Study on the behavior of high-frequency pulsed TIG arc and molten pool flow of Inconel-52M welding wire

KUANG Xiaocong1,2,QI Bojin1,YANG Jianping3,LU Yingyan4(1.Department of Material Processing and Control Engineering,School of Mechanical Engineering and Automation,Beijing University of Aeronautics and Astronautics,Beijing,100191,China；2.Beijing Institute of Remote Sensing Equipment,Beijing,100854,China；3.State Key Laboratory of Clean and Efficient Turbomachinery Power Equipment,Dongfang Turbine Co.,Ltd.,Deyang,618000,China；4.Hangzhou Oxygen Plant Group Co.,Ltd.,Hangzhou,310000,China).pp 1-9

Abstract:Based on high-speed camera and image processing technology,the influence of pulse frequency (0-60 kHz) on the behavior of welding arc and molten pool flow of Inconel-52M nickel alloy welding wire was analyzed,as well as their underlying mechanisms.The results indicated that the combination of high-frequency pulse current on conventional low-frequency pulse current could significantly shrink the arc shape,and the arc root size would gradually decrease with the increase of high-frequency pulse frequency.Compared to traditional low-frequency pulse welding,the overall area of the high-frequency pulsed arc decreased,while its core area and proportion increased,leading to improved arc energy concentration and temperature.Under the influence of high-frequency pulse current,both the axial pressure and radial electromagnetic force of the welding arc increased,with maximum increases of 18.0% and 8.1%,respectively.The rise in axial pressure promoted the fluidity of the weld pool,enabling more complete liquid metal flow during the welding process and resulting in a weld morphology characterized by large width and low wetting angle.

Highlights:(1) A novel and effective ultra-high frequency pulsed gas tungsten arc welding (UFP-TIG) technology was proposed for the arc welding of the Inconel-52M nickel alloy welding wire.

(2) Based on image processing technology and electromagnetic theory,the arc energy region division and electromagnetic force model of the UFP-TIG welding arc were constructed,and the influence law and mechanism of UFP current frequency on TIG arc behavior characteristics (arc shape,energy distribution and electromagnetic force) were fully revealed.The interaction between UFP arc behavior,molten pool flow and weld formation of nickel-based alloys was also discussed.

Key words:high-frequency pulse current；welding arc；electromagnetic force；molten pool flow

Reliability prediction and design optimization of BGA solder joint based on multi-fidelity surrogate modelYU Jingdan1,WANG Ru1,WU Wenzhi2,HU Zixiang2,ZHANG Chulei1,WANG Guoxin1,YAN Yan1(1.Beijing Institute of Technology,Beijing,100081,China；2.The 38th Research Institute of China Electronics Technology Group Corporation,Hefei,23008,China).pp 10-16

Abstract:At present,the reliability prediction of solder joints is mostly based on the combination of finite element simulation and single precision surrogate model,which has some problems such as long simulation time,low efficiency and poor accuracy.Therefore,a reliability prediction method for BGA(ball grid array) solder joints based on multi-fidelity model is proposed.Firstly,the convergence of different meshing schemes was verified,and then the high and low precision sample points were designed respectively for finite element analysis (FEA).Secondly,the reliability of solder joints was predicted based on the Co-Kriging model based on multi fidelity FEA data.Finally,the prediction results were compared with the single precision surrogate model,Under the same cost constraints,the multi-fidelity model demonstrates significantly higher prediction accuracy.and NSGA(nondominated sorting genetic algorithm) was used to optimize the model to obtain the corresponding process parameters.The results show that with less simulation cost,the prediction result of multi-fidelity model is better.Under the same prediction accuracy,the number of high-precision sample points of the variable reliability model is only 1/4 of that of the single precision model.At the same time,compared with the neural network prediction model,it converges faster in the optimization process.This paper provides some reference for the research of reliability prediction of solder joint with multi-fidelity model.

Highlights:(1) A multi-fidelity model for predicting the reliability of solder joints is proposed.The required high-precision sample points have reduced by three-quarters compared to a single-precision model.

(2) Convergence tests were conducted on four mesh partitioning methods for finite element analysis of solder joints under temperature cycling conditions.Considering both accuracy and cost conditions,two partitioning methods with better accuracy are proposed.

