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Medium manganese steel represents a promising third-generation advanced high-strength steel. However, achieving excellent plasticity in high-yield-strength medium manganese steel remains challenging, particularly with lower alloying element contents. In this study, we employed an innovative stepwise warm rolling process on 5Mn medium manganese steel, developing a heterolamellar microstructure along the rolling direction. The resulting steel exhibited a yield strength exceeding 1.5 GPa while maintaining a uniform elongation of approximately 29%. The high yield strength is attributed to fine lamellar grains with high dislocation density, while the excellent uniform elongation is due to the synergistic effect of multiple plastic deformation mechanisms, which promoted prolonged strain hardening and delayed the onset of necking. These mechanisms include hetero-deformation induced (HDI) hardening generated during the early deformation of the heterolamellar structure, transformation induced plasticity (TRIP) effect-induced work hardening, and delamination cracking that alleviates interface strain concentration and delays material failure. Collectively, these mechanisms enabled the material to achieve an exceptionally high product of yield strength and uniform elongation of 45 GPa·%. This work provides new insights into the design of high-strength, ductile medium manganese steels, advancing the application of high-performance medium manganese steels.

In order to satisfy the application requirements for strength and toughness of hydropower steels for large pumped storage power plants. In this study, based on the synergy of deformation and phase transition, the trade-off between strength and toughness was broken, and the GPa-grade nano-precipitated steel was prepared by direct quenching and tempering. The effects of Nb–V–Ti composite nano-precipitation behavior and martensite variant selectivity on the strengthening and toughening mechanisms were highlighted. The results show that directly quenched steel has the optimal comprehensive mechanical properties after tempering at 550 °C. Combining the contributions of various strengthening mechanisms, the increase in the yield strength relative to off-line quenching and tempering is mainly attributed to additional dislocation strengthening (∼33 MPa) and precipitation strengthening (∼174 MPa). Direct quenching enhances the homogeneous nucleation of finer mono- and binary precipitates and their stable growth during tempering, while the ternary precipitates do not suffer from elemental inhomogeneities due to lack of re-dissolution. Furthermore, the high-frequency variants of the dominant close-packed plane group tend to form high-angle grain boundaries with different orientations and planar alignments, derived from the refinement of Bain groups induced by the self-plasticity modulation of martensite transition due to the accumulation of deformed geometrically necessary dislocations and finite dislocation slip.

Nature has long inspired technological innovations, fostering the rapidly developing field of bionics. Inspired by the microstructure of bamboo, we have developed a bamboo-like structure for steel. This novel steel achieves a tensile strength exceeding 1200 MPa and a uniform elongation nearing 68%, resulting in a product of strength and uniform elongation up to 83 GPa·%. The high strength of the steel is primarily attributed to its ultra-fine lamellar grains. Additionally, the graded occurrence of multiple deformation mechanisms collectively maintains its exceptional work-hardening capability. This study presents a new approach to enhancing the performance of medium-Mn steels.

Achieving exceptional ductility in ultra-high strength steels has long been a formidable challenge, particularly when the yield strength reaches 2.0 GPa. In this study, we have designed an innovative tri-phase lamellar microstructure in medium Mn steel that successfully achieves both an ultrahigh yield strength of approximately 2.0 GPa and an impressive uniform elongation ranging from 22.5 % to 24.5 %. The ultra-high yield strength of this steel is primarily due to the ultrafine lamellar grain with high-density dislocations and HDI strengthening resulting from meticulously designed tri-phase lamellae. The remarkable ductility is attributed to the synergistic action of multiple plasticity mechanisms. The inherently excellent plasticity of the lamellar ferrite, in coordination with the lamellar martensite, generates significant HDI hardening, thereby suppressing the onset of necking in the early stages of deformation. During the mid-stage of deformation, high strain activates the transformation-induced plasticity effect in the highly stable austenite, which remains stable due to substantial HDI hardening and effectively mitigates strain localization. In the later stages of deformation, delamination cracking relieves stress accumulation at the interfaces, delaying material failure. These mechanisms elevate yield strength and uniform elongation product to 47.3 GPa·%, showcasing the tri-phase lamellar structure’s potential for ultrahigh-strength, high-ductility steels.

The phase transformation mechanism of oxide scale on the surfaces of chromium (Cr)-free carbon steel and 0.9 wt% Cr-containing steel at different coiling temperatures and cooling rates was studied using thermal simulation and electron backscattering diffraction experiments. The results showed that the eutectoid transformation of both the steel followed the “C” curve relationship. The Cr-containing steel had a larger eutectoid transformation area fraction than the Cr-free carbon steel. The nose tip temperature of the eutectoid transformation of the oxide scale on the surfaces of Cr-free carbon steel and 0.9 wt% Cr-containing steel were 420∼510 °C and 420–480 °C, respectively. For the 0.9 wt% Cr-containing steel, the proportion of Σ3 and Σ13b grain boundaries in cubic Fe3O4 increased, followed by a decrease, when the coiling temperature decreased from 610 to 410 °C. The Σ3 and Σ13b grain boundaries of the Fe3O4 low-dimensional coincident site lattice had the highest proportion for 510 °C coiling temperature. The low-dimensional coincident site lattice grain boundaries could be used to enhance crack resistance and improve the oxide scale on the steel plate surface.

