I have 70 att str and def with a dragon plate dragon legs and a whip can i beat a iron dragon

Yes you can, just remember to bring anti fire potions ans well as an antifire shield. it is also advised to bring prayer pots as protect from mele is the best way to fight iron dragons due to their high hit ratio. Good food and runes to cast high alchemy are also very smart as you can stay fighting them longer and high alchemy what they drop if its not worth leaving for. A super set is crucial (super strg- attack - defence potions) Watch out for the steel dragons though, hit harder and have higher defence.

good luck and be safe