Correlation of microstructure and intergranular stress corrosion cracking （IGSCC） susceptibility for the SA508-52M-316L dissimilar metal weld joint in primary water was investigated by the interrupted slow strain ra...Correlation of microstructure and intergranular stress corrosion cracking （IGSCC） susceptibility for the SA508-52M-316L dissimilar metal weld joint in primary water was investigated by the interrupted slow strain rate tension test following a microstructure characterization. The susceptibility to IGSCC in var- ious regions of the dissimilar metal weld joint was observed to follow the order of Alloy 52 Mb〉 the heat affected zone of 316L〉 the dilution zone of Alloy 52 Mw〉 Alloy 52 Mw weld metal. The chromium- depletion at the grain boundary is the dominant factor causing the high IGSCC susceptibility of Alloy 52 Mh. However, IGSCC initiation in the heat affected zone of 316L is attributed to the increase of resid- ual strain adjacent to the grain boundary. In addition, the decrease of chromium content and increase of residual strain adjacent to the grain boundary increase the IGSCC susceptibility of the dilution zone of Alloy 52 Mw.展开更多
Microstructure of the heat affected zone （HAZ） of a 308L-316L stainless steel （SS） weld joint and its corrosion behavior in high temperature water were studied. Peak of the residual strain was observed to approach...Microstructure of the heat affected zone （HAZ） of a 308L-316L stainless steel （SS） weld joint and its corrosion behavior in high temperature water were studied. Peak of the residual strain was observed to approach to the fusion boundary in the HAZ while the strain increased from the top to root areas of the HAZ. The root area of the HAZ shows a lower corrosion resistance in high temperature water than the top and middle areas of the HAZ. This is attributed to a higher level of residual strain in association with a higher density of tangled dislocations in the top area of the HAZ. The results suggest that the residual strain in the HAZ could also promote the SCC through its effect on corrosion, in addition to that on the local microstructure and mechanical property of the steel.展开更多
Many factors influence the fatigue and crack growth behavior of welded joints. Some structures often undergo fairly large static loading before they enter service or variable amplitude cyclic loading when they are in ...Many factors influence the fatigue and crack growth behavior of welded joints. Some structures often undergo fairly large static loading before they enter service or variable amplitude cyclic loading when they are in service. The combined effect of both applied stress and high initial residual stress is expected to cause the residual stresses relaxation. Only a few papers seem to deal with appropriate procedures for fatigue analysis and crack growth by considering the combined effect of variable amplitude cyclic loading with residual stresses relaxation. In this article, some typical welded connections in ship-shaped structures are investigated with 3-D elastic-plastic finite element analysis. The effect of residual stress relaxation, initial residual stress, and the applied load after variable amplitude cyclic loading is revealed, and a formula for predicting the residual stress at hot spot quantitatively is proposed. Based on the formula, an improved fatigue procedure is introduced. Moreover, crack growth of typical weld joints considering residual stresses relaxation is studied.展开更多
The microstructure and mechanical properties（strength, fatigue and formability） of dissimilar/similar weld joints between DP780 and DP980 steels were studied. The microstructure in fusion zone（FZ） was lath martens...The microstructure and mechanical properties（strength, fatigue and formability） of dissimilar/similar weld joints between DP780 and DP980 steels were studied. The microstructure in fusion zone（FZ） was lath martensite（LM）, and alloying elements in the FZ were uniformly distributed. The hardness in the FZ of dissimilar weld joint was similar to the average value（375 HV） of the two similar weld joints. The microstructural evolution in heat affected zone（HAZ） of dissimilar/similar weld joints was as follows：LM（coarse-grained HAZ） →finer LM（fine-grained HAZ） →M-A constituent and ferrite（intercritically HAZ） →tempered martensite（TM） and ferrite（sub-critical HAZ）. Lower hardness in intercritically HAZ and sub-critical HAZ（softening zones） was observed compared to base metal（BM） in dissimilar/similar weld joints. The size of softening zone was 0.2-0.3 mm and reduction in hardness was ~7.6%-12.7% of BM in all the weld joints, which did not influence the tensile properties of weld joints such that fracture location was in BM. Formability of dissimilar weld joints was inferior compared to similar weld joints because of the softening zone, non-uniform microstructure and hardness on the two sides of FZ. The effect of microstructure on fatigue life was not influenced due to the presence of welding concavity.展开更多
By using digital image correlation(DIC), low-cycle fatigue(LCF) behavior of CrMoV weld joint taken from a retired gas turbine rotor after 15-year service was investigated at 500 ℃ and 540 ℃. The most remarkable plas...By using digital image correlation(DIC), low-cycle fatigue(LCF) behavior of CrMoV weld joint taken from a retired gas turbine rotor after 15-year service was investigated at 500 ℃ and 540 ℃. The most remarkable plastic strain was observed in the weld metal(WM), which was up to 6 times of the global strain at mid-life cycle. Due to the cyclic accumulation of local deformation, the stress–strain hysteresis loops relative to tensile or compressive strain concentration area in WM displayed the ratchetting shape. The local deformation accumulation of WM was attributed to the effect of the equiaxed grain zone near the WM center. The accumulated plastic strain was considered as the main fatigue failure mechanism.展开更多
Characterization of the microstructure of the fusion zone of an Alloy 600-82 weld joint was conducted, with focus on the weld residual strain distribution and the comparison of the microstructure of heat affected zone...Characterization of the microstructure of the fusion zone of an Alloy 600-82 weld joint was conducted, with focus on the weld residual strain distribution and the comparison of the microstructure of heat affected zone （HAZ） with that of cold worked alloy. Peak of the residual strain was observed to approach to the fusion boundary in HAZ while the strain increased from the top of the weld to the root. Strain distribution in the HAZ was found to be concentrated adjacent to grain boundaries （GBs）, with a peak of approximately three times of that in grain. Further, triple junctions of the GB appear to cause a higher strain concentration than single GBs. The microstructure of HAZ consists of partially tangled dislocations, which is different from slip bands of high density dislocations in cold worked alloy. This may cause a relatively higher intergranular cracking resistance of HAZ due to the difficulty in transferring tangled dislocations to GB in HAZ under deformation.展开更多
