The effects of phase transformation on mechanical properties and pitting corrosion of 2205 duplex stainless steel were investigated. The amount of a phase in the test specimen varied up to a maximum of 6 % by thermal ...The effects of phase transformation on mechanical properties and pitting corrosion of 2205 duplex stainless steel were investigated. The amount of a phase in the test specimen varied up to a maximum of 6 % by thermal treatment at 850 ℃ for up to 60 min. The results showed that ~ phase markedly increased the hardness and decreased the impact toughness of the test steel. But the increasing tendency of the ultimate tensile strength and the yield strength was not obvious, while the total elongation abruptly decreased with the aging time from 5 to 60 min. SEM impact microfractograph analysis revealed that the types of impact fracture changed from ductile mode to transcrystalline mode when the specimens were aged for 5-60 min. Furthermore, the extent of pitting potential reducing was found to be strongly temperature dependent, more pronounced at the higher temperature. During the incubation period of σ phase nucleation, the pitting corrosion test temperature and the aging time had collaborative effects on evidently displacing the pitting potential towards less noble values. After 15 min, the higher temperature contributed more to decreasing the pitting potential than the aging time.展开更多
Correlation between pitting corrosion behavior and chi（ χ ）phase formed after a short-term aging（5,10 and 15 min）at 850 ℃ of 2205 duplex stainless steel（DSS）was investigated using potentiodynamic polarization ...Correlation between pitting corrosion behavior and chi（ χ ）phase formed after a short-term aging（5,10 and 15 min）at 850 ℃ of 2205 duplex stainless steel（DSS）was investigated using potentiodynamic polarization tests,optical microscopy,and scanning electron microscopy equipped with energy-dispersive spectrum system.Results showed that after aging for 5min,the χ phase initially precipitated at ferrite grain boundaries,developed and then became linked with prolonging aging time.The χ phase was rich in Cr and Mo,resulting in formation of depleted zones nearby.The χ phase could reduce corrosion resistance of DSS and slightly influence its stability,but the specimens still displayed the capacity for repassivation.Some lines of evidence showed that stable pitting corrosion initiated at the boundaries of precipitates.The χ phase was selectively corroded during the first stage of corrosion and then the depleted zones nearby were attacked.In addition,the grain size and volume of precipitates also affected pit nucleation and progress,and suitable size and distribution of χ phase could aggravate pit initiation at precipitate boundaries.The χ phase with considerably low volume fraction and small size was not sensitive position for pit initiation.展开更多
In this research,aging treatments at temperatures of 800 and 900°C for different aging time of 5-60 min were conducted on solution treated as well as hot worked samples of 2205 dual phase stainless steel.The effe...In this research,aging treatments at temperatures of 800 and 900°C for different aging time of 5-60 min were conducted on solution treated as well as hot worked samples of 2205 dual phase stainless steel.The effect of aging treatment on precipitation of intermetallic phases was investigated in undeformed specimens and those subjected to hot deformation with different strain rates of 0.001-1 s-1.It was found that σ precipitation increased by hot working.It was also concluded that the volume fraction of phase increased with deformation temperature and decreased with strain rate.The precipitation of intermetallic phases（i.e.σ and χ） was analyzed by an Avrami-type kinetics equation of %（σ＋χ）=A（1-exp（-ktn）） and the values of n and ln k were estimated for different thermomechanical regimes.The values of n were assessed to increase from 0.4 to 1 with strain rate in the studied range.Otherwise,It was also understood that ln k decreased with strain rate.Microstructural observations by means of optical microscopy and scanning electron microscopy showed that σ particles mostly nucleated at the ferrite-austenite interfaces.But no sign of χ-phase could be seen.This fortified the idea of certain literature that χ-phase always forms at early stages of aging and consumes through the precipitation of σ.展开更多
