Improvement of fabrication efficiency and part performance was the main challenge for the large-scale powder bed fusion(PBF)process.In this study,a dynamic monitoring and feedback system of powder bed temperature fiel...Improvement of fabrication efficiency and part performance was the main challenge for the large-scale powder bed fusion(PBF)process.In this study,a dynamic monitoring and feedback system of powder bed temperature field using an infrared thermal imager has been established and integrated into a four-laser PBF equipment with a working area of 2000 mm×2000 mm.The heat-affected zone(HAZ)temperature field has been controlled by adjusting the scanning speed dynamically.Simultaneously,the relationship among spot size,HAZ temperature,and part performance has been established.The fluctuation of the HAZ temperature in four-laser scanning areas was decreased from 30.85℃to 17.41℃.Thus,the consistency of the sintering performance of the produced large component has been improved.Based on the controllable temperature field,a dynamically adjusting strategy for laser spot size was proposed,by which the fabrication efficiency was improved up to 65.38%.The current research results were of great significance to the further industrial applications of large-scale PBF equipment.展开更多
The evolution of the microstructure and toughness of APL5L X80 pipeline steel after thermal welding simulation was investigated by X-ray diffraction,electron backscatter diffraction,and transmission electron microscop...The evolution of the microstructure and toughness of APL5L X80 pipeline steel after thermal welding simulation was investigated by X-ray diffraction,electron backscatter diffraction,and transmission electron microscopy.The results indicated that primary heat-affected zones can be divided into weld,coarse-grained,fine-grained,intercritical,and sub-critical zones.The microstructure of the weld zone is mainly composed of bainitic ferrite and a small amount of granular bainite;however,the original austenite grains are distributed in the columnar grains.The structure of the coarse-grained zone is similar to that of the weld zone,but the original austenite grains are equiaxed.In contrast,the microstructure in the fine-grained zone is dominated by fine granular bainite,and the effective grain size is only 8.15μm,thus providing the highest toughness in the entire heat-affected zone.The intercritical and subcritical zones were brittle valley regions,and the microstructure was dominated by granular bainite.However,the martensite-austenite(M/A)constituents are present in island chains along the grain boundaries,and the coarse size of the M/A constituents seriously reduces the toughness.The results of the crack propagation analyzes revealed that high-angle grain boundaries can significantly slow down crack growth and change the crack direction,thereby increasing the material toughness.The impact toughness of the low-temperature tempering zone was equivalent to that of the columnar grain zone,and the impact toughness was between those of the critical and fine-grained zones.展开更多
The relationship between the t8/5 and micro-hardness, impact toughness in the heat affected zone （HAZ） of ASME SA213-792 at peak temperature of 1 350 ℃ was studied by thermal simulation. The result shows that the m...The relationship between the t8/5 and micro-hardness, impact toughness in the heat affected zone （HAZ） of ASME SA213-792 at peak temperature of 1 350 ℃ was studied by thermal simulation. The result shows that the micro-hardness of HAZ rises at the beginning and then decreases with increasing of t8/5 , whereas the impact toughness presents reverse trend. The distribution of precipitates in substrate has great influence on the impact toughness of HAZ. When the t8/5 is 40 s, chain-like precipitates lower the impact toughness of HAZ seriously.展开更多
EP-823 steel is one of the candidate materials for accelerator-driven systems/lead-cooled fast reactors （ADS/LFR）. Its weldability was investigated by mechanical property tests and microstructure analysis on the enl...EP-823 steel is one of the candidate materials for accelerator-driven systems/lead-cooled fast reactors （ADS/LFR）. Its weldability was investigated by mechanical property tests and microstructure analysis on the enlarged heat-affected zones （HAZs） made by numerical and physical simulation. The finite element numerical simulation could simulate the welding thermal cycle of the characteristic regions in HAZs with extremely high accuracy, The physical simulation performed on a Gleeble simulator could enlarge the characteristic regions to easily investigate the relationship between the microstructure evolution and the mechanical properties of the HAZs. The results showed that the simulated partially normalized zone comprising tempered martensite, newly formed martensite and more tiny carbides has the highest impact energy. The fully normalized zone exhibits the highest hardness because of the quenched martensite and large carbides. The ductile property of the overheated zone is poor for the residual delta- ferrite phases and the quenched martensite.展开更多
