The effect of post-weld heat treatment on the microstructure characterization of electron beam welded(EBW) joints of Ti3Al-Nb was investigated.The results show that the microstructure of the weld is predominantly meta...The effect of post-weld heat treatment on the microstructure characterization of electron beam welded(EBW) joints of Ti3Al-Nb was investigated.The results show that the microstructure of the weld is predominantly metastable,the columnar crystal metastructure of B2 phase.The microstructure morphology of the weld is significantly influenced by the method of the heat treatment.The microstructure of the weld is laminar structure(Widmanstaten structure) consisted of interphase α2 and B2 after post-weld heat treatment of 1000 ℃/2 h.The mechanism of the post-weld heat treatment makes the hardness distribution of joints homogeneous,but makes the whole joint somehow softened.展开更多
7XXX series aluminium alloys generally present low weldability by fusion welding methods because of the sensitivity to weld solidification cracking, vaporization of strengthening alloys and other defects in the fusion...7XXX series aluminium alloys generally present low weldability by fusion welding methods because of the sensitivity to weld solidification cracking, vaporization of strengthening alloys and other defects in the fusion zone. Friction stir welding(FSW) can be deployed successfully with aluminium alloys. We presented the effect of post-weld heat treatment(PWHT) on the microstructure and mechanical properties of SSM7075 joints. Semi solid plates were butt-welded by FSW at a rotation speed of 1110 r/min, welding speeds of 70 and 110 mm/min. Solution treatment, artificial aging, and T6(solution treatment and artificial aging combined) were applied to the welded joints, each with three samples. It was found that the T6 joints at the speed of 70 mm/min yielded the highest tensile strength of 459.23 MPa. This condition best enhanced the mechanical properties of FSW SSM7075 aluminium alloy joints.展开更多
In order to overcome the limitations of manual post-weld visual inspection approach, an automated inspection system is developed which uses three-dimensioual laser vision system based on the principle of optical trian...In order to overcome the limitations of manual post-weld visual inspection approach, an automated inspection system is developed which uses three-dimensioual laser vision system based on the principle of optical triangulation. The system hardware consists of a modular development kit (MDK), a computer, an actuating mechanism and so on. In image processing algorithms, extraction accuracy of centric line of laser stripe is the critical factor that determines the system performance. So according to the features of laser stripe image, a novel algorithm is developed to detect the central line of laser stripe fast and accurately. Experiments have demonstrated that this system can be used in various weld features inspection of both butt and fillet types of weld. Compared with traditional manual inspection method, this method has obvious dominance. The three-dimensional reconstruction result shows that this system has high accuracy and reliability.展开更多
The electron beam local post-weld heat treatment (EBLPWHT) is a rather new method that provides the advantages of high precision, flexibility and efficiency, energy saving and higher productivity. This paper studies t...The electron beam local post-weld heat treatment (EBLPWHT) is a rather new method that provides the advantages of high precision, flexibility and efficiency, energy saving and higher productivity. This paper studies the effect of two post-weld heat treatment processes on the microstructure, mechanical properties and fracture toughness of an electron beam welded joints in 30CrMnSiNi2A steel. EBLPWHT, in a vacuum chamber, immediately after welding and a traditional furnace whole post-weld heat treatment (FWPWHT) were compared. The experimental results show that, after EBLPWHT treatment, the main microstructure of weld was changed from coarse acicular martensite into lath martensite, HAZ was changed from lath martensite, bainite into lower bainite, and base metal was changed from ferrite and pearlite into upper bainite and residual austenite. The microstructures of different zones of joints in FWPWHT condition were tempered sorbite. The properties of welded joints can be improved by the EBLPWHT in some extent, and especially largely for the fracture toughness of welded joints. However the value of fracture toughness of base metal is comparatively low, so appropriate heat treatment parameters should be explored in the future.展开更多
The influence of temperature during post-weld heat treatment on the microstructure and properties of KMN steel joints was investigated. The results reveal that after heat treatment, the martensite transformed to tempe...The influence of temperature during post-weld heat treatment on the microstructure and properties of KMN steel joints was investigated. The results reveal that after heat treatment, the martensite transformed to tempered sorbite, causing the softening of the resultant joints. XRD test shows that the residual austenite content decreased obviously when the joint was heattreated at 550 ℃ and 580 ℃, which degraded the impact toughness of heat-affected zone ( HAZ). When the heat treatment temperature increased further, the dispersion strengthening from the precipitation of alloying elements improved the impact toughness of HAZ. The aggregation and coarsening of carbide also contributed to the improvement of impact toughness of HAZ.展开更多