Key words:solder joint reliability；life prediction；multi-fidelity model；NSGA

Strengthening mechanism and strain hardening behavior of the stir zone of cold source assistant friction stir welded HSn70-1 tin brass jointXU Nan,ZHANG Baishuo,QI Tianxiang,LIU Zhaoyang,XU Yuzhui,SONG Qining,BAO Yefeng(Hohai University,Changzhou,213022,China).pp 17-22

Abstract:2 mm thick HSn70-1 tin brass plates were joined using cold source assistant friction stir welding.Defect free welded joint was obtained.The microstructure and its effect on the strengthening mechanism and strain hardening behavior were studied by optical microscopy,electron backscatter diffraction,transmission electron microscopy,and tensile test.The obtained results showed that the rapid cooling effect of dry ice and ethanol mixture eliminated the heat-affected zone,and it also restrained dislocation recovery and grain growth in the stir zone.The stir zone exhibited ultra-fine grain structure with high dislocation density.The ultimate tensile strength of the stir zone was 486MPa,which was 53.8% higher than that of the base material,and the fracture elongation reached to 30%.The yield strength of the stir zone also increased by 47.1%compared to that of the base material,and the yield strength of the stir zone was dominated by solid solution strengthening and grain boundary strengthening mechanisms,while the strain hardening behavior was mainly affected by grain size and dislocation density.The nano-scale deformation twins which generated during the tensile test effectively coordinated plastic deformation and alleviated stress concentration,so the strength of the stir zone was improved without remarkable ductility loss.

Highlights:(1) A method for preparing ultrafine grain structures with high dislocation density in the stir zone was proposed.

(2) The mechanism of enhancing strength and ductility in the stir zone of cold source assistant friction stir welded tin brass was revealed.

Key words:tin brass；friction stir welding；microstructure；strengthening mechanism；strain hardening behavior

Study on friction stir welding of magnesium alloy with backing plateREN Daxin,CONG Lingxiang,HAN Ronghao,SONG Gang,LIU Liming(Dalian University of Technology,Dalian,116024,China).pp 23-30

Abstract:In conventional friction stir welding,the length of the stirring pin needs to be strictly matched with the thickness of the welded plate.A too-long or too-short stirring pin will adversely affect the welding effect.To solve this limitation,this paper proposes a new welding process that adds a backing plate of the same material with appropriate thickness to the back of the weld seam.In this process,the length of the stirring pin is greater than the thickness of the welded plate,and the backing plate is fused with the base metal.On the one hand,the requirement for stirring pin length is reduced.On the other hand,the adverse effects of weld seam thinning can be eliminated.The butt welding of 1.5 mm thick AZ31B magnesium alloy was studied by this method.The maximum tensile strength of the weld joint can reach 91.19% of the base metal.In addition,the microstructure and microhardness distribution of the weld beam cross-section were analyzed.The optimal process parameters were obtained by the established convolutional neural network model,and the distribution of joint tensile strength with the change of parameters was predicted.

Highlights:(1) The stirring pin can penetrate the welded plate and eliminate the incomplete fusion defect at the root.

(2) The optional range of the length of the stirring pin is expanded,and the welding process window is broadened.

(3) A reinforced structure is formed on the back of the weld,which offsets the adverse effects of the thinning on the front of the weld.

Key words:friction stir welding；AZ31B magnesium alloy；backing plate；neural network

Determining heat source parameters based on particle swarm optimization for temperature field simulation of EH40/316L high power laser weldingXU Jiajun1,2,HUANG Yu1,WANG Lu1,RONG Youmin1(1.Huazhong University of Science and Technology,Wuhan,430074,China；2.Guangdong HUST Industrial Technology Research Institute,Dongguan,518052,China).pp 31-39

