When you reach Dragon Knight status you will also have the opportunity to unlock Heroic Tiers, which gives you access to the Heroic Quest Board, Heroic Forge and Heroic Battle difficulty levels. New quests are available based on your Heroic Tier, you can submit resources to increase your Heroic Tier and access new quests with greater rewards. The greater your Heroic Tier the harder the battles, but the greater rewards you will get from those battles.
At Heroic level 1 you will get artifacts around 220 value. Each level increases the average artifact value by 10 points, but it is not unheard of to get artifacts worth much more as you progress.
In addition to a special artifacts, scroll or potion for completing a battle at Heroic level, you will also be rewarded 20 Dragonsteel.