The distributions of temperature and residual stresses in thin plates of BT20titanium alloy are numerically analyzed by three-dimensional finite element software duringelectron beam welding and electron beam local pos...The distributions of temperature and residual stresses in thin plates of BT20titanium alloy are numerically analyzed by three-dimensional finite element software duringelectron beam welding and electron beam local post-weld heat treatment (EBLPWHT). Combined withnumerical calculating results, the effects of different EBLPWHT mode and parameters, including heattreating position, heating width and heating time, on the distribution of welding residual stressesare analyzed. The results show that, the residual tensile stresses in weld center can be largelydecreased when the weld is heat treated at back preface of the plate. The numerical results alsoindicated that the magnitude of the residual longitudinal stresses of the weld and the zone vicinityof the weld is decreased, and the range of the residual longitudinal stresses is increased alongwith the increase of heating width and heating time.展开更多
9Cr-1Mo ferritic steels have been used in the conventional power generation plants due to their excellent creep resistance. However, one of the main obstacles in welding 9Cr-1Mo steels is the formation of undesirable ...9Cr-1Mo ferritic steels have been used in the conventional power generation plants due to their excellent creep resistance. However, one of the main obstacles in welding 9Cr-1Mo steels is the formation of undesirable coarse columnar grains in weld metal whieh ean severely compromise the toughness. A new post-weld heat treatment (PWHT) is developed in the present work. Unlike the conventional processes in which the post-weld heat treatment is carried out below Ac1 , the use of temperatures above the Ac1 of 9Cr-1Mo alloy is considered. The new PWHT at a temperature above Ac1 improves the toughness of 9Cr-1Mo weld metals effectively. The improvement in toughness is mainly due to refinement and homogenization of mierostruetures. Key words展开更多
X-ray diffraction was utilized to measure the residual stress of 45 mm UNS N08810 plates after post-weld heat treatment at temperatures of 680℃ and 900℃, which showed reductions of 86.9% and 71.6% in the residual st...X-ray diffraction was utilized to measure the residual stress of 45 mm UNS N08810 plates after post-weld heat treatment at temperatures of 680℃ and 900℃, which showed reductions of 86.9% and 71.6% in the residual stress, respectively. This indicates that post-weld heat treatment can play a significant role in reducing residual stress, while no significant effects on tensile stress and micro-hardness of the welding joint were observed after treatment.展开更多
The mechanical properties of Ti-23Al-17Nb (mole fraction,%) laser beam welding alloy joint at room temperature are comparable to that of the base materials.However,the strength and ductility of the as-welded joint det...The mechanical properties of Ti-23Al-17Nb (mole fraction,%) laser beam welding alloy joint at room temperature are comparable to that of the base materials.However,the strength and ductility of the as-welded joint deteriorate seriously after high temperature circulation.The effect of post-welded heat treatment on the microstructure and mechanical properties of the joint was investigated.The heat treatment was taken at 980 ℃ for 1.5 h,then furnace cooling and air cooling were performed separately.The results indicate that proper post-welded heat treatment improves the ductility of the joint at high temperature.展开更多
Dissimilar joining of Ti_(2)AlNb and Ti60 rolled sheet was performed by laser beam welding.The microstructures and mechanical properties of as-welded and post-weld heat-treated Ti_(2)AlNb/Ti60 joints were investigated...Dissimilar joining of Ti_(2)AlNb and Ti60 rolled sheet was performed by laser beam welding.The microstructures and mechanical properties of as-welded and post-weld heat-treated Ti_(2)AlNb/Ti60 joints were investigated by microstructure observation and mechanical properties testing.The fusion zone(FZ)of the as-welded joint consisted of B_(2)/βmatrix and small S2 balls.The heataffected zones HAZ-Ti_(2)AINb and HAZ-Ti60 for the aswelded joint were characterized asα_(2)+B_(2)/β+O andα'+α+β+S_(2),respectively.The tensile strength and elongation of as-welded sheet were 597.5 MPa and 6.2%at650℃,respectively.Most of the plastic deformation was taken place at the side of Ti60 alloy.With the increase in the heat treatment temperature,the anchoring strength between each other of B_(2)/βgrains was enhanced by the precipitated lamellarα'and O grains at the FZ.The depth of the fracture dimples increased with the heat treat temperature increasing.The heat-treated welding joint at970℃presented a good balance of the tensile strength and plasticity,where the tensile strength and the elongation were enhanced to 669.7 MPa and 7.1%at 650℃,respectively.展开更多
