MAIN TOPICS,ABSTRACTS &KEY WORDS

Analysis of stress distribution characteristics of Zr/Ni circumferential electron beam welded jointsCHEN Guoqing1,TENG Xinyan1,ZHANG Ge1,CAO Hui2(1.State Key Laboratory of Advanced Welding and Joining,Harbin Institute of Technology,Harbin,150001,China；2.Beijing Xinli Machinery Co.Ltd,Beijing,100854,China).pp 1-8

Abstract:Zirconium has good mechanical properties,compatibility with nuclear fuel and radiation resistance,is widely used in the nuclear industry.Nickel has good mechanical properties and corrosion resistance,and is often used as a structural material.There are large differences in thermophysical properties and poor metallurgical compatibility between zirconium/nickel.There is currently no research on fusion welding of zirconium/nickel.In direct welding,the electron beam welded joint is composed of (γ-Ni+Ni5Zr) eutectic+Ni5Zr dendrite composite structure,which leads to welding cracks under residual stress.The tensile strength is only 36.4 MPa.In beam offset welding,the tensile strength of the joint increased to 189 MPa.The finite element simulation research on the stress field and temperature field of the joints under different welding parameters,combined with theoretical calculations,revealed that due to the structure of the weld,there is reheating phenomenon in the initial stage of welding,resulting in high residual stress.Electron beam deflects to Ni side effectively reduces the residual stress and thermal stress of the joint,which is the main reason for the disappearance of cracks.

Highlights:(1) The effective electron beam welded joints of Zr/Ni were successfully prepared for the first time.

(2) The stress distribution in the weld was thoroughly analyzed using the finite element analysis.

(3) The mechanism of crack formation was elucidated through the analysis of the thermal stress field and residual stress field.

Key words:girth weld；finite element analysis；residual stress；weld crack；temperature field

Evaluating solidification cracking susceptibility of Mg alloys and intergranular liquid backfilling during welding

LIU Kun,LI Jie,WANG Hao,JIAN Sijie(Jiangsu University of Science and Technology,Zhenjiang,212100,China).pp 9-15

Abstract:In present work,the widely used Mg alloys ZK61,AZ31,AZ61 and AZ91 were selected for investigating the solidification cracking susceptibility during welding.Transverse motion weldability (TMW) test in two-speed mode was used to evaluate the susceptibility of Mg alloys to solidification cracking during welding.The critical transverse moving speed was obtained and considered as an index to estimate the solidification cracking susceptibility of Mg alloys as ranking: ZK61 >AZ31 >AZ61 >AZ91.The ranking is consistent with the results of one-speed test and predicted results based on│dT/d(fS)1/2│max.It was shown that two-speed test of TMW is effective to evaluate the susceptibility of Mg alloys to solidification cracking.According to the backfilled liquid at the tip of or near the solidification cracking,the intergranular backfilled liquid of ZK61 is discontinuous and the channel is narrow,which is difficult to heal the crack and increases the solidification cracking susceptibility.The liquid backfilling channel of AZ91 is the widest,which is conducive to intergranular liquid backfilling and reduces the solidification crack susceptibility.

Highlights:(1) The critical transverse moving speed was considered as an index for evaluating the solidification cracking susceptibility.

(2) The mechanism of intergranular liquid backfilling for resisting solidification cracking of Mg alloy was revealed.

Key words:magnesium alloy；welding；solidification cracking；intergranular liquid

Pavlou approach based fatigue life prediction for welded structuresWEI Guoqian1,2,3,GUO Zixian2,YAN Mengyu2,ZHAO Gang3(1.Key Laboratory of Metallurgical Equipment and Control Technology,Ministry of Education,Wuhan University of Science and Technology,Wuhan,430081,China；2.Hubei Key Laboratory of Mechanical Transmission and Manufacturing Engineering,Wuhan University of Science and Technology,Wuhan,430081,China；3.Precision Manufacturing Institute,Wuhan University of Science and Technology,Wuhan,430081,China).pp 16-23