In a laser butt joint welding process, it is required that the laser beam focus should be controlled to follow the weld joint path accurately. Small focus wandering off the weld joint may result in insufficient penetr...In a laser butt joint welding process, it is required that the laser beam focus should be controlled to follow the weld joint path accurately. Small focus wandering off the weld joint may result in insufficient penetration or unacceptable welds.Recognition of joint position offset, which describes the deviation between the laser beam focus and the weld joint, is important for adjusting the laser beam focus and obtaining high quality welds. A new method based on the magneto-optical（MO） imaging is applied to measure the micro weld joint whose gap is less than 0.2 mm. The weldments are excited by an external magnetic field, and an MO sensor based on principle of Faraday magneto effect is used to capture the weld joint images. A sequence of MO images which are tested under different magnetic field intensities and different weld joint widths are acquired. By analyzing the MO image characteristics and extracting the weld joint features, the influence of magnetic field intensity and weld joint width on the MO images and detection of weld joint position is observed and summarized.展开更多
The successive alteration o the microstructure from the weld metal zone through weld bond to the heat affected zone of a Cr18Ni13 austenitic-0.45%C steels weld joint was observed in situ using transmission electron mi...The successive alteration o the microstructure from the weld metal zone through weld bond to the heat affected zone of a Cr18Ni13 austenitic-0.45%C steels weld joint was observed in situ using transmission electron microscopy.It was found a new type of microstructure called pearlite-like structure and observed the characteristics of the boundary of dissimilar phases. Based on the definition of various zones of the dissimilar steels weld joint under the optical mi- croscope,the transmission electron microscopic characteristics,including microstructures and compositions,of each zone are described and discussed.展开更多
Based on the investigated microstructure of different zones in the annealed automatic gas tungsten arc weld joint of TA16 and TC4 titanium alloys,the mechanical property of them was assessed under fatigue crack growth...Based on the investigated microstructure of different zones in the annealed automatic gas tungsten arc weld joint of TA16 and TC4 titanium alloys,the mechanical property of them was assessed under fatigue crack growth rate tests.For evaluation of fatigue crack growth rate,three points bending specimens were used.The correlation between the range of stress intensity factor and crack growth rate was determined in different zones of the annealed weld joint.Fatigue crack growth rates were obviously different in different zones of weld joint of dissimilar titanium alloys,due to their different microstructures.Scanning electron microscope examinations were conducted on the fracture surface in order to determine the relevant fracture mechanisms and crack growth mechanisms with respect to the details of microstructure.展开更多
Purpose – Straightness measurement of rail weld joint is of essential importance to railway maintenance. Dueto the lack of efficient measurement equipment, there has been limited in-depth research on rail weld joint ...Purpose – Straightness measurement of rail weld joint is of essential importance to railway maintenance. Dueto the lack of efficient measurement equipment, there has been limited in-depth research on rail weld joint with a5-m wavelength range, leaving a significant knowledge gap in this field.Design/methodology/approach – In this study, the authors used the well-established inertial referencemethod (IR-method), and the state-of-the-art multi-point chord reference method (MCR-method). Two methodshave been applied in different types of rail straightness measurement trollies, respectively. These instrumentswere tested in a high-speed rail section within a certain region of China. The test results were ultimatelyvalidated through using traditional straightedge and feeler gauge methods as reference data to evaluate the railweld joint straightness within the 5-m wavelength range.Findings – The research reveals that IR-method and MCR-method produce reasonably similar measurementresults for wavelengths below 1 m. However, MCR-method outperforms IR-method in terms of accuracy forwavelengths exceeding 3 m. Furthermore, it was observed that IR-method, while operating at a slower speed,carries the risk of derailing and is incapable of detecting rail weld joints and low joints within the track.Originality/value – The research compare two methods’ measurement effects in a longer wavelength rangeand demonstrate the superiority of MCR-method.展开更多
The cavitation erosion of weld joint and base metal of China low activation martensitic（CLAM）steel in liquid lead-bismuth eutectic alloy（LBE）at 550°C was investigated to simulate the cavitation erosion of the...The cavitation erosion of weld joint and base metal of China low activation martensitic（CLAM）steel in liquid lead-bismuth eutectic alloy（LBE）at 550°C was investigated to simulate the cavitation erosion of the first wall and the nuclear main pump impeller in the accelerator driven sub-critical system（ADS）.A suit of ultrasonic cavitation facility was self-designed to study the cavitation erosion.By studying the surface micro topography,roughness and mean pit depth of the tested specimens,it was found that some crater clusters and large scale cracks appeared on the tested specimen surface after the formation of numerous single craters,and the base metal exhibited much better cavitation erosion resistance than the weld bead due to the difference in their mechanical properties and microstructures.In addition,by comparing the results of static corrosion and cavitation erosion,it could be concluded that the cavitation erosion and the dissolution and oxidation corrosion in liquid LBE would accelerate mutually.展开更多
