Carbidic　austempered　ductile　iron(CADI)　is　one　of　the　important　materials　for　grinding　balls　in　ball　mill　due　to　its　excellent　mechanical　properties.　However,　the　failure　mechanism　of　CADI　under　impact　fatigue　is　lack　of　research　because　the　complex　phase　composition　(such　as　graphite　nodules,　ferrite,　retained　austenite　and　carbides)　can　affect　the　performance.　The　effects　of　austenitizing　temperature,　austempering　temperature　and　impact　load　on　CADI　impact　fatigue　cracks　are　analysed　by　the　modified　MLD-10　tester.　The　sample　for　impact　fatigue　is　prepared　by　a　self-made　tester.　The　changes　of　the　sample　surface　and　cross　section　after　impact　fatigue　are　studied,　and　the　failure　mechanism　of　CADI　impact　fatigue　is　revealed.　That　is，a　large　number　of　impact　fatigue　cracks　are　produced　due　to　the　deformation　of　graphite　nodules　and　the　fracture　of　carbides,　resulting　in　the　intergranular　fracture.　Fine　graphite　balls　and　carbides　with　uniform　distribution　are　more　conducive　to　improving　the　impact　fatigue　resistance.　The　high　toughness　CADI　obtained　by　the　super-high　temperature　pretreatment　and　austempering　treatment　is　not　easy　to　fracture　during　the　impact　fatigue　process,　which　shows　that　it　has　broad　application　prospects.　©　2023　Chinese　Mechanical　Engineering　Society.　All　rights　reserved.