Rune of Razorice

Runeforging is a profession-like ability for Death Knights. While it is used like other professions, you don't need to train it; you get new recipies like every few levels as class abilities. There are no skillpoints to train. A Death Knight can only change the runeforged enchant on his weapon at a Rune Forge (obviously). At the moment, you can find Rune Forges at least in Acherus and Shadow Vault in Icecrown.

A runeforged weapon cannot have an enchant other than the temporary enchants, such as sharpening stones. Luckily for Death Knights, the runeforging recipies scale with level and gear. Here's a list of the runeforging recipies and the level a Death Knight receives them.

55 - Rune of Cinderglacier
55 - Rune of Razorice
57 - Rune of Spellbreaking (Only for 1h weapons)
57 - Rune of Spellshattering (Only for 2h weapons)
60 - Rune of Lichbane
63 - Rune of Swordbreaking (Only for 1h weapons)
63 - Rune of Swordshattering (Only for 2h weapons)
70 - Rune of the Fallen Crusader
72 - Rune of the Nerubian Carapace (Only for 1h weapons)
72 - Rune of the Stoneskin Gargoyle (Only for 2h weapons)

plus it the most cool looking rune for your weapon

If you're dual-wielding with double razorice, your weapons WILL NOT create separate debuffs, they will just refresh the current debuff, sorta like what double executioner would do... (except executioner is a buff, and frost vulnerability is a debuff)