In the Republic of Kazakhstan, the regulatory framework in construction based on Eurocodes has been in force since 2015. However, Kazakhstani produced steel has not been studied for compliance with the requirements of...In the Republic of Kazakhstan, the regulatory framework in construction based on Eurocodes has been in force since 2015. However, Kazakhstani produced steel has not been studied for compliance with the requirements of Eurocode 1993. This has resulted in limited use of Kazakhstani structural steel in construction. The feasibility of using structural steel in welded joints has been experimentally investigated. To verify the application of such joints in construction, including earthquake engineering, experimental studies of welded joints made of structural steel produced by Arcelor-Mittal in Temirtau have been carried out. In total, 7 types of structural steel of various thicknesses were selected. Five specimens have been used in each series of tests. The Brinell hardness values of the weld joint, yield strength of steel and tensile strength, relative rupture strain were determined. It was found that for all types of structural steel, the quality of weld joints complied with the requirements of Eurocode 1993—a sample rupture appeared along the plates (main body of the metal), not along the weld joints. It has been established that structural steel produced in the Republic of Kazakhstan fully complies with the requirements of Eurocode 1993. The studies on the dependence of Brinell hardness values of weld joint steel on the yield strength, tensile strength and relative rupture strain have been carried out. The correlation dependences between the values of yield strength of steel and tensile strength, relative rupture strain and BH Brinell hardness were studied. The results of work will allow for significantly increasing the use of Kazakhstani structural steel in seismic and conventional areas of the Republic of Kazakhstan.展开更多
X90 pipeline steel is a new generation of pipeline steel developed after X80 and X100 pipeline steels,and it is now a new research hotspot at home.In order to thoroughly study the effect of applied potential on the so...X90 pipeline steel is a new generation of pipeline steel developed after X80 and X100 pipeline steels,and it is now a new research hotspot at home.In order to thoroughly study the effect of applied potential on the soil stress corrosion cracking(SCC)behavior of X90 pipeline steel,we investigated the SCC behaviors of base metal and weld joint samples in the straight-weld pipe of X90 pipeline steel at different applied potentials in near-neutral solution using electrochemical measurements methods and slow strain rate testing(SSRT).Besides,the fracture surfaces were observed through scanning electron microscope(SEM)and the mechanisms of the corrosion cracking behaviors were analyzed.And the following research results were obtained.First,the polarization curves of the base metal and weld joint samples in the NS4 solution present the typical characteristics of anodic dissolution but no activation–passivation phenomenon happens.Second,in the NS4 solution,the base metal and weld joint samples present SCC sensitivity.The SCC sensitivity indicator which is expressed by yield loss percentage elongation and yield loss percentage elongation area decreases firstly and then increases with the negative increase of the applied potential,and the SCC sensitivity of weld joint is higher than that of base metal.Third,there are three mechanisms on the SCC behaviors of base metal and weld joint samples,i.e.,anodic dissolution mechanism when the applied potential is open circuit potential(EOCP),anodic dissolution and hydrogen embrittlement mechanism when the applied potential is−850 mV,and hydrogen embrittlement mechanism when the applied potential is−1000 mV and−1200 mV.It is concluded that the research results can provide a technical support and theoretical basis for the large-scale application of X90 pipeline steel.展开更多
Stress corrosion cracking(SCC) of an SA508-309 L/308 L–316 L dissimilar metal weld joint in primary pressurized water reactor environment was investigated by the interrupted slow strain rate tension tests following a...Stress corrosion cracking(SCC) of an SA508-309 L/308 L–316 L dissimilar metal weld joint in primary pressurized water reactor environment was investigated by the interrupted slow strain rate tension tests following a microstructure characterization. The 308 L weld metal shows a higher content of δ ferrite than the 309 L weld metal. In addition, no obvious Cr-depletion but carbides precipitation at δ phase boundaries was observed in both 308 L and 309 L weld metals. The slow strain rate tension tests showed that the SCC susceptibility of the base and weld metals of the dissimilar metal weld joint follows the order of SA508 < 308 L weld metal < the heat affected zone of 316 L base metal < 309 L weld metal.The higher SCC susceptibility of 309 L weld metal than that of 308 L weld metal is likely due to the lower content of δ ferrite. In addition, a preferential SCC initiation in the 309 L weld metal adjacent to 308 L weld metal is attributed to few carbides in this region.展开更多
Because of the size limitation of weld joints in different regions, the traditional standard bar specimen is not suitable to investigate the mechanical properties of weld joints. In this study, miniature specimens wer...Because of the size limitation of weld joints in different regions, the traditional standard bar specimen is not suitable to investigate the mechanical properties of weld joints. In this study, miniature specimens were extracted from specific regions(base metal, weld metal, and three heat-affected zones) of API X80 and X70 weld joints. Uniaxial tensile tests were conducted to obtain the mechanical properties of different regions, and then uniaxial ratcheting tests were conducted to investigate the ratcheting behaviors of the different regions under the same peak and nominal stresses. Under both the tensile tests and ratcheting tests, the weld joints exhibit heterogeneous results, such as different mechanical properties and ratcheting behaviors, which were region dependent. Furthermore, the yield strength and yield-to-tensile strength ratio contribute differently to the ratcheting response.展开更多
In order to emulate a skilled human operator determining weld penetration from feature sizes of weld pool,such us topside maximum width and half-length of weld pool, a CCD camera assisted with electronic shutter and c...In order to emulate a skilled human operator determining weld penetration from feature sizes of weld pool,such us topside maximum width and half-length of weld pool, a CCD camera assisted with electronic shutter and composed filter system is used to simultaneously capture topside and backside images of weld pool in the same frame. Neural networks are used to investigate the complicated relationships between the weld penedrion and different parameters, they are capabe of modeling complicated nonlinear functions. Bead-on-plate welding experiments and simulations show that a neural network model has adequate accuracy required for monitoring full penetration duringpulsed GTAW dynamic process.展开更多
