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Simultaneously enhancing the strength, plasticity, and toughness of metal materials has been a prominent research objective. In this study, the precipitation of nano-scale vanadium carbide particles at a lower tempering temperature is controlled to achieve three key benefits: reducing lattice distortion in bainitic ferrite, strengthening through precipitation, and enhancing the toughness of bainitic ferrite, while also maintaining the content and stability of retained austenite. The adopted procedure increases the comprehensive mechanical properties of steel by 17%. In particular, the room-temperature impact toughness is increased by 41%. This comprehensive microstructure optimization endows bainitic steel with an excellent combination of mechanical properties.

Controlling continuous cooling is an important means to control the most important mechanical properties of bainitic steel for frogs in railroad applications. In this paper, a bainitic steel for railway frogs is taken as the research object. By designing different cooling rates in the bainitic transformation medium temperature region, the effect of cooling rate on fatigue crack propagation rate was studied. The results show the sample of 4 °C/s cooling rate exhibits higher strength and impact toughness, while the crack propagation rate near the threshold is significantly lower and the threshold is relatively higher at 0.1 °C/s cooling rate. This is related to the fact that more massive blocky retained austenite and coarse microstructure in the sample at 0.1 °C/s cooling rate are more favorable to the occurrence of crack closure effect, especially in the near-threshold region. The fatigue crack propagation rate of the tested steel in the stable propagation region at 4 °C/s cooling rate is slightly higher than that at 0.1 °C/s. This is related to its complex interface distribution characteristics. However, with the increase of Δ K, the tested steel at 0.1 °C/s cooling rate tends to preferentially fail, which is related to its poor toughness.

Overcoming the trade-off relationship between strength and ductility has always been a challenge. In this article, a neatly arranged ultrafine bainite that is composed of multi-scale retained austenite was obtained by introducing weak chemical heterogeneity in low-alloy steel. The optimized microstructure makes transformation-induced plasticity (TRIP) behavior and coordinating deformation behavior between each phase to be smoother. This results in better comprehensive properties, with 28.5% and 9% increases in uniform elongation and toughness, respectively, and a similar strength. This study provides a new way to improve the properties of low-alloy steels.

Abstract The high‐value utilization of blast furnace slag (BFS) and steel slag (SS) as a valuable resource in the field of carbon reduction represents a green revolution, and also is an indispensable path toward breaking through resource and environmental constraints and achieving high‐quality, sustainable development through solid waste utilization in the steel industry. Achieving resource recycling while harnessing the untapped latent energy of resources and exploring their carbon sequestration capabilities has become a crucial avenue for further valorization through waste utilization. BFS and SS discharged from iron‐making or steel‐making furnaces carry a significant amount of latent heat, especially the calcium oxide component in SS, which gives it a unique advantage in the field of comprehensive BFS and SS utilization and carbonation‐based SS utilization. This article discusses the current research status of low‐carbon‐waste‐heat utilization in the production of microcrystalline glass, cementitious materials, functional adsorbents, and other products through front‐end modification of molten BFS and SS. This report also provides an overview of carbon capture by utilizing BFS and SS, offering insights into the research directions for subsequent heat recovery, online quality adjustment, high‐value utilization, and carbon sequestration using BFS and SS in the steel industry.

Background: Osteoarthritis (OA) presents a formidable challenge, characterized by as-yet-unclear mechanical intricacies within cartilage and the dysregulation of bone homeostasis. Our preliminary data revealed the encouraging potential of a Sargassum polysaccharide (SP), in promoting chondrogenesis. The aim of our study is to comprehensively assess the therapeutic effects of SP on OA models and further elucidate its potential mechanism. Methods: The protective effects of SP were initially evaluated in an inflammation-induced human chondrocyte (C28) cell model. CCK-8 assays, Alcian blue staining, RT-qPCR and Western blotting were used to verify the chondrogenesis of SP in vitro. To assess the efficacy of SP in vivo, surgically induced medial meniscus destabilization (DMM) OA rats underwent an 8-week SP treatment. The therapeutic effects of SP in OA rats were comprehensively evaluated using X-ray imaging, micro-computed tomography (μ-CT), histopathological analysis, as well as immunohistochemical and immunofluorescent staining. Following these assessments, we delved into the potential signaling pathways of SP in inflammatory chondrocytes utilizing RNA-seq analysis. Validation of these findings was conducted through RT-qPCR and western blotting techniques. Results: SP significantly enhance the viability of C28 chondrocytes, and increased the secretion of acidic glycoproteins. Moreover, SP stimulated the expression of chondrogenic genes (Aggrecan, Sox9, Col2a1) and facilitated the synthesis of Collagen II protein in C28 inflammatory chondrocytes. In vivo experiments revealed that SP markedly ameliorated knee joint stenosis, alleviated bone and cartilage injuries, and reduced the histopathological scores in the OA rats. μ-CT analysis confirmed that SP lessened bone impairments in the medial femoral condyle and the subchondral bone of the tibial plateau, significantly improving the microarchitectural parameters of the subchondral bone. Histopathological analyses indicated that SP notably enhanced cartilage quality on the surface of the tibial plateau, leading to increased cartilage thickness and area. Immunohistochemistry staining and immunofluorescence staining corroborated these findings by showing a significant promotion of Collagen II expression in OA joints treated with SP. RNA-seq analysis suggest that SP's effects were mediated through the regulation of the ITGβ1-PI3K-AKT signaling axis, thereby stimulating chondrogenesis. Verification through RT-qPCR and Western blot analyses confirmed that SP significantly upregulated the expression of ITGβ1, p110δ, AKT1, ACAN, and Col2a1. Notably, knock-down of ITGβ1 using siRNA in C28 chondrocytes inhibited the expression of ITGβ1, p110δ, AKT1, and ACAN. However, these inhibitory effects were not completely reversed by supplemental SP intervention. Conclusions: In summary, our findings reveal that SP significantly enhances chondrogenesis both in vitro and in vivo, alleviating OA progression both in bone and cartilage. The observed beneficial effects are intricately linked to the activation of the ITGβ1-PI3K-AKT signaling axis. The translational potential of this article: Our research marks the first instance unveiling the advantageous effects and underlying mechanisms of SP in OA treatment. With its clinical prospects, SP presents compelling new evidence for the advancement of a next-generation polysaccharide drug for OA therapy.

Abstract Electrohydrodynamic processes have emerged as promising methods for fabricating polymetric fiber‐based artificial tubular tissues. Existing review articles focus on the biological applications and processing materials associated with electrohydrodynamic processes in artificial tubular constructs, while overlooking the design and fabrication of these constructs. To address this gap, this review article emphasizes the design and fabrication of tubular tissue constructs enabled by employing electrohydrodynamic processes. This article begins by presenting an overview of two electrohydrodynamic processes: solution electrospinning (SE) and melt electrowriting (MEW). It then delves into the control of the fiber diameter enabled by SE and MEW, offering insights into the manipulation of processing parameters to achieve desired fiber diameters. Additionally, the review highlights cutting‐edge strategies for electrohydrodynamic processes to create tubular structures with customized microarchitectures. This includes fiber alignment control for SE and pore morphology design for MEW. Moreover, the review covers the creation of customized macroscale tubular geometries through collector geometry design. Lastly, a comprehensive survey is presented for designing multiphasic tubular structures specifically for electrohydrodynamic techniques or in tandem with other techniques. The objective of this review is to offer a thorough understanding of the design considerations and potential applications of tubular structures fabricated by electrohydrodynamic processes.