Duplex stainless steels （DSS） with ferritic-austenitic microstructures offer good combination of resistance to pitting corrosion and high strength that are not concomitantly attainable using conventional single phas...Duplex stainless steels （DSS） with ferritic-austenitic microstructures offer good combination of resistance to pitting corrosion and high strength that are not concomitantly attainable using conventional single phase austenitic or ferritic stainless steels, The DSS used in this investigation was 2205 alloy having a stable microstructure consisting of about 45% ferrite and 55% austenite at ambient temperature. In order to investigate aging behavior of this steel and the influences on mechanical properties, different aging treatments were conducted at temperatures of 350-950℃ for various aging time of 15, 30, 60 and 180 min. The aged specimens were subjected to impact testing and hardness measurements. Finally, the changes in microstructure due to aging were studied by optical and scanning electron microscopy. The results showed that aging at temperatures lower than 550℃ for different time had negligible effects on mechanical properties. Besides, no considerable changes in term of precipitation of harmful intermetallic particles were observed in microstructure below this temperature. However, a critical temperature range, 550-650 ℃, was introduced here. Aging in this range led to a significant decrease in toughness and notable increase in hardness. The formation of intermetallic phases such as CT was recognized as the major reason for the observed changes.展开更多
A new resource-saving duplex stainless steel with composition of 19Cr-6Mn-1.0Mo-0.5Ni-0.5W-0.5Cu-0.2N has been developed,and the microstructure,mechanical properties and corrosion properties have been investigated.The...A new resource-saving duplex stainless steel with composition of 19Cr-6Mn-1.0Mo-0.5Ni-0.5W-0.5Cu-0.2N has been developed,and the microstructure,mechanical properties and corrosion properties have been investigated.The results show that the alloy has a balanced ferrite-austenite relation,and the ferrite content rises with the solution treatment temperature.The designed alloy is free of precipitation of sigma phase when aged at 650,750 and 850 ℃ for 3 h,respectively,whereas a few Cr23C6 precipitates are found after being aged at 750 ℃ for 8 h.Charpy impact tests indicate that the impact energy of the alloy is 68,200 and 220 J at-40,0 and 25 ℃,respectively.The designed alloy solution treated at 1050 ℃ for 30 min has a much higher yield strength and similar corrosion resistance compared with those of AISI 304 austenitic stainless steel.Moreover,the production cost of the alloy is about $ 1000 per ton which is lower than that of AISI 304.展开更多
During aging at a temperature ranging from 650 -950 ℃,the ferric matrix in duplex stainless steels undergoes various decomposition processes which could form the precipitates of the Sigma （σ） and Chi （X） phases,...During aging at a temperature ranging from 650 -950 ℃,the ferric matrix in duplex stainless steels undergoes various decomposition processes which could form the precipitates of the Sigma （σ） and Chi （X） phases, as well as nitrides. It is well known that these precipitates lead to a reduction in creep ductility and adversely affect toughness and corrosion properties of steel. This experiment carded out qualitative and quantitative analyses of intermetallic phases and nitrides and established an analytical procedure, including specimen preparation, the choosing of the electrolyte and electrolytic systems,electrolytic isolation,wet chemical separation, and physical and chemical analysis, etc. The residues were collected by ultrasonic cleaning and filtration after galvanostatic electrolysis. Dynamic laser scattering sizer （DLS- sizer） ,scanning electron microscope （SEM） and transmission electron microscope （TEM） were used to examine their structure,modality and size. Qualitative and quantitative analyses were performed by using X-ray diffraction （XRD）, oxygen-nitrogen analyzer and wet chemical analysis. Furthermore, there is a discussion on the effect of isothermal treatment on precipitation that occurs at different temperatures for different periods of time.展开更多
Improved life assessment techniques will enable engineering components to be replaced before failure, thereby reducing the risk of industrial accidents as well as minimizing financial loss due to unscheduled outages. ...Improved life assessment techniques will enable engineering components to be replaced before failure, thereby reducing the risk of industrial accidents as well as minimizing financial loss due to unscheduled outages. For components operating at high temperatures, temperature measurement is very important. In many situations, the environmental conditions are too hostile for conventional techniques to be used. Researchers over the world have been looking for new techniques for temperature measurement and one such device, called Feroplug, has been developed previously by the and coworkers. The Feroplug has been patented in USA, UK and Europe by the British Technology Group. The underlying principle of the Feroplug is based on the transformation of ferrite in some specially designed duplex stainless steels. This paper describes a new invention called Sigmaplug which is a new development of the Feroplug but using an entirely different physical principle. It was discovered that the sigma phase in Fe展开更多