The combined effects of martensite-austenite（MA）constituent and pearlite colony on cleavage crack initiation in the simulated coarse-grained heat-affected zone（CGHAZ）of V-N-Ti microalloyed offshore platform steel ...The combined effects of martensite-austenite（MA）constituent and pearlite colony on cleavage crack initiation in the simulated coarse-grained heat-affected zone（CGHAZ）of V-N-Ti microalloyed offshore platform steel under different heat inputs were investigated.The results of welding simulation,instrumented impact test,and quantitative analysis indicated that the size of the MA constituent decreased with the increase in cooling time,and by contrast,the size of the pearlite colony increased.According to Griffith theory,the critical sizes of cleavage microcracks were calculated.With the increase of cooling time,the calculated microcrack size could be characterized by the size of the MA constituent first,and then fitted with the size of the pearlite colony.Moreover,the calculated microcrack size variation was opposite to the microcrack initiation energy.This phenomenon is probably due to the combined effects of the MA constituent and pearlite colony with increasing the cooling time of the specimen′s temperature from800 to 500 ℃.展开更多
The effects of tempering temperatures on the microstructure and mechanical properties of the simulated coarse-grain heataffected zone(CGHAZ) and inter-critical heat-affected zone(ICHAZ) were investigated for a high-st...The effects of tempering temperatures on the microstructure and mechanical properties of the simulated coarse-grain heataffected zone(CGHAZ) and inter-critical heat-affected zone(ICHAZ) were investigated for a high-strength-high-toughness combination marine engineering steel.The results demonstrate that the microstructure of the simulated CGHAZ and ICHAZ after tempering is characterized by tempering sorbites and coarse grain in the simulated CGHAZ.As tempering temperature increases,the tensile strength of the simulated CGHAZ and ICHAZ decreases and the Charpy absorbed energy of the simulated ICHAZ at-50℃increases remarkably,but the impact toughness of the simulated CGHAZ is not improved.After tempering at 550℃,the coarse flake carbides,which distribute at the prior austenite grain and martensite lath boundaries,deteriorate the impact toughness of the simulated CGHAZ.With the increase in tempering temperature,the morphology and the size of the carbides gradually change from coarse flake to fine granular,which is beneficial to the improvement of impact toughness.However,the coarse-grain size of the simulated CGHAZ and the M23 C6-type carbide precipitated along the grain boundaries weakens the enhancing effect of carbides on impact toughness.展开更多
Single welding thermal–cycles with different input linear energies (ILE)(15, 20, 30, 40, 50 kJ/cm) and peak temperatures (PT) (900, 1050, 1200, 1300, 1350 ℃) were simulated by MMS-300 to study the correlation of tou...Single welding thermal–cycles with different input linear energies (ILE)(15, 20, 30, 40, 50 kJ/cm) and peak temperatures (PT) (900, 1050, 1200, 1300, 1350 ℃) were simulated by MMS-300 to study the correlation of toughness and microstructure in heat-affected zone (HAZ) of a X80 pipeline. The evolution characteristics of microstructure were investigated by OM, SEM and EBSD. The results show that numerous polygonal ferrites and grain boundary ferrites appear, and the sizes apparently decrease as the heat input decreases. Heat input in single welding should be less than 35 kJ/cm to ensure well Charpy impact toughness. The toughness of course grain zone is the lowest when welding heating temperature is 1350 ℃ and it is the weakness part in welded zone. The uniformity of prior austenite grain is worsened as increasing the heat input. Moreover, the characteristics of M-A constituents and high angle grain boundaries (HAGB) are influenced by heat input and PT. In the case of low heat input and PT, higher density of HAGBs, dispersed and fine M-A constituents were observed. Otherwise, with high heat input (≥40 kJ/cm), the effective grain size is almost the diameter of prior austenite grain, and it will decrease the density of HAGB, moreover, coarse M-A constituents which are prone to crack initiation will be generated, thus, the impact toughness of the coarse grain zone will be worsened obviously in welding HAZ.展开更多
With the thermal simulated technology, the continuous cooling transforming curve （SH-CCT） of domestic X80 was measured, and the variation rule of the microstructure of coarsened-grain heat-affected zone（CGHAZ） for...With the thermal simulated technology, the continuous cooling transforming curve （SH-CCT） of domestic X80 was measured, and the variation rule of the microstructure of coarsened-grain heat-affected zone（CGHAZ） for X80 pipeline steel was also investigated. The results indicate that the hardenability and the hydrogen cracking susceptibility of domestic X80 are fairly low.展开更多
基金Supported by National High Technology Research and Development Program of China(863 Program,Grant No.2015AA042503)K.C.Wong Education Foundation.