In this paper, the differences of the impact toughness and microstructure of specimens with (IA specimen) and without intercritical annealing (OIA specimen) after welding thermal simulation were compared to illustrate the effect of intercritical annealing. The results show that after welding thermal simulation, the impact energy of IA specimen is 96.6 J, which is much higher than 5.7 J of OIA specimen. This is because after welding thermal simulation, the high-angle (≥45°) grain boundary density of IA specimen is 0.079 μm−1, which is nearly twice as high as that of OIA specimen. On the other hand, the small-sized M-A constituents (maximum 1 μm) and more retained austenite in IA specimen can effectively deflect or prevent the propagation of the crack, helping to obtain high impact toughness.

The microstructure and impact toughness of subcritically reheated coarse-grained heat-affected zone (SCGHAZ) of X80 pipeline steels with different Mo content (0Mo and 0.11 wt%Mo) were investigated. Gleeble 3500 thermal simulation experiment was used to simulate the heat-affected zone (HAZ) of X80 pipeline circumferential weld, and the two samples were characterized by a series of material testing techniques such as SEM, TEM, EBSD and XRD. The research showed that: Appropriate addition of Mo element can improve the hardenability of the matrix, increase the content of bainitic ferrite (BF) in the microstructure, refine the BF lath, cause plastic deformation, and reduce local stress concentration. The increase of BF content greatly increases the proportion of high angle grain boundary (HAGB) in order to effectively inhibit crack propagation. On the other hand, Mo element influences precipitation with solid solution, reduces the early energy barrier for nucleation, delays the disappearance of dislocation lines at high temperature, forms high-density dislocation grid, so that it can increase the nucleation site for NbC precipitation, prevent the coarsing of NbC, increases the threshold of external stress required for the generation of micropores induced by precipitation, and hinder crack initiation. The impact toughness of SCGHAZ was significantly improved by adjusting the microstructure and second phase morphology of HAZ by using Mo element microalloying.

The hot compression tests of Fe–28Mn–11Al–1.5C–5Cr (wt.%) lightweight steel were carried out by Gleeble-3500 at temperature of 900, 1050 and 1150 °C with strain rates of 0.01 and 1 s−1. The effect of various precipitates on the hot deformation mechanism and dynamic recrystallization (DRX) mechanism was studied by electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). When deformed at 900 °C, the dislocations tend to cut through intragranular κ carbides to form unidirectional microbands and deformation twins. The intergranular precipitates (intergranular κ carbides, B2 (FeAl type) precipitates and (Cr,Mn)23C6 precipitates) hinder the migration of the original grain boundaries, so that the discontinuous DRX (DDRX) is suppressed at the initial stage, but with the increase of strain, the dislocations accumulate at the grain boundaries to promote the nucleation of DRX grains. Meanwhile, the nucleation of DRX grains by continuous DRX (CDRX) mechanism within grains is also activated. Therefore, bimodal distribution of DRX grains is formed at low strain rate of 0.01 s−1, while the degree of DRX is low at high strain rate of 1 s−1. When the deformation temperature is 1050 °C, the content of microbands and deformation twins decreases. There are only a few B2 precipitates at the grain boundaries, so the original grain boundaries tend to bulge to promote DDRX nucleation. When deformed at 1150 °C, large-sized κ carbides are easily formed near the dislocations due to the fast diffusion rate of atoms, which inhibits the formation of microbands and deformation twins, and only slip bands are observed. There is no precipitate on the grain boundary, and the DDRX is the dominant mechanism of DRX. Moreover, the special yield-point-like elongation phenomenon has been proved to be caused by intragranular κ carbides.

Fe–Mn–xAl–C steel ingots have been fabricated by vacuum melting with Al compositions varied from x = 0 to 3 and 5 wt.%, respectively. After properly hot-forging and hot-rolling as well as solution heat treatments, impact toughness tests were carried out at 77 K using a standard full-size of Charpy impact V-notch configuration. It was found that the addition of Al element is more conducive to enhance the cryogenic toughness. The relationship between the cryogenic toughness and the Al composition has been revealed through detailed microstructural studies by electron back scatter diffraction and transmission-electron microscopy. The stack fault energy (SFE) increases with the increase of Al content at various temperature. The plastic deformation is dominated by deformation bands which are dominated by deformation twins (DTs) and ε-martensite at x = 0 and DTs at x = 3 and 5%, respectively. The DTs near fracture the notch-tip area increased in the order of the 0Al, 3Al, and 5Al steel. The DTs with high density, together with their contented dislocations, significantly contributed to the high cryogenic toughness of the studied high manganese steel with higher Al content. Banded ε-martensite will deterioration cryogenic toughness due to its large size compared to DTs at 0Al steel.

