In　contrast　to　the　general　assumption　that　the　WC1-x,　phase　is　stable　only　at　temperatures　above　2500　degrees　C,　in　the　present　study　WC1-x　is　discovered　to　exist　stably　at　room　temperature　in　nanocrystalline　cemented　carbides.　Based　on　characterization　of　the　microstructure,　crystallographic　features　and　orientation　relationships,　the　formation　mechanism　for　the　WC1-x　phase　in　the　nanocrystalline　structure　is　proposed,　and　the　conditions　of　the　surface　energy　and　composition　are　discussed.　(C)　2012　Acta　Materialia　Inc.　Published　by　Elsevier　Ltd.　All　rights　reserved.