During the casting cooling process or the forging process, austenitic stainless steel will remain at around 800 °C for some time. During this period, precipitate particle behaviors in austenitic stainless steel (containing ferrite) will cause a reduction in ductility, which can lead to material cracking. In this study, the effects of aging at 800 °C on the microstructure, impact toughness and microhardness of Z2CND18-12N austenitic stainless steel were systematically investigated. The precipitation processes of the χ and σ phases were characterized by color metallography and back scattered electron (BSE) signals. The toughness was investigated by the Charpy impact test. After the aging treatment, the χ and σ phases precipitated successively in the ferrite, and as the aging duration increased, the χ-phase dissolved and the σ-phase precipitated along the austenite grain boundaries. These all lead to a decrease in toughness and an increase in microhardness. Finally, the relationship between fracture morphology and aging time is discussed herein, and a crack mechanism is given.

Reasonable welding methods are of great significance for optimizing the microstructure and ensuring the mechanical properties of welded joints. In this study, ultra-narrow gap welding (UNGW) and submerged arc welding (SAW) were employed to weld Q355E high-strength low-alloy (HSLA) steel thick plates, and the microstructure and mechanical properties of the welded joints were systematically characterized. The UNGW welded joint exhibits superior comprehensive mechanical properties: a room-temperature tensile strength of 664 MPa with 43.1% elongation at fracture, along with higher microhardness and enhanced impact performance at −40 °C, all of which significantly outperform SAW welded joints. This advantage primarily stems from the faster cooling rate during UNGW, which promotes the formation of beneficial acicular ferrite in the joint microstructure. This study provides theoretical support and technical guidance for welding HSLA steel thick plates.

Mechanical scratches that penetrate the protective layers expose the steel substrate and establish a zinc–steel galvanic couple beneath an electrolyte film. This study develops a mechanism-oriented multiphysics model of scratch-width-dependent galvanic protection loss in hot-dip galvanized (HDG) steel enclosures. The model couples Butler–Volmer interfacial kinetics with equilibrium potentials related through the Nernst framework, Nernst–Planck transport of Zn²⁺, OH⁻, Na⁺, Cl⁻, and dissolved O₂, electrolyte charge conservation, reaction-derived boundary fluxes, a simplified corrosion-product deposition and transport-resistance treatment, and level-set tracking of interface evolution. Numerical field cases at scratch widths of 1, 3, and 5 mm show that widening the scratch increases the exposed-steel cathodic demand and lengthens the ionic-current path from the zinc edges to the scratch center. The resulting ohmic drop reduces the protective current and permits local iron dissolution when the center can no longer be maintained at a sufficiently negative potential. NSS morphology, cross-sectional SEM/EDS, corrosion-depth trends, and XRD observations show qualitative consistency with this mechanism. Under the investigated NSS conditions, a marked descriptive change occurs between the experimentally sampled widths of 2 and 3 mm, with 3 mm representing the first sampled condition showing pronounced protection loss. Because replicate-level corrosion-depth data and independent electrochemical measurements are unavailable, no statistical significance or quantitative model validation is claimed.