Abstract:Fatigue life prediction under variable amplitude loading is an important issue in the integrity analysis of welded structures.Based on the fatigue damage zone concept proposed by Pavlou and the S-N curve recommended in BS7608 standard,an approach to predict fatigue lives of welded structures was realized by FEA heat transfer problem.Fatigue tests under two-level tensile loading block sequences were conducted for load-carrying cruciform welded joints,non-load-carrying cruciform welded joints and butt welded joints,respectively.The fatigue lives of the specimens were estimated according to Miner model,M-H model and Pavlou method.Results showed that the Pavlou method had higher prediction accuracy with more uniform distribution in the error scatter diagram of predicted life versus test life,which validated the rationality and effectiveness of the proposed method.Moreover,the influence of S-N curve survival probability on the life prediction accuracy is discussed.The S-N curve with 2.3% survival probability is suggested to be utilized to obtain satisfactory prediction results.

Highlights:(1)A new fatigue life prediction approach for welded structures based on non-linear fatigue damage accumulation model is investigated.

(2)Base on the Pavlou method,Fatigue Damage Map based damage accumulation calculation framework is presented.

(3)Fatigue Damage Map can be constructed by the S-N curve corresponding to the specific welded joint and the heat transfer solution based on FEA method.

(4)Fatigue tests were conducted and the results verify the rationality and effectiveness of the proposed approach.

Key words:Welded structures；Fatigue life；Variable amplitude loading；Non-linear damage model；S-N curve survival probability

Analysis of morphological characteristics of low vacuum laser welded joint of Ti6Al4V alloyHUANG Ruisheng,LI Xiang,ZOU Jipeng,WU Pengbo,TENG Bin,SU Jinhua,SUN Yuanqi(Harbin Welding Institute Limited Company,Harbin,150028,China).pp 24-29

Abstract:In order to explore the morphology characteristics of the laser welded joint of Ti6Al4V alloy under low vacuum environment,non-penetration welding was performed under 5 Pa ambient pressure.The influence law of laser power and defocus amount on the weld morphology was studied,and the stability and formation interval of the typical joint morphology were analyzed.The results show that the weld bead quality can be obtained by changing the process parameters in a wide range under low vacuum ambient pressure,and the weld penetration increases linearly with the increase of output power.The geometric features of welded joints can be divided into two types:the U shape formed when the line energy utilization factor is less than 0.13 or greater than 0.14,and the V shape formed when the line energy utilization factor is between 0.13 and 0.14.V shape keyhole stability is poor,it is difficult to maintain the quasi steady state,weld penetration depth fluctuation is large,easy to form defects at the bottom of the weld.

Highlights:The morphology characteristics of Ti6Al4V alloy low vacuum laser welding joints were analyzed,and the keyhole stability of typical geometric morphology was calculated.The morphology characteristics were correlated with the line energy utilization factor,and the optimized process window was proposed.

Key words:low vacuum laser welding；titanium alloy；welded joint morphology

Study on the fatigue performance of bobbin tool friction stir welding of 6005A-T6 aluminum alloyZHANG Xinmeng1,GAO Shikang2,3,LI Gaohui2,ZHANG Haifeng3,ZHOU Li2,3,WANG Ping4(1.CRRC Changchun Railway Vehicles Co.LTD,Changchun,130062,China；2.State Key Laboratory of Advanced Welding and Joining,Harbin Institute of Technology,Harbin,150001,China；3.Shandong Provincial Key Laboratory of Special Welding Technology,Harbin Institute of Technology at Weihai,Weihai,264209,China；4.Harbin Institute of Technology at Weihai,Weihai,264209,China).pp 30-36

Abstract:The fatigue tests of bobbin tool friction stir welding profile joints of 3.3 mm thick 6005A-T6 aluminum alloy with different dimensions were carried out to analyze the fatigue performance of the joints.Combined with the macroscopic forming and microstructure evolution of the joint under typical parameters,the fracture behavior of the bobbin tool friction stir welded joint was revealed.The results showed that the tensile fracture of the joint under typical parameters (rotation speed of 1 000 r/min,welding speed of 100 mm/min,width and thickness of parallel section of 11.8 mm and 3.1 mm) was located in the HAZ-RS.The grain structure characteristics in the TMAZ-AS of the joint could influence the fatigue cracks generation and propagation.The SEM analysis of fatigue fracture showed that no obvious defects were found.The fatigue cracks propagation and fracture zones showed typical fatigue fracture characteristics,and the fracture was located in the TMAZ-AS of the joint

Highlights:(1) Bobbin tool friction stir welding of 6005AT6 aluminum alloy with different dimensions had been successfully achieved.

