In this paper the authors discussed the depedence of crack initiation properties on potential and the effect of microstructures on the crack initiation and propagation properties in duplex stainless steels. It was clear that at less noble potential crack initiation occured from ferritic phase near the tip of austenitic phase which was controled by HESCC in this region. On the other hand, at noble potential crack initiated from corrosion pets which was formed at the boundary of ferritic and austenitic phases. As the effect of potential on the time to failure with decreasing the potential the time to failure decreased greatly both in a single ferritic phase stainless steel and duplex stainless steels, but even at the potential of -1.5V vs SCE there were no failures to he observed in a single austentic phase stainless steel, which means that austenitic phase is unsusceptible to HESCC. Additionally, as the effecc of ferrite content on HESCC properties of duplex stainless steels, with decreasing ferrite content the threshold stress increased and crack growth rate decreased greatly, which means that austenitic phase has a keying effect on crack propagating through ferritic phase. At the region of ferrite content less than 45%, threshold stress was nearly as same as the tensile strength of the materials and crack could not propagate through austenitic phase because of the continuousness of the austenitic phase which will prevent crack propagating through ferritic phase. Therefore, ferrite content of 45% should be considered as a critical value for crack initiating and propagating in duplex stainless steels.
本文讨论了双相不锈钢裂纹起裂性能与电位的关系以及微观组织对裂纹起裂和扩展性能的影响。结果表明，在较低的电位下，裂纹起源于奥氏体尖端附近的铁素体相，该区域受HESCC控制。另一方面，在铁素体与奥氏体相界处形成的腐蚀带引发了高电位裂纹。电势对失效时间的影响随着电势的减小，单铁素体相不锈钢和双相不锈钢的失效时间都大大缩短，但即使在-1.5V vs SCE的电势下，单奥氏体相不锈钢中也没有观察到失效，这意味着奥氏体相对HESCC不敏感。此外，由于铁素体含量对双相不锈钢HESCC性能的影响，随着铁素体含量的降低，阈值应力增加，裂纹扩展速率大大降低，这意味着奥氏体相对裂纹通过铁素体相扩展起关键作用。在铁素体含量小于45%的区域，阈值应力与材料的抗拉强度基本一致，由于奥氏体相的连续性，裂纹无法通过奥氏体相扩展，从而阻止了裂纹通过铁素体相扩展。因此，45%的铁素体含量是双相不锈钢裂纹萌生和扩展的临界值。
{"title":"Effect of Electrode Potential and Structure on the Susceptibility to HESCC in Duplex Stainless Steels Analytical Evaluation of Hydrogen Embrittlement Type SCC and Its Mechanism in Duplex Stainless Steel Welds","authors":"Y. Mukai, M. Murata, Jing-bo Wang","doi":"10.2207/QJJWS.9.245","DOIUrl":"https://doi.org/10.2207/QJJWS.9.245","url":null,"abstract":"In this paper the authors discussed the depedence of crack initiation properties on potential and the effect of microstructures on the crack initiation and propagation properties in duplex stainless steels. It was clear that at less noble potential crack initiation occured from ferritic phase near the tip of austenitic phase which was controled by HESCC in this region. On the other hand, at noble potential crack initiated from corrosion pets which was formed at the boundary of ferritic and austenitic phases. As the effect of potential on the time to failure with decreasing the potential the time to failure decreased greatly both in a single ferritic phase stainless steel and duplex stainless steels, but even at the potential of -1.5V vs SCE there were no failures to he observed in a single austentic phase stainless steel, which means that austenitic phase is unsusceptible to HESCC. Additionally, as the effecc of ferrite content on HESCC properties of duplex stainless steels, with decreasing ferrite content the threshold stress increased and crack growth rate decreased greatly, which means that austenitic phase has a keying effect on crack propagating through ferritic phase. At the region of ferrite content less than 45%, threshold stress was nearly as same as the tensile strength of the materials and crack could not propagate through austenitic phase because of the continuousness of the austenitic phase which will prevent crack propagating through ferritic phase. Therefore, ferrite content of 45% should be considered as a critical value for crack initiating and propagating in duplex stainless steels.","PeriodicalId":273687,"journal":{"name":"Transactions of the Japan Welding Society","volume":"66 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126187820","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1900-01-01DOI: 10.2207/qjjws1943.50.373
S. Nakata, Nobuharu Sakabata, Minoru Mouko
Influence of the cross-sectional area of consumable nozzle on the penetration in base plate and its stability and the possibility on the control of welding phenomena by changing the nozzle current is investigated using the mild steel plate with the thickness of 30 mm to develop narrow gap electroslag welding process with high efficiency and low heat input.It is experimentaly shown that the nozzle with large crosssectional area is useful in stable and high current welding process because of dispersing the welding current in slag pool by increasing the nozzle current. So, the method for estimating the nozzle current during welding is designed and, by this method, the nozzle current is estimated under various conditions in connection with the cross-sectional area of the nozzle.Adopting above results to high current narrow gap welding process, it is clarified that more stable and uniform penetration can be obtained by using the nozzle with large cross-sectional area. This result is due to the preheating effect at root faces of base plate in slag pool and dispersing the heat source in slag pool by increase of nozzle current.
