Delta got 7 A310-200 and 7 A310-300 from Pan Am when they took over Pan Am europe (there were more Pan Am A310-300 on order but were not delivered); all of the aircraft were on lease and DL was not unhappy with them, they found it a useful aircraft for lower capacity transatlantic routes; DL went on to order 7 more A310-300s which they leased in a complicated arrangment from Airbus. DL did not have the huge fleet of 763ER aircraft that it now has, so the idea was to fly both types: JFK and CVG tended to have more Airbuses at the beginning and ATL more 763s. Range was only a problem with the A310-200 models (which i think Pan Am received second-hand, dont remember for sure) which was certainly not the fault of the aircraft, the 200 series were never really intended to be a transatlatic aircraft. The 200 series flew routes like JFK-BRU and JFK-ATL, plus some transcon, where its range was adequate.
Then a couple of things happened: DL was losing a fortune on its European operation and quickly cut back many of its new European routes, and, at this point in time, DL as a whole was losing lots of money and had to get much more effecient. Since the A310s were all on lease, and since DL decided that only one transatlantic twin was necessary and that would be the 763, the A310s were disposed of. Shame, they were very comfortable planes, their business class cabins were especially nice for the time.
The planes were in storage for a while, the 200 series planes are now with Fedex, the 300 series planes are all over the place, several with former Soviet Union carriers i believe, and some of the newer "built for Delta examples" are with Air Jamaica. The 7 built for Delta A310s had odd registrations; like N___AB (AirBus) I remember.