This work reveals the significant effects of cobalt(Co)on the microstructure and impact toughness of as-quenched highstrength steels by experimental characterizations and thermo-kinetic analyses.The results show that ...This work reveals the significant effects of cobalt(Co)on the microstructure and impact toughness of as-quenched highstrength steels by experimental characterizations and thermo-kinetic analyses.The results show that the Co-bearing steel exhibits finer blocks and a lower ductile-brittle transition temperature than the steel without Co.Moreover,the Co-bearing steel reveals higher transformation rates at the intermediate stage with bainite volume fraction ranging from around 0.1 to 0.6.The improved impact toughness of the Co-bearing steel results from the higher dense block boundaries dominated by the V1/V2 variant pair.Furthermore,the addition of Co induces a larger transformation driving force and a lower bainite start temperature(BS),thereby contributing to the refinement of blocks and the increase of the V1/V2 variant pair.These findings would be instructive for the composition,microstructure design,and property optimization of high-strength steels.展开更多
As a typical steel,the fatigue of marine high-strength steels has been emphasized by scholars.In this paper,the fatigue performance and crack growth mechanism of a high-strength steel for ships are investigated by exp...As a typical steel,the fatigue of marine high-strength steels has been emphasized by scholars.In this paper,the fatigue performance and crack growth mechanism of a high-strength steel for ships are investigated by experimental methods.First,the fatigue threshold test and fatigue crack growth rate test of this high-strength steel under different stress ratios were carried out.The influence of stress ratio on the fatigue properties of this steel was analyzed.Secondly,scanning electron microscope was used to analyze the crack growth specimen section of this steel.The crack growth and failure mechanism of this steel were revealed.Finally,based on the above research results,the stress ratio effect of high-strength steel was investigated from the perspectives of crack closure and driving force.Considering the fatigue behavior in the near-threshold stage and the destabilization stage,a fatigue crack growth behavior prediction model of highstrength steel was established.The accuracy of the model was verified by test data.Moreover,the applicability of the modified model to various materials and its excellent predictive ability were verified through comparison with literature data and existing models.展开更多
The optimization of deposited metal properties through the addition of rare earth elements to welding materials was explored.Utilizing optical microscope,scanning electron microscope,energy dispersive spectroscope,and...The optimization of deposited metal properties through the addition of rare earth elements to welding materials was explored.Utilizing optical microscope,scanning electron microscope,energy dispersive spectroscope,and X-ray diffractometer,combined with software tools like Matlab,Image-Pro Plus,and CHANNEL5,the influence mechanism of rare earth element addition on the strength,toughness,and inclusions of deposited metal in 1000 MPa grade high-strength steel was investigated.The results indicate that the incorporation of rare earth elements enhances the weldability of the welding materials.With the addition of rare earth elements,the tensile strength of the deposited metal increases from 935 MPa to 960 MPa.However,further addition leads to a decrease in tensile strength,while the yield strength continuously increases by 8.5%-17.2%.The addition of appropriate amounts of rare earth elements results in an increase in acicular ferrite and retained austenite content,as well as grain refinement in the deposited metal,leading to 8.5%-24.3% and 15.6%-42.2% enhancement in impact energy at−40℃ and−60℃,respectively.Additionally,the proper addition of rare earth elements modifies the inclusions and generates fine and dispersed composite inclusions that bond better with the matrix,thereby optimizing the properties of the deposited metal through various mechanisms.Adding an appropriate amount of rare earth elements can significantly enhance the properties of the deposited metal in 1000 MPa grade high-strength steel,and improve the match between high strength and toughness,meeting the demands for high-strength steel used in hydropower applications.展开更多
The influence mechanism of trace Nb on the corrosion resistance of surface corrosion products of high-strength anti-seismic rebar in the simulated marine environment was studied by combining first-principles calculati...The influence mechanism of trace Nb on the corrosion resistance of surface corrosion products of high-strength anti-seismic rebar in the simulated marine environment was studied by combining first-principles calculations with corrosion mass loss method,surface analysis,cross-sectional analysis,quantitative analysis,and electrochemical test.The results demonstrated that the addition of trace Nb effectively improved the compactness and stability of surface corrosion layer of rebar,and the corrosion resistance of corrosion layer increased with the increase in Nb content.The beneficial effect of Nb content on the corrosion layer summarized two important key points.Firstly,the addition of Nb was beneficial to promoting the improvement in the structural stability of α-FeOOH,and α-FeOOH structure of solid solution Nb atoms was beneficial to strengthening the fixation of Cl atoms,thus increasing α/(β+γ)ratio,total impedance value,and corrosion potential.Secondly,the formation of Nb oxides can not only repair the corrosion layer,but also play a role in the fixation Cl atoms,resulting in the improvement in corrosion resistance of corrosion layer.展开更多
Hydrogen embrittlement(HE)remains a critical challenge for high-strength steels.This study comparatively investigates the HE behavior and hydrogen diffusion characteristics of a vanadium-micro-alloyed 42CrNiMoV steel ...Hydrogen embrittlement(HE)remains a critical challenge for high-strength steels.This study comparatively investigates the HE behavior and hydrogen diffusion characteristics of a vanadium-micro-alloyed 42CrNiMoV steel against conventional 40CrNiMo steel through slow strain rate testing(SSRT),hydrogen thermal desorption,and hydrogen permeation measurements.The 42CrNiMoV steel demonstrated better mechanical properties and improved HE resistance under SSRT with both hydrogen pre-charged and in situ charging conditions.Microstructural analysis revealed that vanadium micro-alloying leads to grain refinement and reduces hydrogen diffusivity through vanadium carbides.Fractographic investigations revealed the environment-dependent fracture mechanisms,transitioning from ductile-to brittle-dominated failure modes under different hydrogen-charging conditions.These findings validate that vanadium micro-alloying represents a promising,cost-effective strategy for developing hydrogen-resistant high-strength steels,while emphasizing the crucial need for rigorous hydrogen ingress control in practical applications.展开更多
