Austenitic stainless steel(ASS)is a common material used in high-pressure hydrogen systems.Prolonged exposure to high-pressure hydrogen can cause hydrogen embrittlement(HE),raising significant safety concerns.Selectiv...Austenitic stainless steel(ASS)is a common material used in high-pressure hydrogen systems.Prolonged exposure to high-pressure hydrogen can cause hydrogen embrittlement(HE),raising significant safety concerns.Selective Laser Melting(SLM),known for its high precision,is a promising additive manufacturing technology that has been widely adopted across various industries.Studies have reported that under certain SLM manufacturing conditions and process parameters,the HE resistance of SLM ASS is significantly better than that of conventionally manufactured(CM)ASS,showing great potential for application in high-pressure hydrogen systems.Thus,studying the HE of SLM ASS is crucial for further improving the safety of high-pressure hydrogen systems.This paper provides an overview of the SLM process,reviews the mechanisms of HE and their synergistic effects,and analyzes the HE characteristics of SLM ASS.Additionally,it examines the influence of unique microstructures and SLM process variables on HE of SLM ASS and offers recommendations for future research to enhance the safety of high-pressure hydrogen systems.展开更多
This work investigated the original microstructure of cold-worked alumina-forming austenitic steel,along with its precipitation and dissolution corrosion behaviors in lead-bismuth eutectic with 10-8 wt.%oxygen at 600...This work investigated the original microstructure of cold-worked alumina-forming austenitic steel,along with its precipitation and dissolution corrosion behaviors in lead-bismuth eutectic with 10-8 wt.%oxygen at 600℃,using solution-annealed steel for comparison.Anomalously,cold-worked steel presented milder corrosion compared to solution-annealed steel,with average corrosion depths of 314.3 and 401.0μm after 1700 h exposure.Cold working-induced de-twinning transformed the annealing twin boundaries into normal high-angle grain boundaries(NGBs),increasing NGBs proportion from 36%to 89%.The increased NGBs provided more nucleation sites for intergranular barriers composed of alternate NiAl and M23C6 precipitates,thus better obstructing the dissolution attack.展开更多
High-temperature long-term microstructural instability is an urgent problem to be solved for high-silicon Fe-Cr-Ni austenitic stainless steel.In this study,we propose a novel strategy to improve the microstructural th...High-temperature long-term microstructural instability is an urgent problem to be solved for high-silicon Fe-Cr-Ni austenitic stainless steel.In this study,we propose a novel strategy to improve the microstructural thermal stability of Si-modified Fe-Cr-Ni austenitic steels via N doping.The microstructural evolution behaviors of N-free and N-doping steels were systematically investigated during aging at 783-923 K.The findings indicate that N doping results in substantial grain refinement and improves the strength of the steel.Importantly,it is found that N doping inhibits the premature segregation of Ni,Cr,Si,and Mo at grain boundaries by reducing their diffusion coefficients,thereby suppressing the generation of intergranular M_(6) C carbides during aging at 783 K,achieving superior thermal stability.In contrast,N-free steel exhibits microstructural instability due to theγ→M_(6) C+ferrite transformation during aging at 783 K.At 823 and 873 K,it is concluded that the diffusion of alloying elements accelerates,resulting in the formation of M_(6) C and ferrite in N-doping steel and subsequent microstructural instability.It contributes to a decrease in impact toughness,as microcracks tend to form at the ferrite domain and M_(6) C/ferrite interface with high strain concentration.Notably,when aged at 923 K,N-doping steel exhibits a cellular structure composed of M_(23) C_(6) and M_(6) C carbonitrides,with Nb(C,N)serving as the nucleation site within the grains.This differs from the intragranularχ-phase observed in N-free steel,as the nucleation driving force of theχ-phase decreases with an increasing N content.The study offers valuable insights for the development of fastener materials intended for utilization in lead-cooled fast reactors.展开更多
The effects of niobium on the high-temperature oxidation resistance of austenitic stainless steel were systematically investigated.Two austenitic stainless steels with different Nb contents were prepared and exposed t...The effects of niobium on the high-temperature oxidation resistance of austenitic stainless steel were systematically investigated.Two austenitic stainless steels with different Nb contents were prepared and exposed to air at 850℃for 200 h.Results show that Nb positively affects the high-temperature oxidation resistance of austenitic stainless steels.The matrix organization of austenitic stainless steels with added niobium does not change,while the austenitic grain size is significantly refined,and it also promoted the release of internal stresses in the oxide film,which in turn improved the integrity of the oxide film and adhesion to the substrate.In addition,with the addition of Nb element,a large number of Nb(C,N)particles are diffusely distributed in the matrix.Nb(C,N)phase distributed in the matrix and the niobium-rich layer formed by the diffusion of niobium into the interface between the metal matrix and the oxide film during the high-temperature oxidation process effectively prevents the diffusion of iron into the outer layer and enhances the oxidation resistance at high temperatures.展开更多
Isothermal compression tests were carried out to investigate the hot deformation behavior of a multi-alloyed high-Mn austenitic steel,110Mn12Cr2NY,at temperatures ranging from 800 to 1200℃ and strain rates ranging fr...Isothermal compression tests were carried out to investigate the hot deformation behavior of a multi-alloyed high-Mn austenitic steel,110Mn12Cr2NY,at temperatures ranging from 800 to 1200℃ and strain rates ranging from 0.01 to 1 s^(−1).The results revealed that the critical strain for dynamic recrystallization(DRX)lowered with increasing deformation temperature and decreasing strain rate.The analysis of microstructure pointed to discontinuous dynamic recrystallization(DDRX)as the dominant DRX mechanism,characterized byΣ3 twin boundaries and necklace-like structure during deformation at relatively low temperature and high strain rate.The decrease in strain rate facilitated continuous dynamic recrystallization(CDRX)as an auxiliary nucleation mechanism,leading to a significant decrease in the softening rate in the flow stress curves.When deformed at high temperatures and low strain rates,the preferential growth of<001>oriented grains resulted in the formation of a strong<001>//CD texture,and CDRX associated with<001>grains emerged as the predominant DRX mechanism.Significant DRX occurring at high temperatures and high strain rates yielded fine,defect-free equiaxed grains.Consequently,this region could be employed as the optimal hot working window for 110Mn12Cr2NY steel,with a temperature range of 950–1200℃and a strain rate range of 0.4^(–)1 s^(−1).展开更多
