The impact of casting defects on the weldability of K4951 superalloy was investigated using tungsten inert gas(TIG)welding.The as-cast K4951 superalloy samples with prefabricated U-shaped grooves of varying depths and...The impact of casting defects on the weldability of K4951 superalloy was investigated using tungsten inert gas(TIG)welding.The as-cast K4951 superalloy samples with prefabricated U-shaped grooves of varying depths and widths were TIG welded,and the microstructures,cracks morphology,and precipitated phases were analyzed using optical microscope,scanning electron microscope,transmission electron microscope,and energy dispersive X-ray spectrometer.The results reveal that the dimensions of casting defects significantly affect the weldability of K4951.Deep defects(greater than 2 mm)lead to rapid crack propagation,while wider defects can moderate the propagation process of cracks.Elemental segregation and the formation of precipitated phases,such as MC carbides,are observed in the fusion zone,contributing to welding cracks.An optimal groove aspect ratio(depth-to-width)between 0.2 and 0.5 minimizes crack formation tendency and enhances tensile strength,resulting in a mixed brittle-ductile fracture mode of joint after high-temperature tensile testing.展开更多
High-entropy alloys(HEAs)have become essential materials in the aerospace and defense industries due to their remarkable mechanical properties,which include wear resistance,fatigue endurance,and corrosion resistance.T...High-entropy alloys(HEAs)have become essential materials in the aerospace and defense industries due to their remarkable mechanical properties,which include wear resistance,fatigue endurance,and corrosion resistance.The welding of high-entropy alloys is a cutting-edge field of study that is attracting a lot of interest and investigation from research organizations and businesses.Welding defects including porosity and cracks are challenging problem and limit the development of welding HEAs.This paper provides a comprehensive review of research on weldability of HEAs and the application of diverse welding techniques on welding HEAs over recent years.The forming mechanism and control strategies of defects during welding HEAs were provided in this work.Various welding techniques,including arc welding,laser welding,electron beam welding,friction stir welding,diffusion bonding and explosive welding,have been extensively investigated and applied to improve the microstructure and mechanical properties of HEAs joints.Furthermore,an in-depth review of the microstructure and mechanical properties of HEAs joints obtained by various welding methods is presented.This paper concludes with a discussion of the potential challenges associated with high-entropy alloy welding,thus providing valuable insights for future research efforts in this area.展开更多
Super duplex stainless steels(SDSSs)and hyper duplex stainless steels(HDSSs),with more alloying elements content,are more corrosion resistant than the standard grades.Progresses of research works on weldability of SDS...Super duplex stainless steels(SDSSs)and hyper duplex stainless steels(HDSSs),with more alloying elements content,are more corrosion resistant than the standard grades.Progresses of research works on weldability of SDSSs and HDSSs in recent years are reviewed in this paper.If proper heat input is provided,SDSSs and HDSSs can be welded with most fusion welding processes,while tungsten inert gas welding is the most popular process.SDSSs and HDSSs are more prone to secondary phases precipitation than the standard and lean grades,and heat input for SDSSs and HDSSs welding is restricted to a smaller range.Matching filler materials are usually recommended for SDSSs and HDSSs welding,rather than Ni-riched ones for standard and lean grades.Nitrogen addition in shielding gas is always beneficial.Post weld heat treatment with slow cooling rate will be harmful.Hot cracking tendency of SDSSs and HDSSs joints is not high,but sometimes they can suffer from hydrogen induced stress cracking.展开更多
