Abstract: The 12Cr alloy represents a significant advancement in materials for high-temperature rotor components used in steam turbines. A systematic investigation was conducted through an electron beam welding experiment on 20 mm thick 12Cr heat-resistant steel, focusing on the influence of welding speed on the microstructural characteristics and mechanical properties of the welded joints. The findings reveal that the microstructure of the weld predominantly consists of martensitic lath, characterized by a finer and more uniform grain size compared to the base material. An increase in welding speed correlates with a reduction in heat input, resulting in a refinement of the grain size within both the weld and the heat-affected zone. Utilizing the Kurdjumov-Sachs orientation relationship, it was observed that the martensitic structure was reconstructed from the PAG, indicating that the welding speed has a negligible impact on the dimensions of the original austenite grains. Furthermore, the welded joints displayed a weak cubic texture across varying parameters. Mechanical property assessments demonstrated that the microhardness within the weld zone significantly exceeds that of the base material, with the average hardness value in the thickness direction of the weld increasing in conjunction with the welding speed. The tensile properties of the welded joints exhibited enhancement, as all tensile specimens failed within the base material, yielding an average tensile strength of 968 MPa. The fracture surfaces revealed a dimpled morphology, suggesting a mixed ductile-brittle fracture mechanism.