In Alan Williams' chapter (?) of Companion to Medieval Arms and Armour, titled 'Metallurgy of Medieval Arms and Armour', he analyses a sword from the Mary Rose, pointing out that it is effectively steel welded to an iron core, and showing the purely martensitic microstructure of the edge. He also gives hardness values for various points in the sword, ranging from VPH 592 near the edge (about 55 HRC) to VPH 287 (28 HRC) near the core.

He also shows a chart that suggests that a quenched (and untempered) piece of 30 point (that is, .3% carbon) steel would give the same hardness (590 VPH). Since the edge is purely martensitic, this suggests to me that the steel was of a very low carbon content.

My question is, how functional would such a low-carbon weapon be? And more importantly, how does the iron core of case carburised or otherwise steel-encased sword affect its a) Durability, and b) its flex? Does it make it more likely to take a set (than monosteel)? To fracture? What effects does a lack of tempering have?

I'm tempted to think these swords (hardened, low carbon exterior and iron core) would be more likely to take a set and more likely to fracture, but that's just my assumption. Case-carburised swords, with their high-carbon exterior are well beyond my guesses, however.

Good Question Alexander

The period blades have a tendency to be more like a rough mix of carbon content than a set level. The result is the hardness will vary in a piece.

The case carburized and iron core pieces would have a tendency to be more ductile, i.e. possibly take a set easier but would allow an easier bend back to shape and would not be prone to fracture as the iron with no carbon in it would be very malleable.

As these swords are made from steel/iron mixes that are small batch smelts each sword would probably have a slightly different make up on the molecular level.

That’s the quick answer. :) The structure of period blades can be very complex and I am working on an article that will deal with some of the hardness issues.

Best
Craig