The small punch test technique facilitates the convenient acquisition of the mechanical properties of in-service equipment materials and the assessment of their remaining service life through sampling.However,the weld...The small punch test technique facilitates the convenient acquisition of the mechanical properties of in-service equipment materials and the assessment of their remaining service life through sampling.However,the weldability of components with thin walls after small punch sampling,such as ethylene cracking furnace tubes,requires further investigation.Therefore,the weldability of in-service ethylene cracking furnace tubes following small punch sampling was investigated through nondestructive testing,microstructural characterization,and mechanical testing.Additionally,the impact of small punch sampling size and residual stress on the creep performance of the specimens was studied using an improved ductility exhaustion model.The results indicate that both the surface and interior of the weld repair areas on new furnace tubes and service-exposed furnace tubes after small-punch sampling are defect-free,exhibiting good weld quality.The strength of the specimens after weld repair was higher than that before sampling,whereas toughness decreased.Weld repair following small punch sampling of furnace tubes is both feasible and necessary.Furthermore,a linear relationship was observed between specimen thickness,diameter,and creep fracture time.The residual stress of welding affects the creep performance of the specimen under different stresses.展开更多
Duplex stainless steels(DSSs)show better corrosion resistance with higher strength than traditional austenite stainless steels in many aggressive environments,and can be welded properly with almost every welding proce...Duplex stainless steels(DSSs)show better corrosion resistance with higher strength than traditional austenite stainless steels in many aggressive environments,and can be welded properly with almost every welding processes,if proper heat input is provided.Progresses of research works on weldability of DSSs in recent years are reviewed in this paper.Balance control of ferrite/austenite phases is most important for DSSs welding.The phases balance can be controlled with filler materials,nitrogen addition in shielding gas,heat input,post weld heat treatment,and alternating magnetic field.Too high cooling rate results in not only extra ferrite,but also chromium nitride precipitation.While too low cooling rate or heating repeatedly results in precipitation of secondary austenite and intermetallic compounds.In both situations,mechanical properties and corrosion resistance of the DSS joints deteriorate.Recommended upper and lower limits of heat input and maximum interpass temperature should be observed.展开更多
Weldability test was carried out on the newly developed fine grain, low sulphur, high strength and high toughness pipeline steel of X80 and its matching SAW wire. Test of maximum hardness in welding heat-affected zone...Weldability test was carried out on the newly developed fine grain, low sulphur, high strength and high toughness pipeline steel of X80 and its matching SAW wire. Test of maximum hardness in welding heat-affected zone and test of Y groove cracking show that X80 steel features low hardenability and good cracking resistance. The submerged arc welding joint made with the newly developed low carbon and multi-alloyed SAW wire of WGX2 exhibits a little higher strength than the base metal, qualified bending performance, under maximum limitation hardness and good impact toughness, which can completely meet the technical requirement of X80 steel. Despite somewhat coarsening the grain size in welding heat-affected zone is still much finer than that of traditional steels, and the microstructure in weld metal is almost full acicular ferrite. The results show that X80 steel and WGX2 wire are of great weldability.展开更多
The weldability of a ferritic ductile cast iron was investigated as a function of different consumables and welding conditions. A 23 full factorial experimental design was used to analyze the effect of factors and the...The weldability of a ferritic ductile cast iron was investigated as a function of different consumables and welding conditions. A 23 full factorial experimental design was used to analyze the effect of factors and their interac- tions on ultimate tensile strength of weldments. The shielded metal arc welding （SMAW） process was used with two types of consumables （E7018 and ENi-CI） under eight different conditions using as-cast samples. The microstructur- al evolution and fracture mechanisms were investigated by optical microscopy and scanning electron microscopy （SEM）, respectively. The hardness, tensile and impact tests were also performed to determine the weld quality. Based on experiment design, preheat, consumable, cooling condition, preheat cooling and preheat-consumable inter- actions were significant factors. Preheat is the most effective factor and in the case of E7018, preheat and cooling conditions were the most sensible factors. It was found that buttering was the most appropriate welding method for ferritic ductile cast iron.展开更多