文摘Improvement of fabrication efficiency and part performance was the main challenge for the large-scale powder bed fusion(PBF)process.In this study,a dynamic monitoring and feedback system of powder bed temperature field using an infrared thermal imager has been established and integrated into a four-laser PBF equipment with a working area of 2000 mm×2000 mm.The heat-affected zone(HAZ)temperature field has been controlled by adjusting the scanning speed dynamically.Simultaneously,the relationship among spot size,HAZ temperature,and part performance has been established.The fluctuation of the HAZ temperature in four-laser scanning areas was decreased from 30.85℃to 17.41℃.Thus,the consistency of the sintering performance of the produced large component has been improved.Based on the controllable temperature field,a dynamically adjusting strategy for laser spot size was proposed,by which the fabrication efficiency was improved up to 65.38%.The current research results were of great significance to the further industrial applications of large-scale PBF equipment.
基金The authors appreciate the financial support from National Key Research and Development Program of China(2017YFBO304900).
文摘The evolution of the microstructure and toughness of APL5L X80 pipeline steel after thermal welding simulation was investigated by X-ray diffraction,electron backscatter diffraction,and transmission electron microscopy.The results indicated that primary heat-affected zones can be divided into weld,coarse-grained,fine-grained,intercritical,and sub-critical zones.The microstructure of the weld zone is mainly composed of bainitic ferrite and a small amount of granular bainite;however,the original austenite grains are distributed in the columnar grains.The structure of the coarse-grained zone is similar to that of the weld zone,but the original austenite grains are equiaxed.In contrast,the microstructure in the fine-grained zone is dominated by fine granular bainite,and the effective grain size is only 8.15μm,thus providing the highest toughness in the entire heat-affected zone.The intercritical and subcritical zones were brittle valley regions,and the microstructure was dominated by granular bainite.However,the martensite-austenite(M/A)constituents are present in island chains along the grain boundaries,and the coarse size of the M/A constituents seriously reduces the toughness.The results of the crack propagation analyzes revealed that high-angle grain boundaries can significantly slow down crack growth and change the crack direction,thereby increasing the material toughness.The impact toughness of the low-temperature tempering zone was equivalent to that of the columnar grain zone,and the impact toughness was between those of the critical and fine-grained zones.
文摘The relationship between the t8/5 and micro-hardness, impact toughness in the heat affected zone （HAZ） of ASME SA213-792 at peak temperature of 1 350 ℃ was studied by thermal simulation. The result shows that the micro-hardness of HAZ rises at the beginning and then decreases with increasing of t8/5 , whereas the impact toughness presents reverse trend. The distribution of precipitates in substrate has great influence on the impact toughness of HAZ. When the t8/5 is 40 s, chain-like precipitates lower the impact toughness of HAZ seriously.
基金financial support from the National Natural Science Foundation of China(NSFC)under grant No.91226204the Chinese Academy of Science Strategic Pilot Project(The Future of Advanced Nuclear Energy,ADS Evolution System)under grant No.XDA03010304
文摘EP-823 steel is one of the candidate materials for accelerator-driven systems/lead-cooled fast reactors （ADS/LFR）. Its weldability was investigated by mechanical property tests and microstructure analysis on the enlarged heat-affected zones （HAZs） made by numerical and physical simulation. The finite element numerical simulation could simulate the welding thermal cycle of the characteristic regions in HAZs with extremely high accuracy, The physical simulation performed on a Gleeble simulator could enlarge the characteristic regions to easily investigate the relationship between the microstructure evolution and the mechanical properties of the HAZs. The results showed that the simulated partially normalized zone comprising tempered martensite, newly formed martensite and more tiny carbides has the highest impact energy. The fully normalized zone exhibits the highest hardness because of the quenched martensite and large carbides. The ductile property of the overheated zone is poor for the residual delta- ferrite phases and the quenched martensite.
