A321
Flight Crew Air Transport Pilot (ATP)
Aircraft Equipment Problem Critical
Flight Crew Landed in Emergency Condition; Flight Crew Returned To Departure Airport
Aircraft
Upon takeoff from ZZZ; ECAM item Hot Brakes illuminated at same time of command for gear up.  Checking brake temperature we noticed the temps were 300 and increasing.  Decision made to keep gear extended; and keep speed at 230 or less.  Even with gear extended brakes continued to increase temperature to maybe a max of 450/475 indicated on the wheel page.  Captain requested priority handing; received vectors back to airport and landed uneventful with CFR crews following us to gate.  On ground with brake fans on; temperature stayed around a max of 400/420. It turns out brake Number 2 was dragging or locking up; resulting in one of the brake disc to disintegrate.
A321 First Officer reported ECAM item Hot Brakes after takeoff resulting in a return to departure airport.