The strongest steel is forged by the fires of hell. It is pounded and struck repeatedly before it's plunged back into the molten fire. The fire gives it power and flexibility, and the blows give it STRENGTH. Those two thing make the metal pliable and able to withstand every battle it's called upon to fight.
Sherrilyn Kenyon (2007). “Devil May Cry: A Dark-Hunter Novel”, p.87, Macmillan