<p>This study investigates PM60 and S390 powder metallurgy high-speed steels through a comprehensive “vacuum gas quenching + cryogenic treatment + multiple high-temperature tempering” process. The research systematically characterizes mechanical properties and microstructural evolution using XRD, SEM–EDS, and TEM techniques to analyze phase composition, alloying element distribution in carbides, and crystallographic orientation relationships, establishing robust “process–property–structure” correlations. Key findings include: The optimal parameter combination for PM60 powder metallurgy high-speed steel achieves a hardness of 67.9 HRC, bending strength of 4232 MPa, and fracture toughness of 811 MPa·m^1/2. For S390 powder metallurgy high-speed steel, the optimal processing parameters yield a hardness of 65.1 HRC, bending strength of 5135 MPa, and fracture toughness of 1197 MPa·m^1/2. V-rich MC-type carbides exhibit discrete dispersion, forming semi-coherent interfaces with the martensite matrix through approximate K–S orientation relationships. M₆C carbides preferentially precipitate along grain boundaries with approximate B–N orientation relationships, effectively inhibiting grain growth and enhancing high-temperature stability. Significant crystallographic differences between these carbide types make direct orientation relationships improbable, with independent precipitation observed in most cases without detectable orientation correlation.</p>