The previous research on two-step austempering processes have been mainly focused on the bainitic transformation kinetics, with few details the relationships between the parameters of two-step austempering process and the wear properties and fatigue lifetime. In this paper, the effects of two-step austempering process on wear resistance and fatigue life of high carbon nano-bainite steel were investigated. The results show that the first-step bainite with high volume fraction prolongs the total bainite transformation time. The two-step austempering samples contain finer bainitic ferrite plate and higher volume fraction of retained austenite, as well as resent excellent hardnesses, tensile properties, wear resistance and fatigue lifetime. In particular, the wear resistance of the 50%-290 °C sample is better than that of the 210 °C sample, this is caused by the transformation of the high fraction of retained austenite in the two-step austempering samples into hard martensite and the microstructure refinement zone that forms on the surface of the sample during the wear process. The 50%-290 °C sample have better fatigue properties at low total strain amplitudes (0.7% and 0.8%). When the total strain amplitude is 0.7%, the fatigue life of the 50%-290 °C sample is 57.5% higher than that of the 210 °C sample, which is because of the higher yield strength and finer microstructure of the 50%-290 °C sample. These results support the later study of controlling two-step austempering process for high-carbon nanostructured steels.

The dependence of low cycle fatigue (LCF) behavior and microstructure evolution of Fe–22Mn-0.6C twinning-induced plasticity (TWIP) steel on the alloying element Al has been investigated under fully reversed total strain amplitude control with a nominal strain rate of 0.006 s−1 and strain amplitudes ranging from 0.002 to 0.010 at room temperature. The results indicate a strong dependence of LCF response and evolved microstructure on the addition of Al, owing to its effect on the stacking fault energy (SFE). At all strain amplitudes, the 3Al steel with a higher SFE exhibits a visibly lower cyclic hardening and a higher cyclic softening, resulting in a lower cyclic yield strength than the 0Al steel. As compared with the 0Al steel, the relatively higher SFE of the 3Al steel causes higher accumulated plastic strain, decreased slip planarity and weaker reversibility of dislocations, thereby decreasing the fatigue life. The optical microstructure is featured by increase in slip band density with increasing strain amplitude for both steels. However, the slip band density of the 3Al steel is higher than that of the 0Al steel. Moreover, cyclic loading promotes the formation of dislocation cells, rough labyrinths as well as planar dislocation arrays. Deformation twins are observed only in the 0Al steel with a visible lower critical twinning stress due to its low SFE as compared to the 3Al steel.

A coupled model of micro-segregation and macro-heat transfer was established to study the solute micro-segregation behaviour of bainite rail steel in the continuous casting process. The effects of solute elements, effective cooling rate of the mushy zone (Ceff), and MnS precipitation on the solute micro-segregation and characteristic solidification temperatures were analysed. The results show that Ceff gradually decreases from the surface of the bloom to the centre as the solidification of the molten steel progresses, and the maximum effective cooling rate is in the corner of the bloom. During the solidification of bainite rail steel, the micro-segregation degree of P and S is more serious, followed by C, Si, Mo, etc. At the later stage of solidification, the precipitation of MnS leads to a decrease in the micro-segregation degree of S and Mn. Carbon mainly affects the solute micro-segregation behaviour by changing the solidification mode of molten steel, while the initial S and Mn contents in molten steel have no obvious effect on the micro-segregation degree of C, Si, Cr, Ni, Mo, and P. Ceff has different effects on the micro-segregation behaviors of different solute elements. An increase in C, Mn, and S content and in Ceff will advance the MnS precipitation time and lead to an increase in the amount of MnS precipitation. Increasing the initial C, Mn, and S content in molten steel leads to a decrease in both ZST and ZDT.

Controlling continuous cooling is considered an effective means of producing high-strength and high-toughness bainitic steel. A medium carbon bainite frog steel is designed. By combining a thermal dilatometer with in-situ high-temperature metallography, the influence of continuous cooling rate on the phase transformation of bainitic steel in the medium temperature range (500-365 °C) is studied. The microstructure and crystallographic orientation are characterized. The results indicate that with the increase of cooling rate in the temperature range for bainitic transformation, the initial temperature of bainitic transformation significantly decreases, and the transformation kinetics enhance, which causes the cooling rate for obtaining a maximum fraction of bainite significantly shifts to the left. As the cooling rate increases, the morphology of the bainite changes from a mixture of granular and coarse lath-like forms to fine lath-like forms. The volume fraction and average size of retained austenite as well as the size of bainite laths decrease with the increase of cooling rate. In addition, there are significant differences in the high-angle interface under different cooling rates, which is related to the variant selection mechanism of bainitic transformation at different cooling rates. The research results reveal the transformation process and microstructure evolution of bainite under different cooling rates in the medium temperature range, providing support for the microstructure control and performance optimization of bainite frog steel under continuous cooling control.

Rapid tempering at high temperature is beneficial to release residual stress. However, the evolution of microstructure and mechanical properties of ultrafine bainitic steel after rapid tempering at high temperature is still unclear. In this research, the effect of rapid tempering at high temperature on microstructure, mechanical properties and mechanical stability of retained austenite (RA) of a medium-carbon ultrafine bainitic steel were studied in detail. Results show that after a rapid tempering at 550 °C, the volume fraction of RA decreased gradually, and the carbon atoms in bainitic ferrite (BF) gradually diffused out of the lattice and finally formed carbides, and the BF plate gradually coarsened. When the tempering time is only 2 min, the carbon clusters formed, strengthening the matrix and stabilizing the RA, which result in the highest yield strength, and the highest impact toughness of the steel. With the extension of tempering time, nano-carbides precipitated and gradually grew up, and the dislocation density in steel decreased, resulting in a gradual decrease in the yield strength of the steel and the mechanical stability of RA. However, the deformation ability and strain hardening ability of the BF matrix gradually increase, so that the tensile strength of the steel gradually increases. The decomposition of RA and the formation of brittle martensite making the impact toughness of the steel gradually decrease. This study can provide theoretical support for the development of rapid tempering process of ultrafine bainitic steel.