Corrosion is an essential issue limiting the application of high-strength low-carbon steel in seawater environment. The impact of retained austenite on its corrosion behavior with immersion experiments and related cor...Corrosion is an essential issue limiting the application of high-strength low-carbon steel in seawater environment. The impact of retained austenite on its corrosion behavior with immersion experiments and related corrosion sensor technology was explored. A model that clarifies the micro-galvanic effect and the heat-induced changes to the shape and composition of retained austenite was used to discuss the findings. The results indicated that retained austenite was generated following an intercritical process and demonstrated approximately 48 mV higher Volta potential than the matrix. The retained austenite content first increased and then decreased with increasing intercritical temperatures, while reaching the maximum value of 8.5% at 660℃. With the increase in retained austenite content, the corrosion rate was increased by up to 32.8% compared to “quenching + tempering” (QT) specimen. The interfaces between the retained austenite and matrix were the priority nucleation sites for corrosion. Moreover, the retained austenite reduced the corrosion resistance of the steel by increasing the micro-galvanic effect and reducing rust layer compactness.展开更多
The AlMgScZr high-strength aluminum alloy fabricated by selective laser melting(SLM)technology exhibits a“bimodal microstructure”,resulting in significant non-uniform deformation during thermal deformation.This stud...The AlMgScZr high-strength aluminum alloy fabricated by selective laser melting(SLM)technology exhibits a“bimodal microstructure”,resulting in significant non-uniform deformation during thermal deformation.This study investigates the flow behavior of SLM-processed AlMgScZr aluminum alloy utilizing the Gleeble-1500D thermal simulation machine.The true stress-strain curves were amended based on the friction theory.Through determining the Zener-Hollomon parameters,the correlation between flow stress,deformation temperature,and strain rate during the high-temperature thermoplastic deformation of SLM-processed AlMgScZr aluminum alloy with a“bimodal microstructure”was established.In addition,the microstructural evolution during thermal deformation was analyzed.The results indicated that the predicted flow stress values obtained from the Arrhenius constitutive equation with coupled correction of thermal deformation parameters closely matched the experimental values.The correlation coefficient and the average absolute relative error of the corrected model were 0.999 and 2.766%,respectively,accurately predicting the thermoplastic deformation behavior of SLM-processed high-strength aluminum alloy with a“bimodal microstructure”.Furthermore,hot processing maps at different strains were established,identifying stable and unstable regions under different deformation conditions.Microstructural observations revealed different thermal deformation mechanisms under various deformation temperatures.Specifically,dynamic recrystallization characteristics dominated the microstructure at lower temperatures(300-360℃),while dynamic recovery was dominant at higher temperatures(390-500℃).展开更多
This study deals with the development of a 780-MPa-class hot-rolled advanced high-strength steel(AHSS)with an ultrahigh elongation at break of approximately 30%and strength-ductility product exceeding 24 GPa·%,in...This study deals with the development of a 780-MPa-class hot-rolled advanced high-strength steel(AHSS)with an ultrahigh elongation at break of approximately 30%and strength-ductility product exceeding 24 GPa·%,indicating the excellent formability of the newly developed AHSS.The microstructure of the newly developed 780-MPa-class AHSS consists mainly of the triplex phase of ferrite,bainite,and retained austenite with a volume fraction of 10%±2%.The stability of the retained austenite in the newly developed AHSS is much higher than that of conventional transformation-induced plasticity steels,in which the retained austenite is prone to transformation into martensite under deformation.At a pre-strain lower than 1.2%,the volume fraction of the retained austenite and the elongation at break of the present 780-MPa-class AHSS remain almost unchanged,showing a high tolerance in the process window during leveling or straightening.Therefore,the present 780-MPa-class AHSS is particularly suitable for the production of components with complex shapes.展开更多
High-strength aluminum alloys are widely used in industries such as aerospace,automotive,and defense due to their excellent strength-to-weight ratio and good mechanical properties.However,optimizing their mechanical p...High-strength aluminum alloys are widely used in industries such as aerospace,automotive,and defense due to their excellent strength-to-weight ratio and good mechanical properties.However,optimizing their mechanical properties while maintaining cost-effectiveness and processing efficiency remains a significant challenge.This paper investigates the fundamental aspects of microstructure control and mechanical property optimization in high-strength aluminum alloys.It focuses on the influence of alloy composition,heat treatments,and processing techniques on the material's strength,ductility,toughness,fatigue resistance,corrosion resistance,and wear properties.The paper also explores the role of advanced experimental techniques,such as metallographic analysis,mechanical testing,and X-ray diffraction(XRD),in characterizing the microstructure and mechanical performance of these alloys.Moreover,it emphasizes the importance of microstructure refinement,solid solution strengthening,precipitation hardening,and the addition of specific alloying elements in optimizing the alloy's overall performance.The review provides valuable insights into the key strategies for designing high-strength aluminum alloys with enhanced mechanical properties,focusing on their applications in high-performance engineering fields.展开更多
High-order asymmetric flatness defects resulting from the abnormal state of roll system are the main issue of precision rolling mill in the manufacturing process of high-strength thin strip.Due to the difficulty of mo...High-order asymmetric flatness defects resulting from the abnormal state of roll system are the main issue of precision rolling mill in the manufacturing process of high-strength thin strip.Due to the difficulty of monitoring and adjusting the abnormal state,the spatial state of roll system cannot be controlled by traditional methods.It is difficult to fundamentally improve these high-order asymmetric flatness defects.Therefore,a digital twin model of flatness control process for S6-high rolling mill was established,which could be used to analyze the influence of the abnormal state on the flatness control characteristic and propose improvement strategies.The internal relationship between the force state of side support roll system and the abnormal state of roll system was proposed.The XGBoost algorithm model was established to analyze the contribution degree of the side support roll system force to the flatness characteristic quantity.The abnormal state of roll system in the S6-high rolling mill can be diagnosed by analyzing the flatness characteristic difference between flatness value of the rolled strip and calculated characteristic value of finite element simulation.The flatness optimization model of the gray wolf optimization–long short-term memory non-dominated sorting whale optimization algorithm(GWO-LSTM-NSWOA)was established,and the decision-making selection was made from the Pareto frontier based on the flatness requirements of cold rolling to regulate the abnormal state of the roll system.The results indicate that the contribution degree of the force of the side support roll system to the flatness characteristics is more than 25%,which is the main influence of high-order asymmetric flatness defect.The performance of the GWO-LSTM flatness feature prediction model has clear advantages over back propagation and LSTM.The practical applications show that optimizing the force of side support roll system can reduce the high point of high-strength strip flatness from 13.2 to 6 IU and decrease the percentage of low-strength strip flatness defects from 1.6%to 1.2%.This optimization greatly reduced the proportion of flatness defects,improved the accuracy level of flatness control of precision rolling mill,and provided a guarantee for the stable production of thin strip.展开更多