(2) The relationship between dimension and fatigue properties of profiles was investigated.Combined with the microstructure evolution,the fatigue fracture behavior of the joint was revealed.

Key words:friction stir welding；6005A-T6 aluminum alloy profile joint；fatigue crack growth

Research on microstructure evolution and mechanical properties of gradient sandwich filler metal during brazingZHANG Guanxing,ZHONG Sujuan,SHEN Yuanxun,DONG Hongwei,XUE Hangyan(State Key Laboratory of Advanced Brazing Filler Metals &Technology,Zhengzhou Research Institute of Mechanical Engineering Co.,Ltd,Zhengzhou,450001,China).pp 37-43

Abstract:Sandwich composite filler metal is an important technical means to realize reliable brazing connection between cemented carbide and steel.The microstructure of the composite layer and the interface layer between the composite layer and the matrix has an important influence on the mechanical properties.The microstructure evolution of brazing joint of gradient sandwich composite filler metal under different brazing temperature and time conditions was systematically studied,and the key factors affecting the mechanical properties were analyzed.The research results showed that the interfacial formation of gradient sandwich filler metal with steel and carbide matrix could be divided into four stages: interfacial structure formation,growth,fusion and rearrangement.The CuMn2 layer in the middle of the gradient filler metal gradually changed from the initial continuous shape to an isolated island surrounded by low Mn copper solid solution with the extension of holding time.As the holding time continued,CuMn2 layer disappeared and the whole brazing joint was composed of copper solid solution,silver solid solution and silver copper eutectic.The shear strength of the brazing joint reached the highest 285 MPa when the temperature was kept at 780 ℃ for 2.5 min.At this time,the Co and Ni elements had long range diffusion and accumulated near the CuMn2 interlayer,which improved the strength and toughness of the CuMn2 interlayer.The Co-based particle strengthening phase was distributed in the root of the fracture dimple.Further extension of holding time,Co,Ni and other brazing elements began to disperse,the brazing structure coarsened,the strength decreased.

Highlights:(1) The microstructure evolution of brazed joints between cemented carbide and steel with gradient sandwich filler metal was studied.

(2) The mechanism of reinforcing brazing seam with Co-based reinforced particles was clarified.

Key words:gradient sandwich filler metal；interfacial diffusion；shear strength

High temperature tensile fracture characteristics of F GH96/IN718 inertial friction welded jointLIANG Wu1,2,ZHOU Jun1,2,ZHANG Chunbo1,2,ZHANG Lu3,WU Yanquan1,2,LI Yunlei1,2(1.Harbin Welding Institute Limited Company,Harbin,150028,China；2.Heilongjiang Provincial Key Laboratory of Advanced Friction Welding Technology and Equipment,Harbin,150028,China；3.AECC Commercial Aircraft Engine Co.,Ltd.,Shanghai,200241,China).pp 44-52

