Ironblood is a heavy armor set. When you take damage, you have an 8% chance to turn your blood into pure iron and gain Major Protection for 10 seconds, reducing your damage taken by 30%, but your Movement Speed is reduced by 50%. This effect can occur once every 15 seconds.
The Ironblood set is part of the Horns of the Reach DLC. It drops in Falkreath Hold in Craglorn. Each set item is bound on pickup. You can acquire heavy armor, weapons and jewelry of this set in the Dreadhorn motif style.