AISI 321 stainless steel has excellent resistance to intergranular corrosion and is generally used in nuclear power reactor vessels and other components. The as-cast and wrought structures are quite different in hot workability, so physical simulation, electron back-scatter diffraction, and hot processing maps were used to study the mechanical behavior and microstructure evolution of as-cast nuclear grade 321 stainless steel in the temperature range of 900–1200 °C and strain rate range of 0.01–10 s⁻¹. The results showed that the flow curve presented work-hardening characteristics. The activation energy was calculated as 478 kJ/mol. The fraction of dynamic recrystallization (DRX) increased with increasing deformation temperature and decreasing strain rate. DRX grain size decreased with increasing Z value. Combining the hot working map and DRX state map, the suggested hot working window was 1000–1200 °C and 0.01–0.1 s⁻¹. The main form of instability was necklace DRX. The nucleation mechanism of DRX was the migration of subgrains. The δ phase reduced the activation energy and promoted DRX nucleation of the tested steel.

Precipitation occurs easily during the hot forming of high-nitrogen austenitic stainless steels, which reduces their hot ductility significantly. The effect of grain size on the hot ductility of high-nitrogen austenitic stainless steel in the presence of precipitates was investigated. Different grain sizes of 18Mn18Cr0.5N steel specimens, with and without precipitates, were hot-tension tested. The precipitate morphology, fracture surface, and cracks were studied by scanning electron microscopy, transmission electron microscopy, and electron backscatter diffraction analysis. For the 18Mn18Cr0.5N steel, damage-formation strains of all grain-size specimens were reduced by the precipitates during the hot-tension test. Crack-formation sites were located at grain boundaries and were independent of the Taylor factor. A larger grain size resulted in an increased sensitivity of the fracture strain to precipitates. When the grain size was smaller than 51 μm, the fracture strain became insensitive to the precipitates. A method was suggested to mitigate surface cracking for metal materials with a high precipitation tendency.

Mooring chains are key components of offshore floating photovoltaic systems. Although their service safety is often affected by the harsh service environment, the influence of surface roughness on their corrosion resistance is not clear. This study investigated the corrosion behavior of mooring chain steel using cyclic salt-spray corrosion and electrochemical tests. Scanning electron microscopy, energy-dispersive spectrometry, optical profilometry, and other analytical techniques were used to study the composition and morphology of the corrosion products. The corrosion behavior was studied by electrochemical polarization curves, alternating current impedance spectroscopy, and X-ray photoelectron spectroscopy. The results show that the salt-spray corrosion resistance of mooring chain steel significantly improved with the reduction in specimen surface roughness, and the number and depth of corrosion pits were reduced. Mass loss after 24 h of salt-spray corrosion was exponentially related to initial roughness ($\mathrm{Ra}$). Improved surface roughness significantly increased the pitting potential of the specimens, widened the passivation range, and enhanced the repassivation capability, thus significantly improving the pitting resistance. The pitting potential is linearly related to the initial roughness of the specimen. The oxide contents of Fe, Mo, and Si in the passivation film tended to increase with a smoother surface, which contributes to its densification. This effectively blocks chloride ion attack, thus improving the corrosion resistance of the mooring chain steel.

Superheavy forgings are increasingly used in the nuclear industry. The strain rate is extremely low during hot forging due to the huge size of the superheavy forging; in fact, the surface temperature of the forging decreases obviously during each deformation step. Hot-deformation behavior differs from that of isothermal deformation. In this study, 18Mn18Cr0.6N steel was selected as a model material. Hot-compression tests were conducted using a Gleeble 3800 simulator at a strain rate of 10⁻⁴ s⁻¹ and continuous cooling rates of 0.0125 Ks⁻¹ and 0.025 Ks⁻¹. The microstructure was observed using electron backscatter diffraction analysis and transmission electron microscopy. The flow stress increased with increasing strain: the higher the cooling rate, the higher was the hardening rate. Continuous cooling inhibited dynamic recrystallization by delaying its nucleation. The subgrain/cell size increased linearly with increasing final temperature of deformation in the temperature range 1273 to 1448 K. An intense texture formed in 0.8-strained specimens and the matrix exhibited a low Taylor factor orientation. Most dislocations were separately distributed in subgrains and did not entangle with each other or with the subgrain boundary. Dislocation arrays transferred easily through boundaries and dislocation accumulation at boundaries was weak. This study contributes to understanding the hot-forging process of superheavy forgings.