The dilatometric curves of Q690 steel at different cooling rates were tested using Gleeble 3800 to study the continuous cooling transformation behavior of high-strength steel with low welding crack sensitivity.The con...The dilatometric curves of Q690 steel at different cooling rates were tested using Gleeble 3800 to study the continuous cooling transformation behavior of high-strength steel with low welding crack sensitivity.The continuous cooling transformation curves of Q690 steel were constructed according to the transformation tem-peratures determined using dilatometric curves and corresponding microstructures at different cooling rates.The results show that the microstructure of Q690 steel remarkably changed with the increase in the cooling rate.The matrix of the steel was ferrite and pearlite when the cooling rate was between 0.1 K/s and 0.5 K/s.With increasing cooling rate, the microstructure of the steel was considerably refined, and the Vickers hardness of the steel increased.When the cooling rate reached 1 K/s, the microstructure of the steel was further refined, and bainite transformation occurred.Polygonal ferrite almost disappeared from the steel when the cooling rate reached 10 K/s, and the matrix was mainly composed of bainite and a small amount of lath martensite.With the increase in the cooling rate, the ferrite decreased and martensite increased in the steel, resulting in higher Vickers hardness.When the cooling rate reached 30 K/s, the microstructure of the tested steel was full martensite matrix.展开更多
A secondary-cooling-segment electromagnetic stirring(S-EMS)experiment was performed at 150 A and 4 Hz to evaluate the effect of S-EMS on solidification characterization near the white band.The upper and lower parts of...A secondary-cooling-segment electromagnetic stirring(S-EMS)experiment was performed at 150 A and 4 Hz to evaluate the effect of S-EMS on solidification characterization near the white band.The upper and lower parts of the white band exhibited average secondary dendritic arm spacing of 205.4 and 214.4μm,respectively.The S-EMS operation resulted in large Lorentz forces and cooling intensity,which could produce additional dendritic arms with low carbon concentrations,leading to local negative segregation.Moreover,a 3D flow-temperature-magnetic coupling numerical model was established.The results revealed that the magnetic induction intensity and Lorentz force were symmetrically distributed along rollers S1 and S2.The average velocity magnitude increased by approximately 42.52%,58.69%,and 64.11%for liquid fractions of 0.7,0.8,and 0.9,respectively.During the S-EMS operation,the Lorentz force may alter the velocity of the solidification front and promote the dissipation of superheat.Additionally,the influence of S-EMS on grain nucleation and growth was investigated using Gibbs free energy theory and component undercooling.Furthermore,a formation model for the white band was established,and the mechanism of white band formation was elucidated according to the changes in the solute-enriched layer,solute precipitation,and diffusion.展开更多
Zwitterionic polymers are polymers containing a pair of oppositely charged groups in their repeating units,which facilitate the formation of a hydration layer on the surface through ionic solvation.This strong hydrati...Zwitterionic polymers are polymers containing a pair of oppositely charged groups in their repeating units,which facilitate the formation of a hydration layer on the surface through ionic solvation.This strong hydration results in the remarkable properties of zwitterionic polymer hydrogels,including antifouling,lubricating,and anti-freezing capabilities.Owing to these properties,zwitterionic polymer hydrogels have attracted notable attention in biomedical and engineering fields.However,the superhydrophilicity of zwitterionic polymer hydrogels renders them brittle and weak,considerably limiting their use in load-bearing applications.Thus,there is an urgent need to improve the mechanical properties of zwitterionic hydrogels.In this work,we systematically review mechanical enhancement strategies for zwitterionic polymer hydrogels.We cover strate-gies applicable to hybrid and pure high-strength zwitterionic polymer hydrogels.Additionally,we discuss the advantages and limitations of various strength enhancement strategies.展开更多
The effects of heat treatment on microstructure and creep properties of β high-strength titanium alloy,Ti-3.5Al-5Mo-6V-3Cr-2Sn-0.5Fe,were studied.After solution treatment at 790℃ and aging treatment(HT1),the microst...The effects of heat treatment on microstructure and creep properties of β high-strength titanium alloy,Ti-3.5Al-5Mo-6V-3Cr-2Sn-0.5Fe,were studied.After solution treatment at 790℃ and aging treatment(HT1),the microstructure is composed of equiaxedαp phase,β phase,α_(p) phase,and becomes β phase and α_(s) phases after solution treatment at 840℃ and aging treatment(HT2).The creep behavior at 400℃ was analyzed.The stress exponents of both alloys are between 1 and 2,indicating that the diffusional creep mechanism is one of the dominant creep mechanisms.The alloy after HT2 treatment has better creep resistance and a subsequent creep test on this alloy was performed at 450℃ under 400 MPa.The creep fracture has the mixed ductile-brittle characteristics.The phase interfaces can hinder the dislocation movement,and theαs phase can coordinate with the matrix to deform,thereby reducing the occurrence of intragranular cracks.展开更多
In order to improve the brittleness of high-strength cement mortar,calcium carbonate（CaCO3） whiskers are incorporated to strengthen and toughen the high-strength cement mortar.The compressive strength,flexural stren...In order to improve the brittleness of high-strength cement mortar,calcium carbonate（CaCO3） whiskers are incorporated to strengthen and toughen the high-strength cement mortar.The compressive strength,flexural strength,split tensile strength and work of fracture are measured.Microstructures and micromechanical behaviors are investigated using scanning electron microscopy.The strengthening and toughening mechanisms and the efficiency of whisker-reinforced high-strength cement mortar are discussed.The results show that the addition of CaCO3 whiskers brings positive effects on the high-strength cement mortar.The strengthening and toughening mechanisms are whisker-cement coalition debonding,whisker peeling,whisker impact breakage and whisker bridging.Crack deflection is one efficient mechanism,but it is hard to be achieved in high-strength cement mortar.And the interfacial bonding strength between whiskers and the cement mortar matrix should be appropriately weak to introduce more crack deflection mechanisms to strengthen and toughen the cement mortar efficiently.展开更多