Abstract:In order to achieve highly reliable connection of FGH96 and IN718 dissimilar high-temperature alloys for aerospace applications,to provide basic data and theoretical support for the safety evaluation and life prediction of aero-engines key components.Scanning electron microscopy and metallurgical microscopy were used to study the FGH96 and IN718 dissimilar high-temperature alloy inertia friction welding joint microstructure morphology and high-temperature tensile specimens fracture morphology and fracture location.Test results show that the weld zone FGH96 and IN718 were equiaxed grain organization,the grain size is about 2 μm,the weld zone γ′ and δ strengthening phase were completely dissolved,the heat-force affected zone FGH96 side of the grain γ′also was completely dissolved,the IN718 side δ strengthening phase occured partially dissolved,the short rod-like shape was disappeared,coarse and fine crystal organization coexisted.The welded joint 650 ℃ high temperature tensile specimens were fractured with the weld zone,but the average tensile strength up to 1 080.8 MPa,basically with IN718 parent material equal strength,the high-temperature tensile specimens crack location were in the edge of the sample weld zone,the crack from the weld zone was mainly due to γ′ and δ strengthening phase basically all dissolved,the strengthening effect disappeared,the performance was reduced.The crack was generated along the grain boundary from the weld fusion line to the specimen internal expansion,the crack from the specimen edge weld area around the same time to the specimen internal expansion,under the action of axial tension to form a "platform +crater" fracture characteristics,when the crack from the specimen edge weld area local location to the specimen internal expansion,under the action of axial tension to form "platform +shear" fracture characteristics.

Highlights:Through FGH96 and IN718 dissimilar high-temperature alloy inertia friction welding test and high-temperature tensile fracture characteristics,reveal the FGH96 and IN718 dissimilar high-temperature alloy inertia friction welded joint fracture characteristics,clarify the "platform+crater" and"platform+shear" the formation of two types of characteristic fracture causes.

Key words:dissimilar high-temperature alloys；inertial friction welding；high-temperature stretching；fracture characteristics

Development of a closed loop control system for discharge parameters of electric spark depositionHOU Yujie1,HAN Hongbiao1,2,3,YANG Xin1,ZHENG Guangzhen1(1.Henan University of Science and Technology,Luoyang,471003,China；2.Henan Key Laboratory for Machinery Design and Transmission System,Luoyang,471003,China；3.Longmen Laboratory,Luoyang,471000,China).pp 53-59

Abstract:In order to realize the automation of electric spark deposition (ESD),a closed loop control system of discharge parameters for ESD was developed.Discharge parameters during deposition are collected in real time.Based on the linear law that the average discharge pulse voltage is inversely proportional to the contact force,the closed-loop control of the average discharge pulse voltage is achieved by the feed motor and the feed slide adjusting the contact force between the workpiece and the electrode,and thus the automatic feed adjustment of electrode is realized.The analog circuit,digital control circuit and control software of the control system are designed by modular technology,which can shorten the development period,ensure the reliability and facilitate the upgrade and expansion.The test results of ESD show that the developed closed loop control system of discharge parameters can realize the stable contact between electrode and workpiece and obtain uniform and dense deposition layer,which is convenient to realize the automatic operation of ESD and is conducive to the popularization and application of ESD technology.

Highlights:Based on the linear law that the average voltage of discharge pulse is inversely proportional to the contact force,a closed loop control system of discharge parameters for ESD is designed by using modular technology.The stable contact between electrode and workpiece is realized and uniform and dense deposition layer is obtained.

Key words:electric spark deposition；discharge parameters；closed-loop control；contact force

Solidification behavior and characteristics of molten pool of high manganese austenitic steel for cryogenic applicationHE Qiong1,WANG Honghong2,WANG Yangwen2,ZHANG Fuwei3,LI Xiaochen3(1.State Key Collaborative Innovation Center for Advanced Steels,Wuhan University of Science and Technology,Wuhan,430081,China；2.The State Key Laboratory of Refractories and Metallurgy,Wuhan University of Science and Technology,Wuhan,430081,China；3.China Merchants Jinling Shipyard (Yangzhou) Dingheng Co.,Ltd,Yangzhou,225217,China).pp 60-66

