The　grain　refinement　resulting　from　a　rejuvenation　heat　treatment　(RHT)　of　Alloy　718　was　investigated　by　using　both　metallographic　analysis　and　orientation　imaging　microscopy　(OIM).　A　step　heat　treatment　was　used　to　show　that　a　phase　transformation　induced　recrystallization　process　did　not　occur　and　supported　static　recrystallization　as　the　method　by　which　grain　refinement　occurred.　Prior　deformed　grains　in　the　wrought　Alloy　718　microstructure　were　subject　to　recrystallization　during　RHT　once　the　intragranular　delta-phase　pinning　grain　boundaries　was　dissolved.　The　coexistence　of　fully　recrystallized,　substructured　and　deformed　grains　in　the　rejuvenated　microstructure　revealed　by　OIM　showed　that　an　inhomogeneous　recrystallization　process　occurred　during　RHT.　Both　the　orientation　relationship　of　grains　and　the　behavior　of　grain　boundaries　involved　in　the　recrystallization　process　were　differentiated　based　on　OIM　characterization.　(C)　2007　Published　by　Elsevier　B.V.