The forming quality of high-strength TA18 titanium alloy tube during numerical control bending in changing bending angle β, relative bending radius R/D and tube sizes such as diameter D and wall thickness t was clari...The forming quality of high-strength TA18 titanium alloy tube during numerical control bending in changing bending angle β, relative bending radius R/D and tube sizes such as diameter D and wall thickness t was clarified by finite element simulation. The results show that the distribution of wall thickness change ratio Δt and cross section deformation ratio ΔD are very similar under different β; the Δt and ΔD decrease with the increase of R/D, and to obtain the qualified bent tube, the R/D must be greater than 2.0; the wall thinning ratio Δto slightly increases with larger D and t, while the wall thickening ratio Δti and ΔD increase with the larger D and smaller t; the Δto and ΔD firstly decrease and then increase, while the Δti increases, for the same D/t with the increase of D and t.展开更多
A new Ti-V-Mo complex microalloyed hot-rolled high-strength steel sheet was developed by controlling a thermo-mechanical controlled processing （TMCP） schedule, in particular with variants in coiling temperature. The...A new Ti-V-Mo complex microalloyed hot-rolled high-strength steel sheet was developed by controlling a thermo-mechanical controlled processing （TMCP） schedule, in particular with variants in coiling temperature. The effects of coiling temperature （CT） on various hardening mechanisms and mechanical properties of Ti-V-Mo complex mi- croalloyed high-strength low-alloy steels were investigated. The results revealed that the steels are mainly strengthened by a combined effect of ferrite grain refinement hardening and precipitation hardening. The variation in simulated coiling temperature causes a significant difference in strength, which is mainly attributed to different precipitation hardening increment contributions. When the CT is 600 ℃, the experimental steel has the best mechanical properties： ultimate tensile strength （UTS） 1000 MPa, yield strength （YS） 955 MPa and elongation （EL） 17%. Moreover, about 82 wt% of the total precipitates are nano-sized carbide particles with diameter of 1-10 nm, which is randomly dispersed in the ferrite matrix. The nano-sized carbide particles led to a strong precipitation hardening increment up to 310 MPa.展开更多
Low cycle fatigue behavior of a quenched and tempered high-strength steel(Q960 E) was studied in the strain amplitude ranging from ± 0.5% to ± 1.2% at room temperature. As a result of fatigue loading, the di...Low cycle fatigue behavior of a quenched and tempered high-strength steel(Q960 E) was studied in the strain amplitude ranging from ± 0.5% to ± 1.2% at room temperature. As a result of fatigue loading, the dislocation structural evolution and fracture mechanism were examined and studied by transmission electron microscopy and scanning electron microscopy(SEM). The results showed that this Q960 E steel showed cyclic softening at different strain amplitudes, and the softening tendency was more apparent at strain amplitude of ±(0.6–1.2)% than that at ± 0.5%. The reduction in dislocation density with increasing strain amplitude is responsible for the softening tendency of cyclic stress with the strain amplitude. The material illustrates near-Masing behavior at strain amplitude ranging from ± 0.6% to ± 1.2%. The near-Masing behavior of Q960 E high-strength steel can be the result of stability of martensite lath at different strain amplitudes. Partial transformation from martensite laths to dislocation cells is responsible for the derivation from ideal Masing behavior. In the SEM examination of fracture surfaces, transgranular cracks initiate on the sample surface. Striations can be found during the crack propagation stage.展开更多
The effect of high-strength ammonia nitrogen acclimation on sludge activity in sequencing batch reactor （SBR） was investigated. Two batch experiments, RUN1 and RUN2, were conducted with the influent ammonia nitrogen...The effect of high-strength ammonia nitrogen acclimation on sludge activity in sequencing batch reactor （SBR） was investigated. Two batch experiments, RUN1 and RUN2, were conducted with the influent ammonia nitrogen concentrations 60 and 500 mg/L, respectively. The sludges inoculated from RUN1 and RUN2 were used to treat a series of influent with ammonia nitrogen concentrations of 59, 232, 368, 604 and 1152 mg/L. It is found that the activated sludge acclimated to higher ammonia nitrogen concentrations revealed higher COD and NH 4 ＋ -N removal efficiencies, and slower DHA decrease. The results confirmed that the activities of the bacteria in activated sludge in SBR were inhibited by high-strength ammonia nitrogen, whereas the activated sludge acclimated to high-strength ammonia nitrogen showed substantial resistance to inhibition by influents containing high levels of ammonia nitrogen.展开更多
The corrosion resistance and evolution of corrosion products in medium-carbon high-strength spring steels were investigated in a neutral salt spray(5 wt% Na Cl solution). A formation model of γ-Fe OOH and a transform...The corrosion resistance and evolution of corrosion products in medium-carbon high-strength spring steels were investigated in a neutral salt spray(5 wt% Na Cl solution). A formation model of γ-Fe OOH and a transformation model describing the conversion of γ-Fe OOH to α-Fe OOH were constructed. The results indicated that, at the initial corrosion stage, the corrosion resistance was gradually improved with the addition of Cr; however, with the addition of alloying element V, the corrosion resistance decreased. These results were attributed mainly to the initial corrosion stage being closely related to the matrix microstructure parameters such as grain-boundary character and dislocation density. After the rust layer was formed at a later corrosion stage, the corrosion resistance was reinforced with the addition of Cr and V because Cr strongly influenced the composition, structure, and morphology of the corrosion products. The results presented herein show that Cr was conducive to the transformation of γ-Fe OOH into α-Fe OOH. Moreover, V and Cr exhibited obvious synergy and were enriched in the inner layer of the corrosion products.展开更多
基金supported by the National Natural Science Foundation of China(No.52271089)the financial support from the C hina Postdoctoral Science Foundation(No.2023M732192)。
文摘This work reveals the significant effects of cobalt(Co)on the microstructure and impact toughness of as-quenched highstrength steels by experimental characterizations and thermo-kinetic analyses.The results show that the Co-bearing steel exhibits finer blocks and a lower ductile-brittle transition temperature than the steel without Co.Moreover,the Co-bearing steel reveals higher transformation rates at the intermediate stage with bainite volume fraction ranging from around 0.1 to 0.6.The improved impact toughness of the Co-bearing steel results from the higher dense block boundaries dominated by the V1/V2 variant pair.Furthermore,the addition of Co induces a larger transformation driving force and a lower bainite start temperature(BS),thereby contributing to the refinement of blocks and the increase of the V1/V2 variant pair.These findings would be instructive for the composition,microstructure design,and property optimization of high-strength steels.