Strain-induced precipitation (SIP) behaviors of 7Mo super-austenitic stainless steel (SASS) were studied by strain relaxation test at 850 °C. Our results reveal that sigma (σ) phases are the predominant SIP of 7Mo SASS, with the chemical formula of (FeNi) (CrMo). SIP first precipitates in granular shape at HAGBs, such as deformed grain boundaries (SIP-GBs), interfaces between deformation twin layers and matrix (SIP-TW), and HAGBs inside deformed grains (SIP-HAGBs). This is attributed to the ability of HAGBs for providing high deformation stored energy, nucleation sites, and efficient element diffusion channels. When the nucleation sites at HAGBs become saturated with increasing holding time, needle-like SIPs (SIP-NL) are precipitated along closely packed planes of γ-Fe matrix. The specific orientation relationships between SIP-NL and matrix, namely (−111)γ-Fe//(00–1)σ, [0–11]γ-Fe//[-110]σ or (-1-1-1)γ-Fe//(00–1)σ, [0–11]γ-Fe//[-110]σ, and the needle-like shape are contribute to minimizing interfacial energy and elastic strain energy of SIP, respectively, thereby promoting SIP-NL. The absence of SIP on dislocations can be attributed to the large critical nucleus size of σ phase (about 4.87 nm), which poses challenges for SIP nucleation through dislocation distortion energy. Mo is the controlling element for the nucleation and growth of SIP. SIP can promote cDRX through particle-induced nucleation (PSN) mechanism during the deformation process, while residual high-density dislocations around SIP can also promote cSRX during the holding process. During holding process, the boundaries of recrystallized grains can also serve as nucleation sites for SIP, thereby promoting SIP, and finally form a multi-layer structure of “σ phase/Recrystallization/σ phase”.

Rapid heat treatment is an important method to improve the properties of steel. Moreover, the study of the phase transformation process plays an important role in the formulation of rapid heat treatment. This paper investigates phase transformation behavior and microstructure evolution of ultrafine bainite at varying heating rates, and reveals the influence mechanism of retained austenite on austenitizing. Results showed that the decomposition of retained austenite was influenced by the diffusion of Si element. Therefore, the decomposition temperature of retained austenite is severely affected by the heating rate. Retained austenite completely transformed into cementite and ferrite when heating rate was below 5 °C/s. A small amount of retained austenite was kept when the heating rate was higher than 5 °C/s. The kept austenite effectively suppressed the hysteresis of Ac1 and resulted in a unique mechanism of austenite grain formation. When the heating rate range was 5–10 °C/s, some new austenite skipped the nucleation process and grew directly on the kept austenite, forming the large austenite grains. And other new austenite was obtained via nucleation and growth process. Thus, the grain size of bimodal distribution is formed. This leads to the phenomenon of austenite memory effect. When the heating rate was increased to 50 °C/s and higher, the austenite grain size was less than 14 μm. Therefore, rapid heating makes the phase transition lag. When the heating rate is high enough, part of the austenite is kept, which has an important influence on austenitizing process of the steel.

In the present paper, two austenitic wear-resistant steels, namely 110Mn13 and 0Cr17Ni10Mn5Mo2 steels, were cold-rolled to a same hardness level of ∼270 HV. Mechanical properties and wear resistance under various applied loads were tested. The deformed microstructure, worn surface morphologies and wear debris were discussed to analyze the wear resistance. Results showed that a higher density of deformation twins and dislocations were generated in the 0Cr17Ni10Mn5Mo2 steel to reach a same hardness level with the 110Mn13 steel. Consequently, the 0Cr17Ni10Mn5Mo2 steel obtained higher yield strength (736 MPa) but lower ultimate strength (896 MPa), elongation (30.5%) and strain hardening rate than the 110Mn13 steel when the impact absorption energies were at a similar level of ∼170 J. The weight loss of the 0Cr17Ni10Mn5Mo2 steel reduced by over 40% compared to that of the 110Mn13 steel under the selected wear conditions. With the cold-rolled microstructure, the worn surface of both the test steels produced nanocrystalline layers. The nanocrystalline layer thickness of the 0Cr17Ni10Mn5Mo2 steel was over 5 μm, far larger than that of the 110Mn13 steel. Meanwhile, with the wear debris containing Cr-oxide adhering to the worn surface, which could facilitate the self-lubricating effect, the 0Cr17Ni10Mn5Mo2 steel presented better wear resistance than the 110Mn13 steel.

Abstract Melanin pigments play a critical role in physiological processes and shaping animal behaviour. Fossil melanin is a unique resource for understanding the functional evolution of melanin but the impact of fossilisation on molecular signatures for eumelanin and, especially, phaeomelanin is not fully understood. Here we present a model for the chemical taphonomy of fossil eumelanin and phaeomelanin based on thermal maturation experiments using feathers from extant birds. Our results reveal which molecular signatures are authentic signals for thermally matured eumelanin and phaeomelanin, which signatures are artefacts derived from the maturation of non-melanin molecules, and how these chemical data are impacted by sample preparation. Our model correctly predicts the molecular composition of eumelanins in diverse vertebrate fossils from the Miocene and Cretaceous and, critically, identifies direct molecular evidence for phaeomelanin in these fossils. This taphonomic framework adds to the geochemical toolbox that underpins reconstructions of melanin evolution and of melanin-based coloration in fossil vertebrates.

In the present paper, the effect of strain on the microstructure evolution of 7Mo-0.42N contained cast super austenitic stainless steel (SASS) during compression deformation at 1200 °C was systematically studied to optimize the hot working process. The dynamic recrystallization (DRX) grains size, recrystallization mechanism, annealing twin characteristics, and dislocation evolution during high-temperature deformation at varied strains were examined. Results show that the recrystallization behavior of the SASS during high-temperature compression can be divided into three stages. In stage I, the parent grain boundaries were gradually replaced by recrystallized grains, and observed both cyclic grain refinement and coarsening of grains. In stage II, the recrystallized grains elongated into the parent grain interior from the boundaries until the parent grain was completely covered. Meanwhile, the DRX and abnormal grain growth occurred simultaneously and developed rapidly at this stage. At stage III, the recrystallized grains abnormally grew to ∼76 μm and was deformed again because of the increased strain. The nucleation mechanism also changed during deformation. The discontinuous dynamic recrystallization (DDRX) dominated at stage I and II (ε = 0.1–0.6) with relatively low deformation strain. While in the high strain range of stage III (ε = 0.7–1.0), the continuous dynamic recrystallization (CDRX) took over. These quantitative statistics and analyses of data were carried out in terms of recrystallization grain size and nucleation mechanism under different strain variables, providing experimental basis and theoretical guidance for the production of SASS.

Topologically close-packed phases (TCP phase), with ordered dense-stacked structure, realize the atomic diffusion at high temperatures by forming the defects. In this study, we investigated the σ → γ transformation process at high temperature in cast 7Mo super austenitic stainless steel. Based on in-situ observation and microstructure analysis, it denoted that the modulated structure appeared in σ phase during the transformation process, which caused by the limited mobility of atoms. With extending homogenization time, the new γ phase formed at the boundaries of the modulated structure in σ phase. The size of the σ phase gradually decreased as new γ phase grew up. This discovery enriches the phase transformation mechanism of intermetallic compounds and provides a new sight for applying σ phase at high temperature.