{"title":"Influence of the Cross-sectional Area of Consumable Nozzle on Welding Phenomena in Electrosalg Welding","authors":"S. Nakata, Nobuharu Sakabata, Minoru Mouko","doi":"10.2207/qjjws1943.50.373","DOIUrl":"https://doi.org/10.2207/qjjws1943.50.373","url":null,"abstract":"Influence of the cross-sectional area of consumable nozzle on the penetration in base plate and its stability and the possibility on the control of welding phenomena by changing the nozzle current is investigated using the mild steel plate with the thickness of 30 mm to develop narrow gap electroslag welding process with high efficiency and low heat input.It is experimentaly shown that the nozzle with large crosssectional area is useful in stable and high current welding process because of dispersing the welding current in slag pool by increasing the nozzle current. So, the method for estimating the nozzle current during welding is designed and, by this method, the nozzle current is estimated under various conditions in connection with the cross-sectional area of the nozzle.Adopting above results to high current narrow gap welding process, it is clarified that more stable and uniform penetration can be obtained by using the nozzle with large cross-sectional area. This result is due to the preheating effect at root faces of base plate in slag pool and dispersing the heat source in slag pool by increase of nozzle current.","PeriodicalId":273687,"journal":{"name":"Transactions of the Japan Welding Society","volume":"1242 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114694094","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Carbide precipitation in niclel based alloy takes place at elevated temperature. The tendency of this phenomenon is stronger than in austenitic stainless steel. But the carbide precipitation in HAZ of nickel based alloy has not been investigated enough as that of austenitic stainless steel.The effect of weld thermal cycle on carbide precipiration of 15Cr-75Ni alloy (UNS N06600) and its relation with intergranular corrosion in nitric acid were investigated. And prevention of sensitization in HAZ was investigated from the view point of chemical composition.The susceptibility to intergarnular corrosion in HAZ agreed with the carbide behavior during weld thermal cycle and aging so far as the aging heat treatment condition of this work. The carbide in the base metal overaged is solid soluted and nucleates at the grain boundary by weld thermal cycle, and the carbide precipitated and grew during aging. The chrominm depleted zone has not healed after aged for 15 hours at 823K, so the carbide caused the intergranular sensitization.The sensitization in HAZ of 15Cr-75Ni Alloy can be prevented by the suitable addition of Nb; Nb/ C<40 in weight ratio.
