The　separating　rings　of　a　clutch　in　a　heavy　load　vehicle　are　frequently　replaced　after　a　certain　service　period　due　to　wear.　However,　the　wear　mechanism　of　the　separating　rings　has　not　been　well　studied.　In　the　present　study,　a　worn　separating　ring　is　examined　with　scanning　electron　microscope,　the　metallographic　structures　are　observed　and　the　micro-hardness　is　measured.　Results　showed　that　the　hardness　of　the　slot　surface　is　relatively　low　because　the　surface　layer　is　mainly　composed　of　austenite　but　not　the　preferred　martensite;　under　the　action　of　impact　forces　generated　during　the　separation　process　of　the　ring,　plastic　furrows　and　pits　are　produced　on　the　slot　surface　by　particle　abrasion.　Based　on　these　results,　it　is　concluded　that　the　wear　failure　of　the　separating　ring　is　mainly　caused　by　particle　abrasion.　(c)　2005　Elsevier　Ltd.　All　rights　reserved.