The　phase　precipitation　curves　of　carbidic　ductile　iron　with　Nb　element　were　simulated　by　the　thermodynamic　module　in　JMatPro　software.　The　lattice　mismatch　between　NbC　and　M3C　was　analyzed　using　Bramfitt　two-dimensional　mismatch　theory,　and　the　bonding　strength　(adhesive　work)　and　interface　stability　(interfacial　energy)　of　M3C(100)/NbC(110)　interface　were　calculated　by　using　the　first　principles　method.　The　microstructure　of　carbidic　austempered　ductile　iron　(CADI)　was　observed　by　scanning　electron　microscope　(SEM)　and　transmission　electron　microscope　(TEM).　The　results　show　that　NbC　particles　precipitate　previously　at　1420　degrees　C,　and　the　lattice　mismatch　of　M3C(100)/NbC(110)　is　3.75　%.　Six　interface　models　have　been　constructed　according　to　different　case　and　termination　conditions,　in　which　interface　adhesive　work　of　Case　I/C　interface　is　the　largest　(1.35　J/m(2)),　interfacial　energy　of　Case　I/Fe　interface　is　the　smallest.　The　covalent　bond　has　been　formed　on　the　interface,　which　proves　that　M3C(100)　and　NbC(110)　can　form　a　stable　interface.　The　experimental　results　confirm　the　precipitation　of　NbC　particles.　In　addition,　M3C　grows　beside　NbC　particles　and　they　are　combined　tightly,　indicating　that　NbC　can　act　as　an　effective　heterogeneous　nucleation　site　of　M3C.　(C)　2020　Published　by　Elsevier　B.V.