The effect of Mo on dual-phase precipitation behavior and tensile properties of Fe26Mn8Al1.2C–(2–3.5 wt.%)Mo lightweight austenitic steels after annealing at 700℃was investigated by electron backscatter diffraction...The effect of Mo on dual-phase precipitation behavior and tensile properties of Fe26Mn8Al1.2C–(2–3.5 wt.%)Mo lightweight austenitic steels after annealing at 700℃was investigated by electron backscatter diffraction,transmission electron microscopy,hardness and tensile tests.Alloying with Mo in the steels promotes the precipitation of Mo_(2)C carbides while inhibits the precipitation ofκ-carbides.The addition of Mo exceeding 2.5 wt.%facilitates the precipitation of intragranular Mo_(2)C carbides,whereas with up to 2.5 wt.%Mo,only intergranular Mo_(2)C carbides precipitate.With containing more Mo in the steels,the strength increases due to enhancement of precipitation strengthening and solid solution strengthening,while ductility gradually decreases.3Mo steel exhibits excellent overall mechanical properties,with the synergistic increase in strength,ductility,and work-hardening rate,which can be attributed to the precipitation of fine intragranular Mo_(2)C distributed uniformly in the matrix and the suppression of the formation of coarsenedκ-carbides.However,in 3.5Mo steel,abundant coarsened Mo2C precipitation strongly interacts with dislocations to promote crack propagation along non-coherent interfaces,leading to a high initial work-hardening rate but severe ductility loss.展开更多
The addition of vanadium substantially enhances the strength of the high-nitrogen austenitic stainless steel(HNASS),while maintaining excellent ductility and pitting corrosion resistance.The effects of vanadium microa...The addition of vanadium substantially enhances the strength of the high-nitrogen austenitic stainless steel(HNASS),while maintaining excellent ductility and pitting corrosion resistance.The effects of vanadium microalloying on the microstructure,mechanical properties,and pitting resistance of HNASS were systematically analyzed with a focus on the role of VN during the pitting process.The results suggest that vanadium promoted the precipitation of VN,contributing to grain boundary pinning and grain refinement.As vanadium content increased,the number of precipitates rose,and the average grain size decreased.At lower vanadium content(0-0.2 wt.%),the strength of the material was significantly reinforced with increasing vanadium content,while maintaining excellent ductility and pitting resistance.However,when the vanadium content reached 0.3-0.4 wt.%,precipitates demonstrated a substantially increased number and coarsened,accompanied by the formation of numerous dislocations around the precipitates.This brought about further strength reinforcement but a marked decline in ductility and pitting resistance.Additionally,pitting corrosion was initiated at the matrix-VN interface.Compared to the matrix,VN exhibited higher reactivity and preferentially reacted with Cl−ions,provoking dissolution.However,NH4+generated during the dissolution of VN facilitated repassivation of the material,suppressing further pitting propagation.展开更多
Wire arc additive manufacturing(WAAM)presents a promising approach for fabricating medium-to-large austenitic stainless steel components,which are essential in industries like aerospace,pressure vessels,and heat excha...Wire arc additive manufacturing(WAAM)presents a promising approach for fabricating medium-to-large austenitic stainless steel components,which are essential in industries like aerospace,pressure vessels,and heat exchangers.This research examines the mi-crostructural characteristics and tensile behaviour of SS308L manufactured via the gas metal arc welding-based WAAM(WAAM 308L)process.Tensile tests were conducted at room temperature(RT,25℃),300℃,and 600℃in as-built conditions.The microstructure con-sists primarily of austenite grains with retainedδ-ferrite phases distributed within the austenitic matrix.The ferrite fraction,in terms of fer-rite number(FN),ranged between 2.30 and 4.80 along the build direction from top to bottom.The ferrite fraction in the middle region is 3.60 FN.Tensile strength was higher in the horizontal oriented samples(WAAM 308L-H),while ductility was higher in the vertical ones.Tensile results show a gradual reduction in strength with increasing test temperature,in which significant dynamic strain aging(DSA)is observed at 600℃.The variation in serration behavior between the vertical and horizontal specimens may be attributed to microstructural differences arising from the build orientation.The yield strength(YS),ultimate tensile strength(UTS),and elongation(EL)of WAAM 308L at 600℃were(240±10)MPa,(442±16)MPa,and(54±2.00)%,respectively,in the horizontal orientation(WAAM 308L-H),and(248±9)MPa,(412±19)MPa,and(75±2.80)%,respectively,in the vertical orientation(WAAM 308L-V).Fracture surfaces revealed a transition from ductile dimple fracture at RT and 300℃to a mixed ductile-brittle failure with intergranular facets at 600℃.The research explores the applicability and constraints of WAAM-produced 308L stainless steel in high-temperature conditions,offering crucial in-sights for its use in thermally resistant structural and industrial components.展开更多
1.Introduction The precipitation of κ-carbides is critical for the deformation behavior of Fe-Mn-Al-C austenitic low-density steels[1-5].Ther-momechanical treatment can significantly influence the distribution,size,a...1.Introduction The precipitation of κ-carbides is critical for the deformation behavior of Fe-Mn-Al-C austenitic low-density steels[1-5].Ther-momechanical treatment can significantly influence the distribution,size,and morphology of κ-carbides,and thus regulate the mechanical properties[1,4,6-8].Intragranular κ-carbides precipitate through either nucleation and growth mechanisms[9]or spinodal decomposition[3,5],depending on thermodynamic conditions.展开更多
This study examines the effects of friction stir welding(FSW)and post-weld heat treatment(PWHT)on the grain boundary character distribution and corrosion resistance of cross sectional(top and bottom)regions of nickel-...This study examines the effects of friction stir welding(FSW)and post-weld heat treatment(PWHT)on the grain boundary character distribution and corrosion resistance of cross sectional(top and bottom)regions of nickel-and molybdenum-free high-nitrogen austenitic stainless steel(HNASS).FSW at 400 rpm and 30 mm/min resulted in finer grains(4.18μm)and higher coincident site lattice(CSL)boundaries(32.3%)at the top of the stir zone(SZ)due to dynamic recrystallization(DRX).PWHT at 900℃for 1 h led to grain coarsening(12.91μm the bottom SZ)but enhanced CSL boundaries from 24.6%to 30.2%,improving grain boundary stability.PWHT reduced the kernel average misorientation(KAM)by 14.9%in the SZ-top layer and 20.4%in the SZ-bottom layer,accompanied by a 25%decrease in hardness in the SZ-top layer and 26.7%in the SZ-bottom layer,indicating strain recovery and reduced dislocation density.Potentiodynamic polarization tests(PDP)showed a 18%increase in pitting potential and a 76%reduction in corrosion rate after PWHT.The improvement in corrosion resistance is attributed to the increase inΣ3 twin boundaries,which enhance grain boundary stability and reduce susceptibility to localized corrosion.These findings highlight the role of PWHT in refining the microstructure and strengthening corrosion resistance,making HNASS a promising material for demanding applications.展开更多
