Hi,
The failure of swords in very cold climates is a fairly well known phenomena, indeed, as Tom so correctly points out, of all kinds of steel objects.
I have heard of Japanese swords so failing in the very cold winters of Hokaido. Essentially, it us due to the `Brittle transition temperature' (BTT).
The BTT is a temperature region at which the steel begins to lose all ductility and becomes exceedingly brittle. Alloying elements influence the BTT and it is determined by some kind of impact testing, usually by the Charpy or Izod tests, conducted over a range of temperatures. The temperature range at which the steel begins to exhibit brittle behaviour can thus be determined.
The steels from which old swords were made were a pretty mixed lot, especially when it came to alloying elements. As such, their behaviour at low temperatures was unpredictable.
Cheers
Chris
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