The low-temperature embrittlement limits the service temperature of ferritic and duplex stainless steels.The effects of alloying elements added to Fe-Cr binary system on the low-temperature embrittlement have been rev...The low-temperature embrittlement limits the service temperature of ferritic and duplex stainless steels.The effects of alloying elements added to Fe-Cr binary system on the low-temperature embrittlement have been reviewed critically.Prior literature on the underlying phase transformation,i.e.,phase separation(PS)and changes of mechanical properties,is surveyed.The available literature indicates that the rate of PS is accelerated by Ni or Co in Fe-Cr binary system.The increased kinetics of PS also lead to an enhanced hardening rate during aging for Ni and Co alloyed Fe-Cr alloys.In low Cr(<17 wt.%)ferritic alloys,the additions of Al or Co can reduce embrittlement because these elements contribute to lowering the driving force for PS.The influence of other alloying elements such as Mo,Cu,Mn,Nb,and Ti is inconclusive but also discussed here.Thermodynamic and kinetic calculations were performed to evaluate current CALPHAD databases and to further investigate the thermodynamic and kinetic reasons for the effect of the additional alloying elements added to Fe-Cr alloy on PS.Some indications were provided for improving physically-based predictions of low-temperature embrittlement as well as opportunities to mitigate the phenomenon by alloying.展开更多
Hydrogen embrittlement(HE)in 2 GPa-grade press-hardened steel(PHS)has posed a great risk to its lightweighting application in automotive crash-resistant components.While conventional slow strain rate tensile tests sho...Hydrogen embrittlement(HE)in 2 GPa-grade press-hardened steel(PHS)has posed a great risk to its lightweighting application in automotive crash-resistant components.While conventional slow strain rate tensile tests show that the precharged hydrogen concentration of 3.5 wppm induces a severe loss in strength and ductility,the high strain rate tests conducted at 1–103 s−1 that simulate the crash condition demonstrate no loss in strength and a minimal loss in ductility.Such strain rate dependency cannot be exclusively explained via hydrogen diffusion and redistribution to susceptible prior austenite grain boundaries,as the tensile testing of precharged samples with jumping strain rates offers a sufficient redistribution period at slow-strain-rate loading,but does not necessarily lead to a high level of HE afterwards.Detailed fractography analysis acknowledges that hydrogen-induced microcracks nucleated within early deformation stages are directly responsible for the high HE susceptibility of all test conditions.A phase-field simulation comprising 2 GPa-grade PHS's microstructure features and the hydrogen diffusion under tested loading conditions is applied.The calculation reveals that the hydrogen redistribution behavior is spatially confined to the crack tip areas but to a much greater extent.It thus facilitates continuous crack growth following the main crack with minimal plastic deformation and avoids branching to form secondary cracks.The combined experiments and modeling highlight the vital role of microcracks in the HE performance of 2 GPa-grade PHS,upon which the safety factor of HE in high-strength martensitic steels shall be established.展开更多
Direct evidence of hydrogen-assisted crack nucleation and propagation associated with the δ phase in the selective laser melted GH4169 superalloy was obtained.The analysis of hydrogen trapping sites using thermal des...Direct evidence of hydrogen-assisted crack nucleation and propagation associated with the δ phase in the selective laser melted GH4169 superalloy was obtained.The analysis of hydrogen trapping sites using thermal desorption spectroscopy revealed that the δ phase exhibits strong hydrogen capture capability,with a hydrogen desorption activation energy of 35.45±2.51 kJ/mol.In addition,spatially resolved hydrogen mapping conducted by scanning Kelvin probe force microscopy and hydrogen microprint technique provided further evidence for the δ phase as a deep hydrogen trapping site.The atomic-scale characterization sufficiently reveals the deformation mechanism of the δ phase induced by dislocation accumulation.Hydrogen-promoted dislocation slip localization facilitates the formation of microvoid defects in the δ phase,which is the main reason for the δ phase fracture,and induces intergranular and transgranular cracks.展开更多
Hydrogen dissolved from the moisture or the wire filler is formed on the surface of welded joint due to the driving of high-energy heat source.The diffused hydrogen in the welded joint could cause hydrogen embrittleme...Hydrogen dissolved from the moisture or the wire filler is formed on the surface of welded joint due to the driving of high-energy heat source.The diffused hydrogen in the welded joint could cause hydrogen embrittlement(HE).The important factors determining the HE resistance of welded joints are microstructure style,dislocation distribution,grains characteristics,precipitate particle,and residual stress.Different welding technologies show various heat sources and heat cycles,which result in different characteristics of fusion zone and heat-affected zone.Thus,the HE fracture behavior of welded joint produced by different welded technologies differs greatly.The current stage of HE behavior of welded joint was reviewed to provide fundamental reference for the scientists and engineers engaging in welding.The appearance of hydrogen atoms in the surface or interior of welded joint could weaken the bonding strength and change the fracture mode from ductile to sudden brittle fracture.Generally,the controlling of filler wire and heat input is a practical route to obtain the excellent welded joint with high HE resistance.The inhibition of hydrogen diffusion via the formation of fine coating and the aggregation of hydrogen atoms via the control of microstructure and precipitates are the effective routes to improve HE resistance.展开更多
Powder bed fusion-laser beam with metals(PBF-LB/M)can be used to manufacture intricate NiTi com-ponents.However,the ductility of NiTi alloys fabricated by PBF-LB/M is generally∼20%less than those made via conventiona...Powder bed fusion-laser beam with metals(PBF-LB/M)can be used to manufacture intricate NiTi com-ponents.However,the ductility of NiTi alloys fabricated by PBF-LB/M is generally∼20%less than those made via conventional processes.Although many heat treatment methods have been proposed,solving this issue has been proven difficult.An intractable problem is the brittleness of PBF-LB/M-fabricated NiTi after solid-solution treatment at 1000°C.By investigating the microstructural and fractography change after heat treatment in the range of 100-1000°C,this study found that this ductile-to-brittle transition stems from abnormal oxygen-containing Ti-rich precipitates being generated in the PBF-LB/M fabricated Ni-rich NiTi.We identified laser processing-induced local oxygen segregation and tiny TiO2(B)particles at the fusion and grain boundaries.During the heat treatment at temperatures above 700°C,these ox-ides decompose due to their low thermal stability.After this decomposition,most oxygen diffuses into the matrix,with titanium remaining in local regions.This process enriches titanium in the interfaces,forming a brittle oxygen-rich Ti2 Ni network that is known to hinder the recrystallization process in heat treatment.Furthermore,when subjected to external loading,these precipitates can induce high misfit levels and local distortion,resulting in brittle fractures along the interfaces.Based on these results,we also propose approaches to avoid high-temperature-induced embrittlement in Ni-rich NiTi.展开更多