During the fabrication of large parts by forging,dynamic recrystallization(DRX)is the primary softening mechanism that affects the microstructure and properties of austenitic stainless steel,and an in-depth analysis o...During the fabrication of large parts by forging,dynamic recrystallization(DRX)is the primary softening mechanism that affects the microstructure and properties of austenitic stainless steel,and an in-depth analysis of this process is necessary.The isothermal hot compression tests were conducted to investigate the hot deformation behavior of Fe-21Cr-15Ni-5Mn-2Mo steel,a novel austenitic stainless steel,at strain rates from 0.01 to 10 s^(-1)and temperatures ranging from 950 to 1200℃.Based on the true stress-strain curves derived from the tests,the constitutive model and hot working map for the steel were constructed,and the microstructure evolution of the steel was systematically analyzed.The critical deformation conditions for the occurrence of DRX were determined using the plotted work hardening rate curve.The findings indicate a significant rise in flow stress as strain rate increases or deformation temperature decreases.Concurrently,the strain needed to attain peak stress progressively grows.The activation energy for deformation of the steel is 595.511 kJ/mol,which results from the competition between dynamic softening and work hardening during its hot deformation process.Low strain rate and low temperature(0.01 s^(-1),950℃)are the parameters for the instability zone of the steel,and localized flow and deformation bands are the microstructure manifestations of unstable hot processing.The optimal hot working window for the experimental steel is the medium to high strain rate range and medium to high temperature(0.1−10 s^(-1),1100−1200℃),where the microstructure exhibits randomly oriented,uniformly distributed DRX grains.The bulging of the initial grain boundaries is primarily associated with the nucleation mechanism of DRX.Furthermore,based on the critical strain and peak strain,the kinetics of DRX are predicted by the Avrami equation.展开更多
The nano-scale L1_(2)-Ni_(3)Al precipitates significantly contribute to thermal stability of alumina-forming austenitic(AFA)steels.The coarsening behavior of L1_(2)-Ni_(3)Al precipitates in AFA steels during isotherma...The nano-scale L1_(2)-Ni_(3)Al precipitates significantly contribute to thermal stability of alumina-forming austenitic(AFA)steels.The coarsening behavior of L1_(2)-Ni_(3)Al precipitates in AFA steels during isothermal aging with considering the influence of alloying elements was investigated.The results show that the coarsening rate of L1_(2)-Ni_(3)Al precipitates increases with co-additions of Ni and Cu,and especially,the increase of Cu content promotes the nucleation of L1_(2)-Ni_(3)Al precipitates.A dynamic competition exists between Lifshitz-Slyozov-Wagner theory and transient interface diffusion-controlled theory for coarsening behavior of L1_(2)-Ni_(3)Al precipitates with duration of isothermal aging.Additionally,the transition from L1_(2)-Ni_(3)Al precipitates to B2-NiAl precipitates during isothermal aging results in the formation of a depleted zone of L1_(2)-Ni_(3)Al precipitates around B2-NiAl precipitates,which inhibits the growth of L1_(2)-Ni_(3)Al precipitates.The coarsening of L1_(2)-Ni_(3)Al precipitates significantly contributes to the yield strength of AFA steels.展开更多
It was found that hydrogen induced delayed failure could occur in 308L and 347L weld metals,and the threshold stress intensities of 308L and 347L welds were lower than that of 304L austenitic stainless steel.When dyn...It was found that hydrogen induced delayed failure could occur in 308L and 347L weld metals,and the threshold stress intensities of 308L and 347L welds were lower than that of 304L austenitic stainless steel.When dynamically charged under load on a single edge notched specimen,the threshold stress intensities of 308L,347L and 304L decrease with the increase in the diffusible hydrogen content C 0 and the experimental results are as follows:K ⅠH =85.2-10.7 ln C 0 (308L),K ⅠH =76.1-9.3 ln C 0 (347L),K ⅠH =91.7-10.1 ln C 0 (304L).The morphology of the hydrogen induced delayed fracture in the three materials are correlated with the K Ⅰ and C 0 values.展开更多
Research progress on nitrogen alloyed austenitic stainless steels was expounded through the development of steel grades. In addition, hot topics in the research of nitrogen-alloyed austenitic stainless steels were dis...Research progress on nitrogen alloyed austenitic stainless steels was expounded through the development of steel grades. In addition, hot topics in the research of nitrogen-alloyed austenitic stainless steels were discussed, in cluding the solubility of nitrogen, brittle ductile transition, and welding. On this basis, it was proposed that the fu- ture development tendency of nitrogen alloyed austenitic stainless steels lied in the three fields of high-performance steels, resource saving steels, and biologically friendly steels. The problems encountered during the research of ni- trogen-alloyed austenitic stainless steels were discussed.展开更多
Pitting corrosion and crevice corrosion behaviors of high nitrogen austenitic stainless steels （HNSS） were investigated by electrochemical and immersion testing methods in chloride solution, respectively. The chemic...Pitting corrosion and crevice corrosion behaviors of high nitrogen austenitic stainless steels （HNSS） were investigated by electrochemical and immersion testing methods in chloride solution, respectively. The chemical constitution and composition in the depth of passive films formed on HNSS were analyzed by X-ray photoelectron spectrum （XPS）. HNSS has excellent pitting and crevice corrosion resistance compared to 316L stainless steel. With increasing the nitrogen content in steels, pitting potentials and critical pitting temperature （CPT） increase, and the maximum, average pit depths and average weight loss decrease. The CPT of HNSS is correlated with the alloying element content through the measure of alloying for resistance to corrosion （MARC）. The MARC can be expressed as an equation of CPT=2.55MARC-29. XPS results show that HNSS exhibiting excellent corrosion resistance is attributed to the enrichment of nitrogen on the surface of passive films, which forms ammonium ions increasing the local pH value and facilitating repassivation, and the synergistic effects of molybdenum and nitrogen.展开更多