Carbide-free nano-bainite steel holds significant potential for applications in mining as an ultra-high strength wear-resistant steel, but the wear mechanisms are not yet fully understood. This study aims to explore the effect of austempering temperature on microstructure, mechanical properties and wear resistance of carbide-free nano-bainitic steel. The relationship between the content and mechanical stability of retained austenite (RA) and mechanical properties was investigated to elucidate the mechanisms of pin-on-disc wear and impact wear. The results show that in the range of Ms∼300 °C, the phase transformation incubation period and completion time significantly increase with decreasing austempering temperature, which is mainly related to higher phase transformation driving force resulting from a larger subcooling degree and slow growth of carbon content in RA. Optimal strength and hardness of 2099 MPa and 615 HBW, respectively, are achieved after austempering at 210 °C for 83 h. Austempering at 270 °C for 11 h yields the best balance of strength and plasticity, with a strength-plasticity product of 28.8 GPa%. The micro-cutting mechanism of pin-on-disc wear leads to serious weight loss. The RA with poor mechanical stability accelerates the stress-induced martensite transformation, while internal stress support due to volume expansion reduces the penetration depth of abrasive particles. The weight loss in impact wear is primarily caused by shedding due to fatigue failure. With the increase of RA content and mechanical stability, the persistent stress-induced martensite transformation effectively hinders micro-crack propagation, thereby enhancing impact wear resistance.

In this study, the enhanced passivation effect of Cr-modified rebar compared with carbon rebar has been explored with regard to the formation process of the passive film, which could provide a theoretical basis for the development and application of concrete materials in harsh environments. X-ray photoelectron spectroscopy and capacitance-potential method were used to investigate the composition, structural depth distribution, and semiconductive properties of passive films formed by Cr-modified rebar and carbon rebar in simulated concrete pore solutions with different pH. The kinetics of passive film growth and formation were analyzed by tracking tests of potentiostatic current transients and open circuit potential under natural aeration. The results show that the activation energy of Cr-modified rebar is lower at 14.59 kJ/mol, compared to carbon rebar's 25.36 kJ/mol. In the early stage, Cr-modified rebar can achieve a thinner, more stable initial film in a shorter time than carbon rebar. The rate of reduction of the initial thickening rate of the passive film on Cr-modified rebar is five times than that of carbon rebar per unit pH. The film growth rate after early stage of Cr-modified rebar decreases, whereas that of carbon steel increases, with decreasing pH. The passive film containing Cr oxide or hydroxide enhances the barrier effect of the oxide film to ion migration, and the re-dissociation of Fe oxide hinders the passivation process. This grants the thickness of the stable passive film of the two rebars changing oppositely and the Cr-modified rebar compared to carbon rebar enhance passivation with pH falling.

Faced with the rapid development of large-scale pumped-storage power stations, the trade-off between the strength and toughness of hydropower steels in extreme environments has been limiting their application. The effects of Nb micro-alloying and direct quenching and tempering processes on the strengthening–toughening mechanism of 1000 MPa grade high-strength hydropower steel are studied in this paper, and the precipitation behavior of Nb is discussed. The results showed that only the 0.025Nb steel using the DQT process achieved a cryogenic impact energy of more than 100 J at −60 °C. Under the DQT process, a large number of deformation bands and dislocations were retained, refining the prior austenite grains and providing more nucleation sites for the precipitation of NbC during the cooling process. The DQT process has a more obvious local strain concentration, mainly focusing on the refined lath boundary, which indicates that the refinement of the microstructure also promotes the stacking of dislocations. The improvement in fine grain strengthening and dislocation strengthening by the DQT process jointly led to an increase in strength, resulting in a better combination of strength and toughness.

Heterostructured austenitic stainless steels (ASS) are becoming a significant research area because of their outstanding mechanical properties and considerable potential for various applications. However, the thermal stability of heterogeneous microstructures, particularly the bimodal microstructure, has received limited attention and lacks systematic investigation. Additionally, there is a scarcity of reports regarding the biocompatibility of bimodal microstructures. Herein, the thermal stability and biocompatibility of the bimodal microstructure prepared by cold rolling and annealing in Cr–Mn–N series ASS (without and with Nb microalloying) are studied. The findings demonstrate that the bimodal microstructures of ASS are formed after annealing at 700 °C, 800 °C, and short-time annealing at 900 °C. Moreover, the addition of Nb significantly enhances the thermal stability of the bimodal microstructure and maintains the bimodal feature up to 1000 °C. The thermal stability of bimodal microstructures depends on the competition in coarse and fine grains growth. The good thermal stability of Nb(C, N) at high temperatures leads to consistently higher pinning force within the fine-grained zone. As a result, the growth of fine grains lags behind that of coarse grains, which leads to the persistence of bimodal microstructure at higher temperatures. The bimodal microstructure of ASS demonstrates superior biocompatibility, attributed to its ability to promote higher cell viability, exhibit stronger fibronectin intensity, and facilitate a wider fibronectin expression network in osteoblasts. These characteristics make the bimodal ASS more favorable for osteoblast attachment and proliferation compared to its coarse-grained counterpart. This study significantly enhances our understanding of the thermal stability and cellular functionality of bimodal ASS, highlighting its potential for various biomedical applications.