Abstract:The weld metal of high manganese austenitic steel was prepared by submerged arc welding process with the main composition (wt.%) range of 0.30-0.50 C,22.00-25.00 Mn,3.50-5.50 Cr.The segregation behavior of alloying elements and the solidification characteristics of the molten pool of high manganese austenitic steel were studied by OM,EBSD,EPMA and other analysis methods.The analysis of microstructure and chemical composition shows that there are inhomogeneous mixed zone and partially melted zone (PMZ) in the fusion zone of high manganese austenitic steel welded joints prepared with the same composition system.The alloy element segregation zone of C,Mn and Cr produced by hot rolling in the test steel resulted in partial melting of the PMZ in the fusion zone of the welded joint,and further increases its degree of elemental segregation.The inhomogeneous mixed zone co-crystallizes in the PMZ in the form of cellular crystals,and the distribution of the alloy elements continues the distribution in the PMZ.The molten pool co-crystallizes in the form of cellular crystals on the protruding solid phase peninsula on the PMZ.The width of the initial cytosolic crystals correlates is intrinsically related to the spacing of the hot-rolled segregation bands of the base metal,which is produced by the segregation of alloying elements in the hot rolled strip in the partially melted zone and the concave solid-liquid interface formed by its partial melting.

Highlights:The welding molten poor solidification mode of the novel high manganese austenitic steel is proposed for the first time.The effect of hot rolled segregation band on the width of the solidified nucleation substrate of the molten pool and the initial cellular spacing size is addressed.

Key words:high manganese austenitic steel；partially melted zone；solidification crystallization；segregation

Fatigue fracture mechanism of 304 stainless steel manufactured by laser metal depositionHUANG Weibo,ZHAO Xiaoyu,LU Wenjia,Zhu Lisha,ZHANG Yimin(College of Mechanical and Automotive Engineering,Zhaoqing University,Zhaoqing,526061,China).pp 67-73

Abstract:Laser metal deposition is a widely used laser additive manufacturing technology.The fatigue tests of 304 austenitic stainless steel manufactured by laser metal deposition are carried out and the fatigue fracture mechanism is studied.According to the experimental results,the S-N curve of 304 austenitic stainless steel manufactured by laser metal deposition is drawn.The results show that the stress amplitude has an important effect on the fatigue fracture morphology.The larger the stress amplitude is,the coarser the fatigue fracture is.Under the higher stress amplitude,there are randomly distributed holes and cracks on the surface of the fracture specimen.Material defects such as oxide inclusions and pores are the main causes of fatigue crack initiation,and large local plastic deformation under the large stress amplitude (such as 275 MPa) is also one of the causes of fatigue crack initiation.With the increase of stress amplitude,the fatigue bands become clearer.Under the higher stress amplitude,the intersection of multiple slip systems leads to the expansion of fatigue bands in different plane,and the tire indentation appears in the crack propagation zone.With the increase of stress amplitude,the number of secondary cracks increases due to the increase of plastic deformation in the fatigue crack propagation zone.

Highlights:(1) The stress-strain curve of 304 austenitic stainless steel formed by laser metal deposition was drawn.

(2) The morphologies of fatigue fractures under different cyclic alternating load amplitudes were compared,and the reasons were analyzed.

Key words:laser metal deposition；S-N curve；fatigue fracture mechanism

Investigation of in situ fracture mechanism of ernicrfe-13 welding wire deposited metalWEI Chao,GUO Xiao,HAN Weichao,JIANG Yinglong,LV Xiaochun,XU Lixiang(Harbin Welding Institute Limited Company,Harbin,150028,China).pp 74-80

Abstract:The evolution of microstructure and the initiation and propagation mechanism of microcracks during the tensile process of ERNiCrFe-13 welding wire deposited metal.The microstructure and fracture behavior of deposited metal were studied by in-situ tensile scanning electron microscopy (SEM)and energy dispersive spectroscopy (EDS).The results show that the microstructure of ERNiCrFe-13 welding wire deposited metal is mainly composed of columnar dendrite γ phase(NiCrFe solid solution),Nb and Mo rich in Laves phase(Cr,Fe,Ni)2(Ti,Mo),MC carbides and eutectic structure in the interdendritic.The formation of Laves phase is mainly related to the segregation of Nb and Mo elements during solidification and has a size effect.Horizontal Laves phase size larger than 4 μm is prone to cracking.The fracture mechanism is the initiation of microcracks in the interdendrite precipitated phase under shear stress.Under the action of axial tensile stress,the connection is further extended along grain boundaries to fracture failure.The fracture is ductile and carbide segregation(NbC,TiC) and large Laves phase are the main causes of grain boundary cracks.