Phase field simulations of phase separation in Fe-Cr binary alloys were performed by using the Cahn-Hilliard diffusion function. A new mobility model in relation to aging temperature and Cr content was used in the sim...Phase field simulations of phase separation in Fe-Cr binary alloys were performed by using the Cahn-Hilliard diffusion function. A new mobility model in relation to aging temperature and Cr content was used in the simulations. Two alloys of Fe-30at%Cr and Fe-35at%Cr were investigated at two different aging temperatures of 573 and 673 K. The phase separation kinetics was found to consist of three stages： wavelength modulation, amplitude increase, and coarsening of Cr-enriched regions. A higher thermal aging temperature accelerated the phase separation and increased the wavelength of concentration fluctuation. While the effect of Cr content on the phase separation kinetics was slight, Fe-Cr alloys with a higher Cr content were found to generate a larger number and a finer size of Cr-enriched regions. The simulation results provide consultation for design and safe operation of duplex stainless steel pipes in nuclear power plants.展开更多
Analysis ofZ phase precipitation in 2205 duplex stainless steel aged at 700 and 750 ~C has been investigated systematically. The experimental results showed that X phase forms prior to the precipitation of δ phase an...Analysis ofZ phase precipitation in 2205 duplex stainless steel aged at 700 and 750 ~C has been investigated systematically. The experimental results showed that X phase forms prior to the precipitation of δ phase and disappears once tr phase starts to precipitate. This phenomenon indicates that a phase nucleated and consumed the Z phase. The δ phase nucleated mairdy at ferrite/austenite interface and grew inwards into the ferrite phase. The morphology of a phase reveals a coral-like structure at the temperature of 700 ℃ for 120 min followed by quenching in water. The decomposition of ferrite occurs via the following eutectoid reaction： F---＊o＇＋y2. The selected area diffraction pattern of zone axes is[3 1 3-][3 1 3], indicating a characteristic orientation relationship between X phase and δ-ferrite.展开更多
Phase transformation is one of the factors that would significantly influence the ability to resist cavitation erosion of stainless steels. Due to the specific properties of duplex stainless steel, the heat treatment ...Phase transformation is one of the factors that would significantly influence the ability to resist cavitation erosion of stainless steels. Due to the specific properties of duplex stainless steel, the heat treatment would bring about significant phase transformations. In this paper, we have examined the previous studies on the phase transition of stainless steel, including the literature on the classification of stainless steel, spinodal decomposition, sigma phase transformation, and cavitation erosion of double stainless steel. Through these literature investigations, the destruction of cavitation erosion on duplex stainless steel can be clearly known, and the causes of failure of duplex stainless steel in seawater can be clarified, thus providing a theoretical basis for subsequent scientific research. And the review is about to help assess the possibility of using bulk heat treatment to improve the cavitation erosion (CE) behaviour of the duplex stainless steel 7MoPLUS.展开更多
SAF2507 plates （ 12 mm thickness ） were welded using shield metal arc welding （SMAW） process with E2594 electrode. The microstructure, o-phase, and impact fraetograph of the welded joints were analyzed using optic...SAF2507 plates （ 12 mm thickness ） were welded using shield metal arc welding （SMAW） process with E2594 electrode. The microstructure, o-phase, and impact fraetograph of the welded joints were analyzed using optical microscope and scanning electron mieroseope. The results show that the fusion zone consists of ferrite, chromium nitride, and secondary aastenite precipitation when welding is performed at low heat input （0. 5 kJ/mm）. However, the increase in heat input causes precipitation of brittle o＂ phase at the y/c~ interface in weld metal and heat-affected zone, as well as a brittle fracture along the grain boundary. Heat input in the range of O. 5 kJ/mm to 1.5 kJ/mm is suitable for joining SAF2507 plates.展开更多