A flash tempering process has been demonstrated for low-carbon low-alloy lath martensite, which includes heating the sample to 750 °C (Ac1: 752 °C), dwelling at 750 °C for 2 s, and quenching directly to room temperature. The high temperature accelerated the spread of the supersaturated carbon atoms in the lath martensite, activated the dislocation migrations and thus their combining and annihilation, and promoted the mass recrystallisation. The reduced dwelling time inhibited the coarsening of the martensitic laths and suppressed the growth of the recrystallized structures. The combination of higher temperature and the shorter dwelling period, so-called flash tempering, gives rise to the same microstructure and mechanical properties as those obtained by the conventional tempering process (i.e., dwelling at 600 °C for 1 h). The high efficient flash tempering, possessing significantly reduced energy and time consumptions, may have important consequence in industrialization of tempering process.

Summary: Background: Abnormal liver function was frequently observed in nonalcoholic fatty liver disease (NAFLD) patients infected with SARS-CoV-2. Our aim was to explore the effect of SARS-CoV-2 inactivated vaccines on liver function abnormality among NAFLD patients with COVID-19. Methods: The multi-center retrospective cohort included 517 NAFLD patients with COVID-19 from 1 April to 30 June 2022. Participants who received 2 doses of the vaccine (n = 274) were propensity score matched (PSM) with 243 unvaccinated controls. The primary outcome was liver function abnormality and the secondary outcome was viral shedding duration. Logistic and Cox regression models were used to calculate the odds ratio (OR) and hazard ratio (HR) for the outcomes. Sensitivity analysis was conducted to assess robustness. Findings: PSM identified 171 pairs of vaccinated and unvaccinated patients. Liver function abnormality was less frequent in the vaccinated group (adjusted OR, 0.556 [95% CI (confidence interval), 0.356–0.869], p = 0.010). Additionally, the vaccinated group demonstrated a lower incidence of abnormal bilirubin levels (total bilirubin: adjusted OR, 0.223 [95% CI, 0.072–0.690], p = 0.009; direct bilirubin: adjusted OR, 0.175 [95% CI, 0.080–0.384], p

In this study, we investigate the impact of prior ferrite on the bainite transformation kinetics and microstructure of medium-carbon steel interrupted by an intercritical annealing (IAA) process. It was found that the incubation time and completion time decreased from 687 s and 6018 s to 20 s and 4680 s, with the volume fraction of ferrite increasing from 9.5% to 28.6%, while the maximum transformation rate increased from 00271 μm/s to 0.0436 μm/s. The ferrite/austenite interface is introduced, and the nucleation sites are increased to accelerate the subsequent bainite transformation due to the formation of prior ferrite. However, there is a competitive relationship between the number and activation energy of bainite nucleation. According to the experimental results and theoretical calculations, the activation energy of the bainite transformation in the medium-carbon bainite steel decreases gradually with an increase in the volume fraction of prior ferrite.

The effects of austenitizing and austempering temperatures on the bainite transformation kinetics and the microstructural and mechanical properties of a medium-carbon high-silicon ultra-fine bainitic steel were investigated via dilatometric measurements, microstructural characterization and mechanical tests. It is demonstrated that the optimum austenitizing temperature exists for 0.3 wt.%C ultra-fine bainitic steel. Although the finer austenite grain at 950 °C provides more bainite nuclei site and form finer bainitic ferrite plates, the lower dislocation density in plates and the higher volume fraction of the retained austenite reduces the strength and impact toughness of ultra-fine steel. When the austenitizing temperature exceeds 1000 °C, the true thickness of bainitic ferrite plates and the volume fraction of blocky retained austenite in the bainite microstructure increase significantly with the increases in austenitizing temperature, which do harm to the plasticity and impact toughness. The effect of austempering temperature on the transformation behavior and microstructural morphology of ultra-fine bainite is greater than that of austenitizing temperature. The prior martensite, formed when the austempering temperature below Ms, can refine the bainitic ferrite plates and improve the strength and impact toughness. However, the presence of prior martensite divides the untransformed austenite and inhibits the growth of bainite sheaves, thus prolonging the finishing time of bainite transformation. In addition, prior martensite also strengthens the stability of untransformed austenite though carbon partition and enhances the volume fraction of blocky retained austenite, which reduces the plasticity of ultra-fine bainitic steel. According to the experimental results, the optimum austempering process for 0.3 wt. %C ultra-fine bainitic steel is through austenitization at 1000 °C and austempering at 340 °C.