Abstract:The welding transient temperature field has an important influence on the simulation results of welding residual stress and deformation.To improve the accuracy of the temperature field simulation in EH40/316L high power laser welding,an intelligent calculation method is developed to optimize the empirical parameters of heat source model.This method uses MATLAB software to randomly generate the empirical parameters,calls ANSYS software to execute the APDL command of the welding temperature field simulation,and returns the result data when the calculation is completed.Then,based on the swarm intelligence and evolutionary intelligence of particle swarm optimization algorithm,new empirical parameters of the heat source are generated according to the prediction results.The iterative calculation is carried out until the prediction results are the optimal results.10 cases of empirical parameter optimization are performed,and the parameter sensitivity of heat source model is analyzed according to the optimization results.The results show that the average calculation time of the 10 cases is 30.3 hours,and the maximum,minimum and average prediction errors are 2.84%,2.06% and 2.16% respectively.This indicates a great improvement in the simulation accuracy of welding temperature field.Meanwhile,it can be seen from the response surface of the prediction error and the empirical parameters,that the mathematical function between them is a multi-valley function and has a complex nonlinear relationship.

Highlights:(1) An intelligent calculation method for optimizing the empirical parameters of the heat source model is proposed,which improves the temperature field simulation accuracy of EH40/316L dissimilar steel high-power laser welding.(2) The response surface of the empirical parameters and prediction error of the heat source model is obtained.The sensitivity of the empirical parameters of the heat source model is analyzed.

Key words:high power laser welding；dissimilar steel；welding temperature field simulation；optimization of heat source parameters；particle swarm optimization algorithm

Effect of WC content on the interface microstructure of nickel/tungsten carbide composite brazing coatingWANG Xingxing1,TIAN Jiahao1,WU Shengjin1,KANG Kejia1,LING Zicheng1,DU Quanbin2,WEN Guodong3(1.North China University of Water Resources and Electric Power,Zhengzhou,450045,China；2.Henan Mechanical and Electrical Vocational College,Zhengzhou,451191,China；3.Xi’an University of Science and Technology,Xi’an,710054,China).pp 40-46

Abstract:Nickel/tungsten carbide composite coating has high wear resistance,corrosion resistance,and high hardness characteristics.It is widely used in shield machine parts,rotary blade,and other fields.In order to improve the lifespan of the hydraulic machinery overflow components,the nickel/tungsten carbide composite brazing coating was successfully prepared.It was combined with the surface of austenitic stainless steel by brazing coating method with thermal radiation in vacuum furnace.In the joint,WC particles and nickel-based powder brazing alloys were used as coating materials.The microstructure and interfacial behavior of the brazing coating were analyzed with the scanning electron microscopy,X-ray diffractometer,and metallographic microscopy.The results show that the interface between WC hard-phase and nickel-based brazing alloy achieved mechanical and metallurgical bonding.There is certain component diffusion between the brazing coating and steel substrate.And the thickness of narrowest diffusion area is about 100 μm.When the WC content is lower than 25wt.%,the brazing coating has better wettability on the steel substrate.The internal denseness of the coating stays in high level.Meanwhile,the minimum porosity in the composite coating can be kept at 1.08%.

Highlights:(1) The nickel/tungsten carbide superhard composite coatings on austenitic stainless steel surfaces by vacuum brazing coating method for hydraulic machinery overflow components have been successfully prepared.

(2) Wettability performance of brazing filler metals and interfacial reaction and diffusion of composite brazing coatings are revealed.

Key words:brazing；composite coating；nickel/tungsten carbide interface；interface microstructure；wettability

Vacuum brazing TC4 titanium alloy/ 316L stainless steel with Ti43.76Zr12.50Cu37.49-xNi6.25Cox amorphous filler metalsHAN Wenqian,DONG Honggang,MA Yueting,LI Peng,WU Baosheng,ZHANG Liangliang(Dalian University of Technology,Dalian,116024).pp 47-57

Abstract:Ti-Zr-Cu-Ni-Co amorphous filler metals were designed and prepared for vacuum brazing of TC4 titanium alloy to 316L stainless steel according to the dual-cluster model.The effect of Co content in filler metals on the microstructure,mechanical properties and fracture behavior of brazed joints was investigated.The results showed that the cross section of brazed joint could be divided into TC4/diffusion zone I/brazing seam center zone II/interface zone III/316L.The typical interfacial microstructure of the brazed joints was TC4/β-Ti +Ti2Cu/(Ti,Zr)2(Cu,Ni)+Ti2Cu+Ti2(Cu,Ni)+TiFe/(Fe,Cr)2Ti+α-(Fe,Cr)+τ+γ -(Fe,Ni)+σ/316L.The shear strength of brazed joints first increased,then decreased and then increased with the increase of Co content.The maximum shear strength of 310 MPa was obtained at 1.56% Co.When Co element was not added,brazed joints fractured in the center of the brazing seam (zone II).And when the Co content was 1.56～ 6.24%,brazed joints fractured near the interface zone(zone III) of 316L base metal.The fracture mode was typical cleavage fracture.

