B737 crew experiences a strong smoke odor with a hot metallic scent shortly after takeoff. QRH procedures are complied with; an emergency is declared; and flight returns to departure airport. Maintenance can find no cause and the crew flies two more legs with no difficulties.

Narrative

Shortly after takeoff at first flap retraction I smelled a strong smoke odor. It seemed to have a hot metallic scent. At flaps up the Flight Attendants called to report a strong smoke odor throughout the cabin. The A Flight Attendant reported seeing a smoky haze in the forward cabin. They were quite concerned and thought there was a fire somewhere on the airplane. I leveled the airplane at 10;000 ft. The airplane was flying fine and all systems seemed to be operating normally. The co-pilot and I discussed our options: continue or return. The weather was a bit better here so we chose to return. I declared an emergency with Center and had the emergency vehicles meet the airplane in the event the airplane was actually on fire. We proceeded direct to the IAF with clearance to fly the RNP/RNAV approach via the published holding pattern. We accomplished the QRC/QRH procedure; and the smoke smell on the flight deck seemed to totally dissipate when the recirculating fans were turned off. We completed all checklists prior to turning inbound on the approach. A normal approach and landing was made. After landing the fire department saw no signs of fire from our airplane. I had the co-pilot make a PA to remain seated and we taxied to the gate. At the gate; I made a PA to the passengers on our reasons for returning. Maintenance inspected the aircraft. I helped with engine runs and air conditioning operation. The problem could not be duplicated. I then spoke with the crew and they agreed to continue with the trip. With the aircraft signed off; we flew the next two legs without any further events.