In this work, an innovative cyclic intercritical quenching process has been proposed for achieving excellent mechanical properties in terms of strength and plasticity, which results in a lamellar martensitic-ferritic dual-phase steel. The microstructural evolution under cyclic heat treatment was thoroughly investigated, and the mechanism that enables the lamellar structure to enhance its strength-plasticity matching was also explored. The experimental results revealed that the incomplete austenitization process inhibits the coarsening of the reversed austenite, and the cyclic intercritical quenching procedure finer and more evenly distributes the reversed austenite. The single intercritical quenching (C1) generated mostly massive martensite with traces of ferrite, whereas three-cyclic intercritical quenching (C3) yielded a fine and uniformly distributed lamellar structure. A comparison in terms of the mechanical properties between C3 and C1 steels indicates that uniform elongation, total elongation, and the product of strength and uniform elongation of the C3 steel increased by 85.4%, 47.3%, and 65.0%, respectively, while ultimate tensile strength was dropped by only 11.0%. In addition, the yield ratio of C3 steel is just 0.48. The slight decrease in strength is due to the fine lamellar microstructure. The high plasticity is attributed to the good deformation compatibility between lamellar ferrite and lamellar martensite with excellent plastic deformability. Therefore, cyclic mechanical heat treatment is very promising for the production of low-cost dual-phase steels.

Although tempering is an effective method to improve the mechanical properties of steel, its influence on corrosion behavior has been controversial. Therefore, we conducted this study to assess the effects of different tempering temperatures on the corrosion resistance of low alloy steel in wet atmosphere using an immersion test, salt spray test, electrochemical measurement, and morphology characterization and phase analysis. The results showed that defects and the highly reactive nature of high angle grain boundaries (HAGBs) of bare steels are preferentially corroded. In the initial stage of corrosion, the tempering temperature affects the distribution of low angle grain boundaries (LAGBs). The specimens tempered at low tempering temperatures corroded lightly because of low interface energy. In the later stage of corrosion, the corrosion resistance of the specimens still depends on the matrix due to the limited protection of the rust layer. Thus, the charge transfer resistance improves and the corrosion resistance becomes better with the decrease of tempering temperature.

Advanced high-strength steels (AHSS) have a wide range of applications in equipment safety and lightweight design, and enhancing the strength of AHSS to the ultra-high level of 2 GPa is currently a key focus. In this study, a new process of thermo-mechanical control process followed by direct quenching and partitioning (TMCP-DQP) was developed based on Fe-0.4C-1Mn-0.6Si (wt.%) low-alloy steel, and the effects of microstructure evolution on mechanical properties under TMCP-DQP process and conventional hot rolled quenched and tempered process (HR-QT) were comparatively studied. The results show that the TMCP-DQP process not only shortened the processing steps but also achieved outstanding comprehensive mechanical properties. The TMCP-DQP steel exhibited a tensile strength of 2.23 GPa, accompanied by 11.9% elongation and a Brinell hardness of 624 HBW, with an impact toughness of 28.5 J at −20 °C. In contrast, the HR-QT steel exhibited tensile strengths ranging from 2.16 GPa to 1.7 GPa and elongations between 5.2% and 12.2%. The microstructure of TMCP-DQP steel primarily consisted of lath martensite, containing thin-film retained austenite (RA), nanoscale rod-shaped carbides, and a minor number of nanoscale twins. The volume fraction of RA reached 7.7%, with an average carbon content of 7.1 at.% measured by three-dimensional atom probe tomography (3DAP). Compared with the HR-QT process, the TMCP-DQP process resulted in a finer microstructure, with a prior austenite grain (PAG) size of 11.91 μm, forming packets and blocks with widths of 5.12 μm and 1.63 μm. The TMCP-DQP process achieved the ultra-high strength of low-alloy steel through the synergistic effects of grain refinement, dislocation strengthening, and precipitation strengthening. The dynamic partitioning stage stabilized the RA through carbon enrichment, while the relaxation stage reduced a small portion of the dislocations generated by thermal deformation, and the self-tempering stage eliminated internal stresses, all guaranteeing considerable ductility and toughness. The TMCP-DQP process may offer a means for industries to streamline their manufacturing processes and provide a technological reference for producing 2.2 GPa grade AHSS.

