There are eight iron lord artifacts that you must get and equip for this achievement:
Memory of Felwinter
Memory of Gheleon
Memory of Jolder
Memory of Perun
Memory of Radejast
Memory of Silimar
Memory of Skorri
Memory of Timor
These artifacts can only be bought from Tyra, who is located in Felwinters Peak at the top of the main stairs. In order to do so you must obtain a Iron Lords' Legacy. You gain one legacy after beating the "Artifacts of the Iron Lords" quest and this quest can be repeated once per week. Tyra will only give you one legacy per week which means it will take a minimum of eight weeks to gain all artifacts. Also, this doesn't mean you'll end up getting the last few artifacts you need during the week your playing. However, you can shorten that time exponentially if you decide to play through the rise of iron storyline on two or three characters. This will allow you to gather two or three artifacts a week!
A few more things to know:
*Every Tuesday you recieve a new quest from Tyra.
*After the latest patch, this achievement has been fixed for anyone having trouble unlocking it. If the achievement is locked after completing the requirements, log out of your profile through the destiny menu and then log back in.
If you have any questions or concerns feel free to comment below.