From Lexicanum

A Frost Blade (either in the form of a sword or an axe) is an ornate type of chain weapon used solely by the Space Wolves chapter, each one is hand-crafted by a Master Iron Priest and incorporates the diamond-hard fangs of the Fenris Ice Kraken. They are highly sought after and in the skilled hands of a Space Marine they can be comparable in effect to most Power Weapons.

Sources

Codex: Space Wolves (3rd Edition) (pg15)