This study investigates the corrosion-assisted fatigue crack growth rate(FCGR)of 16 mm thick AA 7075-T651 friction stir welded(FSW)joints.Compact tension(CT)specimens were extracted from both the base material and FSW...This study investigates the corrosion-assisted fatigue crack growth rate(FCGR)of 16 mm thick AA 7075-T651 friction stir welded(FSW)joints.Compact tension(CT)specimens were extracted from both the base material and FSW joints to evaluate FCGR under varying corrosion exposure durations(0,7,30,60,and 90 days)at a constant stress ratio of 0.5.Microstructural analysis of the welds was conducted using optical and transmission electron microscopy(TEM).Results indicate that the critical stress intensity factor range(ΔK_(cr))of FSW joints is lower than that of the base material,primarily due to precipitate dissolution in the weld zone during the FSW process,as confirmed by TEM analysis.The fatigue life of FSW joints was significantly lower than that of the base material,but with prolonged exposure to seawater corrosion,the gap in fatigue life narrowed.Specimens exposed to seawater for more than 60days exhibited minimal differences in fatigue life between the base material and the FSW joints.This was attributed to the higher corrosion rate of the base material compared to the weld nugget,resulting in the formation of deeper pits that facilitated crack initiation and accelerated fatigue failure.The findings conclude that extended corrosion exposure leads to similar fatigue life and crack growth behaviour in both the base material and FSW joints.SEM and EDX analysis of AA7075-T651 revealed corrosion pits and rust products in initiation zones,ductile striations in growth regions,and secondary cracks with micro voids in fracture zones.FSW joints exhibited ultra-fine grains,smooth ductile fracture in initiation and growth regions,and brittle fracture in the fracture zones under both corroded and uncorroded conditions.展开更多
Cu–Ni and Cu–Co–Ni superhydrophobic films were constructed on the surface of B10 copper–nickel alloy welded joints using a two-step process of electrodeposition and stearic acid modification.The chemical compositi...Cu–Ni and Cu–Co–Ni superhydrophobic films were constructed on the surface of B10 copper–nickel alloy welded joints using a two-step process of electrodeposition and stearic acid modification.The chemical composition of the film surface was determined using surface characterization techniques.The corrosion resistance of the films was characterized using electrochemical impedance spectroscopy,potentiodynamic polarization,and scanning Kelvin probe microscopy at multiple scales.The thermal stability,mechanical stability,and self-cleaning properties of the films were also characterized.It was determined that the Cu–Co–Ni superhydrophobic film exhibited the best performance,with a static water contact angle of 159.3°,a roll-off angle of 2.3°,a charge transfer resistance 3300 times higher than the substrate,a self-corrosion current density nearly three orders of magnitude lower,and a surface Kelvin potential increase of 420 mV.The film demonstrated good thermal stability,excellent mechanical stability,and outstanding self-cleaning properties.Combining with previous studies,it was found that Co elements in the film contribute to the formation of a uniform and dense film,Ni elements enhance the adhesion and corrosion resistance between the films,and the combination of Co and Ni elements promotes uniform surface potential and further improves the corrosion resistance and interfilm adhesion of the films.展开更多
Hydrogen dissolved from the moisture or the wire filler is formed on the surface of welded joint due to the driving of high-energy heat source.The diffused hydrogen in the welded joint could cause hydrogen embrittleme...Hydrogen dissolved from the moisture or the wire filler is formed on the surface of welded joint due to the driving of high-energy heat source.The diffused hydrogen in the welded joint could cause hydrogen embrittlement(HE).The important factors determining the HE resistance of welded joints are microstructure style,dislocation distribution,grains characteristics,precipitate particle,and residual stress.Different welding technologies show various heat sources and heat cycles,which result in different characteristics of fusion zone and heat-affected zone.Thus,the HE fracture behavior of welded joint produced by different welded technologies differs greatly.The current stage of HE behavior of welded joint was reviewed to provide fundamental reference for the scientists and engineers engaging in welding.The appearance of hydrogen atoms in the surface or interior of welded joint could weaken the bonding strength and change the fracture mode from ductile to sudden brittle fracture.Generally,the controlling of filler wire and heat input is a practical route to obtain the excellent welded joint with high HE resistance.The inhibition of hydrogen diffusion via the formation of fine coating and the aggregation of hydrogen atoms via the control of microstructure and precipitates are the effective routes to improve HE resistance.展开更多
In this paper,Desulfovibrio vulgaris corrosion of X80 steel welded joint with different heat inputs was carefully investigated.The results confirmed that in the sterile medium,general corrosion rate and lo-calized cor...In this paper,Desulfovibrio vulgaris corrosion of X80 steel welded joint with different heat inputs was carefully investigated.The results confirmed that in the sterile medium,general corrosion rate and lo-calized corrosion susceptibility of heat affected zone(HAZ)were higher than those of weld zone(WZ)and base metal(BM).In the inoculated medium,the general corrosion rate of HAZ was still higher than that of WZ and BM.However,the number and depth of corrosion pits on WZ and BM surfaces,as well as the localized corrosion susceptibility,were much higher than those in HAZ,which was opposite to that in sterile environment,suggesting that the Desulfovibrio vulgaris corrosion of the welded joint was selective.With heat input increasing from 0.57 kJ/mm to 1.29 kJ/mm,general corrosion rate and localized corrosion susceptibility of HAZ and WZ simultaneously decreased in sterile or inoculated medium.In in-oculated medium,localized corrosion of HAZ decreased more sharply than weld zone.Within the range of heat inputs tested,the study discerned a positive correlation:higher heat inputs correlated with an enhanced corrosion resistance of welded joint,irrespective of environmental conditions being sterile or inoculated.The findings provide a solid basis for the welding parameter determination to steel pipelines in oil and gas transportation.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.51571204)
文摘Correlation of microstructure and intergranular stress corrosion cracking （IGSCC） susceptibility for the SA508-52M-316L dissimilar metal weld joint in primary water was investigated by the interrupted slow strain rate tension test following a microstructure characterization. The susceptibility to IGSCC in var- ious regions of the dissimilar metal weld joint was observed to follow the order of Alloy 52 Mb〉 the heat affected zone of 316L〉 the dilution zone of Alloy 52 Mw〉 Alloy 52 Mw weld metal. The chromium- depletion at the grain boundary is the dominant factor causing the high IGSCC susceptibility of Alloy 52 Mh. However, IGSCC initiation in the heat affected zone of 316L is attributed to the increase of resid- ual strain adjacent to the grain boundary. In addition, the decrease of chromium content and increase of residual strain adjacent to the grain boundary increase the IGSCC susceptibility of the dilution zone of Alloy 52 Mw.