A simple and feasible method for the production of high nitrogen austenitic stainless steels involves nitrogen gas alloying and adding nitrided ferroalloys under normal atmospheric conditions. Alloying by nitrogen gas...A simple and feasible method for the production of high nitrogen austenitic stainless steels involves nitrogen gas alloying and adding nitrided ferroalloys under normal atmospheric conditions. Alloying by nitrogen gas bubbling in Fe-Cr-Mn-Mo series alloys was carried out in MoSi2 resistance furnace and air induction furnace under normal atmospheric conditions. The results showed that nitrogen alloying could be accelerated by increasing nitrogen gas flow rate, prolonging residence time of bubbles, increasing gas/molten steel interfaces, and decreasing the sulphur and oxygen contents in molten steel. Nitrogen content of 0.69% in 18Crl8Mn was obtained using air induction furnace by bubbling of nitrogen gas from porous plug. In addition, the nickel-free, high nitrogen austenitic stainless steels with sound and compact macrostructure had been produced in the laboratory using vacuum induction furnace and electroslag remelting furnace under nitrogen atmosphere by the addition of nitrided alloy with the maximum nitrogen content of 0.81%. Pores were observed in the ingots obtained by melting and casting in vacuum induction furnace with the addition of nitrided ferroalloys and under nitrogen atmosphere. After electroslag remelting of the cast ingots, they were all sound and were free of pores. The yield of nitrogen increased with the decrease of melting rate in the ESR process. Due to electroslag remelting under nitrogen atmosphere and the consequential addition of aluminum as deoxidizer to the slag, the loss of manganese decreased obviously. There existed mainly irregular Al2O3 inclusions and MnS inclusions in ESR ingots, and the size of most of the inclusions was less than 5 um. After homogenization of the hot rolled plate at 1 150℃ × 1 h followed by water quenching, the microstructure consisted of homogeneous austenite.展开更多
The influence of N on the precipitation behavior,associated corrosion,and mechanical properties of S32654 were investigated by microstructural,electrochemical,and mechanical analyses.Increasing the N content results i...The influence of N on the precipitation behavior,associated corrosion,and mechanical properties of S32654 were investigated by microstructural,electrochemical,and mechanical analyses.Increasing the N content results in several alterations:(1) grain refinement,which promotes intergranular precipitation;(2) a linear increase in the driving force for Cr2 N and Mo activity,which accelerates the precipitation of intergranular Cr2 N and π phase,respectively;(3) a linear decrease in the driving force for σ phase and Cr activity,which suppresses the formation of intragranular σ phase.The total amount of precipitates first decreased and then increased with the N content increasing.Furthermore,the intergranular corrosion susceptibility depended substantially on the total amount of precipitates and also first exhibited a decreasing and then an increasing trend as the N content increased.In addition,aging precipitation caused a considerable decrement in the ultimate tensile strength(UTS) and a remarkable increment in the yield strength(YS).Both the UTS and YS always increased with N content increasing throughout the solution and aging process.Whereas the elongation was considerably sensitive to the aging treatment,it exhibited marginal variation with the N content increasing.展开更多
The fine grained structures of nickel-free high nitrogen austenitic stainless steels had been obtained by means of cold rolling and subsequent annealing. The relationship between microstructure and mechanical properti...The fine grained structures of nickel-free high nitrogen austenitic stainless steels had been obtained by means of cold rolling and subsequent annealing. The relationship between microstructure and mechanical properties and gain size of nickel-free high nitrogen austenitic stainless steels was examined. High strength and good ductility of the steel were found. In the grain size range, the Hall-Petch dependency for yield stress, tensile strength, and hardness was valid for grain size ranges for the nickel-free high nitrogen austenitic stainless steel. In the present study, the ductility of cold rolled nickel-free high nitrogen austenitic stainless steel decreased with annealing time when the grain size was refined. The fracture surfaces of the tensile specimens in the grain size range were covered with dimples as usually seen in a ductile fracture mode.展开更多
In the present study,the effect of aging heat treatment at 650,750,and 850？C on the impact toughness of 316L austenitic stainless steel,2205 duplex stainless steel and their weldments has been investigated.Welding pr...In the present study,the effect of aging heat treatment at 650,750,and 850？C on the impact toughness of 316L austenitic stainless steel,2205 duplex stainless steel and their weldments has been investigated.Welding process was conducted using the TIG（tungsten inert gas） welding technique.Instrumented impact testing,at room temperature,was employed to determine the effect of aging treatment on the impact properties of investigated materials.Aging treatment resulted in degradation in the impact toughness as demonstrated by the reduction in the impact fracture energy and deformation parameters（strain hardening capacity,fracture deffection,and crack initiation and propagation energy）.The degree of embrittlement was more noticeable in duplex stainless steel parent and weld-metal than in 316L stainless steel and became greater with the increase of aging temperature.The degradation in impact toughness was discussed in relation to the observed precipitation of the intermetallic sigma phase in the microstructure of the stainless steel weldments and the corresponding fracture surface morphology.展开更多
A series of high nitrogen austenitic stainless steels were successfully developed with a pressurized electroslag remelting furnace. Nitride additives and deoxidizer were packed into the stainless steel pipes, and then...A series of high nitrogen austenitic stainless steels were successfully developed with a pressurized electroslag remelting furnace. Nitride additives and deoxidizer were packed into the stainless steel pipes, and then the stainless steel pipes were welded on the surface of an electrode with low nitrogen content to prepare a compound electrode. Using Si3N4 as a nitrogen alloying source, the silicon contents in the ingots were prone to be out of the specification range, the electric current fluctuated greatly and the surface qualities of the ingots were poor. The surface qualities of the ingots were improved with FeCrN as a nitrogen alloying source. The sound and compact macrostructure ingot with the maximum nitrogen content of 1.21wt% can be obtained. The 18Cr18Mn2Mo0.9N high nitrogen austenitic stainless steel exhibits high strength and good ductility at room temperature. The steel shows typical ductile-brittle transition behavior and excellent pitting corrosion resistance properties.展开更多
基金finncially supported by the National Natural Science Foundation of China(No.52075183)the Guangdong Basic and Applied Research Fundamental(No.2023A1515010692)the Key-Area Research and Development Program of Guangdong Province(Nos.2024B1111080002 and 2020B0404020004).