Abstract Photo‐assisted uranium reduction from uranium mine wastewater is expected to overcome the competition between impurity ions and U(VI) in the traditional process. Here, B‐TiO2@Co2P‐X S‐scheme heterojunction with metal‐oxygen‐hydrogen (M‐O‐H) is developed insitu modification for photo‐assisted U(VI) (hexavalent uranium) reduction. Relying on the DFT calculation and Hard‐Soft‐Acid‐Base (HSAB) theory, the introduction of metal‐oxygen‐hydrogen (M‐O‐H, hard base) metallic bonds in the B‐TiO2@Co2P‐X is found to enhance the hydrophilicity and the capture capability for uranyl ion (hard acid). Accordingly, B‐TiO2@Co2P‐500 hybrid nanosheets exhibit excellent U(VI) reduction ability (>98%) in the presence of competing ions. By self‐consistent energy band calculations and in‐situ KPFM spectral analysis, the formation of the internal electric field between B‐TiO2 and Co2P at the heterojunction is proven, offering a strong driving force and atomic transportation highway for accelerating the S‐scheme charge carriers directed migration and promoting the photocatalytic reduction of uranium. This work provides a valuable route to explore the functionally modified photocatalyst with high‐efficiency photoelectron separation for U(VI) reduction.

Abstract Additive manufacturing (AM) enables the tailored production of precision fibrous scaffolds toward various engineered tissue models. Moreover, by functionalizing scaffolds in either a uniform or gradient pattern of biomolecules, different target tissues can be fabricated in vitro to capture key characteristics of in vivo cellular microenvironments. However, current engineered tissue models lack the appropriate cellular cues that are needed to deterministically direct cell behavior. Specifically, tunable and reproducible scaffold‐guided stimuli are identified herein as the missing link between biomaterial structure and cellular behavior. Therefore, the bottleneck of precision control is addressed here over the immobilization of patterned biomolecular stimuli with either uniform or gradient distribution over the AM‐enabled 3D biomaterial model as a function of different growth factors exposure variables, protocols, and various scaffold architectural design parameters. The produced study outcomes herein will improve the directing and guiding of biological cell attachment and growth direction in the context of scaffold‐guided stimuli techniques. Therefore, unprecedented control is presented here over 3D structured biomaterial gradient functionalization and immobilization of biomolecules toward biomimetic tissue architectures.

Hot deformation behaviors and dynamic softening mechanisms of the 7Mo super-austenitic stainless steel (SASS) were studied in the temperature range of 1000–1200 °C and stain rate of 0.001–10 s−1. It is found the optimum windows of hot deformation are mainly in the temperature range of 1030–1200 °C and strain rate range of 0.001–0.07 s−1, and temperature range of 1050–1200 °C and strain rate of 10 s−1. The apparent activation energy of 7Mo SASS has reached 558.9 kJ mol−1, which is about 100–180 kJ mol−1 larger than ordinary austenitic stainless steels and about 60–95 kJ mol−1 larger than 4.5–6 wt.% Mo super-austenitic stainless steels. Due to high stacking fault energy (SFE, 161.2 mJ m−2), planar gliding of dislocations is the main deformation mechanism of 7Mo SASS. As a result, dynamic recovery (DRV) and continuous dynamic recrystallization (CDRX) are easy to occur and play dominant roles in dynamic softening mechanism of this steel. In addition, at strain rate of 10 s−1, especially at low temperature, the appearance of microbands (MBs) significantly promotes CDRX. Large initial sigma precipitates and micron-sized dynamic sigma precipitates also promote CDRX through the particle-stimulated nucleation (PSN) mechanism.

Ausforming at 900 °C with 30% reduction in V and N micro-alloyed steel could induce VN precipitation, which has low lattice misfit (1.8%) with bainitic ferrite in a particular crystal orientation. The incubation period of bainitic transformation was shortened by introducing VN. A further ausforming at 300 °C with different strains prior to isothermal transformation was carried out, which provided more nucleation points and more distortion-energy storage for bainitic transformation. The incubation period was dramatically shortened and bainitic transformation was notably accelerated. There existed a competition between accelerating nucleation and suppressing growth after low temperature ausforming with different strains, and a small strain resulted in a more significant acceleration and a higher degree of bainitic transformation. In addition, thinner bainitic ferrite and finer blocky retained austenite were obtained after low temperature ausforming. The orientation relationship between bainitic ferrite and austenite in the ausformed steel were K–S and N–W relationships.

Solutes segregating at the grain boundary (GB) have a significant influence on the mechanical and chemical properties of steel. In this study, the segregation effects of Si, P, and S on γ-Fe ∑5 (210)[001] GB were systematically analyzed with solution energy, segregation energy, and tensile tests by using a first principles calculation. Si, P, and S are preferred to segregate at substitutional sites in the first layer near the GB. The variation in atomic configuration and electron distribution were investigated by the analysis of bond lengths, charge density, charge density difference, and density of states (DOS), which is caused by the atomic size and electronegativity of solute atoms. Through tensile tests, it was found that Si has a strengthening effect on GB, while P and S exhibit embrittlement effects at low concentration. As the concentration of solutes increase, the segregation sites of P are different from the others owing to the tendency to form Fe3P. The exhibited embrittlement effect is mitigated at first and then aggravated. However, in both cases Si and S show aggravating embrittlement effects on GB cohesion, while the effect of Si changes from strengthening to embrittlement. This work provides comprehensive insights into the effects of Si, P, and S, which will be a useful guidance in steel design.

Effect of Ce and Mn on solidification behaviors and mechanical properties of 7Mo super austenitic stainless steel was investigated via in-situ observations, thermodynamic calculations and microstructural characterization. The results show that the network eutectic microstructure had higher hardness compare with ordinary cast structure. And increasing Ce and Mn can both improve the hardness which could be attributed to the effect of Ce and Mn on the solidification microstructure. Analyses indicate that Ce acted as inclusions and atoms to shorten the solidification interval and refine the microstructure to reduce the σ phase. This finer microstructure increased the average hardness. While increasing Mn content modified Ce–O inclusions into Ce–Mn–O compound inclusions which reduced nucleation sites. Mn also promoted the segregation of Cr and Mo in the liquid to decrease the solidification rate, leading to microstructure coarsening and high content of σ phase. This study may provide a theoretical basis for the composition design and applications of the 7Mo super austenitic stainless steel.

In-situ observation and microstructure analysis were combined with the nanoindentation to study the effect of the orientation relationship between the σ and γ phases on the mechanical property of the 7Mo super austenite stainless steel. The results from the HRTEM and the nanoindentation indicate that the semi-coherent interface (111)γ // (001)σ (which is composed of several atomic layers in the absence of element segregation) produced by eutectic transformation, effectively improves the strength of the interface.

The bainitic transformation behavior of samples with different scales was observed with dilatometer (DIL), high-temperature laser scanning confocal microscope (LCSM), and environmental transmission electron microscope (ETEM). Results show that the bainitic transformation behavior varies according to the geometrical size of samples, and it is mainly manifested in transformation units and growth rates of units. The nucleation and growth processes of finer bainitic subunits, accompanied by dislocation movement, were observed by ETEM. At the same time, the radial lengthening and broadening rates of bainitic ferrite (BF) plates were quantitatively measured. The former is 82 times the latter. The broadening time of BF plates accounts for 97.3% of the total time of the growth.