The weldability of the ZhS6U nickel-based superalloy, which is prone to solidification cracking during electron-beam welding(EBW) repair processes, was investigated. The effects of two different pre-weld heat-treatmen...The weldability of the ZhS6U nickel-based superalloy, which is prone to solidification cracking during electron-beam welding(EBW) repair processes, was investigated. The effects of two different pre-weld heat-treatment cycles on the final microstructure before and after welding were examined. Welds were made on flat coupons using an EBW machine, and the two heat-treatment cycles were designed to reduce γ′ liquation before welding. Microstructural features were also examined by optical and scanning electron microscopy. The results showed that the change in the morphology and size of the γ′ precipitates in the pre-weld heat-treatment cycles changed the ability of the superalloy to release the tensile stresses caused by the matrix phase cooling after EBW. The high hardness in the welded coupons subjected to the first heat-treatment cycle resulted in greater resistance to stress release by the base alloy, and the concentration of stress in the base metal caused liquation cracks in the heat-affected zone and solidification cracks in the weld area.展开更多
The weldability is an important property to metal materials. Materials weldability becomes worse with the yield strength increasing. The experimental results indicate that the specific shock waves treatment could impr...The weldability is an important property to metal materials. Materials weldability becomes worse with the yield strength increasing. The experimental results indicate that the specific shock waves treatment could improve the weldability of steels such as 16MnR, SM 58Q, e.g. increase the notch toughness of coarse grains zone in HAZ and decrease cold cracking sensibility. The work would explore initially the mechanisms of improvement of weldability by shock waves. The further study on the low alloy high strength steel WEL TEN80 indicates that the shock waves may increase the material weldability on this grade of trength.展开更多
The weldability of 12MnNiVR was examined in terms of the simulated HAZ continuous cooling transformation (SH-CCT) diagram,microstructure and mechanical properties of the simulated coarse grain heat-affected zone (CGHA...The weldability of 12MnNiVR was examined in terms of the simulated HAZ continuous cooling transformation (SH-CCT) diagram,microstructure and mechanical properties of the simulated coarse grain heat-affected zone (CGHAZ).When t 8/5 is shorter,the microstructure mainly consists of lath bainite.When t 8/5 is 60 s,the microstructure becomes coarser bainite.Some acicular ferrite appears beside lath bainite when t 8/5 =100s.Finally,a microstructure composed of polygonal ferrite,acicular ferrite,and small amount pearlite is obtained with a small amount of bainite at t 8/5 】100s.With the increase of t 8/5,the hardness of CGHAZ decreases considerably.The minimum impact toughness of CGHAZ appears at t 8/5 =100s.The hardness and the toughness of CGHAZ remain above the specified values for steel 12MnNiVR.展开更多
Based on the offshore standard DNV-OS-F101-2010,girth welding tests and girth weldability evaluations were carried out for the X65 and X70 UOE submarine pipelines of 3 wall thickness gauges,in which semi-automatic gas...Based on the offshore standard DNV-OS-F101-2010,girth welding tests and girth weldability evaluations were carried out for the X65 and X70 UOE submarine pipelines of 3 wall thickness gauges,in which semi-automatic gas metal arc welding （GMAW） was adopted matched with metal powder flux cored wire. The girth welding procedure specification （WPS） was optimized to obtain good quality and cold-crack-free girth weld joint without preheating and post-weld heat treatment. At the same time, porosities, inclusions and incomplete fusion defects were avoided. Girth weld joints were evaluated for tensile strength, bending, Vickers hardness, charpy impact toughness and crack tip opening displacement （CTOD） fracture toughness. Results show that all the girth weld joints have good mechanical performances,indicating that the irth weldabilitv of Baosteel＇ s UOE submarine pipelines is excellent in the case of semi-automatic GMAW.展开更多
