Research on failure mechanism is essential for the prolonging of gun barrel lifetime. To explore the gun barrel failure mechanism, the damage characteristics of a machine gun barrel were characterized. The results show that the failure of the gun barrel is correlated with the peeling of the Cr layer on the bore surface and the softening of the bore matrix. The damage of the Cr layer varies along the axial direction. From the gun tail to the muzzle, the damage mode of the Cr layer changes from peeling to wearing. The damage rate in both the tail and the muzzle is higher than that in the middle of the barrel. The matrix close to the bore surface is softened due to the high temperatures caused by stress–relief–annealing and shooting. The gun tail suffers from higher temperatures, thus being softened more seriously than the other parts. The softened matrix results in an increase in the tendency of plastic deformation of the bore surface and an increment in the bore diameter, which leads to a decrease in the firing accuracy.

The effects of cold rolling reduction rates and recrystallization annealing temperature on the microstructure, texture, and anisotropic properties of high-strength low-alloy (HSLA) steel were investigated using scanning electron microscopy and electron backscatter diffraction. The results revealed that the constituents of recrystallized, substructured, and deformed structures were strongly affected by cold rolling reduction rates ranging from 33.3% to 66.7% and recrystallization temperatures ranging from 780 to 840 °C. At an annealing temperature of 820 °C, when the cold rolling reduction rate was 33.3%, HSLA steel exhibited a low percentage of recrystallization, with cubic, γ-linear, rolled, and Z-texture (the texture at Euler angles φ1 = 30° and Φ = 20°–30°) structures. The rolled texture and Z-texture increased the strength anisotropy and disappeared at high cold rolling reduction rates. When the annealing temperature was increased from 780 °C to 820 °C, the proportion of recrystallized grains increased, the rolling texture disappeared, and grain orientation gradually gathered in the cubic texture and γ line texture, resulting in low anisotropy of strength. At an annealing temperature of 840 °C, the deformation of the grain disappeared; however, the anisotropy increased compared to annealing at 820 °C because of the formation of a new texture of {001}<−1–20>.

The effect of aging treatments at various temperatures on the mechanical properties and microstructure of 10B21 cold heading steel with a 20% reduction in area (ε = 0.1) was investigated. The mechanical properties were evaluated based on tensile tests and hardness tests, while the evolution of microstructure was observed by using an optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM) and X-ray diffraction (XRD). The results reveal that aging treatment enhance the strength and hardness of 10B21 cold heading steel after drawing, and the highest values of strength and hardness are attained at an aging temperature of 300 °C. Specifically, the yield and ultrahigh tensile strength after aging at 300 °C are measured at 620 MPa and 685 MPa, respectively, which are 30 MPa and 50 MPa higher than the cold-drawn sample. Moreover, the hardness after aging at 300 °C reaches 293 HV, which has an increase of 30 HV compared to the cold-drawn state. The improvement in mechanical properties may be related to the strain-aging mechanism and the increased density of dislocations. In addition, the analysis of the TEM results reveal that the presence of the second-phase Ti(C,N) contributes to pinning the dislocations, whereas the dislocations are pinned between the cementite (Fe₃C) lamellar and stacked at the grain boundaries, leading to strain hardening of the material.