： The effect of isothermal aging treatment on the mechanical and corrosion properties of 2205 duplex stainless steel was investigated by means of impact toughness test and micro-hardness measurement in combination wi...： The effect of isothermal aging treatment on the mechanical and corrosion properties of 2205 duplex stainless steel was investigated by means of impact toughness test and micro-hardness measurement in combination with the critical pitting temperature （CPT） technique. The corresponding fractography of the steel was then observed after the impact toughness test. The results demonstrated that, at the critical temperature for precipitation of the sigma （σ） phase, e. g., 850 ℃, the impact toughness decreased rapidly and the micro-hardness increased gradually with increasing aging time. The CPT decreased from 61 to 15 ℃ as the aging time increased from 4 rain to 8 h. In addition, optical microscopy, transmission electron microscope （TEM） and X-ray diffraction studies showed that the ferrite in the steel transformed into secondary austenite and σ phase.展开更多
Very high cycle fatigue behaviors of two bainite/martensite dual-phase steels were investigated.One of the steels was cyclic rapid heat treated and its microstructures were refined. Fatigue strength of the steel is 22...Very high cycle fatigue behaviors of two bainite/martensite dual-phase steels were investigated.One of the steels was cyclic rapid heat treated and its microstructures were refined. Fatigue strength of the steel is 225 MPa higher than that without refining.Observation of fracture surfaces show that the fatigue cracks initiate at bainites for non-refined steel and at non-metallic inclusions for the refined steel.The size of inclusions is much smaller than that of bainites which results in the improvement of fatigue strength.展开更多
Duplex stainless steel UNS S31803 samples were cross-rolled with a true strain of ε = 2 followed by annealing at 1323 K for 2 min and 240 min, respectively. The distributions of intervariant boundary planes in the pr...Duplex stainless steel UNS S31803 samples were cross-rolled with a true strain of ε = 2 followed by annealing at 1323 K for 2 min and 240 min, respectively. The distributions of intervariant boundary planes in the precipitated austenite（A） from ferrite（F） and phase boundary planes conforming to Kurdjumov-Sache（K-S） orientation relationship（OR） were characterized by electron backscatter diffraction（EBSD） and the five-para me ter analysis（FPA） method, respectively. The intervariant boundary planes with misorientation angle of 60° around 〈111 〉 and 〈011 〉 occur frequently and tend to terminate on the {111} plane. At the grain size level of 4 μm, the phase boundary appears to be connected with the K-S OR terminating on{110}F ｜｜ {111}A at the early stage of annealing. When the grain size reaches approximately 20 μm, phase boundary was modified into {541}F｜｜{533}A due to twinning in austenite during annealing.展开更多
基金Item Sponsored by Special Project of Education Depart ment of Shaanxi Province of China (07JK309)Project of Science andTechnology Research and Development Program of Shaanxi Province of China (2010K10-13)
文摘The effects of phase transformation on mechanical properties and pitting corrosion of 2205 duplex stainless steel were investigated. The amount of a phase in the test specimen varied up to a maximum of 6 % by thermal treatment at 850 ℃ for up to 60 min. The results showed that ~ phase markedly increased the hardness and decreased the impact toughness of the test steel. But the increasing tendency of the ultimate tensile strength and the yield strength was not obvious, while the total elongation abruptly decreased with the aging time from 5 to 60 min. SEM impact microfractograph analysis revealed that the types of impact fracture changed from ductile mode to transcrystalline mode when the specimens were aged for 5-60 min. Furthermore, the extent of pitting potential reducing was found to be strongly temperature dependent, more pronounced at the higher temperature. During the incubation period of σ phase nucleation, the pitting corrosion test temperature and the aging time had collaborative effects on evidently displacing the pitting potential towards less noble values. After 15 min, the higher temperature contributed more to decreasing the pitting potential than the aging time.