文摘Austenitic stainless steel(ASS)is a common material used in high-pressure hydrogen systems.Prolonged exposure to high-pressure hydrogen can cause hydrogen embrittlement(HE),raising significant safety concerns.Selective Laser Melting(SLM),known for its high precision,is a promising additive manufacturing technology that has been widely adopted across various industries.Studies have reported that under certain SLM manufacturing conditions and process parameters,the HE resistance of SLM ASS is significantly better than that of conventionally manufactured(CM)ASS,showing great potential for application in high-pressure hydrogen systems.Thus,studying the HE of SLM ASS is crucial for further improving the safety of high-pressure hydrogen systems.This paper provides an overview of the SLM process,reviews the mechanisms of HE and their synergistic effects,and analyzes the HE characteristics of SLM ASS.Additionally,it examines the influence of unique microstructures and SLM process variables on HE of SLM ASS and offers recommendations for future research to enhance the safety of high-pressure hydrogen systems.
基金supported by the Nuclear Technology R&D Program.
文摘This work investigated the original microstructure of cold-worked alumina-forming austenitic steel,along with its precipitation and dissolution corrosion behaviors in lead-bismuth eutectic with 10-8 wt.%oxygen at 600℃,using solution-annealed steel for comparison.Anomalously,cold-worked steel presented milder corrosion compared to solution-annealed steel,with average corrosion depths of 314.3 and 401.0μm after 1700 h exposure.Cold working-induced de-twinning transformed the annealing twin boundaries into normal high-angle grain boundaries(NGBs),increasing NGBs proportion from 36%to 89%.The increased NGBs provided more nucleation sites for intergranular barriers composed of alternate NiAl and M23C6 precipitates,thus better obstructing the dissolution attack.
基金funded by the LingChuang Research Project of China National Nuclear Corporation and the Natural Science Foun-dation of Liaoning Province(No.2023-MS-019).
文摘High-temperature long-term microstructural instability is an urgent problem to be solved for high-silicon Fe-Cr-Ni austenitic stainless steel.In this study,we propose a novel strategy to improve the microstructural thermal stability of Si-modified Fe-Cr-Ni austenitic steels via N doping.The microstructural evolution behaviors of N-free and N-doping steels were systematically investigated during aging at 783-923 K.The findings indicate that N doping results in substantial grain refinement and improves the strength of the steel.Importantly,it is found that N doping inhibits the premature segregation of Ni,Cr,Si,and Mo at grain boundaries by reducing their diffusion coefficients,thereby suppressing the generation of intergranular M_(6) C carbides during aging at 783 K,achieving superior thermal stability.In contrast,N-free steel exhibits microstructural instability due to theγ→M_(6) C+ferrite transformation during aging at 783 K.At 823 and 873 K,it is concluded that the diffusion of alloying elements accelerates,resulting in the formation of M_(6) C and ferrite in N-doping steel and subsequent microstructural instability.It contributes to a decrease in impact toughness,as microcracks tend to form at the ferrite domain and M_(6) C/ferrite interface with high strain concentration.Notably,when aged at 923 K,N-doping steel exhibits a cellular structure composed of M_(23) C_(6) and M_(6) C carbonitrides,with Nb(C,N)serving as the nucleation site within the grains.This differs from the intragranularχ-phase observed in N-free steel,as the nucleation driving force of theχ-phase decreases with an increasing N content.The study offers valuable insights for the development of fastener materials intended for utilization in lead-cooled fast reactors.
基金support of this work by the Major Program of Science and Technology in Shanxi Province(202202050201019)the National Natural Science Foundation of China(52271067)Shaanxi Outstanding Youth Fund Project(2021JC-45).
文摘The effects of niobium on the high-temperature oxidation resistance of austenitic stainless steel were systematically investigated.Two austenitic stainless steels with different Nb contents were prepared and exposed to air at 850℃for 200 h.Results show that Nb positively affects the high-temperature oxidation resistance of austenitic stainless steels.The matrix organization of austenitic stainless steels with added niobium does not change,while the austenitic grain size is significantly refined,and it also promoted the release of internal stresses in the oxide film,which in turn improved the integrity of the oxide film and adhesion to the substrate.In addition,with the addition of Nb element,a large number of Nb(C,N)particles are diffusely distributed in the matrix.Nb(C,N)phase distributed in the matrix and the niobium-rich layer formed by the diffusion of niobium into the interface between the metal matrix and the oxide film during the high-temperature oxidation process effectively prevents the diffusion of iron into the outer layer and enhances the oxidation resistance at high temperatures.
基金the National Natural Science Foundation of China(Nos.52474427,52201143,and 52171049)the Science and Technology Project of Hebei Education Department(No.BJK2023033)the Hebei Province Innovation Ability Promotion Project(No.22567609H).
文摘Isothermal compression tests were carried out to investigate the hot deformation behavior of a multi-alloyed high-Mn austenitic steel,110Mn12Cr2NY,at temperatures ranging from 800 to 1200℃ and strain rates ranging from 0.01 to 1 s^(−1).The results revealed that the critical strain for dynamic recrystallization(DRX)lowered with increasing deformation temperature and decreasing strain rate.The analysis of microstructure pointed to discontinuous dynamic recrystallization(DDRX)as the dominant DRX mechanism,characterized byΣ3 twin boundaries and necklace-like structure during deformation at relatively low temperature and high strain rate.The decrease in strain rate facilitated continuous dynamic recrystallization(CDRX)as an auxiliary nucleation mechanism,leading to a significant decrease in the softening rate in the flow stress curves.When deformed at high temperatures and low strain rates,the preferential growth of<001>oriented grains resulted in the formation of a strong<001>//CD texture,and CDRX associated with<001>grains emerged as the predominant DRX mechanism.Significant DRX occurring at high temperatures and high strain rates yielded fine,defect-free equiaxed grains.Consequently,this region could be employed as the optimal hot working window for 110Mn12Cr2NY steel,with a temperature range of 950–1200℃and a strain rate range of 0.4^(–)1 s^(−1).