基金financially supported by the National Natural Science Foundation of China(Grant No.51571204)
文摘Microstructure of the heat affected zone （HAZ） of a 308L-316L stainless steel （SS） weld joint and its corrosion behavior in high temperature water were studied. Peak of the residual strain was observed to approach to the fusion boundary in the HAZ while the strain increased from the top to root areas of the HAZ. The root area of the HAZ shows a lower corrosion resistance in high temperature water than the top and middle areas of the HAZ. This is attributed to a higher level of residual strain in association with a higher density of tangled dislocations in the top area of the HAZ. The results suggest that the residual strain in the HAZ could also promote the SCC through its effect on corrosion, in addition to that on the local microstructure and mechanical property of the steel.
基金supported by the National Natural Science Foundation of China(No.50609009)Natural Science Foundation of College of Jiangsu Province(No.07KJD580056)
文摘Many factors influence the fatigue and crack growth behavior of welded joints. Some structures often undergo fairly large static loading before they enter service or variable amplitude cyclic loading when they are in service. The combined effect of both applied stress and high initial residual stress is expected to cause the residual stresses relaxation. Only a few papers seem to deal with appropriate procedures for fatigue analysis and crack growth by considering the combined effect of variable amplitude cyclic loading with residual stresses relaxation. In this article, some typical welded connections in ship-shaped structures are investigated with 3-D elastic-plastic finite element analysis. The effect of residual stress relaxation, initial residual stress, and the applied load after variable amplitude cyclic loading is revealed, and a formula for predicting the residual stress at hot spot quantitatively is proposed. Based on the formula, an improved fatigue procedure is introduced. Moreover, crack growth of typical weld joints considering residual stresses relaxation is studied.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.51274063 and 51305285)the National Program on Key Basic Research Project(Grant No.2011CB606306-2)+1 种基金the Open Research Fund from the State Key Laboratory of Rolling and Automation,Northeastern University(Grant No.2016005)the Project Funded by China Postdoctoral Science Foundation(Grant No.2016M601877)
文摘The microstructure and mechanical properties（strength, fatigue and formability） of dissimilar/similar weld joints between DP780 and DP980 steels were studied. The microstructure in fusion zone（FZ） was lath martensite（LM）, and alloying elements in the FZ were uniformly distributed. The hardness in the FZ of dissimilar weld joint was similar to the average value（375 HV） of the two similar weld joints. The microstructural evolution in heat affected zone（HAZ） of dissimilar/similar weld joints was as follows：LM（coarse-grained HAZ） →finer LM（fine-grained HAZ） →M-A constituent and ferrite（intercritically HAZ） →tempered martensite（TM） and ferrite（sub-critical HAZ）. Lower hardness in intercritically HAZ and sub-critical HAZ（softening zones） was observed compared to base metal（BM） in dissimilar/similar weld joints. The size of softening zone was 0.2-0.3 mm and reduction in hardness was ~7.6%-12.7% of BM in all the weld joints, which did not influence the tensile properties of weld joints such that fracture location was in BM. Formability of dissimilar weld joints was inferior compared to similar weld joints because of the softening zone, non-uniform microstructure and hardness on the two sides of FZ. The effect of microstructure on fatigue life was not influenced due to the presence of welding concavity.
基金supports by the SJTU Global Strategic Partnership Fund(2019-2021 SJTU-OU)the National Natural Science Foundation of China(No.52001200)the experimental supports by Instrumental Analysis Center of SJTU。
文摘By using digital image correlation(DIC), low-cycle fatigue(LCF) behavior of CrMoV weld joint taken from a retired gas turbine rotor after 15-year service was investigated at 500 ℃ and 540 ℃. The most remarkable plastic strain was observed in the weld metal(WM), which was up to 6 times of the global strain at mid-life cycle. Due to the cyclic accumulation of local deformation, the stress–strain hysteresis loops relative to tensile or compressive strain concentration area in WM displayed the ratchetting shape. The local deformation accumulation of WM was attributed to the effect of the equiaxed grain zone near the WM center. The accumulated plastic strain was considered as the main fatigue failure mechanism.