The as-rolled AZ31 Mg alloy sheets are welded by friction stir welding(FSW) in this study, followed by annealing and hot rolling with different reductions. The effects of welding speed and the rolling reduction on t...The as-rolled AZ31 Mg alloy sheets are welded by friction stir welding(FSW) in this study, followed by annealing and hot rolling with different reductions. The effects of welding speed and the rolling reduction on the microstructure, tensile properties, microhardness and fracture surfaces of the specimens are investigated. The results show that the microstructures of the FSW joint in different regions become more and more consistent as the hot rolling reduction increases. The mechanical properties of the FSW joints and the joint coefficient are improved with increasing rolling reduction; however,the hardness value in the stirred zone decreases firstly and then increases. When the rolling reduction is 50%, the tensile strength of FSW joint is close to that of base metal. The sample L_3 achieves the best comprehensive properties, with the yield strength, ultimate tensile strength and elongation of 162, 287.9 MPa, and 17.9%, respectively.展开更多
In as-welded state,each region of 2219 aluminum alloy TIG-welded joint shows diff erent microstructure and microhardness due to the diff erent welding heat cycles and the resulting evolution of second phases.After the...In as-welded state,each region of 2219 aluminum alloy TIG-welded joint shows diff erent microstructure and microhardness due to the diff erent welding heat cycles and the resulting evolution of second phases.After the post-weld heat treatment,both the amount and the size of the eutectic structure orθphases decreased.Correspondingly,both the Cu content inα-Al matrix and the microhardness increased to a similar level in each region of the joint,and the tensile strength of the entire joint was greatly improved.Post-weld heat treatment played the role of solid solution strengthening and aging strengthening.After the post-weld heat treatment,the weld performance became similar to other regions,but weld reinforcements lost their reinforcing eff ect on the weld and their existence was more of an adverse eff ect.The joint without weld reinforcements after the post-weld heat treatment had the optimal tensile properties,and the specimens randomly crack in the weld zone.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
The evolution of Cr23C6 carbides in the deposited metal (DM) of a high-chromium nickel-based alloy was investigated after the post-weld heat treatment (PWHT) at 650, 750, 850, and 950 ℃, respectively. With the in...The evolution of Cr23C6 carbides in the deposited metal (DM) of a high-chromium nickel-based alloy was investigated after the post-weld heat treatment (PWHT) at 650, 750, 850, and 950 ℃, respectively. With the increase in temperature, the morphology of the Cr23C6 carbides at the grain boundaries was transformed from the continuous lamellar- like to the semi-continuous rod-like and then to the discontinuous granular. Besides, the needle-like Cr23C6 carbides precipitated from 7 matrix after PWHT at 850 ℃. The coarsening kinetics of the needle-like Cr23C6 carbides obeyed the Lifshitz-Slyozov-Wagner law with the growth speed of 4.93 μm3/h in length and 5.56 ×10^-3 μm3/h in width. Moreover, the ratio of the carbide length to width increased rapidly at first and then flattened as the holding time increased to 850 ℃. The results of electrochemical corrosion experiment indicated that the needled-like Cr23C6 carbides impaired the corrosion resistance of DM due to the formation of chromium depletion around the carbides.展开更多
文摘The effect of post-weld heat treatment on the microstructure characterization of electron beam welded(EBW) joints of Ti3Al-Nb was investigated.The results show that the microstructure of the weld is predominantly metastable,the columnar crystal metastructure of B2 phase.The microstructure morphology of the weld is significantly influenced by the method of the heat treatment.The microstructure of the weld is laminar structure(Widmanstaten structure) consisted of interphase α2 and B2 after post-weld heat treatment of 1000 ℃/2 h.The mechanism of the post-weld heat treatment makes the hardness distribution of joints homogeneous,but makes the whole joint somehow softened.
基金Partially Funded by National Research Universities(NRU)(ENG 5805855)Faculty of Engineering,Prince of Songkla University,Hatyai Songkhla,Thailand
文摘7XXX series aluminium alloys generally present low weldability by fusion welding methods because of the sensitivity to weld solidification cracking, vaporization of strengthening alloys and other defects in the fusion zone. Friction stir welding(FSW) can be deployed successfully with aluminium alloys. We presented the effect of post-weld heat treatment(PWHT) on the microstructure and mechanical properties of SSM7075 joints. Semi solid plates were butt-welded by FSW at a rotation speed of 1110 r/min, welding speeds of 70 and 110 mm/min. Solution treatment, artificial aging, and T6(solution treatment and artificial aging combined) were applied to the welded joints, each with three samples. It was found that the T6 joints at the speed of 70 mm/min yielded the highest tensile strength of 459.23 MPa. This condition best enhanced the mechanical properties of FSW SSM7075 aluminium alloy joints.
