Clarifying the generalizability mechanisms in Cr-Ni-Mo-V gun barrel steels: insights to microstructural evolution and softening behavior

• Mechanical strength of Cr-Ni-Mo-V gun barrel steels declines sharply above 500℃ (0.36 T m ), The strength at 700°C is 1/6 ∼ 1/5 of the values at room temperature. • Nanoscale MC and M 3 C carbides undergo Ostwald ripening at elevated temperatures, partially dissolving and coarsening into M 7 C 3 and M 23 C 6 carbides. • Thermal instability of carbides leads to a significant loss in high-temperature strength, underscoring the importance of stable second-phase particles in gun barrel steel design. This study investigates the degradation of mechanical properties and microstructural evolution mechanisms of Cr-Ni-Mo-V barrel steels at elevated temperatures, driven by the failure of gun barrel steels under extreme conditions. Mechanical testing shows excellent strength at room temperature (RT), with a tensile strength of 1350 ± 20 MPa and a yield strength of 1180 ± 25 MPa. However, significant softening occurs above 500°C, with tensile and yield strengths dropping to 223 ± 10 MPa and 186 ± 10 MPa at 700°C, representing only 1/5–1/6 of RT values. Microstructural analysis reveals that nanoscale MC and M 3 C carbides undergo Ostwald ripening at higher temperatures, leading to partial dissolution and coarsening into M 7 C 3 and M 23 C 6 carbides. This weakens the dislocation pinning effect, promoting dislocation slip and pile-up at grain boundaries, causing localized stress concentration and recrystallization. These changes reduce the effectiveness of both grain boundary and dislocation strengthening. Additionally, carbide coarsening beyond the critical size (d c ) shifts the precipitation strengthening mechanism from dislocation shearing to bypassing, significantly reducing precipitation strengthening. The degradation of these strengthening mechanisms aggravates the softening of gun barrel steels at 500°C–700°C, highlighting the critical importance of designing thermally stable second-phase particles to maintain elevated-temperature strength.