基金Item Sponsored by National Natural Science Foundation of China(51371123)Special Scientific Research Fund for the Doctoral Program of Higher Education of China(2013140211003)Natural Science Foundation of Shanxi Province of China(2014011002)
文摘Correlation between pitting corrosion behavior and chi（ χ ）phase formed after a short-term aging（5,10 and 15 min）at 850 ℃ of 2205 duplex stainless steel（DSS）was investigated using potentiodynamic polarization tests,optical microscopy,and scanning electron microscopy equipped with energy-dispersive spectrum system.Results showed that after aging for 5min,the χ phase initially precipitated at ferrite grain boundaries,developed and then became linked with prolonging aging time.The χ phase was rich in Cr and Mo,resulting in formation of depleted zones nearby.The χ phase could reduce corrosion resistance of DSS and slightly influence its stability,but the specimens still displayed the capacity for repassivation.Some lines of evidence showed that stable pitting corrosion initiated at the boundaries of precipitates.The χ phase was selectively corroded during the first stage of corrosion and then the depleted zones nearby were attacked.In addition,the grain size and volume of precipitates also affected pit nucleation and progress,and suitable size and distribution of χ phase could aggravate pit initiation at precipitate boundaries.The χ phase with considerably low volume fraction and small size was not sensitive position for pit initiation.
文摘In this research,aging treatments at temperatures of 800 and 900°C for different aging time of 5-60 min were conducted on solution treated as well as hot worked samples of 2205 dual phase stainless steel.The effect of aging treatment on precipitation of intermetallic phases was investigated in undeformed specimens and those subjected to hot deformation with different strain rates of 0.001-1 s-1.It was found that σ precipitation increased by hot working.It was also concluded that the volume fraction of phase increased with deformation temperature and decreased with strain rate.The precipitation of intermetallic phases（i.e.σ and χ） was analyzed by an Avrami-type kinetics equation of %（σ＋χ）=A（1-exp（-ktn）） and the values of n and ln k were estimated for different thermomechanical regimes.The values of n were assessed to increase from 0.4 to 1 with strain rate in the studied range.Otherwise,It was also understood that ln k decreased with strain rate.Microstructural observations by means of optical microscopy and scanning electron microscopy showed that σ particles mostly nucleated at the ferrite-austenite interfaces.But no sign of χ-phase could be seen.This fortified the idea of certain literature that χ-phase always forms at early stages of aging and consumes through the precipitation of σ.
文摘Duplex stainless steels （DSS） with ferritic-austenitic microstructures offer good combination of resistance to pitting corrosion and high strength that are not concomitantly attainable using conventional single phase austenitic or ferritic stainless steels, The DSS used in this investigation was 2205 alloy having a stable microstructure consisting of about 45% ferrite and 55% austenite at ambient temperature. In order to investigate aging behavior of this steel and the influences on mechanical properties, different aging treatments were conducted at temperatures of 350-950℃ for various aging time of 15, 30, 60 and 180 min. The aged specimens were subjected to impact testing and hardness measurements. Finally, the changes in microstructure due to aging were studied by optical and scanning electron microscopy. The results showed that aging at temperatures lower than 550℃ for different time had negligible effects on mechanical properties. Besides, no considerable changes in term of precipitation of harmful intermetallic particles were observed in microstructure below this temperature. However, a critical temperature range, 550-650 ℃, was introduced here. Aging in this range led to a significant decrease in toughness and notable increase in hardness. The formation of intermetallic phases such as CT was recognized as the major reason for the observed changes.
