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.

This study compares the hydrogen embrittlement susceptibility of a Fe-30Mn-8Al-1.2C austenitic low-density steel aged at 600 °C for 0 (RX), 1 min (A1) and 60 min (A60), each exhibiting varying sizes and distributions of nano-sized κ-carbides. Slow strain rate tests were conducted to assess hydrogen embrittlement susceptibility, while thermal desorption analysis was applied to investigate hydrogen trapping behaviors. Fracture surface analysis was employed to discuss the associated failure mechanisms. The results suggest that nano-sized κ-carbides with sizes ranging from 2–4 nm play a crucial role in mitigating hydrogen embrittlement, contrasting with the exacerbating effect of coarse grain boundary κ-carbides. This highlights the significance of controlling the sizes and morphology of precipitates in designing hydrogen-resistant materials.

Ultra-high-strength quenching and partitioning (Q&P) steels have achieved remarkable lightweight effect in automotive manufacture due to the excellent mechanical performances. However, the problem of sheared-edge cracking greatly limits their application. In this work, the damage generated in the shearing process of QP980 steel is experimentally investigated via microstructure characterization and micro-/macromechanical property evaluation. Moreover, the shearing deformation is simulated with six widely used damage models. The experimental results reveal that microvoids, microcracks, and work-hardening behavior are the main damage factors affecting the formability of sheared edges. Microvoids mainly formed at phase interfaces have a small size (≤5 μm), while microvoids generated from inclusions with a small number have a large size (>5 μm). As deformation continuously grows, microvoids distributed around the sheared surface are split into microcracks, which act as crack initiators in the subsequent forming step. Additionally, the highest microhardness in the fracture zone further enhances the susceptibility of edge cracking. Furthermore, the optimum damage model for QP980 steel was determined by developing user-defined subroutine VUSDFLD in Abaqus, which can be used in the prediction of fracture behavior of QP980 steel to reduce the risk of edge cracking.

This laboratory study aimed to reveal the inner connects between the microstructure and corrosion properties of a RE microalloyed ultra-thin cast strip (UCS) steel. The microstructure mainly consisted of homogeneous polygonal ferrite (PF) with a small amount of pearlite (P), while adding multiple alloying elements led to the appearance of granular bainite (GB) and bainitic ferrite (BF). RE elements strongly promoted the homogenization and refinement of microstructure by segregating towards the solid–liquid interface. Potentiodynamic polarization, EIS, and weight loss curves under wet–dry immersion test confirmed that the corrosion behavior was significantly improved by RE, while the addition of RE had no obvious change on tensile strength. The corrosion resistance of the homogeneous single-phase microstructure was proved to be better than that of multiphase microstructure. Hence, RE had a remarkable influence on improving corrosion resistance when the experimental steels processed single-phase microstructures.

This work investigates the microstructure and inclusions of a compacted graphite iron (CGI) alloyed by Ce and La rare earth (RE) elements. In our study, alloying elemental distribution and solute segregation were characterized by methods of secondary ion mass spectrometry (SIMS) and a three-dimensional atom probe (3DAP) with high sensitivity and spatial resolution. RE sulfide, MgS, carbide, and composite inclusions formed during solidification and provided heterogeneous nucleation cores for the nucleation of the graphite. Significant solute clustering in the matrix, coupled with the segregation of solute to grain boundaries, was observed. C, Mn, Cr, and V were soluted in cementite and promoted the precipitation of cementite, while Si was found to be soluted in ferrite. Cu is usually distributed uniformly in ferrite, but some Cu-rich atom clusters were observed to segregate towards the interface between the ferrite and cementite, stabilizing the pearlite. In addition, P, as a segregation element, was enriched along the boundaries continuously. The RE elements participated in the formation of inclusions, consuming harmful elements such as As and P, and also promoted the heterogeneous nucleation of the graphite and segregated, in the form of solute atoms, at its interfaces.