This study aimed to investigate the growth behavior of key precipitates in 9–12 wt.% Cr ferritic/martensitic heat-resistant steel as a function of tempering duration. Tempering was carried out at 670 °C for durations between 1 h and 300 h. The precipitates identified were M₂₃C₆, Laves phase, Nb-rich MX, and V-rich MX, each exhibiting distinct growth behavior with increasing tempering time. Transmission electron microscopy (TEM) was used to quantitatively analyze their growth behavior. The results revealed that M₂₃C₆, Laves phase, and V-rich MX underwent progressive coarsening with time, whereas Nb-rich MX showed negligible growth even after prolonged tempering. Based on the quantified data, a precipitate-growth model was implemented in MatCalc, and the key parameters were derived and validated against experimental data. The modeling results showed excellent agreement with experimental observations, confirming that the proposed model can reliably predict the microstructural evolution of ferritic/martensitic heat-resistant steel under long-term high-temperature exposure relevant to USC applications.

In this study, the perforation behaviors of commercial Armox 500T and Armox 600T were investigated under various projectile velocities. The failure mechanisms were analyzed from the macroscopic to the nanoscale using X-ray computed tomography (X-ray CT), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM). Under complete perforation conditions, Armox 600T exhibited greater initial resistance owing to its higher hardness but suffered severe rear-side damage (plugging and spalling). By contrast, Armox 500T exhibited extensive ductile hole expansion, maintaining a residual volume of approximately 99%. Microstructural characterization demonstrated that adiabatic shear bands (ASBs) were prominent near the perforation surfaces and along the radial cracks in both steels. The occurrence of dynamic recrystallization and even localized melting inside the ASBs induced microcracks along the ASB/matrix interfaces and prior austenite grain (PAG) boundaries, eventually coalescing into the observed macroscopic radial cracks. These findings suggest that the design of high-performance armor steels should be based on an optimized balance between hardness and dynamic damage tolerance.

Laser beam welding (LBW) offers low thermal distortion for thin austenitic stainless steel sheets but is sensitive to butt-joint fit-up and edge quality. This study compared machined and sheared joint edges under selected autogenous and ER308L filler-wire LBW conditions. Bead geometry, defects, microstructure, microhardness, tensile properties, and fracture behavior were characterized using conventional microscopy, EBSD-KAM, and three-dimensional digital image correlation (3D-DIC). The machined-edge autogenous condition (LBW-A-M) produced a stable bead with 0.04 mm top underfill and only a small number of internal discontinuities, while its tensile properties remained close to those of the base metal and fracture occurred in the base metal. In contrast, the sheared-edge autogenous condition (LBW-A-S) exhibited 0.24 mm top underfill, 0.18 mm misalignment, multiple pores, and localized strain near the weld, with tensile strength and elongation of 682.31 MPa and 44.04%, respectively. Under the selected filler-wire conditions, no measurable top underfill was observed, although pores remained. Because the autogenous and filler-wire modes used different process parameters and heat inputs, cross-mode differences are condition-specific rather than isolated filler-wire effects. Overall, joint-edge preparation and fit-up control remained important for thin-sheet LBW.