Very interesting. As for it's being purely decorative, I don't know, but I would guess not.
My reasoning is that I know, for instance, that some old Anglo-Saxon swords are constructed in a similar way. The main body of the blade is made out of a fairly low-carbon steel/iron, and then a high-carbon steel edge is welded on. Like pattern-welding, this is another technique for obtaining a hard edge which stays sharp while maintaining the flexibility of a lower carbon metal (the other problem for higher-carbon steel, at least early steel, is that it tends to be much more brittle, and thus blades made purely of high-carbon steel have a greater risk of shattering, breaking).
just my thoughts. JP probably knows more for this particular piece...