文摘As a typical steel,the fatigue of marine high-strength steels has been emphasized by scholars.In this paper,the fatigue performance and crack growth mechanism of a high-strength steel for ships are investigated by experimental methods.First,the fatigue threshold test and fatigue crack growth rate test of this high-strength steel under different stress ratios were carried out.The influence of stress ratio on the fatigue properties of this steel was analyzed.Secondly,scanning electron microscope was used to analyze the crack growth specimen section of this steel.The crack growth and failure mechanism of this steel were revealed.Finally,based on the above research results,the stress ratio effect of high-strength steel was investigated from the perspectives of crack closure and driving force.Considering the fatigue behavior in the near-threshold stage and the destabilization stage,a fatigue crack growth behavior prediction model of highstrength steel was established.The accuracy of the model was verified by test data.Moreover,the applicability of the modified model to various materials and its excellent predictive ability were verified through comparison with literature data and existing models.
基金Provincial Key Research and Development Plan of Heilongjiang(2022ZX04A01)。
文摘The optimization of deposited metal properties through the addition of rare earth elements to welding materials was explored.Utilizing optical microscope,scanning electron microscope,energy dispersive spectroscope,and X-ray diffractometer,combined with software tools like Matlab,Image-Pro Plus,and CHANNEL5,the influence mechanism of rare earth element addition on the strength,toughness,and inclusions of deposited metal in 1000 MPa grade high-strength steel was investigated.The results indicate that the incorporation of rare earth elements enhances the weldability of the welding materials.With the addition of rare earth elements,the tensile strength of the deposited metal increases from 935 MPa to 960 MPa.However,further addition leads to a decrease in tensile strength,while the yield strength continuously increases by 8.5%-17.2%.The addition of appropriate amounts of rare earth elements results in an increase in acicular ferrite and retained austenite content,as well as grain refinement in the deposited metal,leading to 8.5%-24.3% and 15.6%-42.2% enhancement in impact energy at−40℃ and−60℃,respectively.Additionally,the proper addition of rare earth elements modifies the inclusions and generates fine and dispersed composite inclusions that bond better with the matrix,thereby optimizing the properties of the deposited metal through various mechanisms.Adding an appropriate amount of rare earth elements can significantly enhance the properties of the deposited metal in 1000 MPa grade high-strength steel,and improve the match between high strength and toughness,meeting the demands for high-strength steel used in hydropower applications.
基金supported by National Natural Science Foundation of China(Grant No.52074095)Guizhou Provincial Basic Research Program(Natural Science)(Grant No.QKHJC-ZK[2023]YB072)+2 种基金Guizhou Provincial Key Technology R&D Program(Grant No.QKHZC[2023]YB404)Guizhou Provincial Key Technology R&D Program(Grant No.QKHZC[2022]YB053)The numerical calculation of the first-principles was supported and assisted by the High-Performance Computing Center of Guizhou University.
文摘The influence mechanism of trace Nb on the corrosion resistance of surface corrosion products of high-strength anti-seismic rebar in the simulated marine environment was studied by combining first-principles calculations with corrosion mass loss method,surface analysis,cross-sectional analysis,quantitative analysis,and electrochemical test.The results demonstrated that the addition of trace Nb effectively improved the compactness and stability of surface corrosion layer of rebar,and the corrosion resistance of corrosion layer increased with the increase in Nb content.The beneficial effect of Nb content on the corrosion layer summarized two important key points.Firstly,the addition of Nb was beneficial to promoting the improvement in the structural stability of α-FeOOH,and α-FeOOH structure of solid solution Nb atoms was beneficial to strengthening the fixation of Cl atoms,thus increasing α/(β+γ)ratio,total impedance value,and corrosion potential.Secondly,the formation of Nb oxides can not only repair the corrosion layer,but also play a role in the fixation Cl atoms,resulting in the improvement in corrosion resistance of corrosion layer.
基金supported by the Natural Science Foundation of Shanghai(No.23ZR1421700).
