Abstract: By analyzing the microstructure characteristics and precipitation behavior of 25Cr3Ni3MoNb steel for rapid-fire gun barrel, the deformation behavior at 700 ℃ was studied in detail, and the influence of material microstructure on high temperature mechanical properties at 700 ℃ was explored. The results show that there is a competitive relationship between work hardening and dynamic softening during the deformation process at 700 ℃. Meanwhile, the deformation behavior of the 25Cr3Ni3MoNb steel at 700 ℃ is closely related to the austenitizing temperature, and ultimately affects the mechanical properties of the material. As the austenitizing temperature increases from 980 ℃ to 1020 ℃, the density of defects in the material decreases. After tempering, the size of precipitates increases. Then tension at 700 ℃, the tensile strength R_m decreases from 354 MPa to 237 MPa, and the yield strength R_p0.2 decreases from 312 MPa to 221 MPa. The specimen austenitized at 980 ℃ exhibits a greater work hardening rate and smaller dynamic softening rate, because the volume fraction of carbides pinning dislocations are more inside the specimen. The pinning effect also makes the process of dynamic recovery more difficult and thus exhibits higher high-temperature yield strength.

Key words: gun barrel steel, austenitizing temperature, high-temperature strength, precipitation