High entropy alloys usually show good weldability.The weldability problems of high entropy alloys are segregation,cracks,and hardening or softening of weld,etc.When an Al_(x)CoCrFeNi alloy is welded,Al and Ni will seg...High entropy alloys usually show good weldability.The weldability problems of high entropy alloys are segregation,cracks,and hardening or softening of weld,etc.When an Al_(x)CoCrFeNi alloy is welded,Al and Ni will segregate to the interdendritic region in the weld,but the degree of segregation is less than that of the base metal.When an Al_(x)CoCrCu_(x)FeNi alloy or a CoCrCu_(x)FeNi alloy is welded,Cu tends to segregate to the interdendritic region in the weld.Increasing the cooling rate of the welding process,such as with laser welding,is conducive to reducing the segregation in the weld.The segregation in the weld and the heat affected zone,especially the segregation of Cu,will lead to the generation of hot cracks.Hot cracking is the main form of cracking in high entropy alloys joints.Welding will lead to changes in the hardness of the weld.The main factors affecting the hardness change are the grain sizes and the precipitations.With laser welding,if the base metal is cold rolled,the hardness of the weld will decrease.If the base metal is hot rolled and annealed or cast,the hardness of the weld will increase.With TIG welding,the hardness of the weld is usually lower than that of the base metal,unless the grain of the base metal is particularly coarse before welding.With friction stir welding,recrystallization and grain refinement occur in the stir zone,and the hardness of the stir zone will be significantly improved no matter the original base metal is cold rolled or cast.展开更多
CO2-shielded welding experiments of newly developed, 780 MPa super-high strength heavy-duty truck crossbeam steel were conducted, and the microstructure, microhardness, mechanical properties, and impact tough- hess of...CO2-shielded welding experiments of newly developed, 780 MPa super-high strength heavy-duty truck crossbeam steel were conducted, and the microstructure, microhardness, mechanical properties, and impact tough- hess of the welded joint were studied. The evolution of the microstructure of the welded joint occurred as follows.. welding seam （acicular ferrite＋proeutectoid ferrite）→fusion zone （granular bainite-long strip M/A island）→coarse grain zone （granular bainite-long strip or short bar M/A island）→fine grain zone （ferrite＋ pearlite＋ blocky M/A is- land）→mixed grained zone （ferrite＋granular bainite＋blocky M/A island）→base metal （proeutectoid ferrite＋gran- ular bainite-hlocky or granular M/A island）. Increasing the density of the grain boundaries can effectively improve the impact toughness, and the blocky M/A island hindered crack propagation more effectively than the long strip M/A island. The new hot-rolled 780 MPa super-high strength steel had excellent weldability. The welding technology was applied under the following conditions： welding voltage was 20 to 21 V, welding current was 200 to 210 A, and the gas flow rate was 25 L/rain.展开更多
Transformation induced plasticity （TRIP） steel exhibited high or rather high carbon equivalent （CE） because of its chemical composition, which was a particularly detrimental factor affecting weldability of steels....Transformation induced plasticity （TRIP） steel exhibited high or rather high carbon equivalent （CE） because of its chemical composition, which was a particularly detrimental factor affecting weldability of steels. Thus the weldability of a TRIP steel （grade 600） containing （in mass percent, %） 0.11C-1. 19Si-1.67Mn was extensively studied. The mechanical properties and impact toughness of butt joint, the welding crack susceptibility of weld and heat affected zone （HAZ） for tee joint, control thermal severity （CTS） of the welded joint, and Y shape 60° butt joint were measured after the gas metal arc welding （GMAW） test. The tensile strength of the weld was higher than 700 MPa. Both in the fusion zone （FZ） and HAZ for butt joint, the impact toughness was much higher than 27 J, either at room temperature or at -20 ℃, indicating good low temperature impact ductility of the weld of TRIP 600 steel. In addition, welding crack susceptibility tests revealed that weldments were free of surface crack and other imperfection. All experimental results of this steel showed fairly good weldability. For application, the crossmember in automobile made of this steel exhibited excellent weldability, and fatigue and durability tests were also accomplished for crossmember assembly.展开更多