文摘Hydrogen embrittlement(HE)remains a critical challenge for high-strength steels.This study comparatively investigates the HE behavior and hydrogen diffusion characteristics of a vanadium-micro-alloyed 42CrNiMoV steel against conventional 40CrNiMo steel through slow strain rate testing(SSRT),hydrogen thermal desorption,and hydrogen permeation measurements.The 42CrNiMoV steel demonstrated better mechanical properties and improved HE resistance under SSRT with both hydrogen pre-charged and in situ charging conditions.Microstructural analysis revealed that vanadium micro-alloying leads to grain refinement and reduces hydrogen diffusivity through vanadium carbides.Fractographic investigations revealed the environment-dependent fracture mechanisms,transitioning from ductile-to brittle-dominated failure modes under different hydrogen-charging conditions.These findings validate that vanadium micro-alloying represents a promising,cost-effective strategy for developing hydrogen-resistant high-strength steels,while emphasizing the crucial need for rigorous hydrogen ingress control in practical applications.
文摘Corrosion is an essential issue limiting the application of high-strength low-carbon steel in seawater environment. The impact of retained austenite on its corrosion behavior with immersion experiments and related corrosion sensor technology was explored. A model that clarifies the micro-galvanic effect and the heat-induced changes to the shape and composition of retained austenite was used to discuss the findings. The results indicated that retained austenite was generated following an intercritical process and demonstrated approximately 48 mV higher Volta potential than the matrix. The retained austenite content first increased and then decreased with increasing intercritical temperatures, while reaching the maximum value of 8.5% at 660℃. With the increase in retained austenite content, the corrosion rate was increased by up to 32.8% compared to “quenching + tempering” (QT) specimen. The interfaces between the retained austenite and matrix were the priority nucleation sites for corrosion. Moreover, the retained austenite reduced the corrosion resistance of the steel by increasing the micro-galvanic effect and reducing rust layer compactness.
基金Project(22KJB430023)supported by the Natural Science Foundation for Colleges and Universities of Jiangsu Province,ChinaProject(1172922101)supported by the Youth Science and Technology Innovation Project of Jiangsu University of Science and Technology,China。
文摘The AlMgScZr high-strength aluminum alloy fabricated by selective laser melting(SLM)technology exhibits a“bimodal microstructure”,resulting in significant non-uniform deformation during thermal deformation.This study investigates the flow behavior of SLM-processed AlMgScZr aluminum alloy utilizing the Gleeble-1500D thermal simulation machine.The true stress-strain curves were amended based on the friction theory.Through determining the Zener-Hollomon parameters,the correlation between flow stress,deformation temperature,and strain rate during the high-temperature thermoplastic deformation of SLM-processed AlMgScZr aluminum alloy with a“bimodal microstructure”was established.In addition,the microstructural evolution during thermal deformation was analyzed.The results indicated that the predicted flow stress values obtained from the Arrhenius constitutive equation with coupled correction of thermal deformation parameters closely matched the experimental values.The correlation coefficient and the average absolute relative error of the corrected model were 0.999 and 2.766%,respectively,accurately predicting the thermoplastic deformation behavior of SLM-processed high-strength aluminum alloy with a“bimodal microstructure”.Furthermore,hot processing maps at different strains were established,identifying stable and unstable regions under different deformation conditions.Microstructural observations revealed different thermal deformation mechanisms under various deformation temperatures.Specifically,dynamic recrystallization characteristics dominated the microstructure at lower temperatures(300-360℃),while dynamic recovery was dominant at higher temperatures(390-500℃).
文摘This study deals with the development of a 780-MPa-class hot-rolled advanced high-strength steel(AHSS)with an ultrahigh elongation at break of approximately 30%and strength-ductility product exceeding 24 GPa·%,indicating the excellent formability of the newly developed AHSS.The microstructure of the newly developed 780-MPa-class AHSS consists mainly of the triplex phase of ferrite,bainite,and retained austenite with a volume fraction of 10%±2%.The stability of the retained austenite in the newly developed AHSS is much higher than that of conventional transformation-induced plasticity steels,in which the retained austenite is prone to transformation into martensite under deformation.At a pre-strain lower than 1.2%,the volume fraction of the retained austenite and the elongation at break of the present 780-MPa-class AHSS remain almost unchanged,showing a high tolerance in the process window during leveling or straightening.Therefore,the present 780-MPa-class AHSS is particularly suitable for the production of components with complex shapes.
文摘High-strength aluminum alloys are widely used in industries such as aerospace,automotive,and defense due to their excellent strength-to-weight ratio and good mechanical properties.However,optimizing their mechanical properties while maintaining cost-effectiveness and processing efficiency remains a significant challenge.This paper investigates the fundamental aspects of microstructure control and mechanical property optimization in high-strength aluminum alloys.It focuses on the influence of alloy composition,heat treatments,and processing techniques on the material's strength,ductility,toughness,fatigue resistance,corrosion resistance,and wear properties.The paper also explores the role of advanced experimental techniques,such as metallographic analysis,mechanical testing,and X-ray diffraction(XRD),in characterizing the microstructure and mechanical performance of these alloys.Moreover,it emphasizes the importance of microstructure refinement,solid solution strengthening,precipitation hardening,and the addition of specific alloying elements in optimizing the alloy's overall performance.The review provides valuable insights into the key strategies for designing high-strength aluminum alloys with enhanced mechanical properties,focusing on their applications in high-performance engineering fields.
基金financially supported by the National Key Research and Development Program of China(Grant No.2023YFB3812602).