文摘In order to overcome the limitations of manual post-weld visual inspection approach, an automated inspection system is developed which uses three-dimensioual laser vision system based on the principle of optical triangulation. The system hardware consists of a modular development kit (MDK), a computer, an actuating mechanism and so on. In image processing algorithms, extraction accuracy of centric line of laser stripe is the critical factor that determines the system performance. So according to the features of laser stripe image, a novel algorithm is developed to detect the central line of laser stripe fast and accurately. Experiments have demonstrated that this system can be used in various weld features inspection of both butt and fillet types of weld. Compared with traditional manual inspection method, this method has obvious dominance. The three-dimensional reconstruction result shows that this system has high accuracy and reliability.
文摘The electron beam local post-weld heat treatment (EBLPWHT) is a rather new method that provides the advantages of high precision, flexibility and efficiency, energy saving and higher productivity. This paper studies the effect of two post-weld heat treatment processes on the microstructure, mechanical properties and fracture toughness of an electron beam welded joints in 30CrMnSiNi2A steel. EBLPWHT, in a vacuum chamber, immediately after welding and a traditional furnace whole post-weld heat treatment (FWPWHT) were compared. The experimental results show that, after EBLPWHT treatment, the main microstructure of weld was changed from coarse acicular martensite into lath martensite, HAZ was changed from lath martensite, bainite into lower bainite, and base metal was changed from ferrite and pearlite into upper bainite and residual austenite. The microstructures of different zones of joints in FWPWHT condition were tempered sorbite. The properties of welded joints can be improved by the EBLPWHT in some extent, and especially largely for the fracture toughness of welded joints. However the value of fracture toughness of base metal is comparatively low, so appropriate heat treatment parameters should be explored in the future.
文摘The influence of temperature during post-weld heat treatment on the microstructure and properties of KMN steel joints was investigated. The results reveal that after heat treatment, the martensite transformed to tempered sorbite, causing the softening of the resultant joints. XRD test shows that the residual austenite content decreased obviously when the joint was heattreated at 550 ℃ and 580 ℃, which degraded the impact toughness of heat-affected zone ( HAZ). When the heat treatment temperature increased further, the dispersion strengthening from the precipitation of alloying elements improved the impact toughness of HAZ. The aggregation and coarsening of carbide also contributed to the improvement of impact toughness of HAZ.
基金This project is supported by Foundation of National Defense Technology Key Laboratory, China (No.99JS50.3.2JW1402).
文摘The distributions of temperature and residual stresses in thin plates of BT20titanium alloy are numerically analyzed by three-dimensional finite element software duringelectron beam welding and electron beam local post-weld heat treatment (EBLPWHT). Combined withnumerical calculating results, the effects of different EBLPWHT mode and parameters, including heattreating position, heating width and heating time, on the distribution of welding residual stressesare analyzed. The results show that, the residual tensile stresses in weld center can be largelydecreased when the weld is heat treated at back preface of the plate. The numerical results alsoindicated that the magnitude of the residual longitudinal stresses of the weld and the zone vicinityof the weld is decreased, and the range of the residual longitudinal stresses is increased alongwith the increase of heating width and heating time.
文摘9Cr-1Mo ferritic steels have been used in the conventional power generation plants due to their excellent creep resistance. However, one of the main obstacles in welding 9Cr-1Mo steels is the formation of undesirable coarse columnar grains in weld metal whieh ean severely compromise the toughness. A new post-weld heat treatment (PWHT) is developed in the present work. Unlike the conventional processes in which the post-weld heat treatment is carried out below Ac1 , the use of temperatures above the Ac1 of 9Cr-1Mo alloy is considered. The new PWHT at a temperature above Ac1 improves the toughness of 9Cr-1Mo weld metals effectively. The improvement in toughness is mainly due to refinement and homogenization of mierostruetures. Key words
文摘X-ray diffraction was utilized to measure the residual stress of 45 mm UNS N08810 plates after post-weld heat treatment at temperatures of 680℃ and 900℃, which showed reductions of 86.9% and 71.6% in the residual stress, respectively. This indicates that post-weld heat treatment can play a significant role in reducing residual stress, while no significant effects on tensile stress and micro-hardness of the welding joint were observed after treatment.
文摘The mechanical properties of Ti-23Al-17Nb (mole fraction,%) laser beam welding alloy joint at room temperature are comparable to that of the base materials.However,the strength and ductility of the as-welded joint deteriorate seriously after high temperature circulation.The effect of post-welded heat treatment on the microstructure and mechanical properties of the joint was investigated.The heat treatment was taken at 980 ℃ for 1.5 h,then furnace cooling and air cooling were performed separately.The results indicate that proper post-welded heat treatment improves the ductility of the joint at high temperature.