Ferrite rolling is generally used to produce deep-drawn steel sheets, which can replace cold rolling to achieve short-flow production. Realizing low-cost production of deep-drawn steel. However, the deep-drawn performance of ferrite rolling products is not as good as the deep-drawn performance of cold rolled products. Of which dynamic recrystallization microstructure have a great effect on the deep-drawn performance. In the present study, ferrite steel was compressed at different deformation parameters (including deformation temperatures and strain rates) in a thermo-mechanical testing system to simulate the deformation behavior during the ferrite regions. The flow behavior of the ferrite steel was studied, and processing maps of the ferrite steel were plotted. The relationship between the Zener-Hollomon parameter and the dynamic recrystallization mechanisms of the ferrite steel was studied in this paper. The microstructure evolution in the steel was characterized by optical microstructure, electron backscatter diffraction, and transmission electron microscopy. The results show that both dynamic recovery and dynamic recrystallization happened during deformation process. The main softening mechanism was dynamic recovery. Discontinuous dynamic recrystallization, continuous dynamic recrystallization and geometric dynamic recrystallization were found in ferrite steel. Meanwhile, it was found that a corresponding relationship between dynamic recrystallization mechanisms and ln Zener-Hollomon values. At high ln Zener-Hollomon value, the dynamic recrystallization mechanism was discontinuous dynamic recrystallization. At middle ln Zener-Hollomon value, the dynamic recrystallization mechanism was continuous dynamic recrystallization. At low ln Zener-Hollomon value, the dynamic recrystallization mechanism in addition to continuous dynamic recrystallization and geometric dynamic recrystallization.

We investigate the effect of pure darkness and UV illumination on the corrosion process of 3Ni weathering steels involved in both marine atmospheric environments. The corrosion behavior of 3Ni steel in both environments was assessed by cyclic acceleration experiments, electrochemical measurements, morphological analysis and physical phase analysis. The results show that UV illumination affects the corrosion process through the photovoltaic effect of the corrosion products, with photoelectrons and photo-vacancies participating in the redox reaction between the substrate and the atmospheric environment, thereby affecting the corrosion rate of 3Ni steel, the physical composition of the corrosion products and the denseness of the rust layer.

This paper investigates the influence of niobium on the thermal stability of ultra-fine bainite microstructures and their mechanical properties by means of an isothermal transformation at 340 °C, followed by tempering in the range of 200–700 °C for two medium-carbon, carbide-free bainitic steels with and without 0.018 wt. % Nb. The results reveal that ultra-fine bainite microstructures, especially film-like retained austenite, is refined, and the average carbon content of retained austenite is also improved as a result of the addition of Nb element. Both of the bainitic steels in this paper exhibit good thermal stability at low temperatures (≤400 °C) and precipitation hardening arising from carbide precipitation following tempering at 500 °C. The precipitation strengthening compensates for the decrease in strength induced by the decrement in the dislocation density and coarsening of the bainitic ferrite plates during tempering process. M23C6- and MC-type carbides are precipitated in Nb-free and Nb steels, respectively, when the tempering temperature exceeds 400 °C. The further coarsening of the carbides and bainitic ferrite plates, and the decrement in the dislocation density in the latter, relate to the decrease in the mechanical properties for both of the tested bainitic steels following tempering at 500 and 600 °C. Compared to those in the bainitic steel without Nb, the larger size and superior thermal stability of MC-type carbides results in greater strength and elongation of the bainitic steel containing 0.018 wt. % of the Nb element, but does harm to its impact toughness after tempering at 700 °C.

In the present work, we reported the microstructure and mechanical properties of CrxMnFeNi high-entropy alloy (HEA). The microstructures of the HEAs were characterized by scanning electron microscopy (SEM) with electron back-scattered diffraction (EBSD) and energy dispersive spectrometer (EDS) system, X-ray diffraction (XRD), and transmission electron microscopy (TEM). Mechanical properties of the HEAs were measured by nano-indentation and tensile test. The results showed that the single face-centered cubic (FCC) structure was transformed into the FCC and body-centered cubic (BCC) dual-phase when the Cr content was higher than the threshold value. Also, in the dual-phase HEAs, the fraction of the BCC phase increased proportionally with the increasing Cr content. There was an excellent correlation between the phase composition and the corresponding concentration of the valence electron concentration (VEC). The single FCC phase structure alloy demonstrated lower yield strength and higher tensile ductility. In the dual-phase alloys, the presence of the BCC phase notably strengthened the alloy but deteriorated its ductility. The close relationship between the mechanical properties of the alloy and each phase and the effect of the FCC/BCC dual-phase were discussed. It was confirmed that the grain refinement and higher Hall–Petch strengthening coefficient caused by the BCC phase formation showed a good strength-ductility matching mechanism in the dual-phase alloys.

Summary: Surface immobilization of metal complexes or clusters with an exact metal number and coordination structure on solid supports is essential in many industrial applications. However, methods for physically isolating individual homogeneous catalyst molecules on a support surface are rare. By selectively depositing TiO2 sieving layers around supported Co(salen) single molecules or gold clusters with hydrophobic ligands, we realize molecular surface isolation via selective atomic layer deposition. The obtained catalysts are reusable in chiral hydrolytic kinetic resolution and styrene oxidation. Surface isolation also prevents the leaching and aggregation of gold clusters after removing the ligands at high temperature. The activity and selectivity for styrene oxidation to benzaldehyde over isolated single gold atoms are optimized with an enhanced Au-TiO2 interface. This method provides a simple way to immobilize homogeneous catalysts on inexpensive supports and shows excellent potential for industrialization.