Highlights:(1) Ti-Zr-Cu-Ni-Co amorphous filler metals were designed and prepared based on the dual-cluster model.(2) The effect of Co content in filler metals on the microstructure,mechanical properties and fracture behavior of brazed joints was elucidated.

Key words:vacuum brazing；amorphous filler metal；titanium alloy/stainless steel dissimilar metal；microstructure；shear strength

Influence factors and control methods of droplet transfer in narrow gap P-GMAW overhead welding positionLIU Wenji,XIAO Yu,YANG Jiasheng,ZHU Pengfei(Tiangong University,Tianjin,300387,China).pp 58-63

Abstract:When conducting narrow gap all position welding of pipelines,welding defects are easy to occur near the overhead welding position,which restricts the quality and efficiency of pipeline construction.Aiming at the problem of poor formation and low reliability of overhead welding position in automatic pipe welding,this paper studies the influence of wire feeding speed,arc length correction,contact nozzle distance to molten pool and other factors on droplet transfer in P-GMAW process.It is found that increasing the arc length correction coefficient can increase the heat input of the arc to the side wall,which can alleviate the problem of poor side wall fusion,but will make the droplet transfer path difficult to control,Therefore,when the welding gun moves to the overhead welding position,short arc welding shall be adopted and the heat input to the side wall shall be supplemented by increasing the side stop time and swing;Increasing the wire feeding speed is conducive to obtaining smaller droplets,higher transfer frequency,reducing the distance between the contact tip and the molten pool,increasing the electromagnetic force and reducing the droplet size,which is more conducive to the transfer of droplets to the molten pool in overhead welding position.The research results have certain guiding significance for the process design of pipe narrow gap welding.

Highlights:This paper Studied the influence of parameters on droplet transfer during narrow gap full position P-GMAW process in pipelines,and the method of controlling welding parameters to achieve better droplet transfer.

Key words:droplet transfer；Swing arc；MIG welding；Narrow gap welding

Study on sensitization characteristics of TP347H stainless steel welded jointsLI Chengan1,FENG Daochen1,ZHANG Lin2,ZHENG Wenjian1,CHENG Mao3,LU Xianjing3,YANG Jianguo1(1.Zhejiang University of Technology,Hangzhou,310014,China；2.CFHI Dalian Nuclear Power and Petrochemical Equipment Co.,Ltd.,Dalian 116113,China；3.Zhejiang Academy of Special Equipment Science,Hangzhou,310020,China).pp 64-72

Abstract:In order to clarify the sensitization characteristics of TP347H stainless steel welded joints,the welded joints were heat treated at different temperatures,and the changes of sensitization degrees at different temperatures were studied.The results showed that an obvious sensitization trend was observed in the heat-affected zone(HAZ) of welded joints.During the sensitization process,because the binding energy of Nb atoms on the grain boundary is higher than that of Cr atoms,coarse primary niobium carbon compounds are formed first,and then fine secondary niobium carbon compounds are formed.When the temperature is kept at 700 ℃,the sensitization degree of the HAZ of the welded joint shows a trend of first increasing and then decreasing.When the temperature reaches 800 ℃ and above,heat treatment no longer increases the sensitization degree of the HAZ of the joint.Comparing with the sensitization characteristics of F347H joints with 21 000 h in the actual production line,it is confirmed that the sensitization limit can be reached by holding the welded joints of TP347H at 650 ℃ for 100 h.The reason is that the content of Nb is several times that of C,most of C combines with Nb to form NbC,and the diffusion of C in the grain has been fully combined with Cr.The resulting sensitization reaches an equilibrium state.

Highlights:(1) Confirmed that TP347H stainless steel welded joint was heat treated at 650 for 100h can reach the sensitization limit.