A new procedure was proposed for evaluating the weldability of nickel-base superalloys. The theory is on the basis of two microstructural patterns. In pattern I, the weld microstructure exhibits severe alloying segreg...A new procedure was proposed for evaluating the weldability of nickel-base superalloys. The theory is on the basis of two microstructural patterns. In pattern I, the weld microstructure exhibits severe alloying segregation, many low-melting eutectic structures, and low weldability. The weld requires a weaker etchant and a shorter time for etching. In pattern Ⅱ, the weld microstructure displays less alloying segregation, low quantity of eutectic structures, and high weldability. The weld needs a stronger etchant and a longer time for etching. Five superalloys containing different amounts of Nb and Ti were designed to verify the patterns. After welding operations, the welds were etched by four etchants with different corrosivities. The weldability was determined by TG-DSC measurements. The metallography and weldability results confirmed the theoretic patterns. Finally, the etchant corrosivity and etching time were proposed as new criteria to evaluate the weldability of nickel-base superalloys.展开更多
The NiSix based alloy typically has poor weldability due to its lower ductility. A limited amount of work has been performed on the weldability of NiSix based alloys. Therefore, the effect of heat treatment and weldin...The NiSix based alloy typically has poor weldability due to its lower ductility. A limited amount of work has been performed on the weldability of NiSix based alloys. Therefore, the effect of heat treatment and welding parameters on weldability of the alloys, and the relationship between the weldability and microstructure were studied. The results show that the as-cast Ni-Si-Nb-B alloy （Ni 76. 5%, Si 20%, Nb 3%, and B 0. 5%） could be successfully welded after preheating at 600 ℃. The welding procedure should be performed on the alloys before any heat treatment and a preheating at 600 ℃ should be used. The fusion zone is harder than the matrix due to a large amount of 7 phase and a finer microstructure. The cracks are predominantly intergranular in heat affected zone and associated with the needle-like ）, phase. The heat treatment before welding increases the tendency of cracking in the fusion zone.展开更多
Based on API STD 1104-2005 and CSA Z662-2007, field girth welding tests and girth weldability evaluations were executed for three types of wall thickness X70 UOE pipeline, in which the most popular main line girth wel...Based on API STD 1104-2005 and CSA Z662-2007, field girth welding tests and girth weldability evaluations were executed for three types of wall thickness X70 UOE pipeline, in which the most popular main line girth welding method, single-wire automatic gas metal arc welding （GMAW）, was used. The welding procedure specification was optimized to achieve a good quality and cold-crack-free girth weld joint without preheating or post-weld heat treatment. In addition ,porosities ,inclusions ,and incomplete fusion defects were avoided. The tensile strength,bending ,Vickers hardness,Charpy V-notch impact toughness, and crack tip opening displacement fracture toughness of the girth weld joint were evaluated, and the field girth weldability of Baosteel＇ s X70 UOE pipeline is joint exhibited good mechanical performance. Thus, the excellent for automatic GMAW.展开更多
Maximum hardness test in weld heat-affected zone（HAZ）,oblique Y-groove cracking test and mechanical property test of welding joint of 1 000 MPa grade ultra-low carbon bainitic steel were carried out,so as to researc...Maximum hardness test in weld heat-affected zone（HAZ）,oblique Y-groove cracking test and mechanical property test of welding joint of 1 000 MPa grade ultra-low carbon bainitic steel were carried out,so as to research the weldability of the steel.The results show that the steel has lower cold cracking sensitivity,and preheating temperature of 100 ℃ can help completely eliminate cold cracks,generating good process weldability.The increase of preheating temperature can reduce the hardening degree of heat-affected zone.The strength of welding joint decreases and hardness reduces when heat inputs increase,and excellent mechanical properties can be obtained when low welding heat inputs are used.Fine lath bainites of different orientations combined with a few granular bainites that effectively split the original coarse austenite grains are the foundation of good properties.展开更多