In this study,we investigated the correlation between the pre-strain and hydrogen embrittlement(HE)mechanisms in medium-Mn steel.Intercritically annealed Fe-7Mn-0.2C-3Al(wt.%)steel,which showed a two-phase microstruct...In this study,we investigated the correlation between the pre-strain and hydrogen embrittlement(HE)mechanisms in medium-Mn steel.Intercritically annealed Fe-7Mn-0.2C-3Al(wt.%)steel,which showed a two-phase microstructure comprising α ferrite and γR retained austenite,was used as a model alloy.As the pre-strain level increased from 0%to 45%,the volume fraction of γR gradually decreased owing to the strain-inducedα′martensite transformation accompanied by an increase in dislocation density.The HE resistance decreased with increasing the pre-strain level because the sample with a higher pre-strain level revealed a higher amount of dissolved hydrogen,combined with a more extensive brittle fracture region owing to the enhanced diffusion and permeation of hydrogen from the reduced γR fraction.Ad-ditionally,the H-assisted crack in the sample without pre-strain was initiated and propagated from the γR grains when the strain-induced α′phase was formed,because most of the dissolved hydrogen was concentrated in the γR grains,and these grains were predominantly deformed compared to the other phases.However,the pre-strained sample showed more pronounced multiple H-assisted cracking at the constituent phases,such as α and α′,because it exhibited relatively well-dispersed hydrogen atoms and reduced microstrain localization at the γR grains,due to the reduced γR fraction.展开更多
The effect of rare-earth cerium on impurity P-induced embrittlement for an advanced SA508Gr.4N reactor pressure vessels steel is investigated by virtue of microstructural characterization,Auger electron spectroscopy(A...The effect of rare-earth cerium on impurity P-induced embrittlement for an advanced SA508Gr.4N reactor pressure vessels steel is investigated by virtue of microstructural characterization,Auger electron spectroscopy(AES),and spin-polarized density functional theory(DFT)calculations.The ductile-to-brittle transition temperatures(DBTTs)are evaluated by Charpy impact testing,and grain boundary segregation(GBS)of P is quantified by AES.Trace addition of Ce can effectively reduce GBS level of P,thereby substantially decreasing the embrittlement induced by P.A linear correlation between DBTT(℃)and GBS level of P(Cp,at.%)is observed for both undoped and Ce-doped samples,being expressed as DBTT=13.13C_(p)-335.70(undoped)and DBTT=12.67C_(p)-350.78(Ce-doped).In the absence of GBS of P,the incorporation of Ce appears to play a pivotal role in augmenting the intrinsic toughness.These results imply that the impact of Ce on impurity P-induced embrittlement may be attributed to a combination of increasing the intrinsic toughness and lowering GBS of P.DFT calculations indicate that there is a negligible interaction between Ce and P in the ternary alloy,and thus GBS of P and Ce is mainly site-competitive.展开更多
Medium-entropy alloys(MEAs)that exhibit transformation-induced plasticity(TRIP)from face-centered cubic(FCC)to body-centered cubic(BCC)are considered promising for liquid hydrogen environments due to their remarkable ...Medium-entropy alloys(MEAs)that exhibit transformation-induced plasticity(TRIP)from face-centered cubic(FCC)to body-centered cubic(BCC)are considered promising for liquid hydrogen environments due to their remarkable cryogenic strength.Nonetheless,studies on hydrogen embrittlement(HE)in BCC-TRIP MEAs have not been conducted,although the TRIP effect and consequent BCC martensite usually deteriorate HE susceptibility.In these alloys,initial as-quenched martensite alters hydrogen diffusion and trap behavior,and deformation-induced martensitic transformation(DIMT)provides preferred crack propagation sites,which critically affects HE susceptibility.Therefore,this study aims to investigate the HE behav-ior of BCC-TRIP MEAs by designing four V10 Cr_(10)Co_(30)Fe_(50-x)Ni_(x)(x=0,1,2,and 3 at%)MEAs,adjusting both the initial phase constituent and phase metastability.A decreased Ni content leads to a reduced fraction and mechanical stability of FCC,which in turn increases HE susceptibility,as determined through electro-chemical hydrogen pre-charging and slow-strain rate tests The permeation test and thermal desorption analysis reveal that the hydrogen diffusivity and content are affected by initial BCC fraction,interconnectivity of BCC,and refined FCC.As these initial phase constituents differ between the alloys with FCC-and BCC-dominant initial phase,microstructural factors affecting HE are unveiled discretely among these alloy groups by correlation of hydrogen-induced crack behavior with hydrogen diffusion and trap behavior.In alloys with an FCC-dominant initial phase,the initial BCC fraction and DIMT initiation rate emerge as critical factors,rather than the extent of DIMT.For BCC-dominant alloys,the primary contributor is an increase in the initial BCC fraction,rather than the extent or rate of DIMT.The unraveled roles of microstructural factors provide insights into designing HE-resistant BCC-TRIP MEAs.展开更多
The liquid metal embrittlement(LME)of advanced high-strength steels caused by zinc(Zn)has become a critical issue hindering their widespread application in the automotive industry.In this study,atomic-scale simulation...The liquid metal embrittlement(LME)of advanced high-strength steels caused by zinc(Zn)has become a critical issue hindering their widespread application in the automotive industry.In this study,atomic-scale simulations are carried out to elucidate the underlying cause of this phenomenon,namely grain boundary embrittlement due to Zn segregation at iron(Fe)grain boundaries.A machine learning moment tensor interatomic potential for the Fe-Zn binary system is developed,based on which the thermodynamics of grain boundary segregation is evaluated.The yielded segregation energy spectrum of Zn in BCC Fe reveals the quantitative relationship between the average segregation concentration of Zn at Fe grain boundaries and the macroscopic Zn content,temperature,and fraction of grain boundary atoms.It suggests a strong thermodynamic driving force for Zn segregation at the Fe grain boundaries,which correlates directly with the grain boundary energy:high-energy grain boundaries can accommodate a large amount of Zn atoms,while low-energy grain boundaries exhibit a certain degree of repulsion to Zn.Kinetically,Zn enters the grain boundaries more easily through diffusion than by penetration.Nonetheless,the grain boundary embrittlement caused by Zn penetration is more severe than that by Zn diffusion.The embrittlement effect generally increases linearly with the increase in Zn concentration at the grain boundary.Altogether,it suggests that the LME in steels induced by grain boundary segregation of Zn emerges as a combined consequence of Zn melt penetration and solid-state diffusion of Zn atoms.展开更多
