about swords, iron/steel and some physics

[XorX]

so, for not hijacking the "roman edged weapons" thread any more, I begin a new one here.

I think there is some confusion about steel / iron, ist`s use and treatment.

Bryan wrote: "Jürgen,

I wasn't referring at all about hardening steel, or more specifically iron, since steel making reliably was spotty at best. What I was referring to is the flexibility of swords, which is not just a matter of carbon content, but from my understanding, a matter of heat treatment (quenching and tempering). I understand and agree with you that most swords of the time period wouldn't have had this treatment. But as someone knowledgeable about sword making you can't argue that what Philon was describing wasn''t a sword that had obviously been tempered, regardless of its steel content. With that description, you can't come to any other conclusion. So whatever you previously thought of, know now that while it may not have been prevalent, tempering in some way, shape or form, existed in the 2nd Cent. BC time period, at least by the Celts."

heat treatment of steel (I will use the word steel in the whole, because all we talk about here is steel by chemical definition: "an alloy of iron with other elements, mainly carbon") only makes sense and has an effect if there is an amount of carbon higher than ~ 0,4% contained in the steel. Steel with carbon below that can be quenched and tempered as often as you want, there will be no effect of hardness, flexibility or anything else.
I sure agree that what Philon describes here is a blade which was correctly heat treated, but this effect is not possibly in a blade made in a composite construction with mainly soft steel used and steel with more than 0.4%C used only for the cutting edges. such constructions and weaker ones are the mass of the blades examined for a long timeframe.

about pattern welding and other "visible combinations of different steels": I`d never say that pattern welding was a step forward in blade-making in the sense of an "evolution". Patterns as we see them in mass in the 3rd-5th century roman blades and later in 6th-8th century germanic spathae dont make a blade stronger. they make them more beautiful and fancy. 8+)
a blade core constructed of several very tiny pieces in a "chaotic" order with many possibilities to break due to welding faults is not a step forward in a technical sense. it`s just nice

Bryan also wrote: "Where are you getting info that Roman swords weren't flexible? Is this a guess or based off of archaeological remains?"

well, you can`t take originals and bend around a bit to see what happens, but I`ve made some reconstructions the last years using different original shapes and different proven composite techniques and period materials e.g. different welded steels. tests showed that these blades perform exactly as physical laws and the characteristics of the materials let suppose (see: "Die römische Armee im Experiment")

there are for sure possibilities of composing different steels to a blade which perform better than others, but all of them have their limits. it`s a big difference between blades made in modern mono-steels and ones made from welded steels.

Bryan also wrote: " Most swords are not purposely made stiff (mainly thrusting swords such as estoc or rapiers), so this level of springiness and flexibility would be the norm for well built swords and sabers throughout the ages. Flexibility of this type is absolutely necessary for a good cutting sword, and the various gladii were known to be cut and thrust swords with a well forward center of balance."

This level of springiness was not the norm up to the 10th century, it was something special. the known forms of composites to make blades are mostly not able to provide such flexibility, but a blade made from a single bar of quite high-carbon-steel is. because it can be hardened and tempered. there are some blades of this type throgh the ages, but it was never a mass of them.
mass production of single-bar-swords begins as late as ca. 900 a.d.. a good example are the non-patterned ULFBERHT-blades

flexibility is not necessary for the use of a cutting sword. best example everybody knows of are traditionally made katana: they have a superhard edge, tough sides and a soft core. when improperly used, they bend, some of them even crack in the cutting edge in such a cause.
there are some composites in katana blades which are a bit stiffer, but none of them provides flexibility like a spring. they aren`t even able to do so because most of the blade doesn`t contain enough carbon to get a proper heat treatment. springiness normally is achieved by hardening a complete bar and then tempering it.

So: no carbonno hardeningno temperingno flexibility

a low degree of flexibility can be achieved by work-hardening, which is in fact a work-strengthening, but in this way you can only do a treatment to very thin pieces. the core of a blade will stay ductile and the flexibility is quite limited.

about hardness, strength and flexibility:

technical definitions: hardness is the ability to resist against the penetration by another object
strength is the ability to resist deformation
flexibility / springiness is the ability to bend to some degree without plastic deformation
strength and hardness are a big contrast to achieve in a blade, that`s the main challenge in
making blades

these 3 physical abilities have to be combined in every tool /sword/..., but the one who makes an item is always limited by his material sources, his knowledge, finance, etc.,...