{"title":"Carbide Precipitation and Corrosion Resistance in HAZ of 15Cr-75Ni Alloy","authors":"K. Ogawa, M. Miura, T. Minami","doi":"10.2207/QJJWS.6.530","DOIUrl":"https://doi.org/10.2207/QJJWS.6.530","url":null,"abstract":"Carbide precipitation in niclel based alloy takes place at elevated temperature. The tendency of this phenomenon is stronger than in austenitic stainless steel. But the carbide precipitation in HAZ of nickel based alloy has not been investigated enough as that of austenitic stainless steel.The effect of weld thermal cycle on carbide precipiration of 15Cr-75Ni alloy (UNS N06600) and its relation with intergranular corrosion in nitric acid were investigated. And prevention of sensitization in HAZ was investigated from the view point of chemical composition.The susceptibility to intergarnular corrosion in HAZ agreed with the carbide behavior during weld thermal cycle and aging so far as the aging heat treatment condition of this work. The carbide in the base metal overaged is solid soluted and nucleates at the grain boundary by weld thermal cycle, and the carbide precipitated and grew during aging. The chrominm depleted zone has not healed after aged for 15 hours at 823K, so the carbide caused the intergranular sensitization.The sensitization in HAZ of 15Cr-75Ni Alloy can be prevented by the suitable addition of Nb; Nb/ C<40 in weight ratio.","PeriodicalId":273687,"journal":{"name":"Transactions of the Japan Welding Society","volume":"64 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121418942","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Continuous postheating for 1-5 hours at same temperature as preheating was carried out on weld cracking test of 80 kgf/mm2 tension steel, and following result were obtained.(1) Continuous postheating was recognized to be very useful to reduce the preheating temperature to prevent weld cracking.(2) The preheating temperature was reduced to 80°C by 1 hour postheating from 150°C which is the temperature without any postheating, and to 60°C by 5 hour postheating.
{"title":"Effect of Continuous Postheating Time on Reduction of Preheating Temperature.","authors":"Y. Nishio, Kozo Kito, S. Kanemitsu","doi":"10.2207/QJJWS.9.442","DOIUrl":"https://doi.org/10.2207/QJJWS.9.442","url":null,"abstract":"Continuous postheating for 1-5 hours at same temperature as preheating was carried out on weld cracking test of 80 kgf/mm2 tension steel, and following result were obtained.(1) Continuous postheating was recognized to be very useful to reduce the preheating temperature to prevent weld cracking.(2) The preheating temperature was reduced to 80°C by 1 hour postheating from 150°C which is the temperature without any postheating, and to 60°C by 5 hour postheating.","PeriodicalId":273687,"journal":{"name":"Transactions of the Japan Welding Society","volume":"83 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123930033","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Mechanical and metallurgical heterogeneity in wled joints, which is caused by thermal prestraining cycles, have an important effect upon their deformation and strength behaviors. If the mechanical properties of steels and weld metals subjected to thermal prestraining cycles can be estimated conveniently, it is easy to analyze the deformation behaviors of weld joints by use of numerical computation procedures.In this study three kinds of weld metals, which are formed at weld joints of a carbon steel (SM41B), an austenitic stainless steel (SUS304) and a martensitic cast steel (SCS5), were used for experiments. Their mechanical properties depended upon the thermal prestraining conditions, for example, peak temperature, retention time at constant temperature, multi-thermal prestraining cycles. The experimental results indicated that elastic limit, yield stress, strength coefficient and strain hardening exponent of materials sub-jected to thermal prestraining cycles could be expressed as a function of Vickers hardness.As an application, the material constants for elastic-plastic FEM analysis were determined from the Vickers hardness distribution of weld and butt weld joint were analyzed in terms of plastic zone extension from the view of mechanical heterogeneity.