Understanding the weldability of steel in relation to the use of carbon equivalent is very necessary </span><span style="white-space:normal;font-family:"">for</span><span style...Understanding the weldability of steel in relation to the use of carbon equivalent is very necessary </span><span style="white-space:normal;font-family:"">for</span><span style="white-space:normal;font-family:""> the welding industry. The study was poised to unearth the fundamentals of carbon equivalent as applied in evaluating the weldability of steel. The study used </span><span style="white-space:normal;font-family:"">a </span><span style="white-space:normal;font-family:"">two-stage design approach to address the problem of carbon equivalence weldability of steel, thus, survey and experimental. Two different steels were tested to ascertain their chemical composition which could inform carbon equivalent calculation, and the results revealed microalloy and low alloy steels respectively. In subjecting the microalloy steel to carbon equivalent analyses of the AWS and IIW coefficients;revealed a value (CEV) = 0.11 each, suggesting that this microalloy steel has excellent weldability;no preheat</span><span style="white-space:normal;font-family:"">ing</span><span style="white-space:normal;font-family:""> is required. A successful welding operation on this steel does not depend on preheat</span><span style="white-space:normal;font-family:"">ing</span><span style="white-space:normal;font-family:"">.<b> </b>Also</span><span style="white-space:normal;font-family:"">,</span><span style="white-space:normal;font-family:""> the average results of the low alloy steel revealed a value (CEV) = 0.37 and 0.32 respectively, suggesting that this type of steel has very good weldability and may require </span><span style="white-space:normal;font-family:"">to </span><span style="white-space:normal;font-family:"">preheat. It is recommended that welders have </span><span style="white-space:normal;font-family:"">a </span><span style="white-space:normal;font-family:"">general idea about the weldability of steel with regard to carbon equivalent calculation. In addition</span><span style="white-space:normal;font-family:"">,</span><span style="white-space:normal;font-family:""> they should understand the chemical compositions of steels they are dealing with.展开更多
The weldability of copper-bearing aging steel is evaluated using calculated cracking susceptibility index Pcm,oblique Y-groove cracking test,heat-affected zone （HAZ） maximum hardness measurement,submerged arc weldi...The weldability of copper-bearing aging steel is evaluated using calculated cracking susceptibility index Pcm,oblique Y-groove cracking test,heat-affected zone （HAZ） maximum hardness measurement,submerged arc welding （SAW） test and gas metal arc welding （GMAW） test.The results show that this copper-bearing aging steel has low hardenability and cold cracking susceptibility.SAW test of 40 mm thick plate with WS03 wire matched by CHF101 flux reveals that the welded joints obtain high strength and good impact toughness at low temperature.The HAZ has no hardening but there exists a slightly softening phenomenon.Thus,line energy should be limited or controlled strictly to avoid softening behavior in HAZ during SAW.GMAW tests of 12mm and 24mm thick plates using WER70NH wire show that the tensile strength of joints reaches 720MPa,higher than the stipulated strength requirement of base metal.The average impact energy at-40℃ in the welded joints is more than 140J exceeding minimum stipulated requirement by a wide margin.There are no hardening and softening behaviors in the heat-affected zones of GMAW.All weld metals exhibit acicular ferrite （AF） plus small amount of proeutectoid ferrite （PF） structure,of which the former can significantly improve impact toughness of weld metal.The predominant microstructure in coarse grain HAZ is bainite.展开更多
基金National Natural Science Foundation of China(52201054,52175368)National Science and Technology Major Projects(J2019-VI-0018-0133)+2 种基金Liaoning Provincial Science and Technology Program(2023-BS-019,2023-MS-020)National Key R&D Program of China(2021YFB3700401)Key Specialized Research and Development Break-Through-Unveiling and Commanding the Special Project Program in Liaoning Province(2021JH15)。
文摘The impact of casting defects on the weldability of K4951 superalloy was investigated using tungsten inert gas(TIG)welding.The as-cast K4951 superalloy samples with prefabricated U-shaped grooves of varying depths and widths were TIG welded,and the microstructures,cracks morphology,and precipitated phases were analyzed using optical microscope,scanning electron microscope,transmission electron microscope,and energy dispersive X-ray spectrometer.The results reveal that the dimensions of casting defects significantly affect the weldability of K4951.Deep defects(greater than 2 mm)lead to rapid crack propagation,while wider defects can moderate the propagation process of cracks.Elemental segregation and the formation of precipitated phases,such as MC carbides,are observed in the fusion zone,contributing to welding cracks.An optimal groove aspect ratio(depth-to-width)between 0.2 and 0.5 minimizes crack formation tendency and enhances tensile strength,resulting in a mixed brittle-ductile fracture mode of joint after high-temperature tensile testing.