文摘High-order asymmetric flatness defects resulting from the abnormal state of roll system are the main issue of precision rolling mill in the manufacturing process of high-strength thin strip.Due to the difficulty of monitoring and adjusting the abnormal state,the spatial state of roll system cannot be controlled by traditional methods.It is difficult to fundamentally improve these high-order asymmetric flatness defects.Therefore,a digital twin model of flatness control process for S6-high rolling mill was established,which could be used to analyze the influence of the abnormal state on the flatness control characteristic and propose improvement strategies.The internal relationship between the force state of side support roll system and the abnormal state of roll system was proposed.The XGBoost algorithm model was established to analyze the contribution degree of the side support roll system force to the flatness characteristic quantity.The abnormal state of roll system in the S6-high rolling mill can be diagnosed by analyzing the flatness characteristic difference between flatness value of the rolled strip and calculated characteristic value of finite element simulation.The flatness optimization model of the gray wolf optimization–long short-term memory non-dominated sorting whale optimization algorithm(GWO-LSTM-NSWOA)was established,and the decision-making selection was made from the Pareto frontier based on the flatness requirements of cold rolling to regulate the abnormal state of the roll system.The results indicate that the contribution degree of the force of the side support roll system to the flatness characteristics is more than 25%,which is the main influence of high-order asymmetric flatness defect.The performance of the GWO-LSTM flatness feature prediction model has clear advantages over back propagation and LSTM.The practical applications show that optimizing the force of side support roll system can reduce the high point of high-strength strip flatness from 13.2 to 6 IU and decrease the percentage of low-strength strip flatness defects from 1.6%to 1.2%.This optimization greatly reduced the proportion of flatness defects,improved the accuracy level of flatness control of precision rolling mill,and provided a guarantee for the stable production of thin strip.
文摘The dilatometric curves of Q690 steel at different cooling rates were tested using Gleeble 3800 to study the continuous cooling transformation behavior of high-strength steel with low welding crack sensitivity.The continuous cooling transformation curves of Q690 steel were constructed according to the transformation tem-peratures determined using dilatometric curves and corresponding microstructures at different cooling rates.The results show that the microstructure of Q690 steel remarkably changed with the increase in the cooling rate.The matrix of the steel was ferrite and pearlite when the cooling rate was between 0.1 K/s and 0.5 K/s.With increasing cooling rate, the microstructure of the steel was considerably refined, and the Vickers hardness of the steel increased.When the cooling rate reached 1 K/s, the microstructure of the steel was further refined, and bainite transformation occurred.Polygonal ferrite almost disappeared from the steel when the cooling rate reached 10 K/s, and the matrix was mainly composed of bainite and a small amount of lath martensite.With the increase in the cooling rate, the ferrite decreased and martensite increased in the steel, resulting in higher Vickers hardness.When the cooling rate reached 30 K/s, the microstructure of the tested steel was full martensite matrix.
基金supported by the National Natural Science Foundation of China(No.51774031)the Project funded by China Postdoctoral Science Foundation(No.2023M730230).
文摘A secondary-cooling-segment electromagnetic stirring(S-EMS)experiment was performed at 150 A and 4 Hz to evaluate the effect of S-EMS on solidification characterization near the white band.The upper and lower parts of the white band exhibited average secondary dendritic arm spacing of 205.4 and 214.4μm,respectively.The S-EMS operation resulted in large Lorentz forces and cooling intensity,which could produce additional dendritic arms with low carbon concentrations,leading to local negative segregation.Moreover,a 3D flow-temperature-magnetic coupling numerical model was established.The results revealed that the magnetic induction intensity and Lorentz force were symmetrically distributed along rollers S1 and S2.The average velocity magnitude increased by approximately 42.52%,58.69%,and 64.11%for liquid fractions of 0.7,0.8,and 0.9,respectively.During the S-EMS operation,the Lorentz force may alter the velocity of the solidification front and promote the dissipation of superheat.Additionally,the influence of S-EMS on grain nucleation and growth was investigated using Gibbs free energy theory and component undercooling.Furthermore,a formation model for the white band was established,and the mechanism of white band formation was elucidated according to the changes in the solute-enriched layer,solute precipitation,and diffusion.
基金supported by the National Natural Science Foundation of China(Nos.T2222013,52233008 and 52073203).
文摘Zwitterionic polymers are polymers containing a pair of oppositely charged groups in their repeating units,which facilitate the formation of a hydration layer on the surface through ionic solvation.This strong hydration results in the remarkable properties of zwitterionic polymer hydrogels,including antifouling,lubricating,and anti-freezing capabilities.Owing to these properties,zwitterionic polymer hydrogels have attracted notable attention in biomedical and engineering fields.However,the superhydrophilicity of zwitterionic polymer hydrogels renders them brittle and weak,considerably limiting their use in load-bearing applications.Thus,there is an urgent need to improve the mechanical properties of zwitterionic hydrogels.In this work,we systematically review mechanical enhancement strategies for zwitterionic polymer hydrogels.We cover strate-gies applicable to hybrid and pure high-strength zwitterionic polymer hydrogels.Additionally,we discuss the advantages and limitations of various strength enhancement strategies.
基金supported by the National Natural Science Foundation of China(No.51975147)。
文摘The effects of heat treatment on microstructure and creep properties of β high-strength titanium alloy,Ti-3.5Al-5Mo-6V-3Cr-2Sn-0.5Fe,were studied.After solution treatment at 790℃ and aging treatment(HT1),the microstructure is composed of equiaxedαp phase,β phase,α_(p) phase,and becomes β phase and α_(s) phases after solution treatment at 840℃ and aging treatment(HT2).The creep behavior at 400℃ was analyzed.The stress exponents of both alloys are between 1 and 2,indicating that the diffusional creep mechanism is one of the dominant creep mechanisms.The alloy after HT2 treatment has better creep resistance and a subsequent creep test on this alloy was performed at 450℃ under 400 MPa.The creep fracture has the mixed ductile-brittle characteristics.The phase interfaces can hinder the dislocation movement,and theαs phase can coordinate with the matrix to deform,thereby reducing the occurrence of intragranular cracks.
基金The National Natural Science Foundation of China (No.51102035)
文摘In order to improve the brittleness of high-strength cement mortar,calcium carbonate（CaCO3） whiskers are incorporated to strengthen and toughen the high-strength cement mortar.The compressive strength,flexural strength,split tensile strength and work of fracture are measured.Microstructures and micromechanical behaviors are investigated using scanning electron microscopy.The strengthening and toughening mechanisms and the efficiency of whisker-reinforced high-strength cement mortar are discussed.The results show that the addition of CaCO3 whiskers brings positive effects on the high-strength cement mortar.The strengthening and toughening mechanisms are whisker-cement coalition debonding,whisker peeling,whisker impact breakage and whisker bridging.Crack deflection is one efficient mechanism,but it is hard to be achieved in high-strength cement mortar.And the interfacial bonding strength between whiskers and the cement mortar matrix should be appropriately weak to introduce more crack deflection mechanisms to strengthen and toughen the cement mortar efficiently.
