Construct Lock( Races of Eberron, p. 119)
Your knowledge of construct nature allows you to deal extra damage to or even immobilize such foes.
base attack bonus +2, Warforged,
You gain a +2 bonus on damage rolls against creatures with the construct type (including living constructs). If you roll a critical threat against a construct, you can forego the confirmation roll to make another attack roll using the same modifier. If this second attack also hits and deals at least 1 point of damage, the construct must succeed on a Fortitude save (DC 10 + 1/2 your character level + your Con modifier) or be rendered immobile and helpless for 1 round (as if it had been paralyzed).
If you spend an action point to improve an attack roll against a construct and hit with the attack, the attack roll is automatically considered to be a critical threat regardless of the number rolled on the die.