You can either take the armor from Ashur or get all 100 steel ingots. To get it from Ashur you either have to kill him or reverse pickpocket him with a fully repaired Enclave Power Armor. Use the Chinese Stealth Armor or a stealth Boy. You can also shoot Ashur with a Mesmetron and he will go hostile towards his own guards and they will eventually kill him. You can loot him without the guards going hostile.