{"title":"Mechanical properties of weld metals subjected to thermal prestraining cycles and its application to deformation analysis of weld joint.","authors":"Y. Itoh, K. Nagata, Tetsu Yanuki, Tadao Mori","doi":"10.2207/QJJWS.3.862","DOIUrl":"https://doi.org/10.2207/QJJWS.3.862","url":null,"abstract":"Mechanical and metallurgical heterogeneity in wled joints, which is caused by thermal prestraining cycles, have an important effect upon their deformation and strength behaviors. If the mechanical properties of steels and weld metals subjected to thermal prestraining cycles can be estimated conveniently, it is easy to analyze the deformation behaviors of weld joints by use of numerical computation procedures.In this study three kinds of weld metals, which are formed at weld joints of a carbon steel (SM41B), an austenitic stainless steel (SUS304) and a martensitic cast steel (SCS5), were used for experiments. Their mechanical properties depended upon the thermal prestraining conditions, for example, peak temperature, retention time at constant temperature, multi-thermal prestraining cycles. The experimental results indicated that elastic limit, yield stress, strength coefficient and strain hardening exponent of materials sub-jected to thermal prestraining cycles could be expressed as a function of Vickers hardness.As an application, the material constants for elastic-plastic FEM analysis were determined from the Vickers hardness distribution of weld and butt weld joint were analyzed in terms of plastic zone extension from the view of mechanical heterogeneity.","PeriodicalId":273687,"journal":{"name":"Transactions of the Japan Welding Society","volume":"41 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128147059","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Crack closure behavior in fatigue crack propagation process was induced by plastic deformation near crack. In the paper, the effect of plastic deformation on fatigue crack closure in low strength material and its welded joint was studied.The results are as follows. Crack closure would be caused by plastic deformation near crack surface. Generally, crack opening ratio in high yield strength material is higher than that in low yield one. This tendency based on the degree of deformation near crack surface. In addition, in welded joint, crack propagation rate was higher than mother metal, though crack opening ratio showed almost 1 by the effect of residual stress. This could be explained by the effect of restrain for plastic deformation, which was induced by existence of compresive stress field ahead of crack.
{"title":"Effect of Plastic Deformation on Fatigue Crack Closure Behavior in Low Yield Strength Material and Its Welded Joint","authors":"Y. Mukai, M. Murata","doi":"10.2207/qjjws.9.423","DOIUrl":"https://doi.org/10.2207/qjjws.9.423","url":null,"abstract":"Crack closure behavior in fatigue crack propagation process was induced by plastic deformation near crack. In the paper, the effect of plastic deformation on fatigue crack closure in low strength material and its welded joint was studied.The results are as follows. Crack closure would be caused by plastic deformation near crack surface. Generally, crack opening ratio in high yield strength material is higher than that in low yield one. This tendency based on the degree of deformation near crack surface. In addition, in welded joint, crack propagation rate was higher than mother metal, though crack opening ratio showed almost 1 by the effect of residual stress. This could be explained by the effect of restrain for plastic deformation, which was induced by existence of compresive stress field ahead of crack.","PeriodicalId":273687,"journal":{"name":"Transactions of the Japan Welding Society","volume":"56 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126632807","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Arc sensor, which utilizes the welding arc as a sensor, gives important groove information during welding. Automatic seam tracking control system with arc sensor developed by NKK has a fesature, that a turning point of transverse weaving with constant arc length control (AVC) is decided by the condition, when torch height reaches to constant set level. Under applying above control system, variation of groove and deposition area can be detected from the trace of weaving. The automatic real-time bead height control system has been developed utilizing above detected information. The area and width of weaving trace has close corelation with the area of groove and deposition. Experiments conducted with varied groove width proved satisfactory control ability for all position TIG welding.
{"title":"Automatic real-time bead height control with arc sensor in TIG welding.","authors":"H. Nomura, Y. Sugitani, Yasuo Suzuki","doi":"10.2207/QJJWS.4.20","DOIUrl":"https://doi.org/10.2207/QJJWS.4.20","url":null,"abstract":"Arc sensor, which utilizes the welding arc as a sensor, gives important groove information during welding. Automatic seam tracking control system with arc sensor developed by NKK has a fesature, that a turning point of transverse weaving with constant arc length control (AVC) is decided by the condition, when torch height reaches to constant set level. Under applying above control system, variation of groove and deposition area can be detected from the trace of weaving. The automatic real-time bead height control system has been developed utilizing above detected information. The area and width of weaving trace has close corelation with the area of groove and deposition. Experiments conducted with varied groove width proved satisfactory control ability for all position TIG welding.","PeriodicalId":273687,"journal":{"name":"Transactions of the Japan Welding Society","volume":"119 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116609104","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Preheating procedure is applied to prevent cold cracking in steel construction. Then local preheating near the weld line is generally applied, because preheating whole the construction can not be did simultaneously. In case of using electric heaters as means of fecal preheating, the temperature of their heaters can be controlled by sensor fitted on some distance from the weld line. So it is necessary to estimate the temperature on weld line by temperature on the position of sensor.In this report, we derive the theoretical formula that finds the temperature of the other position but weld line during preheating, and cooling temperature and time on the weld line can be estimated by using the calculated values. We compared experimental data under various welding conditions with calculated values.
