You can use this guide if you want.
Credit: Batman Arkham Videos
You don't need to see the whole thing.
As soon as the Medical Center building blows up you are given a signal to pinpoint. This signal leads towards the Sionis Steel Mill. Once you arrive there, you have to find a way in and the only way is to go through the main chimney. After doing so, you have to jump across to the area in front of you and continue down that path. You will have to sprint under the pipes, climb several pipes then climb even more pipes. After passing them, you need to get out your batclaw and shoot it at the vault filled with water to wet the iron fence. This will allow you to go down to the area where you have to go down and hold yourself, then climb to the next bit. This next bit requires you to go on the iron fence and jump on the other, this is pretty simple. Soon after, blow up the floor and go down there. Navigate through the area until it says to pull out your batarang and aim it towards the button. Pushing the button, you go into the vent and go through it until you see a bunch of goons through the vent. You should have the steam achievement now.