基金Project(52105351)supported by the National Natural Science Foundation of ChinaProject(24KJA460002)supported by the Natural Science Foundation of the Higher Education Institutions of Jiangsu Province,ChinaProject(G2023014009L)supported by the High-end Foreign Experts Recruitment Plan of China。
文摘High-entropy alloys(HEAs)have become essential materials in the aerospace and defense industries due to their remarkable mechanical properties,which include wear resistance,fatigue endurance,and corrosion resistance.The welding of high-entropy alloys is a cutting-edge field of study that is attracting a lot of interest and investigation from research organizations and businesses.Welding defects including porosity and cracks are challenging problem and limit the development of welding HEAs.This paper provides a comprehensive review of research on weldability of HEAs and the application of diverse welding techniques on welding HEAs over recent years.The forming mechanism and control strategies of defects during welding HEAs were provided in this work.Various welding techniques,including arc welding,laser welding,electron beam welding,friction stir welding,diffusion bonding and explosive welding,have been extensively investigated and applied to improve the microstructure and mechanical properties of HEAs joints.Furthermore,an in-depth review of the microstructure and mechanical properties of HEAs joints obtained by various welding methods is presented.This paper concludes with a discussion of the potential challenges associated with high-entropy alloy welding,thus providing valuable insights for future research efforts in this area.
文摘Super duplex stainless steels(SDSSs)and hyper duplex stainless steels(HDSSs),with more alloying elements content,are more corrosion resistant than the standard grades.Progresses of research works on weldability of SDSSs and HDSSs in recent years are reviewed in this paper.If proper heat input is provided,SDSSs and HDSSs can be welded with most fusion welding processes,while tungsten inert gas welding is the most popular process.SDSSs and HDSSs are more prone to secondary phases precipitation than the standard and lean grades,and heat input for SDSSs and HDSSs welding is restricted to a smaller range.Matching filler materials are usually recommended for SDSSs and HDSSs welding,rather than Ni-riched ones for standard and lean grades.Nitrogen addition in shielding gas is always beneficial.Post weld heat treatment with slow cooling rate will be harmful.Hot cracking tendency of SDSSs and HDSSs joints is not high,but sometimes they can suffer from hydrogen induced stress cracking.
基金supports provided by the National Natural Science Foundation of China(No.52372330).
文摘The small punch test technique facilitates the convenient acquisition of the mechanical properties of in-service equipment materials and the assessment of their remaining service life through sampling.However,the weldability of components with thin walls after small punch sampling,such as ethylene cracking furnace tubes,requires further investigation.Therefore,the weldability of in-service ethylene cracking furnace tubes following small punch sampling was investigated through nondestructive testing,microstructural characterization,and mechanical testing.Additionally,the impact of small punch sampling size and residual stress on the creep performance of the specimens was studied using an improved ductility exhaustion model.The results indicate that both the surface and interior of the weld repair areas on new furnace tubes and service-exposed furnace tubes after small-punch sampling are defect-free,exhibiting good weld quality.The strength of the specimens after weld repair was higher than that before sampling,whereas toughness decreased.Weld repair following small punch sampling of furnace tubes is both feasible and necessary.Furthermore,a linear relationship was observed between specimen thickness,diameter,and creep fracture time.The residual stress of welding affects the creep performance of the specimen under different stresses.
文摘Duplex stainless steels(DSSs)show better corrosion resistance with higher strength than traditional austenite stainless steels in many aggressive environments,and can be welded properly with almost every welding processes,if proper heat input is provided.Progresses of research works on weldability of DSSs in recent years are reviewed in this paper.Balance control of ferrite/austenite phases is most important for DSSs welding.The phases balance can be controlled with filler materials,nitrogen addition in shielding gas,heat input,post weld heat treatment,and alternating magnetic field.Too high cooling rate results in not only extra ferrite,but also chromium nitride precipitation.While too low cooling rate or heating repeatedly results in precipitation of secondary austenite and intermetallic compounds.In both situations,mechanical properties and corrosion resistance of the DSS joints deteriorate.Recommended upper and lower limits of heat input and maximum interpass temperature should be observed.