基金Item Sponsored by Key Project of Science and Technology Commission of Shanghai Municipality of China(065211026)Innovation Fund of Education Commission of Shanghai Municipality of China(09yz20)
文摘A new resource-saving duplex stainless steel with composition of 19Cr-6Mn-1.0Mo-0.5Ni-0.5W-0.5Cu-0.2N has been developed,and the microstructure,mechanical properties and corrosion properties have been investigated.The results show that the alloy has a balanced ferrite-austenite relation,and the ferrite content rises with the solution treatment temperature.The designed alloy is free of precipitation of sigma phase when aged at 650,750 and 850 ℃ for 3 h,respectively,whereas a few Cr23C6 precipitates are found after being aged at 750 ℃ for 8 h.Charpy impact tests indicate that the impact energy of the alloy is 68,200 and 220 J at-40,0 and 25 ℃,respectively.The designed alloy solution treated at 1050 ℃ for 30 min has a much higher yield strength and similar corrosion resistance compared with those of AISI 304 austenitic stainless steel.Moreover,the production cost of the alloy is about $ 1000 per ton which is lower than that of AISI 304.
文摘During aging at a temperature ranging from 650 -950 ℃,the ferric matrix in duplex stainless steels undergoes various decomposition processes which could form the precipitates of the Sigma （σ） and Chi （X） phases, as well as nitrides. It is well known that these precipitates lead to a reduction in creep ductility and adversely affect toughness and corrosion properties of steel. This experiment carded out qualitative and quantitative analyses of intermetallic phases and nitrides and established an analytical procedure, including specimen preparation, the choosing of the electrolyte and electrolytic systems,electrolytic isolation,wet chemical separation, and physical and chemical analysis, etc. The residues were collected by ultrasonic cleaning and filtration after galvanostatic electrolysis. Dynamic laser scattering sizer （DLS- sizer） ,scanning electron microscope （SEM） and transmission electron microscope （TEM） were used to examine their structure,modality and size. Qualitative and quantitative analyses were performed by using X-ray diffraction （XRD）, oxygen-nitrogen analyzer and wet chemical analysis. Furthermore, there is a discussion on the effect of isothermal treatment on precipitation that occurs at different temperatures for different periods of time.
文摘Improved life assessment techniques will enable engineering components to be replaced before failure, thereby reducing the risk of industrial accidents as well as minimizing financial loss due to unscheduled outages. For components operating at high temperatures, temperature measurement is very important. In many situations, the environmental conditions are too hostile for conventional techniques to be used. Researchers over the world have been looking for new techniques for temperature measurement and one such device, called Feroplug, has been developed previously by the and coworkers. The Feroplug has been patented in USA, UK and Europe by the British Technology Group. The underlying principle of the Feroplug is based on the transformation of ferrite in some specially designed duplex stainless steels. This paper describes a new invention called Sigmaplug which is a new development of the Feroplug but using an entirely different physical principle. It was discovered that the sigma phase in Fe
基金the National High-Tech Research and Development Program of China(Nos.2012AA03A507 and 2012AA050901)the Na-tional Science and Technology Major Project of China(No.2011ZX06004)
文摘Phase field simulations of phase separation in Fe-Cr binary alloys were performed by using the Cahn-Hilliard diffusion function. A new mobility model in relation to aging temperature and Cr content was used in the simulations. Two alloys of Fe-30at%Cr and Fe-35at%Cr were investigated at two different aging temperatures of 573 and 673 K. The phase separation kinetics was found to consist of three stages： wavelength modulation, amplitude increase, and coarsening of Cr-enriched regions. A higher thermal aging temperature accelerated the phase separation and increased the wavelength of concentration fluctuation. While the effect of Cr content on the phase separation kinetics was slight, Fe-Cr alloys with a higher Cr content were found to generate a larger number and a finer size of Cr-enriched regions. The simulation results provide consultation for design and safe operation of duplex stainless steel pipes in nuclear power plants.
基金Funded by the School Foundation of North University of China,the Science and Technology Projects of Jiancaoping District of Taiyuan Citythe Natural Science Foundation of Shanxi Province,China(Nos.2013011014-1,2015011036,2014011024-1)the National Natural Science Foundation of China(No.51201154)
文摘Analysis ofZ phase precipitation in 2205 duplex stainless steel aged at 700 and 750 ~C has been investigated systematically. The experimental results showed that X phase forms prior to the precipitation of δ phase and disappears once tr phase starts to precipitate. This phenomenon indicates that a phase nucleated and consumed the Z phase. The δ phase nucleated mairdy at ferrite/austenite interface and grew inwards into the ferrite phase. The morphology of a phase reveals a coral-like structure at the temperature of 700 ℃ for 120 min followed by quenching in water. The decomposition of ferrite occurs via the following eutectoid reaction： F---＊o＇＋y2. The selected area diffraction pattern of zone axes is[3 1 3-][3 1 3], indicating a characteristic orientation relationship between X phase and δ-ferrite.
