World of Warcraft has two specialization for blacksmiths. You can now choose to be an Armorsmith and create new armor designed exclusively for armorsmiths or you can be a weaponsmith. Choosing Weaponsmith you'll have the ability to create a subspecialty in either axesmithing, swordsmithing, and hammersmithing.
At blacksmithing skill level 200 and having a character reach level 40 you can choose what specialty you want to develop. When you specialize you are granted access to recipes that you will not have access to any other way. Subspecialties are taught by trainers found in Everlook, Winterspring. For Axesmithing you'll seek out Kilram, for Hammersmithing you'll go to Lilith the Lithe, and for Swordsmithing you'll need to find Seril Scourgebane.
When you take a specialty make really sure that you want that specialty because it will cost a ton of gold to unlearn it. You also need to make sure to drop the specialty at the blacksmithing trainer where you learned it.
Armorsmithing – This is trained at either Grumnus Steelshaper for Alliance or Horde has Okothos Ironrager. To drop this skill it costs 25 gold for levels 40-50, 50 gold for levels 51-65, and 100 gold for levels higher than 66.
Weaponsmithing – This is trained at either Ironus Coldsteel for Alliance and Borgosh Corebender for the Horde side. To drop this skill it costs 5 gold for levels 40-65 and 10 gold for levels higher than 66.
Axesmithing – This is trained at Kilram in Everlook. To drop this skill it costs 25 gold for levels 40-50, 50 gold for levels 51-65, and 100 gold for levels above 66.
Hammersmithing – This is trained at Lilith the Lithe in Everlook. To drop this skill it costs 25 gold for levels 40-50, 50 gold for levels 51-65, and 100 gold for levels above 66.
Swordsmithing – This is trained at Seril Scourgebane in Everlook. To drop this skill it costs 25 gold for levels 40-50, 50 gold for levels 51-65, and 100 gold for levels above 66.
To gain access to the special recipes in World of Warcraft that you can receive through a specialization or a subspecialization you are going to have to train in that field before you will get to have the access to those recipes. Browse the recipes and see which ones you'd like to have and choose wisely, as it cost gold to unlearn a specialty and relearn another one in its place.