Blacksmithing quests

Alliance

 * Supplying the Front
 * Gearing Redridge

Horde

 * Barbaric Battlements
 * On Iron Pauldrons
 * Trampled Under Foot
 * Horns of Frenzy

Alliance/Horde

 * Sweet Serenity
 * Corruption (blacksmithing)
 * Snakestone of the Shadow Huntress
 * the quest chain.
 * the quests for the Imperial Plate armor given by Derotain Mudsipper in Gadgetzan in Tanaris:
 * Imperial Plate Belt (quest)
 * Imperial Plate Boots (quest)
 * Imperial Plate Bracer
 * Imperial Plate Chest (quest)
 * Imperial Plate Helm (quest)
 * Imperial Plate Leggings (quest)
 * Imperial Plate Shoulders (quest)
 * the blacksmithing quests at Darkmoon Faire

Legion
As with other professions in Legion, Blacksmithing has its own questline through which you learn most of the recipes.