Predicting the transition-temperature shift(TTS)induced by neutron irradiation in reactor pressure-vessel(RPV)steels is important for the evaluation and extension of nuclear power-plant lifetimes.Current prediction mo...Predicting the transition-temperature shift(TTS)induced by neutron irradiation in reactor pressure-vessel(RPV)steels is important for the evaluation and extension of nuclear power-plant lifetimes.Current prediction models may fail to properly describe the embrittlement trend curves of Chinese domestic RPV steels with relatively low Cu content.Based on the screened surveillance data of Chinese domestic and similar international RPV steels,we have developed a new fluencedependent model for predicting the irradiation-embrittlement trend.The fast neutron fluence(E>1 MeV)exhibited the highest correlation coefficient with the measured TTS data;thus,it is a crucial parameter in the prediction model.The chemical composition has little relevance to the TTS residual calculated by the fluence-dependent model.The results show that the newly developed model with a simple power-law functional form of the neutron fluence is suitable for predicting the irradiation-embrittlement trend of Chinese domestic RPVs,regardless of the effect of the chemical composition.展开更多
The effects of hydrogen charging time and pressure on the hydrogen embrittlement(HE)susceptibility of X52 pipeline steel material are studied by slow strain rate tensile tests.The fracture morphologies of the specimen...The effects of hydrogen charging time and pressure on the hydrogen embrittlement(HE)susceptibility of X52 pipeline steel material are studied by slow strain rate tensile tests.The fracture morphologies of the specimens are observed by scanning electron microscopy.The HE susceptibility of the X52 pipeline steel material increases with an increase in both hydrogen charging time and hydrogen pressure.At a charging time of 96 h,the HE susceptibility index reaches 45.86%,approximately 3.6 times that at a charging time of 0 h.Similarly,a charging pressure of 4 MPa results in a HE susceptibility index of 31.61%,approximately 2.5 times higher than that at a charging pressure of 0.3 MPa.展开更多
Given the carbon peak and carbon neutrality era,there is an urgent need to develop high-strength steel with remarkable hydrogen embrittlement resistance.This is crucial in enhancing toughness and ensuring the utilizat...Given the carbon peak and carbon neutrality era,there is an urgent need to develop high-strength steel with remarkable hydrogen embrittlement resistance.This is crucial in enhancing toughness and ensuring the utilization of hydrogen in emerging iron and steel materials.Simultaneously,the pursuit of enhanced metallic materials presents a cross-disciplinary scientific and engineering challenge.Developing high-strength,toughened steel with both enhanced strength and hydrogen embrittlement(HE)resistance holds significant theoretical and practical implications.This ensures secure hydrogen utilization and further carbon neutrality objectives within the iron and steel sector.Based on the design principles of high-strength steel HE resistance,this review provides a comprehensive overview of research on designing surface HE resistance and employing nanosized precipitates as intragranular hydrogen traps.It also proposes feasible recommendations and prospects for designing high-strength steel with enhanced HE resistance.展开更多
As a representative of steels available in the market,medium-Mn steel shows vast application prospects in lightweight automobile fields.This review details the research progress of medium-Mn steels,focusing on the fol...As a representative of steels available in the market,medium-Mn steel shows vast application prospects in lightweight automobile fields.This review details the research progress of medium-Mn steels,focusing on the following aspects.The roles of common adding elements,rolling technologies,and various heat treatments on the microstructure and mechanical properties of medium-Mn steel are analyzed,thus pro-viding references for designing tailored medium-Mn steel with excellent performance.Considering that hydrogen embrittlement is a challenge faced in the development of high-strength steel,the hydrogen embrittlement behavior of medium-Mn steel is also discussed,particularly emphasizing the influence of microstructure,hydrogen concentration,strain,etc.Furthermore,practical strategies to improve resistance to hydrogen embrittlement are summarized.Finally,this review provides prospects for the development and research prospects of medium-Mn steel.展开更多
The helium bubbles induced by 14 MeV neutron irradiation can cause intergranular fractures in reduced activation ferritic martensitic steel,which is a candidate structural material for fusion reactors.In order to eluc...The helium bubbles induced by 14 MeV neutron irradiation can cause intergranular fractures in reduced activation ferritic martensitic steel,which is a candidate structural material for fusion reactors.In order to elucidate the susceptibility of different grain boundaries(GBs)to helium-induced embrittlement,the tensile fracture processes of 10 types of GBs with and without helium bubbles in body-centered cubic(bcc)iron at the relevant service temperature of 600 K were investigated via molecular dynamics methods.The results indicate that in the absence of helium bubbles,the GBs studied here can be classified into two distinct categories:brittle GBs and ductile GBs.The atomic scale analysis shows that the plastic deformation of ductile GB at high temperatures originates from complex plastic deformation mechanisms,including the Bain/Burgers path phase transition and deformation twinning,in which the Bain path phase transition is the most dominant plastic deformation mechanism.However,the presence of helium bubbles severely inhibits the plastic deformation channels of the GBs,resulting in a significant decrease in elongation at fractures.For bubble-decorated GBs,the ultimate tensile strength increases with the increase in the misorientation angle.Interestingly,the coherent twin boundary∑3{112}was found to maintain relatively high fracture strength and maximum failure strain under the influence of helium bubbles.展开更多
The aging embrittlement of 30Cr2Ni4MoV steel during service at high temperature has been attributed to the segregation of Si and Mn at grain boundary(GB).We report an alternative mechanism of aging embrittlement of 30...The aging embrittlement of 30Cr2Ni4MoV steel during service at high temperature has been attributed to the segregation of Si and Mn at grain boundary(GB).We report an alternative mechanism of aging embrittlement of 30Cr2Ni4MoV steel.Using atom probe tomography,it is found that the quenched and tempered(QT)30Cr2Ni4MoV steel has already contained obvious Si and Mn segregations at GB,which means that the Si and Mn segregations at GB are not sufficient to induce aging embrittlement.It is discovered for the first time in aged 30Cr2Ni4MoV there newly precipitate many G-phases along GB,and Si and Mn segregations at GB of QT30Cr2Ni4MoV steel are the main reason for the precipitation of G-phase.The hard and brittle G-phase helps to promote crack initiation during impact deformation.Subsequently,the cracks can rapidly propagate along GB due to the distribution of G-phase and the segregation of Si and Mn along the GB,which leads to intergranular cracking and low impact energy as for aged 30Cr2Ni4MoV steel.展开更多
