A　novel　high-vanadium　based　hard　composite　coating　was　synthesized　from　premixed　powders　(V,　Cr,　Mo,　Ti,　Nb)　on　ductile　iron　(DI)　substrate　via　atmospheric　plasma　beam　surface　alloying　process.　The　graded　coating　can　be　divided　into　three　distinct　zones:　upper　alloyed　zone　(AZ)　rich　with　spherical　primary　and　eutectic　submicron　carbides,　middle　melted　zone　(MZ)　with　fine　white　iron　structure　embedded　with　high-carbon　martensite　and　lower　heat　affected　zone　(HAZ)　where　martensite/ledeburite　double　shells　were　substantially　formed.　Spherical　or　bulk-like　primary　carbides　with　diameter　＜　1　mu　m　in　the　middle　AZ　were　formed　via　in-situ　reactions　between　alloy　powders　and　graphites　in　DI,　presenting　a　refined　microstructure　similar　to　high　vanadium-containing　tool　steel.　Microstructural　characterizations　indicate　the　carbides　are　chiefly　globular　MC-type　particles　mixed　with　hard-phases　such　as　M2C,　M7C3,　M23C6,　and　martensite.　EDS　mappings　show　that　MCs　(M　=　V,　Ti,　Nb)　form　together　while　M2C-type　carbides　tend　to　locate　at　the　grain　boundary　or　around　the　MC　particles.　Ti　and　Nb　occur　in　the　MC-type　primary　carbides　besides　V　and　TiC　even　features　as　nuclei.　Though　dependent　upon　the　size,　shape,　type　and　distribution　of　carbides,　the　microhardness　was　obviously　enhanced　in　both　AZ　and　MZ.　(C)　2017　Elsevier　B.　V.　All　rights　reserved.