(2) In the process of sensitization,because the binding energy of Nb atoms on the grain boundary is higher than that of Cr atoms,the coarse niobium carbon compound will be formed first,and then the fine niobium carbon compound will be formed.

(3) When the TP347H stainless steel welded joint was heat treated at 700 ℃,the sensitization degree in the theat affected zone of the welding joint shows a trend of increasing first and then decreasing.

Key words:TP347H stainless steel；sensitization；welded joint；heat treatment；corrosion resistance

Numerical simulation of the influence of thickness of cladding material on stress and strain of welded joint of stainless steel composite plateFENG Yulan,WU Zhisheng,SUN Zhiyu(Taiyuan University of Science and Technology,Taiyuan,030024,China).pp 73-82

Abstract:GTAW technology has been used to fabricate welded connections on composite plates consisting of 304 and Q355 materials.Base material thickness was 13 mm,while cladding material thicknesses ranged from 0.3 mm to 2.0 mm.The influence of different thicknesses of cladding material on the stress and strain of 304/Q355 composite plate welded joint was analyzed by numerical simulation method,and the evolution characteristics of residual stress and strain during welding of stainless steel composite plate with different thicknesses of cladding material were revealed.The results show that the Xray diffraction test results are in good agreement with the numerical simulation results.With the increase of the thickness of the cladding material,the maximum residual stress value of the welded joint section of 304/Q355 composite plate gradually decreases,and the width of the residual stress zone gradually increases.During the welding process from the base weld to the transition weld,the stress concentration zone gradually shrinks to the transition weld zone.Finally,the highest stress concentration area is located in the weld zone of the transition layer,and the maximum stress value is close to the yield strength of the material.In addition,the deformation after welding increases with the increase of the thickness of the cladding material,and the deformation of the composite plate with the thickness of the cladding material 2.0 mm is about 2 mm higher than that of the composite plate with the thickness of the cladding material 0.3 mm,and the direction of the largest deformation is the direction of the weld thickness.

Highlights:(1) The stress and strain distribution of 304/Q355 composite plate welded joints with different thickness of cladding material were analyzed in detail by numerical simulation.

(2) The stress-strain evolution characteristics of 304/Q355 composite plate welded joints with different thickness of cladding material are described by the results of stress-strain field analysis.

Key words:cladding materials thickness；composite plate；stress and strain；numerical simulation

Analysis of side-deflection behavior mechanism of GMAW weld section of cable type welding wireYANG Zekun1,2,XU Kai2,3,YANG Zhanli2,ZHANG Yan2,FEI Dakui2,ZHOU Kun2,YANG Yongbo2(1.China Academy of Machinery Science and Technology Group Co.Ltd.,Beijing,100048,China；2.Harbin Welding Institute Co.Ltd.,Harbin,150028,China；3.Harbin Welding Institute Co.Ltd.,Harbin,150028,China).pp 83-87

Abstract:The side-deflection of weld section in cable type welding wire GMAW will lead to poor fusion of welded joints.Therefore,based on droplet force analysis and the principle of minimum voltage,the mechanism analysis of the change rule of the side-deflection of weld section was carried out.The results show that the current is the key factor affecting the side-deflection of the section.The unique stranded structure of the cable type welding wire causes arc rotation,which leads to the phenomenon of uneven force on the droplet.The transition direction of the droplet is at an angle with the axis of the welding wire,resulting in the phenomenon of side -deflection of the weld section under the action of the droplet impact force.The droplet transition direction gradually tends to the axis,so the side-deflection trend of weld section decreases with the increase of current.

Highlights:Based on the principle of minimum voltage,the characteristics of alternating arc-starting of cable type welding wire are analyzed,and it is found that the uneven force of droplet caused by rotating arc is the fundamental cause of the side-deviation of weld section,and the trend of the side-deviation of section decreases with the increase of current.

