The　effect　of　the　tempering　process　on　the　microstructure　evolution　and　hardness　of　35　wt.%Cr-4　wt.%C　Hypereutectic　High　Chromium　Cast　Iron　(HHCCI)　was　studied　by　means　of　the　scanning　electron　microscope　and　transmission　electron　microscope.　The　results　show　that　with　the　increase　in　tempering　temperature,　the　primary　and　eutectic　carbides　of　HHCCI　have　no　significant　change,　and　the　precipitation　of　secondary　carbides　in　the　matrix　increases　at　first　and　then　decreases.　From　the　TEM　analysis　results,　the　secondary　carbides　after　tempering　are　M23C6,　which　are　rectangular,　and　with　the　extension　of　tempering　time,　a　small　part　of　eutectic　carbides　decompose　and　dissolve　into　the　matrix,　and　the　secondary　carbides　continue　to　precipitate　and　grow,　and　the　length　can　reach　several　microns　to　more　than　10　microns.　With　the　increase　in　tempering　temperature,　the　hardness　of　HHCCI　increases,　and　the　hardness　tends　to　decrease　when　it　exceeds　500 °C.　After　tempering　for　6 h,　the　precipitation　of　secondary　carbides　in　the　matrix　reaches　the　maximum,　and　the　hardness　of　HHCCI　reaches　the　maximum.　After　tempering　holding　time　for　more　than　6 h,　the　hardness　of　HHCCI　decreases　continuously　due　to　the　aggregation　and　growth　of　secondary　carbides.　©　2023,　ASM　International.