To evaluate the room-temperature hydrogen embrittlement susceptibility(HES) of high-pressure hydrogen storage vessels, a modified slow-strain-rate tensile(MSSRT) testing method was proposed for effectively aligning wi...To evaluate the room-temperature hydrogen embrittlement susceptibility(HES) of high-pressure hydrogen storage vessels, a modified slow-strain-rate tensile(MSSRT) testing method was proposed for effectively aligning with their actual operating conditions. The effectiveness of the MSSRT testing method in evaluating the room-temperature HES of steels under high pressure was validated by comparing the results obtained using the conventional slow strain rate tensile(SSRT) and proposed MSSRT testing methods for 30CrMo steel, which is widely used for manufacturing high-pressure hydrogen storage vessels. The tensile properties and fracture morphologies of 23Cr2Ni4MoV steel were then examined using the MSSRT testing method under 35 MPa hydrogen and nitrogen at room temperature. Results indicate that 35 MPa hydrogen exerted a marginal effect on the tensile properties of 23Cr2Ni4MoV steel at room temperature when considering the MSSRT testing method;moreover, the test specimen basically exhibited macroscopic ductile fracture. Furthermore, obvious surface cracking was observed on the fractured specimen tested under hydrogen, whereas surface cracking was not observed on the fractured specimen tested under nitrogen. Hence, the relative reduction of area and surface cracking are necessary criteria for evaluating the room-temperature HES of steels using the MSSRT testing method. Overall, 23Cr2Ni4MoV steel might be unsuitable for manufacturing high-pressure hydrogen storage vessels.展开更多
Hydrogen dissolved in metals as a result of internal and external hydrogen can affect the mechanical properties of the metals, principally through the interactions between hydrogen and material defects. Multiple pheno...Hydrogen dissolved in metals as a result of internal and external hydrogen can affect the mechanical properties of the metals, principally through the interactions between hydrogen and material defects. Multiple phenomena such as hydrogen dissolution, hydrogen diffusion, hydrogen redistribution and hydrogen interactions with vacancies, dislocations, grain boundaries and other phase interfaces are involved in this process. Consequently, several hydrogen embrittlement(HE) mechanisms have been successively proposed to explain the HE phenomena, with the hydrogen-enhanced decohesion mechanism, hydrogenenhanced localized plasticity mechanism and hydrogen-enhanced strain-induced vacancies being some of the most important. Additionally, to reduce the risk of HE for engineering structural materials in service, surface treatments and microstructural optimization of the alloys have been suggested. In this review, we report on the progress of the studies on HE in metals, with a particular focus on steels. It focuses on four aspects:(1) hydrogen diffusion behavior;(2) hydrogen characterization methods;(3) HE mechanisms;and(4) the prevention of HE. The strengths and weaknesses of the current HE mechanisms and HE prevention methods are discussed, and specific research directions for further investigation of fundamental HE mechanisms and methods for preventing HE failure are identified.展开更多
The constant embrittlement curve for constant segregation concentration on grain boundary of impurity element P and relationship between equilibrium grain boundary segregation concentration and operation time for 2.25...The constant embrittlement curve for constant segregation concentration on grain boundary of impurity element P and relationship between equilibrium grain boundary segregation concentration and operation time for 2.25Cr-1Mo steel were derived based on the theory of equilibrium grain boundary segregation.The mechanism of step-cooling test and mechanism of de-embrittlement for 2.25Cr-1Mo steel were explained.The segregation rate will increase but equilibrium grain boundary segregation concentration of impurity element P will decrease as temperature increases in the range of temper embrittlement temperature.There is one critical temperature of embrittlement corresponding to each embrittlement degree.When the further heat treating temperature is higher than critical temperature,the heat treating will become a de-embrittlement process;otherwise,it will be an embrittlement process.The critical temperature of embrittlement will shift to the direction of low temperature as further embrittlement.As a result,some stages of step-cooling test would change into a de-embrittlement process.The grain boundary desegregation function of impurity element P was deduced based on the theory of element diffusion,and the theoretical calculation and experimental results show that the further embrittlement or de-embrittlement mechanism can be interpreted qualitatively and quantitatively by combining the theory of equilibrium grain boundary segregation with constant embrittlement curve.展开更多
The environmental embrittlement of intermetallics Co3Ti, Ni3Al, Fe3Al and TiAl has been investigated by measuring the tensile properties in oxygen and hydrogen at 2×l0-4/s strain rate. The results show that the ...The environmental embrittlement of intermetallics Co3Ti, Ni3Al, Fe3Al and TiAl has been investigated by measuring the tensile properties in oxygen and hydrogen at 2×l0-4/s strain rate. The results show that the hydrogen embrittlement factor in gaseous hydrogen (IH2 ) defined as[(δO2 -δH2 ) / δH2, ] ×l00% of above mentioned four intermetallics is decreased in the sequence of Co3Ti> Ni3Al> Fe3Al> TiAl. This phenomena can be explained by the different catalytic reaction on the surface of matrix metals (such as Ni, Co, Fe, Ti) with decomposition of H2 into atommic hydrogen, leading to hydrogen embrittlement.展开更多
2.25Cr–1Mo–0.25V base metal(BM)and welded metal(WM)with different temper embrittlement states were obtained by isothermal temper embrittlement test.The ductile–brittle transition temperature and the carbide size of...2.25Cr–1Mo–0.25V base metal(BM)and welded metal(WM)with different temper embrittlement states were obtained by isothermal temper embrittlement test.The ductile–brittle transition temperature and the carbide size of temper embrittled 2.25Cr–1Mo–0.25V BM and WM increased with the isothermal tempering time.The increase in temper embrittlement time leads to a decrease in yield strength(YS)and ultimate tensile strength(UTS).Hydrogen embrittlement(HE)can decrease the ductility and increase YS and UTS of the material.The hydrogen embrittlement sensitivity and microstructure analysis both show a combined effect of HE and temper embrittlement.The deeper the temper embrittlement,the more sensitive the material to HE.When the hydrogen content in the material is low,the WM is less susceptible to HE due to its welding defects.展开更多
基金support from the China Scholarship Council(CSC No.201700260207)Swedish Iron and Steel Research Office(Jernkontoret)The EIT RawMaterials Upscaling project EndureIT(No.18317)is acknowledged by PH and WM for financial support.