基金supported by the funding of National Science and Technology Major Project,China(J2019-VI-0019-0134).
文摘The effect of Mo on dual-phase precipitation behavior and tensile properties of Fe26Mn8Al1.2C–(2–3.5 wt.%)Mo lightweight austenitic steels after annealing at 700℃was investigated by electron backscatter diffraction,transmission electron microscopy,hardness and tensile tests.Alloying with Mo in the steels promotes the precipitation of Mo_(2)C carbides while inhibits the precipitation ofκ-carbides.The addition of Mo exceeding 2.5 wt.%facilitates the precipitation of intragranular Mo_(2)C carbides,whereas with up to 2.5 wt.%Mo,only intergranular Mo_(2)C carbides precipitate.With containing more Mo in the steels,the strength increases due to enhancement of precipitation strengthening and solid solution strengthening,while ductility gradually decreases.3Mo steel exhibits excellent overall mechanical properties,with the synergistic increase in strength,ductility,and work-hardening rate,which can be attributed to the precipitation of fine intragranular Mo_(2)C distributed uniformly in the matrix and the suppression of the formation of coarsenedκ-carbides.However,in 3.5Mo steel,abundant coarsened Mo2C precipitation strongly interacts with dislocations to promote crack propagation along non-coherent interfaces,leading to a high initial work-hardening rate but severe ductility loss.
基金founded by National Natural Science Foundations of China(Nos.52231003,52201084,and U21A20113)Major Program(JD)of Hubei Province(No.2023BAA019)+1 种基金Natural Science Foundation of Guangdong Province(No.2024A1515011022)Guangdong Province Basic and Applied Basic Research Fund Offshore Wind Power Joint Fund(No.2023B1515250006).
文摘The addition of vanadium substantially enhances the strength of the high-nitrogen austenitic stainless steel(HNASS),while maintaining excellent ductility and pitting corrosion resistance.The effects of vanadium microalloying on the microstructure,mechanical properties,and pitting resistance of HNASS were systematically analyzed with a focus on the role of VN during the pitting process.The results suggest that vanadium promoted the precipitation of VN,contributing to grain boundary pinning and grain refinement.As vanadium content increased,the number of precipitates rose,and the average grain size decreased.At lower vanadium content(0-0.2 wt.%),the strength of the material was significantly reinforced with increasing vanadium content,while maintaining excellent ductility and pitting resistance.However,when the vanadium content reached 0.3-0.4 wt.%,precipitates demonstrated a substantially increased number and coarsened,accompanied by the formation of numerous dislocations around the precipitates.This brought about further strength reinforcement but a marked decline in ductility and pitting resistance.Additionally,pitting corrosion was initiated at the matrix-VN interface.Compared to the matrix,VN exhibited higher reactivity and preferentially reacted with Cl−ions,provoking dissolution.However,NH4+generated during the dissolution of VN facilitated repassivation of the material,suppressing further pitting propagation.
基金supported by the Korea Institute of Energy Technology Evaluation and Planning(KETEP)and the Ministry of Trade,Industry&Energy(MOTIE)of the Republic of Korea program(No.RS-2025-02603127,Innovation Research Center for Zero-carbon Fuel Gas Turbine Design,Manufacture,and Safety).
文摘Wire arc additive manufacturing(WAAM)presents a promising approach for fabricating medium-to-large austenitic stainless steel components,which are essential in industries like aerospace,pressure vessels,and heat exchangers.This research examines the mi-crostructural characteristics and tensile behaviour of SS308L manufactured via the gas metal arc welding-based WAAM(WAAM 308L)process.Tensile tests were conducted at room temperature(RT,25℃),300℃,and 600℃in as-built conditions.The microstructure con-sists primarily of austenite grains with retainedδ-ferrite phases distributed within the austenitic matrix.The ferrite fraction,in terms of fer-rite number(FN),ranged between 2.30 and 4.80 along the build direction from top to bottom.The ferrite fraction in the middle region is 3.60 FN.Tensile strength was higher in the horizontal oriented samples(WAAM 308L-H),while ductility was higher in the vertical ones.Tensile results show a gradual reduction in strength with increasing test temperature,in which significant dynamic strain aging(DSA)is observed at 600℃.The variation in serration behavior between the vertical and horizontal specimens may be attributed to microstructural differences arising from the build orientation.The yield strength(YS),ultimate tensile strength(UTS),and elongation(EL)of WAAM 308L at 600℃were(240±10)MPa,(442±16)MPa,and(54±2.00)%,respectively,in the horizontal orientation(WAAM 308L-H),and(248±9)MPa,(412±19)MPa,and(75±2.80)%,respectively,in the vertical orientation(WAAM 308L-V).Fracture surfaces revealed a transition from ductile dimple fracture at RT and 300℃to a mixed ductile-brittle failure with intergranular facets at 600℃.The research explores the applicability and constraints of WAAM-produced 308L stainless steel in high-temperature conditions,offering crucial in-sights for its use in thermally resistant structural and industrial components.
基金financially supported by the National Natural Science Foundation of China(grant No 52171108)the Natural Science Foundation of Liaoning Province(grant No 2023-MSBA-037)the Fundamental Research Funds for the Central University(grant No N2402007).
文摘1.Introduction The precipitation of κ-carbides is critical for the deformation behavior of Fe-Mn-Al-C austenitic low-density steels[1-5].Ther-momechanical treatment can significantly influence the distribution,size,and morphology of κ-carbides,and thus regulate the mechanical properties[1,4,6-8].Intragranular κ-carbides precipitate through either nucleation and growth mechanisms[9]or spinodal decomposition[3,5],depending on thermodynamic conditions.