As an advanced near-net-shape processing method in which directly preformed, semi-finished products are created from liquid metals, spray forming has become popular in the development and application of new materials and is supporting industrialization. However, as investigated in this work, the problems of segregation and low hardness exist in the actual industrialization process, particularly for large-diameter M3 high-speed steel. It was here found that the annual ring segregation morphologies were mostly distributed from the edge to 1/2R, with a large number of stripes primarily enriched in C, Mo, and Cr elements, and the degree of segregation was mild. The ring segregation was located at the 1/2R position, where the main elemental enrichments were C, W, Mo, Cr, and V, and the segregation degree was severe. The formation of segregation during deposition is described based on an equilibrium solidification model. A slow cooling rate and heat dissipation from the surface to the inside were judged to be the main factors causing segregation and changes in the carbide morphology. In terms of hardness, with the increase in the quenching temperature to 1230 °C, the tempering hardness increased significantly. The analysis shows that a faster cooling rate in the atomization stage caused the solidified droplets to exhibit rapid solidification characteristics, and there was a higher proportion of MC carbide in the deposited billet. MC carbides cannot be fully dissolved using the conventional heat treatment process, which decreases the C, Cr, Mo, and V contents in the solution and, thus, reduces the secondary hardening capability. The findings show that, when the spray forming process is used to prepare large-diameter materials, it should not be considered a rapid solidification technology simply because of its atomization stage. Moreover, more attention should be paid to the influence of microstructure transformation during atomization and deposition.

Generally, the development of ship plate steels is mainly concerned with the improvement of strength and toughness, such as F32 and F36. Due to the strength–ductility trade-off, it is difficult to combine excellent ductility with strength improvement, resulting in a poor deformation ability of the traditional ship plate steels during collision. In the present study, a series of high-ductility ship plate steels with property gradients were obtained by multi-phase microstructure control. The strength–ductility matching mechanism was analyzed. Meanwhile, the roles of M/A islands and lamellar pearlites in plastic deformation were also revealed. The results show that the microstructure of “quasi-polygonal ferrite + granular bainite + M/A islands + fewer lamellar pearlites” has the best strength–ductility match. The excellent ductility is mainly dependent on dispersive kernel average misorientation, recrystallized grains without distortion, and soft grains. In addition, the longer branch crack can effectively relieve the stress concentration at the tip of the main crack. Compared with lamellar pearlites, the dispersed M/A island grains have a higher strength contribution and more stable γ-fibers, which is beneficial to delay the appearance of internal micro-voids and micro-cracks. However, the lamellar pearlites can coordinate deformation only when the orientation of thinner lamellae exceeds two.

Conventional quenching and tempering were employed to achieve the optimal strength and toughness of low-carbon low-alloy steel. The fracture behavior (crack initiation and propagation) of the steel in the impact process was also analyzed. It was found that the microstructures of the steel after different tempering treatments were mainly composed of martensite, and its mechanical properties were dependent on the tempering temperature. With the increase in tempering temperature, martensitic laths merged and coarsened. Moreover, recovery occurred, causing a decrease in dislocation density. Subsequently, the strength of the steel gradually decreased, and the impact energy increased. When the tempering temperature was 600 °C, the optimal yield strength (557 MPa) and the impact energy (331 J) were achieved. In addition, high angle grain boundaries (HAGBs) affected the impact energy and crack propagation. Cracks were easily deflected when they encountered high angle grain boundaries, and linearly expanded when they encountered low angle grain boundaries (LAGBs).

Summary: Unveiling the distance effect between different sites in multifunctional catalysts remains a major challenge. Herein, we investigate the distance effect by constructing a dual-site distance-controlled tandem catalyst with a five-layered TiO2/Pt/TiO2/Ni/TiO2 tubular nanostructure by template-assisted atomic layer deposition. In this catalyst, the Ni and Pt sites are separated by a porous TiO2 interlayer, and the distance between them can be precisely controlled on the subnanometer scale by altering the thickness of the interlayer, while the inner and outer porous TiO2 layers are designed for structural stability. The catalyst exhibits superior performance for the tandem hydrazine hydrate decomposition to hydrogen and subsequent nitrobenzene hydrogenation when the Ni and Pt site distance is on the subnanometer level. The performance increases with the decrease of the distance and is better than the catalyst without the TiO2 interlayer. Isotopic and kinetic experiments reveal that the distance effect controls the transfer of active hydrogen, which is the rate-determining step of the tandem reaction in a water solvent. Reduced Ti species with oxygen vacancies on the TiO2 interlayer provide the active sites for hydrogen transfer with -Ti-OH surface intermediates via the continuous chemisorption/desorption of water. A smaller distance induces the generation of more active sites for hydrogen transfer and thus higher efficiency in the synergy of Ni and Pt sites. Our work provides new insight for the distance effect of different active sites and the mechanism of intermediate transfer in tandem reactions.