基金financially supported by the Hundred-Talent Program of Chinese Academy of Sciences
文摘Characterization of the microstructure of the fusion zone of an Alloy 600-82 weld joint was conducted, with focus on the weld residual strain distribution and the comparison of the microstructure of heat affected zone （HAZ） with that of cold worked alloy. Peak of the residual strain was observed to approach to the fusion boundary in HAZ while the strain increased from the top of the weld to the root. Strain distribution in the HAZ was found to be concentrated adjacent to grain boundaries （GBs）, with a peak of approximately three times of that in grain. Further, triple junctions of the GB appear to cause a higher strain concentration than single GBs. The microstructure of HAZ consists of partially tangled dislocations, which is different from slip bands of high density dislocations in cold worked alloy. This may cause a relatively higher intergranular cracking resistance of HAZ due to the difficulty in transferring tangled dislocations to GB in HAZ under deformation.
基金Project supported by the National Natural Science Foundation of China(Grant No.51175095)the Natural Science Foundation of Guangdong Province,China(Grant No.10251009001000001)+1 种基金the Guangdong Provincial Project of Science and Technology Innovation of Discipline Construction,China(Grant No.2013KJCX0063)the Science and Technology Plan Project of Guangzhou City,China(Grant No.1563000554)
文摘In a laser butt joint welding process, it is required that the laser beam focus should be controlled to follow the weld joint path accurately. Small focus wandering off the weld joint may result in insufficient penetration or unacceptable welds.Recognition of joint position offset, which describes the deviation between the laser beam focus and the weld joint, is important for adjusting the laser beam focus and obtaining high quality welds. A new method based on the magneto-optical（MO） imaging is applied to measure the micro weld joint whose gap is less than 0.2 mm. The weldments are excited by an external magnetic field, and an MO sensor based on principle of Faraday magneto effect is used to capture the weld joint images. A sequence of MO images which are tested under different magnetic field intensities and different weld joint widths are acquired. By analyzing the MO image characteristics and extracting the weld joint features, the influence of magnetic field intensity and weld joint width on the MO images and detection of weld joint position is observed and summarized.
文摘The successive alteration o the microstructure from the weld metal zone through weld bond to the heat affected zone of a Cr18Ni13 austenitic-0.45%C steels weld joint was observed in situ using transmission electron microscopy.It was found a new type of microstructure called pearlite-like structure and observed the characteristics of the boundary of dissimilar phases. Based on the definition of various zones of the dissimilar steels weld joint under the optical mi- croscope,the transmission electron microscopic characteristics,including microstructures and compositions,of each zone are described and discussed.
基金Funded in Part by the Grant from Technology and Industry for National Defense,China(No.AXXD1818)。
文摘Based on the investigated microstructure of different zones in the annealed automatic gas tungsten arc weld joint of TA16 and TC4 titanium alloys,the mechanical property of them was assessed under fatigue crack growth rate tests.For evaluation of fatigue crack growth rate,three points bending specimens were used.The correlation between the range of stress intensity factor and crack growth rate was determined in different zones of the annealed weld joint.Fatigue crack growth rates were obviously different in different zones of weld joint of dissimilar titanium alloys,due to their different microstructures.Scanning electron microscope examinations were conducted on the fracture surface in order to determine the relevant fracture mechanisms and crack growth mechanisms with respect to the details of microstructure.
文摘Purpose – Straightness measurement of rail weld joint is of essential importance to railway maintenance. Dueto the lack of efficient measurement equipment, there has been limited in-depth research on rail weld joint with a5-m wavelength range, leaving a significant knowledge gap in this field.Design/methodology/approach – In this study, the authors used the well-established inertial referencemethod (IR-method), and the state-of-the-art multi-point chord reference method (MCR-method). Two methodshave been applied in different types of rail straightness measurement trollies, respectively. These instrumentswere tested in a high-speed rail section within a certain region of China. The test results were ultimatelyvalidated through using traditional straightedge and feeler gauge methods as reference data to evaluate the railweld joint straightness within the 5-m wavelength range.Findings – The research reveals that IR-method and MCR-method produce reasonably similar measurementresults for wavelengths below 1 m. However, MCR-method outperforms IR-method in terms of accuracy forwavelengths exceeding 3 m. Furthermore, it was observed that IR-method, while operating at a slower speed,carries the risk of derailing and is incapable of detecting rail weld joints and low joints within the track.Originality/value – The research compare two methods’ measurement effects in a longer wavelength rangeand demonstrate the superiority of MCR-method.
基金supported by the National Natural Science Foundation of China with Grant Nos.51375216 and 51505197the Open-Fund Research of State Key Lab of Advanced Welding and Joining with Grant No.AWJ-16-M07the Fusion Digital Simulation(FDS)Team for support the CLAM steel
文摘The cavitation erosion of weld joint and base metal of China low activation martensitic（CLAM）steel in liquid lead-bismuth eutectic alloy（LBE）at 550°C was investigated to simulate the cavitation erosion of the first wall and the nuclear main pump impeller in the accelerator driven sub-critical system（ADS）.A suit of ultrasonic cavitation facility was self-designed to study the cavitation erosion.By studying the surface micro topography,roughness and mean pit depth of the tested specimens,it was found that some crater clusters and large scale cracks appeared on the tested specimen surface after the formation of numerous single craters,and the base metal exhibited much better cavitation erosion resistance than the weld bead due to the difference in their mechanical properties and microstructures.In addition,by comparing the results of static corrosion and cavitation erosion,it could be concluded that the cavitation erosion and the dissolution and oxidation corrosion in liquid LBE would accelerate mutually.