基金Item Sponsored by Vanitec-CISRI Vanadium Technology Center
文摘The combined effects of martensite-austenite（MA）constituent and pearlite colony on cleavage crack initiation in the simulated coarse-grained heat-affected zone（CGHAZ）of V-N-Ti microalloyed offshore platform steel under different heat inputs were investigated.The results of welding simulation,instrumented impact test,and quantitative analysis indicated that the size of the MA constituent decreased with the increase in cooling time,and by contrast,the size of the pearlite colony increased.According to Griffith theory,the critical sizes of cleavage microcracks were calculated.With the increase of cooling time,the calculated microcrack size could be characterized by the size of the MA constituent first,and then fitted with the size of the pearlite colony.Moreover,the calculated microcrack size variation was opposite to the microcrack initiation energy.This phenomenon is probably due to the combined effects of the MA constituent and pearlite colony with increasing the cooling time of the specimen′s temperature from800 to 500 ℃.
基金financial support of the sponsor from the National Key Research and Development Program of China (No.2016YFB0300601)the Key Programs of Chinese Academy of Sciences (No.GFZD-125-15-003-1).
文摘The effects of tempering temperatures on the microstructure and mechanical properties of the simulated coarse-grain heataffected zone(CGHAZ) and inter-critical heat-affected zone(ICHAZ) were investigated for a high-strength-high-toughness combination marine engineering steel.The results demonstrate that the microstructure of the simulated CGHAZ and ICHAZ after tempering is characterized by tempering sorbites and coarse grain in the simulated CGHAZ.As tempering temperature increases,the tensile strength of the simulated CGHAZ and ICHAZ decreases and the Charpy absorbed energy of the simulated ICHAZ at-50℃increases remarkably,but the impact toughness of the simulated CGHAZ is not improved.After tempering at 550℃,the coarse flake carbides,which distribute at the prior austenite grain and martensite lath boundaries,deteriorate the impact toughness of the simulated CGHAZ.With the increase in tempering temperature,the morphology and the size of the carbides gradually change from coarse flake to fine granular,which is beneficial to the improvement of impact toughness.However,the coarse-grain size of the simulated CGHAZ and the M23 C6-type carbide precipitated along the grain boundaries weakens the enhancing effect of carbides on impact toughness.
基金Fundamental Research Funds for the Central Universities (N090607002)
文摘Single welding thermal–cycles with different input linear energies (ILE)(15, 20, 30, 40, 50 kJ/cm) and peak temperatures (PT) (900, 1050, 1200, 1300, 1350 ℃) were simulated by MMS-300 to study the correlation of toughness and microstructure in heat-affected zone (HAZ) of a X80 pipeline. The evolution characteristics of microstructure were investigated by OM, SEM and EBSD. The results show that numerous polygonal ferrites and grain boundary ferrites appear, and the sizes apparently decrease as the heat input decreases. Heat input in single welding should be less than 35 kJ/cm to ensure well Charpy impact toughness. The toughness of course grain zone is the lowest when welding heating temperature is 1350 ℃ and it is the weakness part in welded zone. The uniformity of prior austenite grain is worsened as increasing the heat input. Moreover, the characteristics of M-A constituents and high angle grain boundaries (HAGB) are influenced by heat input and PT. In the case of low heat input and PT, higher density of HAGBs, dispersed and fine M-A constituents were observed. Otherwise, with high heat input (≥40 kJ/cm), the effective grain size is almost the diameter of prior austenite grain, and it will decrease the density of HAGB, moreover, coarse M-A constituents which are prone to crack initiation will be generated, thus, the impact toughness of the coarse grain zone will be worsened obviously in welding HAZ.
文摘With the thermal simulated technology, the continuous cooling transforming curve （SH-CCT） of domestic X80 was measured, and the variation rule of the microstructure of coarsened-grain heat-affected zone（CGHAZ） for X80 pipeline steel was also investigated. The results indicate that the hardenability and the hydrogen cracking susceptibility of domestic X80 are fairly low.