Interstitial free (IF) steel is widely used in the automotive industry, due to its excellent deep drawing performance. In this study, in order to study the influence of different rolling processes on the texture evolution and deep drawing performance of IF steel, we conducted rolling experiments on IF steel with different temperatures, different reduction rates, and different lubrication conditions. The impact of texture on the deep drawing performance of the steel was also analyzed. The microscopic and macroscopic texture analyses were performed using electron backscatter diffraction (EBSD) and X-ray diffraction (XRD), respectively. Deep drawing performance was analyzed by measuring the r-value. The results showed that in non-lubricated rolling, the r-value increased with the decrease in the reduction rate, and the r-value increased with the increase in the deformation temperature. The maximum value of r is 0.85. But in the case of lubricated rolling, the r-value increased significantly from 0.74 to 1.47 compared to non-lubricated (keeping the reduction rate and the rolling temperature constant). The lubrication reduced the shear deformation of the steel surface, resulting in a γ texture on the surface. Texture uniformity along the thickness direction resulted in an increase in the r-value of the steel.

The thermo-mechanical control processing of Nb-Ti micro-alloyed steel by induction heating in the endless strip production (ESP) line was analyzed to better understand the microstructural evolution and Nb precipitation and dissolution behavior in austenite during rapid heating to high temperatures. The Nb-Ti micro-alloyed steel consisting of 0.05 wt% C and 0.05 wt% Nb was processed through simulated rough rolling at 1050 °C followed by rapid isothermal reheating at 1150 °C. The austenite coarsening behavior and the Nb dissolution behavior at different holding times were compared, and the coarsening kinetics of austenite grains and the dissolution kinetics of precipitates were investigated. It was found that during induction heating, the size of austenite grains gradually increased with the isothermal time, and the amounts of precipitates were greatly reduced. Round precipitates of (Ti, Nb) (C, N) and square precipitates of Ti (C, N) gradually dissolved into the austenite matrix with the holding time. The Nb content in the solution increased from 0.0137 to 0.0299 wt% as the holding time increased from 1 to 40 s; therefore, about 59.8% of the total Nb content dissolved into the austenite matrix during the induction heating process.

In order to better understand the formation mechanism of tertiary oxide scale in high-strength steel during hot rolling, the microtexture of the oxide layer has been characterized and analyzed by the electron backscatter diffraction (EBSD) method. The results show that the Fe3O4 phase in the oxide layer has a two-phase heterogeneous morphology, Fe3O4 in the oxide layer comprises columnar grains, and Fe3O4 near the substrate comprises spherical grains. As the reduction rate increases, the Fe2O3 layer is gradually wedged into the surface of the Fe3O4 layer. Fe3O4 forms a fiber texture at a reduction rate of 10%. The inner layer of the oxide scale comprises spherical grains, and Fe3O4 is preferentially nucleated and precipitated in the direction of Fe surface grains texture. With the increase in the reduction rate, the {112} directional slip system shows the lowest Schmidt factor value, so the grains with a low Schmidt factor exhibit higher stored strain energy. The formation of the spherical Fe3O4 seam layer close to the steel matrix is the result of the combined effect of the stress state at the matrix and ion diffusion.

The objective of this work is to study finite element methods for approximating the solution of convection equations on surfaces embedded in R3. We propose the discontinuous Galerkin (DG) isogeometric analysis (IgA) formulation to solve convection problems on implicitly defined surfaces. Three numerical experiments shows that the numerical scheme converges with the optimal convergence order.

The objective of the study research was to obtain bimodal structured ultrafine-grained ferrite steel with outstanding mechanical properties and excellent corrosion resistance. The bimodal microstructure was fabricated by the cold rolling and annealing process of a dual-phase steel. The influences of the annealing process on microstructure evolution and the mechanical properties of the cold-rolled dual-phase steel were investigated. The effect of bimodal microstructure on corrosion resistance was also studied. The results showed that the bimodal characteristic of ferrite steel was most apparent in cold-rolled samples annealed at 650 °C for 40 min. More importantly, due to the coordinated action of fine-grained strengthening, back-stress strengthening, and precipitation strengthening, the yield strength (517 MPa) of the bimodal microstructure improved significantly, while the total elongation remained at a high level of 26%. The results of corrosion experiments showed that the corrosion resistance of bimodal ferrite steel was better than that of dual-phase steel with the same composition. This was mainly because the Volta potential difference of bimodal ferrite steel was smaller than that of dual-phase steel, which was conducive to forming a protective rust layer.