文摘The low-temperature embrittlement limits the service temperature of ferritic and duplex stainless steels.The effects of alloying elements added to Fe-Cr binary system on the low-temperature embrittlement have been reviewed critically.Prior literature on the underlying phase transformation,i.e.,phase separation(PS)and changes of mechanical properties,is surveyed.The available literature indicates that the rate of PS is accelerated by Ni or Co in Fe-Cr binary system.The increased kinetics of PS also lead to an enhanced hardening rate during aging for Ni and Co alloyed Fe-Cr alloys.In low Cr(<17 wt.%)ferritic alloys,the additions of Al or Co can reduce embrittlement because these elements contribute to lowering the driving force for PS.The influence of other alloying elements such as Mo,Cu,Mn,Nb,and Ti is inconclusive but also discussed here.Thermodynamic and kinetic calculations were performed to evaluate current CALPHAD databases and to further investigate the thermodynamic and kinetic reasons for the effect of the additional alloying elements added to Fe-Cr alloy on PS.Some indications were provided for improving physically-based predictions of low-temperature embrittlement as well as opportunities to mitigate the phenomenon by alloying.
基金support from the National Natural Science Foundation of China(No.52130102)the National Key Research and Development Program of China(No.2019YFA0209900)+5 种基金the Research Grants Council of Hong Kong(No.R7066–18)the Guangzhou Municipal Science and Technology Project(No.202007020007)the Guangdong Basic and Applied Basic Research Foundation of China(No.2020B1515130007)Lunhua He and Mingxin Huang acknowledge the support from the International Partnership Program of the Chinese Academy of Sciences(No.113111KYSB20190029)the key program of the Chinese Academy of Sciences(CAS)China Spallation Neutron Source(CSNS)is acknowledged for supporting neutron diffraction experiments using the General Purpose Powder Diffractometer(GPPD).
文摘Hydrogen embrittlement(HE)in 2 GPa-grade press-hardened steel(PHS)has posed a great risk to its lightweighting application in automotive crash-resistant components.While conventional slow strain rate tensile tests show that the precharged hydrogen concentration of 3.5 wppm induces a severe loss in strength and ductility,the high strain rate tests conducted at 1–103 s−1 that simulate the crash condition demonstrate no loss in strength and a minimal loss in ductility.Such strain rate dependency cannot be exclusively explained via hydrogen diffusion and redistribution to susceptible prior austenite grain boundaries,as the tensile testing of precharged samples with jumping strain rates offers a sufficient redistribution period at slow-strain-rate loading,but does not necessarily lead to a high level of HE afterwards.Detailed fractography analysis acknowledges that hydrogen-induced microcracks nucleated within early deformation stages are directly responsible for the high HE susceptibility of all test conditions.A phase-field simulation comprising 2 GPa-grade PHS's microstructure features and the hydrogen diffusion under tested loading conditions is applied.The calculation reveals that the hydrogen redistribution behavior is spatially confined to the crack tip areas but to a much greater extent.It thus facilitates continuous crack growth following the main crack with minimal plastic deformation and avoids branching to form secondary cracks.The combined experiments and modeling highlight the vital role of microcracks in the HE performance of 2 GPa-grade PHS,upon which the safety factor of HE in high-strength martensitic steels shall be established.
基金financially supported by the National Natural Science Foundation of China(Nos.U21A2044 and 52201060)Science Center for Gas Turbine Project(No.P2022-B-Ⅳ-008-001)China Postdoctoral Science Foundation(Nos.BX20220035 and 2022M710347).
文摘Direct evidence of hydrogen-assisted crack nucleation and propagation associated with the δ phase in the selective laser melted GH4169 superalloy was obtained.The analysis of hydrogen trapping sites using thermal desorption spectroscopy revealed that the δ phase exhibits strong hydrogen capture capability,with a hydrogen desorption activation energy of 35.45±2.51 kJ/mol.In addition,spatially resolved hydrogen mapping conducted by scanning Kelvin probe force microscopy and hydrogen microprint technique provided further evidence for the δ phase as a deep hydrogen trapping site.The atomic-scale characterization sufficiently reveals the deformation mechanism of the δ phase induced by dislocation accumulation.Hydrogen-promoted dislocation slip localization facilitates the formation of microvoid defects in the δ phase,which is the main reason for the δ phase fracture,and induces intergranular and transgranular cracks.
基金supported by Postgraduate Research&Practice Innovation Program of Jiangsu Province(No.SJCX24_2524)National Natural Science Foundation of China(No.52005228).
文摘Hydrogen dissolved from the moisture or the wire filler is formed on the surface of welded joint due to the driving of high-energy heat source.The diffused hydrogen in the welded joint could cause hydrogen embrittlement(HE).The important factors determining the HE resistance of welded joints are microstructure style,dislocation distribution,grains characteristics,precipitate particle,and residual stress.Different welding technologies show various heat sources and heat cycles,which result in different characteristics of fusion zone and heat-affected zone.Thus,the HE fracture behavior of welded joint produced by different welded technologies differs greatly.The current stage of HE behavior of welded joint was reviewed to provide fundamental reference for the scientists and engineers engaging in welding.The appearance of hydrogen atoms in the surface or interior of welded joint could weaken the bonding strength and change the fracture mode from ductile to sudden brittle fracture.Generally,the controlling of filler wire and heat input is a practical route to obtain the excellent welded joint with high HE resistance.The inhibition of hydrogen diffusion via the formation of fine coating and the aggregation of hydrogen atoms via the control of microstructure and precipitates are the effective routes to improve HE resistance.
基金supported by the National Key R&D Program of China(No.2022YFB4600700)The authors gratefully acknowledge the support from the Shenzhen Sci-ence and Technology Innovation Commission through awards(Nos.JCYJ20210324104414040,20220530114400001,and 20220815150609002)+3 种基金Shuai Wang acknowledges support from the Key-Area Research Project of the Guangdong Province Department of Education(No.2022ZDZX3021)the High Level of Special Funds(Nos.G03034K001 and G03034K003)Jiang Yi acknowledges the support from the Guangdong Basic and Applied Basic Research Foundation through awards(No.2024A1515010358)All authors gratefully acknowledge the assistance from Dr.Yang Qiu and Dr.Dongsheng He at SUStech Core Research Facilities.We thank the electron microscope center of KAIPLE Co.Ltd.(Changsha)for the support of microstructural characterizations.
文摘Powder bed fusion-laser beam with metals(PBF-LB/M)can be used to manufacture intricate NiTi com-ponents.However,the ductility of NiTi alloys fabricated by PBF-LB/M is generally∼20%less than those made via conventional processes.Although many heat treatment methods have been proposed,solving this issue has been proven difficult.An intractable problem is the brittleness of PBF-LB/M-fabricated NiTi after solid-solution treatment at 1000°C.By investigating the microstructural and fractography change after heat treatment in the range of 100-1000°C,this study found that this ductile-to-brittle transition stems from abnormal oxygen-containing Ti-rich precipitates being generated in the PBF-LB/M fabricated Ni-rich NiTi.We identified laser processing-induced local oxygen segregation and tiny TiO2(B)particles at the fusion and grain boundaries.During the heat treatment at temperatures above 700°C,these ox-ides decompose due to their low thermal stability.After this decomposition,most oxygen diffuses into the matrix,with titanium remaining in local regions.This process enriches titanium in the interfaces,forming a brittle oxygen-rich Ti2 Ni network that is known to hinder the recrystallization process in heat treatment.Furthermore,when subjected to external loading,these precipitates can induce high misfit levels and local distortion,resulting in brittle fractures along the interfaces.Based on these results,we also propose approaches to avoid high-temperature-induced embrittlement in Ni-rich NiTi.