文摘In the Republic of Kazakhstan, the regulatory framework in construction based on Eurocodes has been in force since 2015. However, Kazakhstani produced steel has not been studied for compliance with the requirements of Eurocode 1993. This has resulted in limited use of Kazakhstani structural steel in construction. The feasibility of using structural steel in welded joints has been experimentally investigated. To verify the application of such joints in construction, including earthquake engineering, experimental studies of welded joints made of structural steel produced by Arcelor-Mittal in Temirtau have been carried out. In total, 7 types of structural steel of various thicknesses were selected. Five specimens have been used in each series of tests. The Brinell hardness values of the weld joint, yield strength of steel and tensile strength, relative rupture strain were determined. It was found that for all types of structural steel, the quality of weld joints complied with the requirements of Eurocode 1993—a sample rupture appeared along the plates (main body of the metal), not along the weld joints. It has been established that structural steel produced in the Republic of Kazakhstan fully complies with the requirements of Eurocode 1993. The studies on the dependence of Brinell hardness values of weld joint steel on the yield strength, tensile strength and relative rupture strain have been carried out. The correlation dependences between the values of yield strength of steel and tensile strength, relative rupture strain and BH Brinell hardness were studied. The results of work will allow for significantly increasing the use of Kazakhstani structural steel in seismic and conventional areas of the Republic of Kazakhstan.
基金supported by the National Key R&D Program of China with Project No.2016YFC0801200.
文摘X90 pipeline steel is a new generation of pipeline steel developed after X80 and X100 pipeline steels,and it is now a new research hotspot at home.In order to thoroughly study the effect of applied potential on the soil stress corrosion cracking(SCC)behavior of X90 pipeline steel,we investigated the SCC behaviors of base metal and weld joint samples in the straight-weld pipe of X90 pipeline steel at different applied potentials in near-neutral solution using electrochemical measurements methods and slow strain rate testing(SSRT).Besides,the fracture surfaces were observed through scanning electron microscope(SEM)and the mechanisms of the corrosion cracking behaviors were analyzed.And the following research results were obtained.First,the polarization curves of the base metal and weld joint samples in the NS4 solution present the typical characteristics of anodic dissolution but no activation–passivation phenomenon happens.Second,in the NS4 solution,the base metal and weld joint samples present SCC sensitivity.The SCC sensitivity indicator which is expressed by yield loss percentage elongation and yield loss percentage elongation area decreases firstly and then increases with the negative increase of the applied potential,and the SCC sensitivity of weld joint is higher than that of base metal.Third,there are three mechanisms on the SCC behaviors of base metal and weld joint samples,i.e.,anodic dissolution mechanism when the applied potential is open circuit potential(EOCP),anodic dissolution and hydrogen embrittlement mechanism when the applied potential is−850 mV,and hydrogen embrittlement mechanism when the applied potential is−1000 mV and−1200 mV.It is concluded that the research results can provide a technical support and theoretical basis for the large-scale application of X90 pipeline steel.
基金supported by the National Natural Science Foundation of China(No.51571204)the support of the Youth Scientific and Innovation Research Team for Advanced Surface Functional Materials(Southwest Petroleum University,No.2018CXTD06)the Young Scholars Development Found of Southwest Petroleum University(No.201899010040).
文摘Stress corrosion cracking(SCC) of an SA508-309 L/308 L–316 L dissimilar metal weld joint in primary pressurized water reactor environment was investigated by the interrupted slow strain rate tension tests following a microstructure characterization. The 308 L weld metal shows a higher content of δ ferrite than the 309 L weld metal. In addition, no obvious Cr-depletion but carbides precipitation at δ phase boundaries was observed in both 308 L and 309 L weld metals. The slow strain rate tension tests showed that the SCC susceptibility of the base and weld metals of the dissimilar metal weld joint follows the order of SA508 < 308 L weld metal < the heat affected zone of 316 L base metal < 309 L weld metal.The higher SCC susceptibility of 309 L weld metal than that of 308 L weld metal is likely due to the lower content of δ ferrite. In addition, a preferential SCC initiation in the 309 L weld metal adjacent to 308 L weld metal is attributed to few carbides in this region.
基金supported by the National Natural Science Foundation of China (No. 51435012)
文摘Because of the size limitation of weld joints in different regions, the traditional standard bar specimen is not suitable to investigate the mechanical properties of weld joints. In this study, miniature specimens were extracted from specific regions(base metal, weld metal, and three heat-affected zones) of API X80 and X70 weld joints. Uniaxial tensile tests were conducted to obtain the mechanical properties of different regions, and then uniaxial ratcheting tests were conducted to investigate the ratcheting behaviors of the different regions under the same peak and nominal stresses. Under both the tensile tests and ratcheting tests, the weld joints exhibit heterogeneous results, such as different mechanical properties and ratcheting behaviors, which were region dependent. Furthermore, the yield strength and yield-to-tensile strength ratio contribute differently to the ratcheting response.
文摘In order to emulate a skilled human operator determining weld penetration from feature sizes of weld pool,such us topside maximum width and half-length of weld pool, a CCD camera assisted with electronic shutter and composed filter system is used to simultaneously capture topside and backside images of weld pool in the same frame. Neural networks are used to investigate the complicated relationships between the weld penedrion and different parameters, they are capabe of modeling complicated nonlinear functions. Bead-on-plate welding experiments and simulations show that a neural network model has adequate accuracy required for monitoring full penetration duringpulsed GTAW dynamic process.
