Metal Dragons

Metal dragons are dragons whose armour are metallic. They generally have a high Defence against Melee and Ranged attacks though they are relatively weak against Magic attacks. Metal dragons drop metal bars when killed, which correspond to the type of metal dragon the player killed. For example, a steel dragon will drop steel bars, and an iron dragon would drop iron bars.

Image	Type	Combat Level	Attacks	Locations	Notes
	Bronze dragon	131	Melee,  Dragonfire(long-ranged)	Brimhaven Dungeon/Catacombs of Kourend	Bronze dragons are the lowest-level metal dragon; however, killing them is difficult since the dragons are never by themselves.
	Iron dragon	189	Melee,  Dragonfire(long-ranged)	Brimhaven Dungeon//Catacombs of Kourend	Iron dragons are among the most commonly killed metal dragon because they are assigned in large numbers by many Slayer masters.
	Steel dragon	246	Melee,  Dragonfire(long-ranged)	Brimhaven Dungeon/Catacombs of Kourend	Steel dragons are found in the same locations as iron dragons, and are much the same except for their much higher Defence.
	Mithril dragon	304	Melee,  Magic,  Ranged,  Dragonfire(extra long-ranged)	Second level of the Ancient Cavern	Mithril dragons are some of the highest-level dragons of any type and are extremely dangerous. They are the only monster to drop the extremely rare Dragon full helm.
	Adamant dragon	338	Slash, Range, Mage,  Dragonfire	Lithkren Vault	Adamant dragons are a metal dragon accessible after completion of Dragon Slayer II. They are the only monster to drop the very rare Dragon metal slice.
	Rune dragon	380	Slash, Range, Mage,  Dragonfire	Lithkren Vault	Rune dragons are the strongest metal dragon, accessible after completion of Dragon Slayer II. They are the only monster to drop the very rare Dragon metal lump.

http://oldschoolrunescape.wikia.com/wiki/Metal_dragons