons, I do these repeated flex tests only with blunt swords (stage combat versions), with about 2mm edge.

As for the point of a blade flexing that much, my thought is along the lines of what Jean said. I.e. the flexibility of the blade is not the aim, but a symptom. Let's imagine a very hard and sharp blade, with an enormous amount of shock resistance at the same time.
Ancient blades could and did break, and we all know there is no such thing as an indestructible sword. But the old records also state that these swords had armour defeating qualities. Note that I did not say armour piercing, for as slashing weapons they were (said to be) able to slice through metal armour of these times.

Of course there may have been some amount of hype even in 13-1400 year old descriptions - who can tell today how much? All we can do is look at the sources and try to assess the reliability of each.
Personally, I don't have a problem with the idea that in those days, smiths were able to achieve even with their limited means more than we can reproduce today. I find that totally fascinating.

Chris, I agree. It appears that the study of ancient European metallurgy (and the creation of the sword) walks a similar path to the study of the techniques to use the weapons created.

Every once and again stepping beyond the bounds of what is reasonable is not only useful but necessary in experimental reconstructive science. . . I just want to help make sure we all get there in one piece to see the results ;)

Wouldn't a blade that flexible also be more likely to twist in a cut and reduce the depth of penetration?