基金financially supported by the National High-level Personnel of Special Support Program(No.W02020239)。
文摘Dissimilar joining of Ti_(2)AlNb and Ti60 rolled sheet was performed by laser beam welding.The microstructures and mechanical properties of as-welded and post-weld heat-treated Ti_(2)AlNb/Ti60 joints were investigated by microstructure observation and mechanical properties testing.The fusion zone(FZ)of the as-welded joint consisted of B_(2)/βmatrix and small S2 balls.The heataffected zones HAZ-Ti_(2)AINb and HAZ-Ti60 for the aswelded joint were characterized asα_(2)+B_(2)/β+O andα'+α+β+S_(2),respectively.The tensile strength and elongation of as-welded sheet were 597.5 MPa and 6.2%at650℃,respectively.Most of the plastic deformation was taken place at the side of Ti60 alloy.With the increase in the heat treatment temperature,the anchoring strength between each other of B_(2)/βgrains was enhanced by the precipitated lamellarα'and O grains at the FZ.The depth of the fracture dimples increased with the heat treat temperature increasing.The heat-treated welding joint at970℃presented a good balance of the tensile strength and plasticity,where the tensile strength and the elongation were enhanced to 669.7 MPa and 7.1%at 650℃,respectively.
基金financial support by the National Key Research and Development Program of China(Project Nos.2016YFB0301100 and 2016YFB0700403)the National Natural Science Foundation(Project No.51601024)+2 种基金the National Key Research,the Chongqing Research Program of Basic Research and Frontier Technology(Project No.cstc2016jcyj A0418)the National Natural Science Foundation of China(Grant No.51701026)the Fundamental Research Funds for the Central Universities(Project No.106112017CDJXY130001)
文摘The as-rolled AZ31 Mg alloy sheets are welded by friction stir welding(FSW) in this study, followed by annealing and hot rolling with different reductions. The effects of welding speed and the rolling reduction on the microstructure, tensile properties, microhardness and fracture surfaces of the specimens are investigated. The results show that the microstructures of the FSW joint in different regions become more and more consistent as the hot rolling reduction increases. The mechanical properties of the FSW joints and the joint coefficient are improved with increasing rolling reduction; however,the hardness value in the stirred zone decreases firstly and then increases. When the rolling reduction is 50%, the tensile strength of FSW joint is close to that of base metal. The sample L_3 achieves the best comprehensive properties, with the yield strength, ultimate tensile strength and elongation of 162, 287.9 MPa, and 17.9%, respectively.
基金supported by the Joint Funds of the National Natural Science Foundation of China (Grant No. U1637601)
文摘In as-welded state,each region of 2219 aluminum alloy TIG-welded joint shows diff erent microstructure and microhardness due to the diff erent welding heat cycles and the resulting evolution of second phases.After the post-weld heat treatment,both the amount and the size of the eutectic structure orθphases decreased.Correspondingly,both the Cu content inα-Al matrix and the microhardness increased to a similar level in each region of the joint,and the tensile strength of the entire joint was greatly improved.Post-weld heat treatment played the role of solid solution strengthening and aging strengthening.After the post-weld heat treatment,the weld performance became similar to other regions,but weld reinforcements lost their reinforcing eff ect on the weld and their existence was more of an adverse eff ect.The joint without weld reinforcements after the post-weld heat treatment had the optimal tensile properties,and the specimens randomly crack in the weld zone.
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.
文摘The evolution of Cr23C6 carbides in the deposited metal (DM) of a high-chromium nickel-based alloy was investigated after the post-weld heat treatment (PWHT) at 650, 750, 850, and 950 ℃, respectively. With the increase in temperature, the morphology of the Cr23C6 carbides at the grain boundaries was transformed from the continuous lamellar- like to the semi-continuous rod-like and then to the discontinuous granular. Besides, the needle-like Cr23C6 carbides precipitated from 7 matrix after PWHT at 850 ℃. The coarsening kinetics of the needle-like Cr23C6 carbides obeyed the Lifshitz-Slyozov-Wagner law with the growth speed of 4.93 μm3/h in length and 5.56 ×10^-3 μm3/h in width. Moreover, the ratio of the carbide length to width increased rapidly at first and then flattened as the holding time increased to 850 ℃. The results of electrochemical corrosion experiment indicated that the needled-like Cr23C6 carbides impaired the corrosion resistance of DM due to the formation of chromium depletion around the carbides.