基金supported by the Korea Institute for Advancement of Technology(KIAT)grant funded by the Korean Government(MOTIE)(P0023676,HRD Program for Industrial Innovation)the National Research Foundation of Korea(NRF)(No.2021R1A6A3A13045008).
文摘In this study,we investigated the correlation between the pre-strain and hydrogen embrittlement(HE)mechanisms in medium-Mn steel.Intercritically annealed Fe-7Mn-0.2C-3Al(wt.%)steel,which showed a two-phase microstructure comprising α ferrite and γR retained austenite,was used as a model alloy.As the pre-strain level increased from 0%to 45%,the volume fraction of γR gradually decreased owing to the strain-inducedα′martensite transformation accompanied by an increase in dislocation density.The HE resistance decreased with increasing the pre-strain level because the sample with a higher pre-strain level revealed a higher amount of dissolved hydrogen,combined with a more extensive brittle fracture region owing to the enhanced diffusion and permeation of hydrogen from the reduced γR fraction.Ad-ditionally,the H-assisted crack in the sample without pre-strain was initiated and propagated from the γR grains when the strain-induced α′phase was formed,because most of the dissolved hydrogen was concentrated in the γR grains,and these grains were predominantly deformed compared to the other phases.However,the pre-strained sample showed more pronounced multiple H-assisted cracking at the constituent phases,such as α and α′,because it exhibited relatively well-dispersed hydrogen atoms and reduced microstrain localization at the γR grains,due to the reduced γR fraction.
基金supported by the China Postdoctoral Science Foundation(No.2023M740973)the Shenzhen Polytechnic University Research Fund,China(No.6023310017K)the National Natural Science Foundation of China(Nos.52071088 and 51871064).
文摘The effect of rare-earth cerium on impurity P-induced embrittlement for an advanced SA508Gr.4N reactor pressure vessels steel is investigated by virtue of microstructural characterization,Auger electron spectroscopy(AES),and spin-polarized density functional theory(DFT)calculations.The ductile-to-brittle transition temperatures(DBTTs)are evaluated by Charpy impact testing,and grain boundary segregation(GBS)of P is quantified by AES.Trace addition of Ce can effectively reduce GBS level of P,thereby substantially decreasing the embrittlement induced by P.A linear correlation between DBTT(℃)and GBS level of P(Cp,at.%)is observed for both undoped and Ce-doped samples,being expressed as DBTT=13.13C_(p)-335.70(undoped)and DBTT=12.67C_(p)-350.78(Ce-doped).In the absence of GBS of P,the incorporation of Ce appears to play a pivotal role in augmenting the intrinsic toughness.These results imply that the impact of Ce on impurity P-induced embrittlement may be attributed to a combination of increasing the intrinsic toughness and lowering GBS of P.DFT calculations indicate that there is a negligible interaction between Ce and P in the ternary alloy,and thus GBS of P and Ce is mainly site-competitive.
基金supported by the Korea Institute for Advance-ment of Technology(KIAT)grant funded by the Korea Government(MOTIE)(HRD Program for Industrial Innovation)(No.P0023676)the National Research Foundation of Korea(NRF)grant funded by the Korea government(MSIT)(Nos.NRF-2022R1A5A1030054 and RS-2023-00281508).
文摘Medium-entropy alloys(MEAs)that exhibit transformation-induced plasticity(TRIP)from face-centered cubic(FCC)to body-centered cubic(BCC)are considered promising for liquid hydrogen environments due to their remarkable cryogenic strength.Nonetheless,studies on hydrogen embrittlement(HE)in BCC-TRIP MEAs have not been conducted,although the TRIP effect and consequent BCC martensite usually deteriorate HE susceptibility.In these alloys,initial as-quenched martensite alters hydrogen diffusion and trap behavior,and deformation-induced martensitic transformation(DIMT)provides preferred crack propagation sites,which critically affects HE susceptibility.Therefore,this study aims to investigate the HE behav-ior of BCC-TRIP MEAs by designing four V10 Cr_(10)Co_(30)Fe_(50-x)Ni_(x)(x=0,1,2,and 3 at%)MEAs,adjusting both the initial phase constituent and phase metastability.A decreased Ni content leads to a reduced fraction and mechanical stability of FCC,which in turn increases HE susceptibility,as determined through electro-chemical hydrogen pre-charging and slow-strain rate tests The permeation test and thermal desorption analysis reveal that the hydrogen diffusivity and content are affected by initial BCC fraction,interconnectivity of BCC,and refined FCC.As these initial phase constituents differ between the alloys with FCC-and BCC-dominant initial phase,microstructural factors affecting HE are unveiled discretely among these alloy groups by correlation of hydrogen-induced crack behavior with hydrogen diffusion and trap behavior.In alloys with an FCC-dominant initial phase,the initial BCC fraction and DIMT initiation rate emerge as critical factors,rather than the extent of DIMT.For BCC-dominant alloys,the primary contributor is an increase in the initial BCC fraction,rather than the extent or rate of DIMT.The unraveled roles of microstructural factors provide insights into designing HE-resistant BCC-TRIP MEAs.
基金financially supported by the National Natural Science Foundation of China(No.52071204)Natural Science Foundation of Shanghai Municipal(No.22ZR1428700)SJTU Kunpeng&Ascend Center of Excellence,and MaGIC of Shanghai Jiao Tong University.
文摘The liquid metal embrittlement(LME)of advanced high-strength steels caused by zinc(Zn)has become a critical issue hindering their widespread application in the automotive industry.In this study,atomic-scale simulations are carried out to elucidate the underlying cause of this phenomenon,namely grain boundary embrittlement due to Zn segregation at iron(Fe)grain boundaries.A machine learning moment tensor interatomic potential for the Fe-Zn binary system is developed,based on which the thermodynamics of grain boundary segregation is evaluated.The yielded segregation energy spectrum of Zn in BCC Fe reveals the quantitative relationship between the average segregation concentration of Zn at Fe grain boundaries and the macroscopic Zn content,temperature,and fraction of grain boundary atoms.It suggests a strong thermodynamic driving force for Zn segregation at the Fe grain boundaries,which correlates directly with the grain boundary energy:high-energy grain boundaries can accommodate a large amount of Zn atoms,while low-energy grain boundaries exhibit a certain degree of repulsion to Zn.Kinetically,Zn enters the grain boundaries more easily through diffusion than by penetration.Nonetheless,the grain boundary embrittlement caused by Zn penetration is more severe than that by Zn diffusion.The embrittlement effect generally increases linearly with the increase in Zn concentration at the grain boundary.Altogether,it suggests that the LME in steels induced by grain boundary segregation of Zn emerges as a combined consequence of Zn melt penetration and solid-state diffusion of Zn atoms.
