A B777 CREW DECLARED AN EMER AND DIVERTED FOLLOWING A STRONG HOT METAL SMELL IN THE AFT GALLEY NEAR DOOR 4L.

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WHILE ON SECOND BREAK; I WAS WOKEN FROM BREAK AND ADVISED BY CAPT THAT WE WERE APPROX 30 MINS FROM GOING 'FEET WET;' AND HE ASKED ME TO INVESTIGATE POSSIBLE ELECTRICAL SMELLS IN LOCATION OF LAST FEW ROWS OF ECONOMY AND AFT GALLEY. OVENS AND MASTER SWITCH HAD BEEN TURNED OFF (AFT GALLEY); AS WELL AS RECIRCULATION FANS. UPON APCHING LAST 4 ROWS OF ECONOMY; I SMELLED A STRONG ODOR WHICH GOT STRONGER; AS I ENTERED AFT GALLEY NEAR DOOR 4L. I LISTENED TO FLT ATTENDANT'S CONCERNS (APPROX 5-6 PRESENT) ABOUT THE STRONG SMELL. INVESTIGATED THE OVENS AND LAVATORIES FOR POSSIBLE SOURCE. NO SMOKE OR FIRE NOTICED. UNABLE TO DETERMINE AND/OR LOCATE SOURCE OF ODOR. NOT AN ELECTRICAL SMELL; BUT MORE OF A 'HOT METAL' SMELL. NO VIDEO/ENTERTAINMENT ISSUES. NO LIGHTS FLICKERING. RETURNED TO COCKPIT SO THAT OTHER FO COULD GIVE A SECOND OPINION. AT FIRST HE DIDN'T SMELL ANYTHING; BUT AS HE WAS ABOUT TO LEAVE THE GALLEY; HE AND 5 OTHER FLT ATTENDANTS GOT A WHIFF OF A CONCENTRATED STRONG SMELL. HE AGREED WITH THE DESCRIPTION OF 'HOT METAL' SMELL AND HIS CONCERN INCREASED. MEANWHILE; CAPT HAD BEEN COMMUNICATING WITH DISPATCH AND MAINT VIA SATCOM ABOUT THE SITUATION. BASED ON OUR CONCERNS ABOUT CONTINUING FLT OVER THE ATLANTIC WITH POSSIBLE DETERIORATION AND/OR INCREASE IN 'HOT METAL' SMELL; AND KNOWING THAT THIS ACFT HAD HAD NUMEROUS ELECTRICAL ISSUES AND FLT CANCELLATIONS THE PAST 2 DAYS; WE DECIDED IT WAS THE PRUDENT AND SAFEST COURSE TO DISCONTINUE OVERWATER FLT AND DIVERT TO FOREIGN OR UNITED STATES ARPT. THE CAPT COORD WITH DISPATCH FOR DIVERSION STATION BEST ABLE TO HANDLE MAINT AND PAX. DURING ATTEMPT TO GET ATC RE-CLRNC FOR DIVERSION; IT BECAME DIFFICULT TO RAISE OCEANIC RADIO. APPROX XA00Z (E OF XXXXX INTXN); COURSE CHANGE DIRECT TO ZZZ1 INITIATED. DSNDED FROM FL350 TO FL345. SQUAWKED 7700. ONCE ESTABLISHED ON DIRECT ROUTING AND PAN; PAN; PAN; COMS MADE WITH OCEANIC RADIO. EMER DECLARED AND RECEIVED CLRNC TO YYYYY INTXN (ETA XA20Z). DISPATCH THEN ADVISED US THAT ZZZ1 WOULD BE BEST UNITED STATES DEST. ATC CLRNC RECEIVED XC20. IN THE EVENT THE SITUATION HAD DETERIORATED; ZZZ2 AND ZZZ1 WERE OPTIONS. AS FLT PROGRESSED; SMELL DISSIPATED UNTIL FINAL APCH INTO ZZZ2 WHEN THE FLT ATTENDANTS NOTED THAT THE 'SMELL' RETURNED AND SEEMED STRONGEST COMING FROM THE AIR VENTS. MECHS DEBRIEFED AT ZZZ2 GATE. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: REPORTER STATED THAT ACR MAINT REMOVED PANELS; CIRCUIT BREAKER PANEL; LAV MOTORS AND COULD FIND NOTHING WRONG WITH THE ACFT. THE CREW FLEW THAT SAME ACFT LATER THAT DAY AND HAD NO ANOMALIES WITH IT.