This study investigated the hot tensile deformation behavior of super austenitic stainless steel (SASS) with different pre-deformation degrees within 1150–1250 ˚C. The influence of pre-deformation on the number of annealing twin (AT), grain size, dislocation evolution, sigma phase precipitation, static recrystallization (SRX), and dynamic recrystallization (DRX) behaviors at hot tensile deformation stages is analyzed. Results show that the thermoplasticity of the SASS increases first and then decreases with the increase of pre-deformation degree at each deformation temperature. The area reduction of the samples pre-deformed for 0 %, 10 %, 20 %, and 25 % are 0.25, 0.32, 0.37, and 0.35, respectively at a tensile temperature of 1150 ˚C. When the pre-deformation degree is within the range of 0–20 %, the deformation storage energy (DSE) gradually increases with the pre-deformation degree. The SRX amount at the high-temperature holding stage and the DRX amount in the high-temperature deformation stage significantly increases, and the grain size gradually decreases. As a result, crack initiation and propagation are inhibited, and thermoplasticity improves. However, when the pre-deformation degree is increased to 25 %, the grains grow abnormally during the high-temperature tensile deformation, and a large number of sigma phases are induced, which deteriorates the thermoplasticity of the SASS.

Single-pass isothermal hot compression tests on four medium-Mn steels with different C and Al contents were conducted using a Gleeble-3500 thermal simulation machine at varying deformation temperatures (900–1150 °C) and strain rates (0.01–5 s−1). Based on friction correction theory, the friction of the test stress–strain data was corrected. On this basis, the Arrhenius constitutive model of experimental steels considering Al content and strain compensation and hot processing maps of different experimental steels at a strain of 0.9 were established. Moreover, the effects of C and Al contents on constitutive model parameters and hot processing performance were analyzed. The results revealed that the increase in C content changed the trend of the thermal deformation activation energy Q with the true strain. The Q value of 2C7Mn3Al increased by about 50 KJ/mol compared with 7Mn3Al at a true strain greater than 0.4. In contrast, increasing the Al content from 0 to 1.14 wt.% decreased the activation energy of thermal deformation in the true strain range of 0.4–0.9. Continuing to increase to 3.30 wt.% increased the Q of 7Mn3Al over 7Mn by about 65 KJ/mol over the full strain range. In comparison, 7Mn1Al exhibited the best hot processing performance under the deformation temperature of 975–1125 °C and strain rate of 0.2–5 s−1. This is due to the addition of C element reduces the δ-ferrite volume fraction, which leads to the precipitation of κ-carbides and causes the formation of microcracks; an increase in Al content from 0 to 1.14 wt.% reduces the austenite stability and improves the hot workability, but a continued increase in the content up to 3.30 wt.% results in the emergence of δ-ferrite in the microstructure, which slows down the austenite DRX and not conducive to the hot processing performance.

In this work, the effects of cold rolling (CR) and cold rolling–cryogenic treatment (CR–CT) on the microstructure and mechanical properties of Fe–32Ni alloy were studied via optical microscopy methods, OM, SEM, XRD, TEM, tensile strength and hardness tester, and tensile testing. The results reveal the grain refinement in the alloy after rolling deformation. When the deformation is higher than 85%, the polygonal austenite grains become layered, and a small amount of martensite forms. Because of the inhibitory effect of cold-rolling deformation before cryogenic treatment on martensitic transformation, the amount of martensite form phase after cryogenic treatment decreases with the increase of deformation. The hardness and strength of the sample, independent of whether the cryogenic treatment is performed, increase with the increase of deformation degree. Under the same deformation rate, the hardness of the CR–CT sample is higher than that of the CR sample, which is related to the hard martensite phase with high dislocation density obtained during cryogenic treatment. The strain hardening behavior of the sample is greatly affected by the deformation degree. With the increase of true strain, the work hardening exponent of CR and CR–CT samples undergoing severe plastic deformation is lower than that at small deformation degree and low dislocation density, which is attributed to the earlier entanglement of high dislocations in CR and CR–CT samples with large deformation degrees.

Phase transformation during austenitizing process and heat treatment process under slow cooling of high-carbon bainitic bearing steel is still unclear. Direct nano-scale microscopic observation and in-situ X-ray diffraction investigations have been used to conduct in-situ investigates of phase transformation of the tested steel, including austenitizing and two-step isothermal process under slow cooling. Results show that the austenitizing process of the sample mainly includes the formation of austenite and dissolution of cementite. Rapid phase transformation stage during the austenitizing process occurs, and it is caused by the diffusion rate of alloying and carbon atoms at different temperatures. The martensitic and bainitic transformation can occur during the low-temperature two-step isothermal transformation. Moreover, the initial bainitic transformation rate greatly accelerates due to the introduction of preformed phase. The evolution of supercooled austenite have been explored to further understand the phase transformation behavior. The analysis of diffraction peak of undercooled austenite shows that the asymmetry of austenite peak occurs before the two-step isothermal process. The asymmetry is attributed to the development of carbon-rich and carbon-poor zones in austenite. The proportion of filmy austenite in austenite increases as the bainitic isothermal time prolonged. Moreover, the increase rate of carbon concentration in filmy untransformed austenite is large.

Abstract The application of microfluidics technology in additive manufacturing is an emerging approach that makes possible the fabrication of functional three-dimensional cell-laden structured biomaterials. A key challenge that needs to be addressed using a microfluidic-based printhead (MBP) is increasing the controllability over the properties of the fabricated microtissue. Herein, an MBP platform is numerically simulated for the fabrication of solid and hollow microfibers using a microfluidic channel system with high level of controllability over the microfiber geometrical outcomes. Specifically, the generation of microfibers is enabled by studying the effects of microfluidic-based bioprinting parameters that capture the different range of design, bioink material, and process parameter dependencies as numerically modeled as a multiphysics problem. Furthermore, the numerical model is verified and validated, exhibiting good agreement with literature-derived experimental data in terms of microfiber geometrical outcomes. Additionally, a predictive mathematical formula that correlates the dimensionless process parameters with dimensionless geometrical outcomes is presented to calculate the geometrical outcomes of the microfibers. This formula is expected to be applicable for bioinks within a prescribed range of the density and viscosity value. The MBP applications are highlighted towards precision fabrication of heterogeneous microstructures with functionally graded properties to be used in organ generation, disease modeling, and drug testing studies.