Highlights:(1)Revealed the microstructure fracture evolution mechanism of ERNiCrFe-13 deposited metal during in-situ tensile at room temperature.

(2) Propose the quantitative criterion of Laves phase cracking with size effect in ERNiCrFe-13 deposited metal.

Key words:nickel base alloy；in situ tension；deposited metal；Laves phase

Research on the interface of composite plate via explosive welding TC1/1060/6061 based on experiments and numerical simulationsYUAN Jiaxin1,SHAO Fei1,BAI Linyue1,XU Qian1,SUN Bin1,WANG Jingtao2(1.Army Engineering University of PLA,Nanjing,210007,China；2.Equipment Price Evaluation Center of Army Armament Department,Beijing,100010,China).pp 81-87

Abstract:Titanium/aluminum composite plate with excellent performance can be obtained by combining thin layer titanium alloy plate with aluminum alloy plate,which has broad application prospects.TC1/1060/6061 composite plate was successfully prepared by explosive welding technology.The interface morphology and interface elements of the two interfaces were tested,and the advantages of 1060 interlayer were analyzed.At the same time,the finite element model consistent with the test conditions was established,and the interface state and welding process were analyzed.Finally,tensile test and shear test were carried out to verify the bonding quality of interface.The results show that the TC1/1060 interface has a linear morphology,and the 1060/6061 interface has a large wavy interface,and each wave is accompanied by the vortex region.The element diffusion range at the TC1/1060 interface is 4.38 μm,and no Ti/Al intermetallic compounds are detected.The numerical simulation reproduces the jetting formation in the process of explosive welding.The interface temperature is distributed along the interface morphology,and the interface pressure reaches the maximum at the collision point,showing an elliptic distribution.The composite plate has high tensile strength and shear strength,which can meet the requirements of structure use.

Highlights:(1) TC1/1060/6061 composite plates were successfully prepared,and the morphology and element diffusion of TC1/1060 interface and 1060/6061 interface were studied.

(2) A numerical model was established to reproduce the interface jetting during explosive welding,and the distribution of temperature and pressure along the interface was analyzed.

(3) According to the Gauss point set in the numerical model,the collision and bonding process of each layer in the explosive welding process is analyzed from the Y-direction velocity.

Key words:explosive welding；Ti/Al composite plate；interface morphology；interface state；mechanical properties

Investigated on the non-uniformity of AA6056 bobbin tool friction stir welding jointWEN Quan1,2,LI Wenya2,WU Xuemeng1,REN Shouwei1,ZHAO Jing1(1.State-Owned Sida Machinery Manufacturing Company,Xianyang,712203,China；2.Shaanxi Key Laboratory of Friction Welding Technology,Northwestern Polytechnical University,Xi'an,710072,China).pp 88-94

Abstract:6056 aluminum alloy with 4mm thickness was welded by bobbin tool friction stir welding,and the non-uniform characteristics of microstructure and mechanical properties of different characteristic areas of the joint were studied.Results show that the equivalent strain of the cross section of the joint is dumbbell shape,which is consistent with the macromorphology of the cross section of the weld.The plastic strain distribution along the left and right sides of the weld center is asymmetrical,and the plastic strain value at the advancing side of the joint is higher than that at the retreating side.The proportion of high angle grain boundary near the advancing side and the middle side is higher than that on the retreating side.The advancing side and middle side are mainly B-typetexture,and the retreating side is A-typetexture.Incomplete dynamic recrystallization occurs in the band pattern area of the weld,and the proportion of deformed grains is 58.9%.The band pattern area is B-typetexture with texture strength of 10.6,which is higher than that of other positions in the stir zone.The strain in the heat affected zone is more than 18%,which is higher than the whole joint with 3.6%.The strain in the thermo-mechanically affected zone is similar to that of the whole joint,while the strain in the stir zone is less than that of the whole joint.

Highlights:(1) Revealing the characteristics of non-uniform microstructure distribution in horizontal direction of the BTFSWed joint.