文摘This study investigates the corrosion-assisted fatigue crack growth rate(FCGR)of 16 mm thick AA 7075-T651 friction stir welded(FSW)joints.Compact tension(CT)specimens were extracted from both the base material and FSW joints to evaluate FCGR under varying corrosion exposure durations(0,7,30,60,and 90 days)at a constant stress ratio of 0.5.Microstructural analysis of the welds was conducted using optical and transmission electron microscopy(TEM).Results indicate that the critical stress intensity factor range(ΔK_(cr))of FSW joints is lower than that of the base material,primarily due to precipitate dissolution in the weld zone during the FSW process,as confirmed by TEM analysis.The fatigue life of FSW joints was significantly lower than that of the base material,but with prolonged exposure to seawater corrosion,the gap in fatigue life narrowed.Specimens exposed to seawater for more than 60days exhibited minimal differences in fatigue life between the base material and the FSW joints.This was attributed to the higher corrosion rate of the base material compared to the weld nugget,resulting in the formation of deeper pits that facilitated crack initiation and accelerated fatigue failure.The findings conclude that extended corrosion exposure leads to similar fatigue life and crack growth behaviour in both the base material and FSW joints.SEM and EDX analysis of AA7075-T651 revealed corrosion pits and rust products in initiation zones,ductile striations in growth regions,and secondary cracks with micro voids in fracture zones.FSW joints exhibited ultra-fine grains,smooth ductile fracture in initiation and growth regions,and brittle fracture in the fracture zones under both corroded and uncorroded conditions.
基金fnancial support by the National Natural Science Foundation of China(Grant No.42176209)the Natural Science Foundation of Shandong Province(Grant No.ZR2021MD064).
文摘Cu–Ni and Cu–Co–Ni superhydrophobic films were constructed on the surface of B10 copper–nickel alloy welded joints using a two-step process of electrodeposition and stearic acid modification.The chemical composition of the film surface was determined using surface characterization techniques.The corrosion resistance of the films was characterized using electrochemical impedance spectroscopy,potentiodynamic polarization,and scanning Kelvin probe microscopy at multiple scales.The thermal stability,mechanical stability,and self-cleaning properties of the films were also characterized.It was determined that the Cu–Co–Ni superhydrophobic film exhibited the best performance,with a static water contact angle of 159.3°,a roll-off angle of 2.3°,a charge transfer resistance 3300 times higher than the substrate,a self-corrosion current density nearly three orders of magnitude lower,and a surface Kelvin potential increase of 420 mV.The film demonstrated good thermal stability,excellent mechanical stability,and outstanding self-cleaning properties.Combining with previous studies,it was found that Co elements in the film contribute to the formation of a uniform and dense film,Ni elements enhance the adhesion and corrosion resistance between the films,and the combination of Co and Ni elements promotes uniform surface potential and further improves the corrosion resistance and interfilm adhesion of the films.
基金supported by Postgraduate Research&Practice Innovation Program of Jiangsu Province(No.SJCX24_2524)National Natural Science Foundation of China(No.52005228).
文摘Hydrogen dissolved from the moisture or the wire filler is formed on the surface of welded joint due to the driving of high-energy heat source.The diffused hydrogen in the welded joint could cause hydrogen embrittlement(HE).The important factors determining the HE resistance of welded joints are microstructure style,dislocation distribution,grains characteristics,precipitate particle,and residual stress.Different welding technologies show various heat sources and heat cycles,which result in different characteristics of fusion zone and heat-affected zone.Thus,the HE fracture behavior of welded joint produced by different welded technologies differs greatly.The current stage of HE behavior of welded joint was reviewed to provide fundamental reference for the scientists and engineers engaging in welding.The appearance of hydrogen atoms in the surface or interior of welded joint could weaken the bonding strength and change the fracture mode from ductile to sudden brittle fracture.Generally,the controlling of filler wire and heat input is a practical route to obtain the excellent welded joint with high HE resistance.The inhibition of hydrogen diffusion via the formation of fine coating and the aggregation of hydrogen atoms via the control of microstructure and precipitates are the effective routes to improve HE resistance.
基金supported by the National Natural Science Foundation of China(Nos.52471096 and 51971191).
文摘In this paper,Desulfovibrio vulgaris corrosion of X80 steel welded joint with different heat inputs was carefully investigated.The results confirmed that in the sterile medium,general corrosion rate and lo-calized corrosion susceptibility of heat affected zone(HAZ)were higher than those of weld zone(WZ)and base metal(BM).In the inoculated medium,the general corrosion rate of HAZ was still higher than that of WZ and BM.However,the number and depth of corrosion pits on WZ and BM surfaces,as well as the localized corrosion susceptibility,were much higher than those in HAZ,which was opposite to that in sterile environment,suggesting that the Desulfovibrio vulgaris corrosion of the welded joint was selective.With heat input increasing from 0.57 kJ/mm to 1.29 kJ/mm,general corrosion rate and localized corrosion susceptibility of HAZ and WZ simultaneously decreased in sterile or inoculated medium.In in-oculated medium,localized corrosion of HAZ decreased more sharply than weld zone.Within the range of heat inputs tested,the study discerned a positive correlation:higher heat inputs correlated with an enhanced corrosion resistance of welded joint,irrespective of environmental conditions being sterile or inoculated.The findings provide a solid basis for the welding parameter determination to steel pipelines in oil and gas transportation.