基金Project(GJJ150810)supported by the Research Project of Science and Technology for Jiangxi Province Department of Education,ChinaProject(gf201501001)supported by National Defense Key Discipline Laboratory of Light Alloy Processing Science and Technology,Nanchang Hangkong University,ChinaProject(BSJJ2015015)supported by Doctor Start-up Fund of Jiangxi Science&Technology Normal University,China
文摘The forming quality of high-strength TA18 titanium alloy tube during numerical control bending in changing bending angle β, relative bending radius R/D and tube sizes such as diameter D and wall thickness t was clarified by finite element simulation. The results show that the distribution of wall thickness change ratio Δt and cross section deformation ratio ΔD are very similar under different β; the Δt and ΔD decrease with the increase of R/D, and to obtain the qualified bent tube, the R/D must be greater than 2.0; the wall thinning ratio Δto slightly increases with larger D and t, while the wall thickening ratio Δti and ΔD increase with the larger D and smaller t; the Δto and ΔD firstly decrease and then increase, while the Δti increases, for the same D/t with the increase of D and t.
基金financially supported by the National Basic Research Program of China(No.2010CB630805)the National Natural Science Foundation of China(No.51201036)China Iron&Steel Research Institute Group(No.12060840A)
文摘A new Ti-V-Mo complex microalloyed hot-rolled high-strength steel sheet was developed by controlling a thermo-mechanical controlled processing （TMCP） schedule, in particular with variants in coiling temperature. The effects of coiling temperature （CT） on various hardening mechanisms and mechanical properties of Ti-V-Mo complex mi- croalloyed high-strength low-alloy steels were investigated. The results revealed that the steels are mainly strengthened by a combined effect of ferrite grain refinement hardening and precipitation hardening. The variation in simulated coiling temperature causes a significant difference in strength, which is mainly attributed to different precipitation hardening increment contributions. When the CT is 600 ℃, the experimental steel has the best mechanical properties： ultimate tensile strength （UTS） 1000 MPa, yield strength （YS） 955 MPa and elongation （EL） 17%. Moreover, about 82 wt% of the total precipitates are nano-sized carbide particles with diameter of 1-10 nm, which is randomly dispersed in the ferrite matrix. The nano-sized carbide particles led to a strong precipitation hardening increment up to 310 MPa.
基金financial supports of the National Natural Science Foundation of China (No. 51674079)Anhui Provincial Natural Science Foundation (Nos. KJ2018A0062, KJ2017A128 and KJ2017A066)
文摘Low cycle fatigue behavior of a quenched and tempered high-strength steel(Q960 E) was studied in the strain amplitude ranging from ± 0.5% to ± 1.2% at room temperature. As a result of fatigue loading, the dislocation structural evolution and fracture mechanism were examined and studied by transmission electron microscopy and scanning electron microscopy(SEM). The results showed that this Q960 E steel showed cyclic softening at different strain amplitudes, and the softening tendency was more apparent at strain amplitude of ±(0.6–1.2)% than that at ± 0.5%. The reduction in dislocation density with increasing strain amplitude is responsible for the softening tendency of cyclic stress with the strain amplitude. The material illustrates near-Masing behavior at strain amplitude ranging from ± 0.6% to ± 1.2%. The near-Masing behavior of Q960 E high-strength steel can be the result of stability of martensite lath at different strain amplitudes. Partial transformation from martensite laths to dislocation cells is responsible for the derivation from ideal Masing behavior. In the SEM examination of fracture surfaces, transgranular cracks initiate on the sample surface. Striations can be found during the crack propagation stage.
基金supported by the Foundation of the Ministry of Education(No.WTWER0702)
文摘The effect of high-strength ammonia nitrogen acclimation on sludge activity in sequencing batch reactor （SBR） was investigated. Two batch experiments, RUN1 and RUN2, were conducted with the influent ammonia nitrogen concentrations 60 and 500 mg/L, respectively. The sludges inoculated from RUN1 and RUN2 were used to treat a series of influent with ammonia nitrogen concentrations of 59, 232, 368, 604 and 1152 mg/L. It is found that the activated sludge acclimated to higher ammonia nitrogen concentrations revealed higher COD and NH 4 ＋ -N removal efficiencies, and slower DHA decrease. The results confirmed that the activities of the bacteria in activated sludge in SBR were inhibited by high-strength ammonia nitrogen, whereas the activated sludge acclimated to high-strength ammonia nitrogen showed substantial resistance to inhibition by influents containing high levels of ammonia nitrogen.
基金financially supported by the National Natural Science Foundation of China (No.51474031)
文摘The corrosion resistance and evolution of corrosion products in medium-carbon high-strength spring steels were investigated in a neutral salt spray(5 wt% Na Cl solution). A formation model of γ-Fe OOH and a transformation model describing the conversion of γ-Fe OOH to α-Fe OOH were constructed. The results indicated that, at the initial corrosion stage, the corrosion resistance was gradually improved with the addition of Cr; however, with the addition of alloying element V, the corrosion resistance decreased. These results were attributed mainly to the initial corrosion stage being closely related to the matrix microstructure parameters such as grain-boundary character and dislocation density. After the rust layer was formed at a later corrosion stage, the corrosion resistance was reinforced with the addition of Cr and V because Cr strongly influenced the composition, structure, and morphology of the corrosion products. The results presented herein show that Cr was conducive to the transformation of γ-Fe OOH into α-Fe OOH. Moreover, V and Cr exhibited obvious synergy and were enriched in the inner layer of the corrosion products.