(2) Clarifying non-uniformity mechanical property characteristics for characteristic zones in the BT-FSWed joint.

Key words:bobbin tool friction stir welding；non-uniformity；microstructure；strain

Effect of aging time on the microstructure and mechanical properties of the SP2215 steel welded jointJIN Xiaokun1,2,ZHANG Shichao2,DIAO Wangzhan3,DU Jinfeng1,LIANG Jun1,ZHANG Zheng2(1.CHN Energy New Energy Technology Research Institute Co.,Ltd.,Beijing,102209；2.Beihang University,Beijing,100191；3.Harbin Boilers Co.,Ltd.,State Key Laboratory of Efficient and Clean Coal-fired Utility Boilers,Harbin,150046).pp 95-105

Abstract:SP2215 tube welded joints (WJ) were prepared by manual gas tungsten arc welding (M-GTAW) and ERNiCr-3 welding wire.The microstructure,mechanical properties and tensile fracture mechanism of the WJ after aging for different times at 650 ℃ were studied.The results show that the microstructure of SP2215 base metal (BM) is composed of austenite,a small amount of twins and primary NbN and Z phase in the as-welded condition,the weld metal (WM) was solidified into columnar dendrite with a completely austenitic structure,and Nb element was segregated between the dendrites and forms the NbC phase,which was distributed in a chain shape.After aging at 650 ℃ for 50 h,M23C6began to precipitate at the austenite grain boundary of SP2215 BM and gradually coarsened with the extension of aging time,at the same time NbC phase gradually precipitated between dendrites and gradually formed into a cluster shape with the increase of aging time.The microhardness of BM and WM increases with the increasing of aging time,and reaches the maximum value at 500 h.The hardness of BM is always higher than that of WM.All the WJ with different aging time were fractured at the weld seam in a ductile manner at room temperature tensile test,however the fracture initiation position and fracture direction changed with the extension of aging time.When the aging time was 0-114 h,the fracture direction was transverse to the columnar dendrite direction,and the crack initiation position was the primary NbC particles between dendrites.When the aging time was 500-2 012 h,the fracture direction was parallel to the columnar dendrite direction,and the crack initiation position is the dendritic core.The fracture position of the WJ changed from the weld seam to the SP2215 side with the increase of aging time at high temperature tensile test at 650 ℃.The WJ aging for 0-114 h fractured at the weld seam in a ductile manner,however the WJ aging for 2 012 h fractured at the SP2215 side in a quasi-cleavage manner.

Highlights:(1) New type domestic austenitic heat-resistant steel SP2215 is intended to be applied to the superheater/ reheater of 630 ℃ ultra-supercritical boiler.

(2) The microstructure of SP2215 welded joint after aging at 650 ℃ for different time was studied.

(3) The tensile properties and fracture mechanism of SP2215 welded joint at room temperature and high temperature after aging at 650 ℃ for different time were studied.

Key words:austenitic heat-resistant steel；welded joint；aging；microstructure；mechanical properties

Prediction of welding deformation in large long straight beams for locomotiveZHANG Yuelai1,HE Qinghe1,ZHU Jiayi1,LIANG Guihui2,ZENG Jiongmeng2,DENG Dean2(1.CRRC Zhuzhou Locomotive Co.,Ltd,Zhuzhou,412001；2.Chongqing University,Chongqing,400045).pp 106-112

Abstract:An efficient enhanced moving heat source model was developed based on the MSC.Marc finite element software platform.The thermo-elastic-plastic finite element method,along with the enhanced moving heat source model,was employed to numerically simulate the welding deformation of a large-scale long straight rolling stock structure measuring 13 832 mm in length.Simultaneously,the welding deformation of the long and straight structure was measured experimentally and compared to the numerical simulation results.This comparison verified the accuracy and feasibility of the developed finite element calculation model for welding deformation in such structures.Subsequently,the developed computational method was used to investigate the impact of different welding sequences on the welding deformation of large long straight structures in rolling stock.The calculation results demonstrate that the welding sequence significantly affects both the mode and magnitude of welding deformation.By adjusting the welding sequence,substantial reduction in welding deformation can be achieved.This study provides guidance for the production of large long straight structures and reduces the process development cycle.