文摘This study examines the effects of friction stir welding(FSW)and post-weld heat treatment(PWHT)on the grain boundary character distribution and corrosion resistance of cross sectional(top and bottom)regions of nickel-and molybdenum-free high-nitrogen austenitic stainless steel(HNASS).FSW at 400 rpm and 30 mm/min resulted in finer grains(4.18μm)and higher coincident site lattice(CSL)boundaries(32.3%)at the top of the stir zone(SZ)due to dynamic recrystallization(DRX).PWHT at 900℃for 1 h led to grain coarsening(12.91μm the bottom SZ)but enhanced CSL boundaries from 24.6%to 30.2%,improving grain boundary stability.PWHT reduced the kernel average misorientation(KAM)by 14.9%in the SZ-top layer and 20.4%in the SZ-bottom layer,accompanied by a 25%decrease in hardness in the SZ-top layer and 26.7%in the SZ-bottom layer,indicating strain recovery and reduced dislocation density.Potentiodynamic polarization tests(PDP)showed a 18%increase in pitting potential and a 76%reduction in corrosion rate after PWHT.The improvement in corrosion resistance is attributed to the increase inΣ3 twin boundaries,which enhance grain boundary stability and reduce susceptibility to localized corrosion.These findings highlight the role of PWHT in refining the microstructure and strengthening corrosion resistance,making HNASS a promising material for demanding applications.
基金financial support from the National Key R&D Program of China(No.2024YFB3713604)the Beijing Municipal Special Program for Science and Technology Service Industry(No.F20241219170567).
文摘During the fabrication of large parts by forging,dynamic recrystallization(DRX)is the primary softening mechanism that affects the microstructure and properties of austenitic stainless steel,and an in-depth analysis of this process is necessary.The isothermal hot compression tests were conducted to investigate the hot deformation behavior of Fe-21Cr-15Ni-5Mn-2Mo steel,a novel austenitic stainless steel,at strain rates from 0.01 to 10 s^(-1)and temperatures ranging from 950 to 1200℃.Based on the true stress-strain curves derived from the tests,the constitutive model and hot working map for the steel were constructed,and the microstructure evolution of the steel was systematically analyzed.The critical deformation conditions for the occurrence of DRX were determined using the plotted work hardening rate curve.The findings indicate a significant rise in flow stress as strain rate increases or deformation temperature decreases.Concurrently,the strain needed to attain peak stress progressively grows.The activation energy for deformation of the steel is 595.511 kJ/mol,which results from the competition between dynamic softening and work hardening during its hot deformation process.Low strain rate and low temperature(0.01 s^(-1),950℃)are the parameters for the instability zone of the steel,and localized flow and deformation bands are the microstructure manifestations of unstable hot processing.The optimal hot working window for the experimental steel is the medium to high strain rate range and medium to high temperature(0.1−10 s^(-1),1100−1200℃),where the microstructure exhibits randomly oriented,uniformly distributed DRX grains.The bulging of the initial grain boundaries is primarily associated with the nucleation mechanism of DRX.Furthermore,based on the critical strain and peak strain,the kinetics of DRX are predicted by the Avrami equation.
基金financial supports from the National Natural Science Foundation of China(Nos.52471004,52171107,52201203)the Industry-University-Research Cooperation Project of Hebei Based Universities and Shijiazhuang City(No.241791237A)the Fundamental Research Funds for the Central Universities(No.N2423030)。
文摘The nano-scale L1_(2)-Ni_(3)Al precipitates significantly contribute to thermal stability of alumina-forming austenitic(AFA)steels.The coarsening behavior of L1_(2)-Ni_(3)Al precipitates in AFA steels during isothermal aging with considering the influence of alloying elements was investigated.The results show that the coarsening rate of L1_(2)-Ni_(3)Al precipitates increases with co-additions of Ni and Cu,and especially,the increase of Cu content promotes the nucleation of L1_(2)-Ni_(3)Al precipitates.A dynamic competition exists between Lifshitz-Slyozov-Wagner theory and transient interface diffusion-controlled theory for coarsening behavior of L1_(2)-Ni_(3)Al precipitates with duration of isothermal aging.Additionally,the transition from L1_(2)-Ni_(3)Al precipitates to B2-NiAl precipitates during isothermal aging results in the formation of a depleted zone of L1_(2)-Ni_(3)Al precipitates around B2-NiAl precipitates,which inhibits the growth of L1_(2)-Ni_(3)Al precipitates.The coarsening of L1_(2)-Ni_(3)Al precipitates significantly contributes to the yield strength of AFA steels.
基金Special Fund for the Major Basic Research Projects(No.G1 9990 650 )
文摘It was found that hydrogen induced delayed failure could occur in 308L and 347L weld metals,and the threshold stress intensities of 308L and 347L welds were lower than that of 304L austenitic stainless steel.When dynamically charged under load on a single edge notched specimen,the threshold stress intensities of 308L,347L and 304L decrease with the increase in the diffusible hydrogen content C 0 and the experimental results are as follows:K ⅠH =85.2-10.7 ln C 0 (308L),K ⅠH =76.1-9.3 ln C 0 (347L),K ⅠH =91.7-10.1 ln C 0 (304L).The morphology of the hydrogen induced delayed fracture in the three materials are correlated with the K Ⅰ and C 0 values.
基金Sponsored by National Science and Technology Support Program of China(2012BAE04B01)
文摘Research progress on nitrogen alloyed austenitic stainless steels was expounded through the development of steel grades. In addition, hot topics in the research of nitrogen-alloyed austenitic stainless steels were discussed, in cluding the solubility of nitrogen, brittle ductile transition, and welding. On this basis, it was proposed that the fu- ture development tendency of nitrogen alloyed austenitic stainless steels lied in the three fields of high-performance steels, resource saving steels, and biologically friendly steels. The problems encountered during the research of ni- trogen-alloyed austenitic stainless steels were discussed.
