YG1500 steel is a martensite precipitation hardening stainless steel. After solution+aging treatment, the Flat noodles martensite structure with high density dislocation and the precipitation of fine precipitation phases with dispersion distribution and coherent relationship with the matrix enable the steel to obtain high strength and toughness. As a high-strength corrosion resistant structural material, YG1500 steel is suitable for manufacturing high stress fasteners requiring high strength and toughness, nuclear reactors, aerospace, ships, petrochemical and other fields due to its high strength, good toughness, good isotropy, and high service temperature. However, in order to better meet the design requirements for safe use of YG1500 steel in complex service environments, higher requirements have been put forward for its fracture toughness.

The results show that (1) the fracture toughness of YG1500 steel bar is closely related to the length of martensitic Flat noodles and the relative frequency of large angle and small angle grain boundaries in the steel. The smaller and uniform martensitic Flat noodles length and the more large angle grain boundaries are, the higher the fracture toughness value of the steel is. (2) The melting speed value of vacuum consumable process is set to 4.2 kg/min, the heating temperature of the final forging heat is set to 1040 ℃, the deformation speed of the final forging heat is set to 100 mm/s, and the strain rate of the final forging heat is 0.1 s ^ -1. Fine and uniform martensite Flat noodles length and more large angle grain boundaries can be obtained, and the fracture toughness value can be significantly improved.