Highlights:(1) An enhanced moving heat source model was developed for thermo-elastic-plastic finite element analysis of welding deformation in large long straight beam structures.

(2) The validity of the enhanced moving heat source model based on thermo-elastic-plastic finite element method is verified.

(3) The influence of welding sequence on the welding deformation of long straight beam structures is clarified.

Key words:large long straight structure；welding deformation；welding sequence；numerical simulation

Welding feasibility analysis of arc preheating scheme for ITER anaerobic copper TIG weldingWANG Hua1,JIN Jing2,HAO Qiangwang2(1.Hefei Keju High Technology Co.,Ltd.,Hefei,230031,China；2.Institute of Plasma Physics,Chinese Academy of Sciences,Hefei,230031,China).pp 113-117

Abstract:The superconducting joint of the internal coil in the vacuum coil system of the device has a high requirement on weld quality because of its bad working environment.In order to verify the feasibility of welding oxygen free copper pipe with arc preheating method,the method of arc preheating with open head was adopted to preheat oxygen free copper pipe to reach the temperature required for welding copper pipe .Nondestructive testing,macroscopic and microscopic examination,and hardness measurement of weld,heat-affected zone and base metal are performed on copper welded joints.The influence of arc preheating on the heat-affected zone is evaluated.The analysis shows that there is no significant difference between the hardness of the heat affected zone and the base metal,but there is a significant difference in the microstructure.The hardness of weld metal is slightly higher.In the observation range,arc preheating has no significant effect on the heat-affected zone.The results show that arc preheating is feasible.

Highlights:(1) An arc preheating TIG welding method is proposed to realize the single-side welding and double-side forming welding of 6 mm oxygen-free copper pipe.

(2) The influence of arc preheating process on the microstructure and hardness of weld area and the heat-affected zone of the weld were systematically studied.

Key words:internal vacuum coil system；arc preheating；oxygen free copper pipe welding；hardness measurement；microstructure

Research progress on advanced joining technology of highnitrogen steelWANG Xingxing1,TIAN Jiahao1,LI Shuai1,FANG Naiwen2,HE Peng3,NI Zenglei1,WEN Guodong4(1.Henan International Joint Laboratory of High-efficiency Special Green Welding,North China University of Water Resources and Electric Power,Zhengzhou,450045,China；2.Harbin Welding Institute Limited Company,Harbin,150028,China；3.State Key Laboratory of Advanced Welding and Joining,Harbin Institute of Technology,Harbin,150001,China；4.Xi'an University of Science and Technology,Xi'an,710054,China).pp 118-128

Abstract:High nitrogen steel offers unique benefits including high strength,toughness,abrasion resistance,and corrosion resistance.The connectors have been widespread application in military equipment,medical instruments,and mining devices.The major domestic and foreign research reports in recent years on gas tungsten arc welding,gas metal arc welding,laser welding and laser-arc hybrid welding,friction stir welding and brazing of high nitrogen steel are summarized in detail.According to the three main classifications of fusion welding,solid-state welding and brazing,the paper systematically reviews the existing various types of high-nitrogen steel welding methods and process control from the aspects of shielding gas,heat input,process parameters and others,introducing the current status of the application of high-nitrogen steel materials in the field of medical devices,oil drilling collars,and armor protection.Finally,the review points out the shortcomings and aspects of the existing research on high nitrogen steel joining systems,expecting to provide information and theoretical basis for the research and application in the fields of high nitrogen steel welding,functional joining of high-strength materials and other related fields.

Highlights:(1) The research status of high nitrogen steel welding technology in recent years was summarized systematically,in addition to the key points and shortcomings of various welding technologies were analyzed.

(2) The paper points out the insufficient of existing research on high nitrogen steel joining,which is of theoretical importance for functional joining in related fields.

Key words:high-nitrogen steel；welding process；joining；mechanical properties