Key words:cable type welding wire；GMAW；weld section side-deviation；droplet transition；the principle of minimum voltage

Weld recognition based on key point detection methodGUO Zhongfeng,LIU Junchi,YANG Junlin(Shenyang University of Technology,Shenyang,110870,China).pp 88-93

Abstract:In order to ensure the quality of automatic welding and improve the accuracy and adaptability of weld identification,a key point detection method for weld feature extraction is proposed.A weld feature extraction network was designed based on the convolutional neural network.The network extracted weld feature by convolution and pool operation.The feature map from deep layer is sampled up,and then the feature map from deep layer and shallow layer are fused to improve the accuracy of weld feature extraction.The feature point position of weld seam is predicted by the thermal image of weld seam,and the recognition and location of many kinds of groove weld seam are realized,and eliminating the need for non-maximum suppression algorithm,which improves the feature extraction speed.The network model is trained by collecting different weld feature images.The experimental results show that the root mean square error of weld feature point location is 0.187 mm.The network model designed in this research has high detection accuracy in the weld feature point recognition task,and has strong adaptability and generalization,and meets the requirements of automatic welding.

Highlights:(1) Weld feature extraction network,deep weld seam feature maps are sampled up and shallow weld seam feature maps are fused to improve feature extraction accuracy.

(2) The thermal image of weld seam is output to predict the position of weld feature points,which does not require non-maximum suppression and improves the speed of feature extraction.

Key words:image processing；deep-learning；weld recognition；feature fusion

Study on microstructure and mechanical properties of 6061 aluminum alloy prepared by oscillating laser-arc hybrid weldingZHANG He1,JIN Jun2,JIANG Ping2,ZHANG Fengdong1,ZHANG Zhenpeng1,ZHOU Zhikai3(1.CRRC Qingdao Sifang Co.,Ltd.,Qingdao,266111,China；2.Huazhong University of Science &Technology,Wuhan,430074,China；3.CARMAN HAAS Laser Technology (Suzhou) Co.,Ltd.,Suzhou,215000,China).pp 94-102

Abstract:The oscillating laser-arc welding was carried out on the 6mm thick 6061 aluminum alloy locked bottom butt joint commonly used for the roof of high-speed rail,and the effect of oscillating frequency on the microstructure and mechanical properties of the weld was systematically studied based on SEM,EBSD and other characterization methods together with the penetration and porosity of the weld as indicators.The results showed that the porosity of the joint was reduced to less than 1% when the oscillating frequency sharply increased to 250 Hz.The weld area near the fusion line was primarily arranged with columnar dendritic structures,while the central arc region of the weld was chiefly composed of equiaxed dendritic structures.Laser oscillating frequency could affect the beam advance distance in per unit cycle,which posed a significant impact on the stirring action of laser beam behind the molten pool.With the increase of the oscillating frequency,the stirring effect of the molten pool was enhanced,which effectively refined the central equiaxed structures and dropped the dendrite sizes from 68 μm to 44 μm.The tensile strength reached their maximum value at the oscillating frequency of 250 Hz,with a maximum tensile strength of 229 MPa,which was about 73% of that of the base metal.Both the reduction of the porosity and the refined dendrites structures of the weld largely created favorable conditions for the improved tensile strength.

Highlights:(1) The oscillating laser-arc welding process was used to achieve high-quality welding of 6061 aluminum alloy locked bottom butt joint,and the tensile strength of the joint reaches 73% of that of the base metal.

(2) The correlation between porosity,microstructure and mechanical properties of 6061 aluminium alloy locked bottom joint was studied.

Key words:oscillating laser-arc welding；oscillating frequency；porosity；microstructure；mechanical properties

Friction stir welding process microstructure and property of weld for Zr-Sn-Nb-Cr-Fe zirconium alloysZHANG Chao,ZHOU Mengbing,TAO Xin,ZHENG Yunxi,WANG Zhiguo,WEI Lianfeng,YANG Canxiang(Fourth Institute of Nuclear Power Institute of China,Chengdu 610213,China).pp 103-108

Abstract:Process performance,microstructure and corrosion properties of friction stir welded (FSW) joints of Zr-Sn-Nb-Cr-Fe zirconium alloys were studied in the present paper.The results indicate that the recommended zirconium alloys FSW joints with good shape and no welding defects were obtained by W-25%Re stir tool under the conditions of 250 rpm rotational speed,40 mm/min welding speed,10 kN axial force and argon protection.In stir zone (SZ),the severe plastic deformation leads to dynamic recrystallization,diffusion of alloying element and grain refinement and grain size increases with the increase of rotational speed.As the same time,a large number of irregularly shaped second phase particles were precipitated at the grain boundaries.These FSW joints prepared by different welding parameters exhibited black,bright and dense oxide film after being corroded in neutral water at 360℃,18.6 MPa for 72 hours.However,the corrosion resistance of FSW joints decreases with the increase of rotational speed.