Strain-induced precipitation (SIP) behaviors of 7Mo super-austenitic stainless steel (SASS) under various deformation conditions were studied by stress relaxation tests. The research demonstrates that sigma phases are the primary SIP phases of 7Mo SASS. Generally, SIP is mainly distributed in granular shape at the boundaries of deformed grains or recrystallized grains, as well as around the deformed microstructure, such as deformation twin layers/matrix interfaces. The variation of deformation parameters can lead to changes in microstructure, therefore influencing the distribution of SIP. For instance, with the temperature increases, the SIP distribution gradually evolves from deformed grain boundaries to recrystallized grain boundaries. The average size of SIP increases with increasing temperature and strain, as well as decreasing strain rate. The SIP content also increases with increasing strain and decreasing strain rate, while exhibiting an initial rise followed by a decline with increasing temperature, reaching its maximum value at 850 °C. The presence of SIP can promote recrystallization by particle-induced nucleation (PSN) mechanism during the hot deformation process. Moreover, the boundaries of these recrystallized grains can also serve as nucleation sites for SIP, therefore promoting SIP. This process can be simplified as SIP→PSNRecrystallization→Nucleation sitesSIP. With the increase in holding time and the consumption of stored energy, the process gradually slows down, leading to the formation of a multi-layer structure, namely SIPs/Recrystallized grains/SIPs structure. Moreover, SIP at recrystallized grain boundaries can hinder the growth of recrystallized grains. Through this study, a comprehensive understanding of the SIP behaviors in 7Mo SASS under different deformation conditions has been achieved, as well as the interaction between SIP and recrystallization. This finding provides valuable insights for effective control or regulation of SIP and optimizing the hot working processes of 7Mo SASS.

The hot compression behavior of 7Mo-0.37N-RE super austenitic stainless steel (SASS), subjected to solution treatment and pre-deformation, is systematically investigated in the temperature range of 900–1200 °C and strain rates of 0.01–10 s−1. The results reveal that, compared with the solution-treated super austenitic stainless steel (ST-SASS), the pre-deformation super austenitic stainless steel (PD-SASS) exhibits high density of dislocations. Consequently, the flow behavior, dynamic softening mechanism, hot workability, and microstructural evolution of the PD-SASS are influenced. In the strain range of 0.1–0.7, the deformation activation energy (Q), Zener-Hollomon parameter (Z) and critical stress for dynamic recrystallization (σc) of the PD-SASS are lower than those of the ST-SASS, implying that dynamic recrystallization (DRX) and dynamic recovery (DRV) are more likely to happen in the PD-SASS. Meanwhile, the distribution and range of power dissipation and instability regions of the ST-SASS and PD-SASS are quite different. Therefore, hot workability and microstructural evolution are significantly altered when the thermal processing range of the ST-SASS and PD-SASS is 1025–1150 °C/0.09–5 s−1 and 980–1150 °C/0.05–10 s−1, respectively. Overall, the processing maps and microstructure reveal that the pre-deformation treatment broadens the hot working range of SASS under same conditions.

Melt electrowriting (MEW) is an emergent approach to fabricate 3D porous structured materials or scaffolds with microscale architectures. Due to its facile implementation, solvent-free process, and high tunability, functionalized MEW-enabled 3D structured materials are widely used to mimic the extracellular matrix, thereby providing a provisional structure for 3D tissue culture. This review firstly describes the state-of-art material design strategies that leverage the unique versatility of MEW to attribute 3D structured materials with tailored fiber diameter, macro-geometry, and micropattern, which is enabled by tuning different process parameters, customizing the collector shape, and designing the programmed toolpath, respectively. Secondly, advances in improving the quality of the MEW-enabled 3D structured materials, including the fiber uniformity and fiber placement accuracy, are comprehensively summarized. The common thread weaving through these advances is the observation that optimizing printing stability requires a synergistic tuning of various design and process parameters. To accomplish this, recent efforts have been made to quantify the fluctuation of the Taylor Cone, jet lag, and fiber diameter to clarify their correlations. The deterioration of fiber placement accuracy represented by the different fiber deviation modes is also systematically reviewed herein. Lastly, the unresolved challenges and prospective outlook in these aspects are also articulated.

A novel process is proposed to introduce ultrafine ferrite in a medium-carbon high-silicon steel that possesses low-temperature bainite. This process is based on the intercritical annealing of the cold-rolled tempered troostite and subsequent austempering at a temperature of 10 °C above martensite start temperature. The acquired microstructures, as well as the mechanical properties, were thoroughly studied and compared with the sample without ultrafine ferrite. Results show that, ultrafine ferrite with a grain size in the range of 0.5–2.0 μm is prepared in the low-temperature bainitic steel. The obtained ultrafine ferrite can be mainly attributed to the recrystallization of cold-rolled tempered troostite during intercritical annealing. Moreover, the introduction of ∼4 vol% ultrafine ferrite into the matrix with low-temperature bainite can simultaneously enhance the tensile strength, yield strength, and impact energy to 1614 MPa, 1074 MPa, and 52 J (half-width Charpy U-notch specimen), respectively, without loss of ductility. The high strength is mainly due to the fine bainitic ferrite laths, while the remarkable ductility and toughness are associated with the moderate contents of ultrafine ferrite and retained austenite within the microstructure.

In this work, the effects of grain size on the tensile properties, serrated flow, Portevin-Le Châtelier (PLC) band evolution, dislocation density, and microstructure evolution of Fe–22Mn-0.6C steel were investigated using digital image correlation (DIC), X-ray diffraction (XRD), transmission electron microscope (TEM) and monotonic tensile tests. Results show that the yield strength, tensile strength, and work hardening value of Fe–22Mn-0.6C steel increase whereas its elongation decreases with decreasing grain size. The critical strain of serration decreases whereas the amplitude of serration increases with decreasing grain size. Moreover, the plateau of serrations is larger and that the strain concentration within PLC bands is more severe in fine-grained steel than in coarse-grained steel. The dynamic strain aging (DSA) behavior of the steel is enhanced by grain refinement. The speed of PLC band movement decreases faster in fine-grained steel than in coarse-grained steel, which results in a decrease in plasticity. XRD and TEM analyses show that the high dislocation density and unique twin substructure may be the main reasons for the strong DSA phenomenon observed in fine-grained steel.

Herein, the hot compression of a super austenitic stainless steel (SASS) containing 7Mo–0.46N–0.02Ce is conducted at different temperatures (900–1200 °C) under a strain rate of 10 s−1. The effect of angle between solidification direction of columnar crystals and loading direction (0°, 30°, 60° and 90°) on microstructural evolution of SASS is studied using OM and EBSD. The results reveal that, at low temperatures of 900 °C and 1000 °C, the dynamic recrystallization (DRX) degree of the 30° and 60° samples is higher than that of the 0° and 90° samples, however, the complete DRX has not occurred. At high temperatures of 1100 °C and 1200 °C, the DRX degree of SASS increases with the decrease of angle between solidification direction of columnar crystals and loading direction. Three kinds of DRX mechanisms for samples with different columnar crystal characteristics are observed, i.e., discontinuous dynamic recrystallization (DDRX), continuous dynamic recrystallization (CDRX) and a combination of DDRX + CDRX mechanism. However, under the same deformation conditions, preferentially triggered and dominant DRX mechanisms of samples with different columnar crystal characteristics are different. In the 0° and 90° samples, a large number of high angle grain boundaries (15° ≤ HAGB ≤65°) are developed, and new DRX grains are formed on them. While in the 30° and 60° samples, preferential expansion nucleation and growth of DRX grains take place on original GBs. At 1200 °C, the DRX degree of SASS reaches a maximum of ∼0.97 when the angle between solidification direction of columnar crystals and loading direction is 0°.