基金supported by the National Key R&D Program of China (No. 2019YFB1900901)the Fundamental Research Funds for the Central Universities (No. 2021MS032)
文摘Predicting the transition-temperature shift(TTS)induced by neutron irradiation in reactor pressure-vessel(RPV)steels is important for the evaluation and extension of nuclear power-plant lifetimes.Current prediction models may fail to properly describe the embrittlement trend curves of Chinese domestic RPV steels with relatively low Cu content.Based on the screened surveillance data of Chinese domestic and similar international RPV steels,we have developed a new fluencedependent model for predicting the irradiation-embrittlement trend.The fast neutron fluence(E>1 MeV)exhibited the highest correlation coefficient with the measured TTS data;thus,it is a crucial parameter in the prediction model.The chemical composition has little relevance to the TTS residual calculated by the fluence-dependent model.The results show that the newly developed model with a simple power-law functional form of the neutron fluence is suitable for predicting the irradiation-embrittlement trend of Chinese domestic RPVs,regardless of the effect of the chemical composition.
基金This work was supported by the National Key R&D Program of China(2021YFB4001601)the Youth Innovation Promotion Association CAS(2022187).
文摘The effects of hydrogen charging time and pressure on the hydrogen embrittlement(HE)susceptibility of X52 pipeline steel material are studied by slow strain rate tensile tests.The fracture morphologies of the specimens are observed by scanning electron microscopy.The HE susceptibility of the X52 pipeline steel material increases with an increase in both hydrogen charging time and hydrogen pressure.At a charging time of 96 h,the HE susceptibility index reaches 45.86%,approximately 3.6 times that at a charging time of 0 h.Similarly,a charging pressure of 4 MPa results in a HE susceptibility index of 31.61%,approximately 2.5 times higher than that at a charging pressure of 0.3 MPa.
基金the National Key Research and Development Program of China(No.2022YFB3709000)the National Natural Science Foundation of China(Nos.52201060 and 51922002)+2 种基金the China Postdoctoral Science Foundation(Nos.BX20220035 and 2022M710347)Science Center for Gas Turbine Project(No.P2022-B-IV-008-001)the Open Fund of State Key Laboratory of New Metal Materials,University of Science and Technology Beijing(No.2022Z-18)。
文摘Given the carbon peak and carbon neutrality era,there is an urgent need to develop high-strength steel with remarkable hydrogen embrittlement resistance.This is crucial in enhancing toughness and ensuring the utilization of hydrogen in emerging iron and steel materials.Simultaneously,the pursuit of enhanced metallic materials presents a cross-disciplinary scientific and engineering challenge.Developing high-strength,toughened steel with both enhanced strength and hydrogen embrittlement(HE)resistance holds significant theoretical and practical implications.This ensures secure hydrogen utilization and further carbon neutrality objectives within the iron and steel sector.Based on the design principles of high-strength steel HE resistance,this review provides a comprehensive overview of research on designing surface HE resistance and employing nanosized precipitates as intragranular hydrogen traps.It also proposes feasible recommendations and prospects for designing high-strength steel with enhanced HE resistance.
基金the financial support received from the National Natural Science Foundation of China(Grant No.U1964204).
文摘As a representative of steels available in the market,medium-Mn steel shows vast application prospects in lightweight automobile fields.This review details the research progress of medium-Mn steels,focusing on the following aspects.The roles of common adding elements,rolling technologies,and various heat treatments on the microstructure and mechanical properties of medium-Mn steel are analyzed,thus pro-viding references for designing tailored medium-Mn steel with excellent performance.Considering that hydrogen embrittlement is a challenge faced in the development of high-strength steel,the hydrogen embrittlement behavior of medium-Mn steel is also discussed,particularly emphasizing the influence of microstructure,hydrogen concentration,strain,etc.Furthermore,practical strategies to improve resistance to hydrogen embrittlement are summarized.Finally,this review provides prospects for the development and research prospects of medium-Mn steel.
基金supported by the National Natural Science Foundation of China(Nos.12175231 and 11805131)Anhui Natural Science Foundation of China(No.2108085J05)+1 种基金the National Key Research and Development Plan of China(No.2018YFE0307101)the Collaborative Innovation Program of the Hefei Science Center,CAS(Nos.2021HSC-CIP020 and 2022HSC-CIP009)。
文摘The helium bubbles induced by 14 MeV neutron irradiation can cause intergranular fractures in reduced activation ferritic martensitic steel,which is a candidate structural material for fusion reactors.In order to elucidate the susceptibility of different grain boundaries(GBs)to helium-induced embrittlement,the tensile fracture processes of 10 types of GBs with and without helium bubbles in body-centered cubic(bcc)iron at the relevant service temperature of 600 K were investigated via molecular dynamics methods.The results indicate that in the absence of helium bubbles,the GBs studied here can be classified into two distinct categories:brittle GBs and ductile GBs.The atomic scale analysis shows that the plastic deformation of ductile GB at high temperatures originates from complex plastic deformation mechanisms,including the Bain/Burgers path phase transition and deformation twinning,in which the Bain path phase transition is the most dominant plastic deformation mechanism.However,the presence of helium bubbles severely inhibits the plastic deformation channels of the GBs,resulting in a significant decrease in elongation at fractures.For bubble-decorated GBs,the ultimate tensile strength increases with the increase in the misorientation angle.Interestingly,the coherent twin boundary∑3{112}was found to maintain relatively high fracture strength and maximum failure strain under the influence of helium bubbles.
基金supported by the Youth Innovation Promotion Association CAS(No.Y2021059)the LingChuang Research Project of China National Nuclear Corporation,the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDA28040200)+1 种基金the Liaoning Unveiling and Commanding Program(2022JH1/10400017)the Innovation Foundation of Institute of Metal Research,CAS(No.2022-PY13).