基金supported by the National Natural Science Foundation of China and Baosteel Group Corporation (No.50534010)
文摘Pitting corrosion and crevice corrosion behaviors of high nitrogen austenitic stainless steels （HNSS） were investigated by electrochemical and immersion testing methods in chloride solution, respectively. The chemical constitution and composition in the depth of passive films formed on HNSS were analyzed by X-ray photoelectron spectrum （XPS）. HNSS has excellent pitting and crevice corrosion resistance compared to 316L stainless steel. With increasing the nitrogen content in steels, pitting potentials and critical pitting temperature （CPT） increase, and the maximum, average pit depths and average weight loss decrease. The CPT of HNSS is correlated with the alloying element content through the measure of alloying for resistance to corrosion （MARC）. The MARC can be expressed as an equation of CPT=2.55MARC-29. XPS results show that HNSS exhibiting excellent corrosion resistance is attributed to the enrichment of nitrogen on the surface of passive films, which forms ammonium ions increasing the local pH value and facilitating repassivation, and the synergistic effects of molybdenum and nitrogen.
基金Item Sponsored by National Natural Science Foundation of China(50534010)
文摘A simple and feasible method for the production of high nitrogen austenitic stainless steels involves nitrogen gas alloying and adding nitrided ferroalloys under normal atmospheric conditions. Alloying by nitrogen gas bubbling in Fe-Cr-Mn-Mo series alloys was carried out in MoSi2 resistance furnace and air induction furnace under normal atmospheric conditions. The results showed that nitrogen alloying could be accelerated by increasing nitrogen gas flow rate, prolonging residence time of bubbles, increasing gas/molten steel interfaces, and decreasing the sulphur and oxygen contents in molten steel. Nitrogen content of 0.69% in 18Crl8Mn was obtained using air induction furnace by bubbling of nitrogen gas from porous plug. In addition, the nickel-free, high nitrogen austenitic stainless steels with sound and compact macrostructure had been produced in the laboratory using vacuum induction furnace and electroslag remelting furnace under nitrogen atmosphere by the addition of nitrided alloy with the maximum nitrogen content of 0.81%. Pores were observed in the ingots obtained by melting and casting in vacuum induction furnace with the addition of nitrided ferroalloys and under nitrogen atmosphere. After electroslag remelting of the cast ingots, they were all sound and were free of pores. The yield of nitrogen increased with the decrease of melting rate in the ESR process. Due to electroslag remelting under nitrogen atmosphere and the consequential addition of aluminum as deoxidizer to the slag, the loss of manganese decreased obviously. There existed mainly irregular Al2O3 inclusions and MnS inclusions in ESR ingots, and the size of most of the inclusions was less than 5 um. After homogenization of the hot rolled plate at 1 150℃ × 1 h followed by water quenching, the microstructure consisted of homogeneous austenite.
基金This work was financially supported by National Natural Science Foundation of China(No.U1860204)the Fundamental Research Funds for the Central Universities(No.N172507002)the Transformation Project of Major Scientific and Technological Achievements in Shenyang(No.Z17-5-003).
文摘The influence of N on the precipitation behavior,associated corrosion,and mechanical properties of S32654 were investigated by microstructural,electrochemical,and mechanical analyses.Increasing the N content results in several alterations:(1) grain refinement,which promotes intergranular precipitation;(2) a linear increase in the driving force for Cr2 N and Mo activity,which accelerates the precipitation of intergranular Cr2 N and π phase,respectively;(3) a linear decrease in the driving force for σ phase and Cr activity,which suppresses the formation of intragranular σ phase.The total amount of precipitates first decreased and then increased with the N content increasing.Furthermore,the intergranular corrosion susceptibility depended substantially on the total amount of precipitates and also first exhibited a decreasing and then an increasing trend as the N content increased.In addition,aging precipitation caused a considerable decrement in the ultimate tensile strength(UTS) and a remarkable increment in the yield strength(YS).Both the UTS and YS always increased with N content increasing throughout the solution and aging process.Whereas the elongation was considerably sensitive to the aging treatment,it exhibited marginal variation with the N content increasing.
基金Item Sponsored by Key Program of National Natural Science Foundation of China (50534010)
文摘The fine grained structures of nickel-free high nitrogen austenitic stainless steels had been obtained by means of cold rolling and subsequent annealing. The relationship between microstructure and mechanical properties and gain size of nickel-free high nitrogen austenitic stainless steels was examined. High strength and good ductility of the steel were found. In the grain size range, the Hall-Petch dependency for yield stress, tensile strength, and hardness was valid for grain size ranges for the nickel-free high nitrogen austenitic stainless steel. In the present study, the ductility of cold rolled nickel-free high nitrogen austenitic stainless steel decreased with annealing time when the grain size was refined. The fracture surfaces of the tensile specimens in the grain size range were covered with dimples as usually seen in a ductile fracture mode.
文摘In the present study,the effect of aging heat treatment at 650,750,and 850？C on the impact toughness of 316L austenitic stainless steel,2205 duplex stainless steel and their weldments has been investigated.Welding process was conducted using the TIG（tungsten inert gas） welding technique.Instrumented impact testing,at room temperature,was employed to determine the effect of aging treatment on the impact properties of investigated materials.Aging treatment resulted in degradation in the impact toughness as demonstrated by the reduction in the impact fracture energy and deformation parameters（strain hardening capacity,fracture deffection,and crack initiation and propagation energy）.The degree of embrittlement was more noticeable in duplex stainless steel parent and weld-metal than in 316L stainless steel and became greater with the increase of aging temperature.The degradation in impact toughness was discussed in relation to the observed precipitation of the intermetallic sigma phase in the microstructure of the stainless steel weldments and the corresponding fracture surface morphology.
基金supported by the National Natural Science Foundation of China(No.50534010)
文摘A series of high nitrogen austenitic stainless steels were successfully developed with a pressurized electroslag remelting furnace. Nitride additives and deoxidizer were packed into the stainless steel pipes, and then the stainless steel pipes were welded on the surface of an electrode with low nitrogen content to prepare a compound electrode. Using Si3N4 as a nitrogen alloying source, the silicon contents in the ingots were prone to be out of the specification range, the electric current fluctuated greatly and the surface qualities of the ingots were poor. The surface qualities of the ingots were improved with FeCrN as a nitrogen alloying source. The sound and compact macrostructure ingot with the maximum nitrogen content of 1.21wt% can be obtained. The 18Cr18Mn2Mo0.9N high nitrogen austenitic stainless steel exhibits high strength and good ductility at room temperature. The steel shows typical ductile-brittle transition behavior and excellent pitting corrosion resistance properties.