Researchers have always aimed to break the trade-off relationship between strength and ductility. In this study, a carbon diffusion strategy was provided to improve the strength and ductility of composite martensite steel simultaneously, as well as increase uniform ductility by 190%. The process strengthens the martensite without losing the hardening ability of austenite constituents and brings in a substantial transition layer. This strategy can also be applied to other composite alloys with light elements, thus providing a pathway for making high-strength and high-ductility materials.

A heterogeneous microstructure composed of multiscale ferrite (spanning ultrafine, fine, and coarse grains) and granular or short rod cementite was obtained by warm rolling pseudoeutectoid microstructure. Combined with the short-time annealing process, the deformation tendency of ferrite grains and the dissolution and precipitation of cementite were adjusted. The mechanical properties of medium carbon steel are close to that of low alloy high strength steel. It was found that the GNDs are distributed in a gradient at the interface of the soft domain, and the closer to the boundary the higher the density, which contributes to the occurrence of the hetero-deformation induced (HDI) hardening mechanism and provides additional strength and plasticity. The increase in elongation of the annealed samples is due to the recrystallization of ferrite and the redistribution of cementite, which realizes the combination of HDI mechanism, Orowan strengthening and annealing softening mechanism. Additional strengthening mechanisms are calculated and a physical model of cementite ripening during annealing is proposed. The tensile fracture shows that the cracks mainly propagate along the grain boundaries of the layered microstructure, and the high density of dimples can make the propagation path of the cracks tortuous and increase the elongation.

In the present paper, hot compression tests on a super austenitic stainless steel (SASS) containing 7Mo–0.46N–0.02Ce were performed at temperatures of 900 °C-1200 °C and strain rates of 0.01–10 s−1. The effect of angle between solidification direction of columnar crystal and loading direction (0°, 30°, 60°, and 90°) on the flow behavior and microstructure evolution of SASS was studied. Results showed that, samples with different columnar crystal characteristics and test conditions displayed various flow behaviors due to the difference in dynamic restoration softening mechanism, flow localization, and shear band formation. With the decrease of the angle between the solidification direction of columnar crystal and loading direction, the deformation activation energy (Q) and the ln Z value of SASS decreased at the true strain of 0.7. It indicates that dynamic recovery (DRV) and dynamic recrystallization (DRX) are more likely to happen in the samples with low angles. The location and range of high efficiency of power dissipation (η) region and instability region of the samples differed much with different columnar crystal characteristics. This means obviously different hot workability and microstructure evolution behaviors. At the true strain of 0.7, no negative η-value region was observed in the 0° sample, and the range of instability region was relatively small. On the whole, SASS presented the optimum hot workability when the angle between the solidification direction of columnar crystal and loading direction was 0°.

Super austenitic stainless steels are expected to replace expensive alloys in harsh environments due to their superior corrosion resistance and mechanical properties. However, the ultra-high alloy contents drive serious segregation in cast steels, where the σ phase is difficult to eliminate. In this study, the microstructural evolution of 7Mo super austenitic stainless steels under different homogenization methods was investigated. The results showed that after isothermal treatment for 30 h at 1250 °C, the σ phase in steels dissolved, while the remelting morphologies appeared at the phase boundaries. Therefore, the stepped solution heat treatment was further conducted to optimize the homogenized microstructure. The samples were heated up to 1220 °C, 1235 °C and 1250 °C with a slow heating rate, and held at these temperatures for 2 h, respectively. The elemental segregation was greatly reduced without incipient remelting and the σ phase was eventually reduced to less than 0.6%. A prolonged incubation below the dissolution temperature will lead to a spontaneous compositional adjustment of the eutectic σ phase, resulting in uphill diffusion of Cr and Mn, and reducing the homogenization efficiency of ISHT, which is avoided by SSHT. The hardness reduced from 228~236 Hv to 220~232 Hv by adopting the cooling process of “furnace cooling + water quench”. In addition, the study noticed that increasing the Ce content or decreasing the Mn content can both refine the homogenized grain size and accelerate diffusion processes. This study provides a theoretical and experimental basis for the process and composition optimization of super austenitic stainless steels.

Background: This study aimed to investigate the effect of ticagrelor combined with omeprazole on patients with acute myocardial infarction (AMI) undergoing primary percutaneous coronary intervention (PCI). Methods: Eighty-six patients with AMI who underwent primary PCI in Xinxiang Central Hospital between July 2015 and December 2016 were included and divided randomly into the observation group and the control group by the draw, with 43 patients in each group. All patients were routinely treated with dual antiplatelet therapy with aspirin plus ticagrelor. Omeprazole was used in the observation group and placebo was used in the control group. Data of baseline patient characteristics, platelet response index (PRI), ADP-induced platelet aggregation (ADP-Ag), major adverse cardiac events (MACE), and incidence of bleeding events were recorded and compared between both groups. Results: PRI and ADP-Ag at 7 days, 1 month, and 6 months after operation in both groups were significantly lower than those in the same group before administration (p

Previous studies have indicated that the preformed martensite has a significant effect on the subsequent bainite transformation of nanobainite bearing steel, but its effects on the microstructure and mechanical properties are still unclear. In this paper, the effects of preformed martensite and its volume fraction on microstructure and mechanical properties of nanobainite bearing steel were investigated by using scanning electron microscope, transmission electron microscope, X-ray diffractometer and wear resistance experiments. It was demonstrated that the introduction of preformed martensite can refine bainitic microstructure and increase the volume fraction of retained austenite, but reduces the mechanical stability of retained austenite. When the volume fraction of preformed martensite is less than 20%, the hardness and wear resistance of nanobainite bearing steel gradually increases with the increase in the volume fraction of preformed martensite, but the toughness of steel decreases gradually. When the volume fraction of preformed martensite reaches 25%, the properties of nanobainite bearing steel, especially the wear resistance, obviously deteriorate. The optimized volume fraction of preformed martensite is ~10%–15% by comprehensive comparison the mechanical properties of nanobainite bearing steel.

Microglia activation, increased IL-6 and decreased TGF-β were found in depressed patients or in animal models of depression. IL-6 enhances T helper 17 cell differentiation, thereby causing an imbalance between Th17 and Treg cells, which induces neuroinflammation and neuronal dysfunction. However, whether imbalances between IL-6 and TGF-β and between Th17 and Treg occur in depression and whether depression can be improved upon restoring these imbalances are unknown. Treg promoter IL-2 (1500UI/0.1 mL/day) was used to treat a mouse model of depression induced by chronic unpredictable mild stress (CUMS). The behavior and concentrations of IL-6, TGF-β, Th17, IL-17A, IL-17Rc, Treg-related factors (helios and STAT5), astrocyte A1 phenotype S100β, microglia M1 phenotype Iba-1, indoleamine-2,3-dioxygenase (IDO) enzyme, corticosterone (CORT) and neurotransmitters were evaluated. When compared to controls, CUMS reduced sucrose preference, the number of entries into and the time spent in the open arms of the elevated plus maze and the exploration in the “open field”, while it increased the immobility time in tail suspension, which was ameliorated by IL-2 treatment. RoRα, S100β, IL-17A, IL-17Rc, IL-6, Iba-1, IDO enzyme and CORT concentrations were significantly increased, and Helios, FoxP3+, STAT5 and TGF-β were significantly decreased by CUMS, which were significantly attenuated by IL-2 when compared to the CUMS group. The NE, DA and 5-HT contents and those of their metabolites were decreased by CUMS, which returned to control levels after IL-2 treatment. The study demonstrated that imbalances between IL-6 and TGF-β and between Th17and Treg occurred in the hippocampus of the depression model. IL-2 attenuated depression- and anxiety-like behaviors and normalized the neurotransmitter concentration and the activity of the IDO enzyme, astrocytes and microglia through restoring both balances, but it did not decrease the CORT concentration.