Highlights:(1) Technological exploration and microstructure research of 4.5 mm thick zirconium alloy are carried out by using friction stir welding technology.

(2) The autoclave corrosion test on friction stir welding joints of zirconium alloy is carried out.

Key words:zirconium alloys；friction stir welding；welding process performance；microstructure；corrosion property

Effect of long term high temperature aging on CGHAZ microstructure of T23 water wall welded jointYIN Shaohua1,2,WANG Yuwei3,SUN Zhiqiang1,ZHANG Zhenhua4(1.Suzhou Nuclear Power Research Institute Co.,Ltd,Suzhou 215004,China；2.Tianjin University,Tianjin 300350,China；3.CHN Energy Jiangsu Electric Power Co.,Ltd,Nanjing 210036,China；4.CHN Energy Xuzhou Power Co.,Ltd,Xuzhou 221166,China).pp 109-115

Abstract:The micro-mechanism of reheat crack formation in coarse grain heat affected zone (CGHAZ) of welded joint of T23 water wall tube without heat treatment after welding was analyzed by high temperature aging method.It reveals the internal reason that T23 water wall joint without heat treatment is easy to crack and leak in short-term operation after unit startup.The hardness,microstructure and precipitates of welded joints of water wall after unaged and high temperature aging treatment were systematically analyzed by means of material characterization.The results show that after aging at 530 ℃ for 100 h,the hardness of CGHAZ appears secondary hardening caused by intragranular dispersion strengthening.With the increase of aging (running) time,the hardness of CGHAZ gradually decreases,but after aging for 1 000 h,the hardness of CGHAZ is still 319 HV,which is higher than the standard requirement.After aging at 600 ℃,the hardness of CGHAZ decreases with the increase of aging time.The hardness of CGHAZ decreased due to the recovery of microstructure,recrystallization,broadening of martensite lath,reduction of dislocation density,and precipitation of C and alloy elements from the matrix,which is higher than the hardness increased due to dispersion and precipitation of MX carbide in the grain.M23C6 carbide gradually precipitates and grows at grain boundaries and subgrain boundaries.

Highlights:(1) The internal causes of cracking and leakage of welded joints of T23 water wall without heat treatment in engineering after short-term operation are revealed.

(2) The microscopic mechanism of no secondary hardening in CGHAZ zone after aging at 600 ℃ is revealed.

Key words:high temperature aging；T23 steel；water cooling wall；CGHAZ；reheat crack

Research status and application progress of narrow gap welding technology for thick platesTENG Bin1,2,FAN Chenglei1,XU Kai2,WU Pengbo2,NIE Xin2,HUANG Ruisheng2(1.Harbin Institute of Technology,Harbin,150001,China；2.Harbin Welding Institute Limited Company,Harbin,150028,China).pp 116-128

Abstract:Narrow gap welding technology has become the first choice for welding thick plate structures in modern industrial production.Its technical and economic advantages determine it to become one of the main directions of the future development of thick plate welding technology.In recent years,with the continuous exploration and research and the development of scientific and technological workers,a variety of narrow gap welding methods have emerged.In this paper,narrow gap welding manufacturing technology is systematically described,introducing the narrow gap welding manufacturing technology such as electric arc welding,laser welding,and laser-arc hybrid welding.Meanwhile,this paper outlines the factors influencing the quality and efficiency of the manufacturing process of narrow gap welding with different heat sources,and summarizes the process characteristics and application areas of narrow gap welding with different heat sources.Subsequently,combined with the development status of related technologies at home and abroad,this paper summarizes the problems faced by narrow gap welding manufacturing technology and puts forward subsequent development proposals,with a view to providing references for researchers in related fields.

Highlights:This paper comprehensively discusses the research status of narrow gap welding technology in recent years,briefly expounds the characteristics and application status of various narrow gap welding methods,and puts forward the future development trend and key technical difficulties of narrow gap welding technology.

Key words:narrow gap welding；electric arc welding；laser welding；laser-arc hybrid welding