文摘The aging embrittlement of 30Cr2Ni4MoV steel during service at high temperature has been attributed to the segregation of Si and Mn at grain boundary(GB).We report an alternative mechanism of aging embrittlement of 30Cr2Ni4MoV steel.Using atom probe tomography,it is found that the quenched and tempered(QT)30Cr2Ni4MoV steel has already contained obvious Si and Mn segregations at GB,which means that the Si and Mn segregations at GB are not sufficient to induce aging embrittlement.It is discovered for the first time in aged 30Cr2Ni4MoV there newly precipitate many G-phases along GB,and Si and Mn segregations at GB of QT30Cr2Ni4MoV steel are the main reason for the precipitation of G-phase.The hard and brittle G-phase helps to promote crack initiation during impact deformation.Subsequently,the cracks can rapidly propagate along GB due to the distribution of G-phase and the segregation of Si and Mn along the GB,which leads to intergranular cracking and low impact energy as for aged 30Cr2Ni4MoV steel.
基金Supported by National Key Research and Development Program of China (Grant No. 2023YFB3408300)the Doctoral Science and Technology Foundation of Hefei General Machinery Research Institute Co.Ltd.(Grant No. 2023010792)。
文摘To evaluate the room-temperature hydrogen embrittlement susceptibility(HES) of high-pressure hydrogen storage vessels, a modified slow-strain-rate tensile(MSSRT) testing method was proposed for effectively aligning with their actual operating conditions. The effectiveness of the MSSRT testing method in evaluating the room-temperature HES of steels under high pressure was validated by comparing the results obtained using the conventional slow strain rate tensile(SSRT) and proposed MSSRT testing methods for 30CrMo steel, which is widely used for manufacturing high-pressure hydrogen storage vessels. The tensile properties and fracture morphologies of 23Cr2Ni4MoV steel were then examined using the MSSRT testing method under 35 MPa hydrogen and nitrogen at room temperature. Results indicate that 35 MPa hydrogen exerted a marginal effect on the tensile properties of 23Cr2Ni4MoV steel at room temperature when considering the MSSRT testing method;moreover, the test specimen basically exhibited macroscopic ductile fracture. Furthermore, obvious surface cracking was observed on the fractured specimen tested under hydrogen, whereas surface cracking was not observed on the fractured specimen tested under nitrogen. Hence, the relative reduction of area and surface cracking are necessary criteria for evaluating the room-temperature HES of steels using the MSSRT testing method. Overall, 23Cr2Ni4MoV steel might be unsuitable for manufacturing high-pressure hydrogen storage vessels.
基金the National Natural Science Foundation of China(No.51505477)the Guangdong Provincial Key S&T Special Project(Nos.2017B020235001 and 20198010943001)+1 种基金the Guangdong Education Department Fund(No.2016KQNCX005)basic start-up fund of Sun-Yat Sen University(45000-18841218)。
文摘Hydrogen dissolved in metals as a result of internal and external hydrogen can affect the mechanical properties of the metals, principally through the interactions between hydrogen and material defects. Multiple phenomena such as hydrogen dissolution, hydrogen diffusion, hydrogen redistribution and hydrogen interactions with vacancies, dislocations, grain boundaries and other phase interfaces are involved in this process. Consequently, several hydrogen embrittlement(HE) mechanisms have been successively proposed to explain the HE phenomena, with the hydrogen-enhanced decohesion mechanism, hydrogenenhanced localized plasticity mechanism and hydrogen-enhanced strain-induced vacancies being some of the most important. Additionally, to reduce the risk of HE for engineering structural materials in service, surface treatments and microstructural optimization of the alloys have been suggested. In this review, we report on the progress of the studies on HE in metals, with a particular focus on steels. It focuses on four aspects:(1) hydrogen diffusion behavior;(2) hydrogen characterization methods;(3) HE mechanisms;and(4) the prevention of HE. The strengths and weaknesses of the current HE mechanisms and HE prevention methods are discussed, and specific research directions for further investigation of fundamental HE mechanisms and methods for preventing HE failure are identified.
基金Item Sponsored by Graduate Student Scientific Innovation Project of Jiangsu Province of China(CX09B_131Z)
文摘The constant embrittlement curve for constant segregation concentration on grain boundary of impurity element P and relationship between equilibrium grain boundary segregation concentration and operation time for 2.25Cr-1Mo steel were derived based on the theory of equilibrium grain boundary segregation.The mechanism of step-cooling test and mechanism of de-embrittlement for 2.25Cr-1Mo steel were explained.The segregation rate will increase but equilibrium grain boundary segregation concentration of impurity element P will decrease as temperature increases in the range of temper embrittlement temperature.There is one critical temperature of embrittlement corresponding to each embrittlement degree.When the further heat treating temperature is higher than critical temperature,the heat treating will become a de-embrittlement process;otherwise,it will be an embrittlement process.The critical temperature of embrittlement will shift to the direction of low temperature as further embrittlement.As a result,some stages of step-cooling test would change into a de-embrittlement process.The grain boundary desegregation function of impurity element P was deduced based on the theory of element diffusion,and the theoretical calculation and experimental results show that the further embrittlement or de-embrittlement mechanism can be interpreted qualitatively and quantitatively by combining the theory of equilibrium grain boundary segregation with constant embrittlement curve.
文摘The environmental embrittlement of intermetallics Co3Ti, Ni3Al, Fe3Al and TiAl has been investigated by measuring the tensile properties in oxygen and hydrogen at 2×l0-4/s strain rate. The results show that the hydrogen embrittlement factor in gaseous hydrogen (IH2 ) defined as[(δO2 -δH2 ) / δH2, ] ×l00% of above mentioned four intermetallics is decreased in the sequence of Co3Ti> Ni3Al> Fe3Al> TiAl. This phenomena can be explained by the different catalytic reaction on the surface of matrix metals (such as Ni, Co, Fe, Ti) with decomposition of H2 into atommic hydrogen, leading to hydrogen embrittlement.
基金the financial supports of National Key R&D Program of China(No.2018YFC0808800).
文摘2.25Cr–1Mo–0.25V base metal(BM)and welded metal(WM)with different temper embrittlement states were obtained by isothermal temper embrittlement test.The ductile–brittle transition temperature and the carbide size of temper embrittled 2.25Cr–1Mo–0.25V BM and WM increased with the isothermal tempering time.The increase in temper embrittlement time leads to a decrease in yield strength(YS)and ultimate tensile strength(UTS).Hydrogen embrittlement(HE)can decrease the ductility and increase YS and UTS of the material.The hydrogen embrittlement sensitivity and microstructure analysis both show a combined effect of HE and temper embrittlement.The deeper the temper embrittlement,the more sensitive the material to HE.When the hydrogen content in the material is low,the WM is less susceptible to HE due to its welding defects.