Bearings are the most important component of nearly all mechanical equipment, as they guarantee the steady running of the equipment, which is especially important for high-end equipment such as high-speed trains and shield tunneling machines. Requirements regarding the quality of bearings are increasing with the rapid development in technology. A country’s bearings manufacturing level directly reflects the level of that country’s steel metallurgy and machinery manufacturing. The performance of the bearing steel is the critical factor that determines the quality of a bearing. The development of new bearing steel with higher performance is the ambition of material researchers and the expectation of the manufacturing industry. Many famous bearing manufacturing enterprises are competing to develop the new generation of bearing steel. Nanostructured bainitic bearing steel (NBBS), which is a newly developed bearing steel, not only possesses high strength and toughness, but also exhibits excellent wear resistance and rolling contact fatigue (RCF) resistance. In recent years, relevant achievements in NBBS in China have led to significant progress in this field. NBBS was first used in China to manufacture large bearings for wind turbines and heavy-duty bearings, with excellent performance. As a result, NBBS and its corresponding heat-treatment process have been included in the national and industry standards for the first time. The bearing industry considers the exploitation of NBBS to be epoch-making, and has termed this kind of bearing as the second generation of bainitic bearing. In this paper, the development of NBBS is reviewed in detail, including its advantages and disadvantages. Further research directions for NBBS are also proposed. Keywords: Nanostructured bainitic bearing steel, Bearing steel, Nanostructured bainite, Development

Potentials for describing interatomic interactions in a γFe-Mn-C-N multicomponent system, modified Hadfield steel, where face-centered cubic (f.c.c.) iron is the main component, are proposed. To describe the Fe-Fe interactions in austenite, it is proposed to use Lau EAM potential. For all other interactions, Morse potentials are proposed, the parameters of which were found from various experimental characteristics: in particular, the energy of dissolution and migration of an impurity in an f.c.c. iron crystal, the radius of atoms, their electronegativity, mutual binding energy, etc. The found potentials are intended for modeling the atomic structures and processes occurring at the atomic level in Hadfield steel using relatively large computational cells by the molecular dynamics method.

In this paper, a new low-carbon alloy gear steel is designed via Si/Al alloying. The carburizing and austempering, at a temperature slightly higher than the martensitic transformation point (Ms) of the surface and much lower than the Ms of the core, for different times, were carried out on the newly designed gear steel. After heat treatment, a series of different microstructures (superfine bainitic ferrite + retained austenite, superfine bainitic ferrite + martensite + retained austenite, and martensite + retained austenite) were obtained on the surface, whilst the low-carbon lath martensitic microstructure was obtained in the core. The microstructure of the surface was examined using optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The phase composition was analyzed using X-ray diffraction (XRD). The hardness and wear resistance of the surface as well as the hardness distribution of carburizing layer of the samples with different microstructures were studied. The results show that the Si/Al-rich gear steel, after carburizing and austempering at 200 °C for 8 h, not only has excellent mechanical properties but also has high wear resistance, which meets the technical requirements of heavy-duty gear steel. The research work in this paper can provide a data reference for the application of carburized steel with mixed microstructures of bainitic ferrite and martensite in the design of heavy-duty gear.

An austenite-ferrite duplex low-density steel (Fe–12Mn–7Al–0.2C–0.6Si, wt%) was designed and fabricated by cold rolling and annealing at different temperatures. The tensile properties, microstructure evolution, deformation mechanism and stacking fault energy (SFE) of the steel were systemically investigated at ambient temperature. Results show two phases of fine equiaxed austenite and coarse band-like δ-ferrite in the microstructure of the steel. With increasing annealing temperature, the yield and tensile strengths decrease while the total elongation increases. At initial strains, the deformation is mainly concentrated in the fine austenite and grain boundaries of the coarse δ-ferrite, and the interior of the coarse δ-ferrite gradually deforms with further increase in the strain to 0.3. No twinning-induced plasticity (TWIP) or transformation-induced plasticity (TRIP) occurred during the tensile deformation. Considering element segregation and two-phase proportion, the chemical composition of austenite was measured more precisely. The SFE of the austenite is 39.7 mJ/m2, and the critical stress required to produce deformation twins is significantly higher than the maximum flow stress of the steel.

Osteosarcoma (OS) is a malignant bone tumor that frequently occurs in adolescents. It has a high rate of pulmonary metastasis and mortality. Previous studies have demonstrated that human bone marrow mesenchymal stem cells (hBMSCs) can promote the malignant progression in various tumors, including OS. Also, it is recognized that exosomes derived from hBMSCs (hBMSC-Exos) mediate cell-to-cell communication and exhibit similar effects on the development of various tumors. However, the role of hBMSC-Exos in the development of OS is still unclear and the underlying mechanism needs to be elucidated. Our results show that hBMSC-derived exosomes promote OS cell proliferation, migration, and invasion. Meanwhile, silencing autophagy-related gene 5 (ATG5) in OS cells abolishes the pro-tumor effects of hBMSC-Exos in vitro and in vivo. Our present study demonstrates that hBMSC-Exos promotes tumorigenesis and metastasis by promoting oncogenic autophagy in OS. Keywords: Exosomes, hBMSCs, Autophagy, Osteosarcoma

Welding heat input greatly influences the microstructure and impacts the affected zone’s toughness. To interpret the relationships between the welding heat input, microstructure, and low-temperature toughness of the coarse-grained heat-affected zone (CGHAZ) of Mo-V-Ti-N-B steels, welding heat cycles with different heat inputs (25–75 kJ cm ^−1 ) were performed on a Gleeble 3500 simulator. Intragranular ferrite in the simulated samples subjected to different thermal cycles was characterized and quantified, and the impact energies of simulated samples were evaluated at −20 °C. Upon increasing the heat input, the intragranular ferrite content rose sharply from 4.3% to 76.0%. The V(C, N) enrichment on the precipitate surface increased the size of precipitates, providing favourable nucleation conditions for intragranular ferrite. The prior austenite grain (PAG) and martensite/austenite (M/A) constituents became rough, and the content of the M/A constituent increased while the impact energy of the CGHAZ increased. This behaviour occurred due to the formation of intragranular acicular ferrite (IGAF), which refined the microstructure of the CGHAZ. Grain refinement eliminated the negative influence of higher M/A content on the impact toughness of the CGHAZ.