文摘Phase transformation is one of the factors that would significantly influence the ability to resist cavitation erosion of stainless steels. Due to the specific properties of duplex stainless steel, the heat treatment would bring about significant phase transformations. In this paper, we have examined the previous studies on the phase transition of stainless steel, including the literature on the classification of stainless steel, spinodal decomposition, sigma phase transformation, and cavitation erosion of double stainless steel. Through these literature investigations, the destruction of cavitation erosion on duplex stainless steel can be clearly known, and the causes of failure of duplex stainless steel in seawater can be clarified, thus providing a theoretical basis for subsequent scientific research. And the review is about to help assess the possibility of using bulk heat treatment to improve the cavitation erosion (CE) behaviour of the duplex stainless steel 7MoPLUS.
文摘SAF2507 plates （ 12 mm thickness ） were welded using shield metal arc welding （SMAW） process with E2594 electrode. The microstructure, o-phase, and impact fraetograph of the welded joints were analyzed using optical microscope and scanning electron mieroseope. The results show that the fusion zone consists of ferrite, chromium nitride, and secondary aastenite precipitation when welding is performed at low heat input （0. 5 kJ/mm）. However, the increase in heat input causes precipitation of brittle o＂ phase at the y/c~ interface in weld metal and heat-affected zone, as well as a brittle fracture along the grain boundary. Heat input in the range of O. 5 kJ/mm to 1.5 kJ/mm is suitable for joining SAF2507 plates.
文摘： The effect of isothermal aging treatment on the mechanical and corrosion properties of 2205 duplex stainless steel was investigated by means of impact toughness test and micro-hardness measurement in combination with the critical pitting temperature （CPT） technique. The corresponding fractography of the steel was then observed after the impact toughness test. The results demonstrated that, at the critical temperature for precipitation of the sigma （σ） phase, e. g., 850 ℃, the impact toughness decreased rapidly and the micro-hardness increased gradually with increasing aging time. The CPT decreased from 61 to 15 ℃ as the aging time increased from 4 rain to 8 h. In addition, optical microscopy, transmission electron microscope （TEM） and X-ray diffraction studies showed that the ferrite in the steel transformed into secondary austenite and σ phase.
文摘Very high cycle fatigue behaviors of two bainite/martensite dual-phase steels were investigated.One of the steels was cyclic rapid heat treated and its microstructures were refined. Fatigue strength of the steel is 225 MPa higher than that without refining.Observation of fracture surfaces show that the fatigue cracks initiate at bainites for non-refined steel and at non-metallic inclusions for the refined steel.The size of inclusions is much smaller than that of bainites which results in the improvement of fatigue strength.
基金financially by the National Natural Science Foundation of China (Nos. 51471100 and 51171095)
文摘Duplex stainless steel UNS S31803 samples were cross-rolled with a true strain of ε = 2 followed by annealing at 1323 K for 2 min and 240 min, respectively. The distributions of intervariant boundary planes in the precipitated austenite（A） from ferrite（F） and phase boundary planes conforming to Kurdjumov-Sache（K-S） orientation relationship（OR） were characterized by electron backscatter diffraction（EBSD） and the five-para me ter analysis（FPA） method, respectively. The intervariant boundary planes with misorientation angle of 60° around 〈111 〉 and 〈011 〉 occur frequently and tend to terminate on the {111} plane. At the grain size level of 4 μm, the phase boundary appears to be connected with the K-S OR terminating on{110}F ｜｜ {111}A at the early stage of annealing. When the grain size reaches approximately 20 μm, phase boundary was modified into {541}F｜｜{533}A due to twinning in austenite during annealing.