{"title":"Predicting Heating and Cooling Times due to Local Preheating","authors":"T. Terasaki, K. Ishimoto","doi":"10.2207/QJJWS.9.446","DOIUrl":"https://doi.org/10.2207/QJJWS.9.446","url":null,"abstract":"Preheating procedure is applied to prevent cold cracking in steel construction. Then local preheating near the weld line is generally applied, because preheating whole the construction can not be did simultaneously. In case of using electric heaters as means of fecal preheating, the temperature of their heaters can be controlled by sensor fitted on some distance from the weld line. So it is necessary to estimate the temperature on weld line by temperature on the position of sensor.In this report, we derive the theoretical formula that finds the temperature of the other position but weld line during preheating, and cooling temperature and time on the weld line can be estimated by using the calculated values. We compared experimental data under various welding conditions with calculated values.","PeriodicalId":273687,"journal":{"name":"Transactions of the Japan Welding Society","volume":"128 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115712463","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The automatic seam tracking system by arc sensor method developed by NKK has an original feature, that a weaving arc in a groove performs groove surface tracking under constant arc length control (AVC or ACC) and the turning point of weaving is controlled by the condition when torch height reaches to constant preset level. In this system, weaving width well corresponds to groove width independently to variation of deposited amount of metal. Namely, variation value of weaving width is same as that of groove width. Based on this relationship, welding speed control system has been developed. Where, only the variation value of weaving width is used as detected parameter, and optimum value of welding speed to keep bead height constant is calculated and output at every cycle of weaving. The pulsed MAG arc welding system for multi-pass welding of V shaped butt joint has been developed. Main function of this system is adaptive microcomputer control with above mentioned arc sensor method, such as seam tracking, weaving width control and bead height control for every pass of welding.In addition, following functions are also composed: built-up sequence control where number of passes is automatically decided from weaving width, simplified operating system by man-machine dialogic style with liquid crystal display and a key board, and use of a couple of optical fiber cable for transmission of multiple control signals. This system has been already applied to the fabrication of steel box columns.
{"title":"Automatic Real-Time Bead Height Control with Arc Sensor (Report 2) : Development of Multi-Pass MAG Arc Welding System","authors":"H. Nomura, Y. Sugitani, N. Tamaoki","doi":"10.2207/QJJWS.4.508","DOIUrl":"https://doi.org/10.2207/QJJWS.4.508","url":null,"abstract":"The automatic seam tracking system by arc sensor method developed by NKK has an original feature, that a weaving arc in a groove performs groove surface tracking under constant arc length control (AVC or ACC) and the turning point of weaving is controlled by the condition when torch height reaches to constant preset level. In this system, weaving width well corresponds to groove width independently to variation of deposited amount of metal. Namely, variation value of weaving width is same as that of groove width. Based on this relationship, welding speed control system has been developed. Where, only the variation value of weaving width is used as detected parameter, and optimum value of welding speed to keep bead height constant is calculated and output at every cycle of weaving. The pulsed MAG arc welding system for multi-pass welding of V shaped butt joint has been developed. Main function of this system is adaptive microcomputer control with above mentioned arc sensor method, such as seam tracking, weaving width control and bead height control for every pass of welding.In addition, following functions are also composed: built-up sequence control where number of passes is automatically decided from weaving width, simplified operating system by man-machine dialogic style with liquid crystal display and a key board, and use of a couple of optical fiber cable for transmission of multiple control signals. This system has been already applied to the fabrication of steel box columns.","PeriodicalId":273687,"journal":{"name":"Transactions of the Japan Welding Society","volume":"36 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130766146","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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