An　Fe-12Cr-1.5B-Al　alloy　containing　different　amount　of　Al　was　melted　in　a　vacuum　induction　furnace.　Effects　of　aluminum　addition　on　solidification　structure　and　hardness　of　the　Fe-12Cr-1.5B-Al　alloy　were　studied　by　means　of　optical　microscope　(OM),　scanning　electron　microscopy　(SEM),　X-ray　diffraction　(XRD),　energy　dispersive　spectrometer　(EDS)　analysis　and　hardness　test.　The　results　show　that　the　as-cast　microstructure　of　the　aluminum-free　Fe-Cr-B　alloy　consists　of　matrix　and　hard　phases.　The　matrix　is　mainly　composed　of　martensite　and　a　small　amount　of　austenite.　The　hard　phases　are　M2(B,C),　M7(C,B)3　and　M23(C,B)6　types.　The　addition　of　aluminum　element　changes　the　matrix　into　pearlite　and　ferrite　and　has　no　obvious　effect　on　the　hard　phases.　When　the　content　of　aluminum　is　more　than　6%,　a　part　of　Al　and　Fe　are　combined　to　form　iron　and　aluminum　intermetallic　compound.　Cr　element　is　mainly　observed　in　the　hard　phase,　and　the　matrix　also　contains　an　amount　of　Cr　element.　B　element　is　mainly　found　in　the　M2(B,C)　phase.　Al　element　is　mainly　detected　in　the　matrix　and　iron　and　aluminum　intermetallic　compounds.　The　Rockwell　hardness　of　the　aluminum-free　Fe-Cr-B　alloy　is　61.1　HRC.　The　Rockwell　hardness　and　Vickers　hardness　of　the　Fe-12Cr-1.5B-Al　alloy　shows　a　trend　of　slow　increase　after　sharp　decrease　with　the　inereasing　of　the　aluminum　content.　©　2016,　Editorial　Office　of　Transactions　of　Materials　and　Heat　Treatment.　All　right　reserved.