Boron-bearing　high　speed　steels　are　widely　used　in　roller　materials　because　of　their　improved　wear　resistance　and　toughness.　In　present　work,　aluminum　was　added　into　boron　high　speed　steel　and　the　aging-hardening　behavior　and　microstructures　of　tempered　boron　high　speed　steel　at　various　tempering　temperatures　were　investigated　by　means　of　scanning　electron　microscopy　(SEM),　X-ray　diffraction　(XRD),　Energy　dispersive　spectrometry　(EDS)　and　HR-150A　Rockwell　hardness　tester.　The　results　show　that　the　bulk　hardness　of　boron　high　speed　steel　gradually　enhances　with　the　increasing　destabilized　temperature.　Aluminum　addition　cuts　down　the　bulk　hardness　and　delays　the　hardening　process,　thus　leading　to　high　the　hardening　value　of　boron　high　speed　steel　shifting　to　higher　destabilized　temperature.　After　tempering　process,　boron-bearing　high　speed　steel　displays　precipitate-hardening　behavior　at　the　tempered　temperature　of　about　520°C.　The　bulk　hardness　of　boron-bearing　high　speed　steel　achieves　60.5　HRC　as　a　maximum　value　when　the　aluminum　addition　is　0.6　wt.%.　More　aluminum　addition　can　result　in　lower　precipitate-hardening　rate　and　bulk　hardness.　The　microstructures　of　boron　high　speed　steel　tempered　at　520°C　consist　of　eutectic　borides　and　tempered　martensite　dispersed　a　lot　of　secondary　precipitates.　XRD　and　TEM　results　indicate　that　the　precipitate-hardening　properties　of　boron　high　speed　steel　depend　on　precipitates　and　square　degree　of　martensite.　©　2017　Trans　Tech　Publications,　Switzerland.