文摘Weldability test was carried out on the newly developed fine grain, low sulphur, high strength and high toughness pipeline steel of X80 and its matching SAW wire. Test of maximum hardness in welding heat-affected zone and test of Y groove cracking show that X80 steel features low hardenability and good cracking resistance. The submerged arc welding joint made with the newly developed low carbon and multi-alloyed SAW wire of WGX2 exhibits a little higher strength than the base metal, qualified bending performance, under maximum limitation hardness and good impact toughness, which can completely meet the technical requirement of X80 steel. Despite somewhat coarsening the grain size in welding heat-affected zone is still much finer than that of traditional steels, and the microstructure in weld metal is almost full acicular ferrite. The results show that X80 steel and WGX2 wire are of great weldability.
文摘The weldability of a ferritic ductile cast iron was investigated as a function of different consumables and welding conditions. A 23 full factorial experimental design was used to analyze the effect of factors and their interac- tions on ultimate tensile strength of weldments. The shielded metal arc welding （SMAW） process was used with two types of consumables （E7018 and ENi-CI） under eight different conditions using as-cast samples. The microstructur- al evolution and fracture mechanisms were investigated by optical microscopy and scanning electron microscopy （SEM）, respectively. The hardness, tensile and impact tests were also performed to determine the weld quality. Based on experiment design, preheat, consumable, cooling condition, preheat cooling and preheat-consumable inter- actions were significant factors. Preheat is the most effective factor and in the case of E7018, preheat and cooling conditions were the most sensible factors. It was found that buttering was the most appropriate welding method for ferritic ductile cast iron.
文摘The weldability of the ZhS6U nickel-based superalloy, which is prone to solidification cracking during electron-beam welding(EBW) repair processes, was investigated. The effects of two different pre-weld heat-treatment cycles on the final microstructure before and after welding were examined. Welds were made on flat coupons using an EBW machine, and the two heat-treatment cycles were designed to reduce γ′ liquation before welding. Microstructural features were also examined by optical and scanning electron microscopy. The results showed that the change in the morphology and size of the γ′ precipitates in the pre-weld heat-treatment cycles changed the ability of the superalloy to release the tensile stresses caused by the matrix phase cooling after EBW. The high hardness in the welded coupons subjected to the first heat-treatment cycle resulted in greater resistance to stress release by the base alloy, and the concentration of stress in the base metal caused liquation cracks in the heat-affected zone and solidification cracks in the weld area.
文摘The weldability is an important property to metal materials. Materials weldability becomes worse with the yield strength increasing. The experimental results indicate that the specific shock waves treatment could improve the weldability of steels such as 16MnR, SM 58Q, e.g. increase the notch toughness of coarse grains zone in HAZ and decrease cold cracking sensibility. The work would explore initially the mechanisms of improvement of weldability by shock waves. The further study on the low alloy high strength steel WEL TEN80 indicates that the shock waves may increase the material weldability on this grade of trength.
文摘The weldability of 12MnNiVR was examined in terms of the simulated HAZ continuous cooling transformation (SH-CCT) diagram,microstructure and mechanical properties of the simulated coarse grain heat-affected zone (CGHAZ).When t 8/5 is shorter,the microstructure mainly consists of lath bainite.When t 8/5 is 60 s,the microstructure becomes coarser bainite.Some acicular ferrite appears beside lath bainite when t 8/5 =100s.Finally,a microstructure composed of polygonal ferrite,acicular ferrite,and small amount pearlite is obtained with a small amount of bainite at t 8/5 】100s.With the increase of t 8/5,the hardness of CGHAZ decreases considerably.The minimum impact toughness of CGHAZ appears at t 8/5 =100s.The hardness and the toughness of CGHAZ remain above the specified values for steel 12MnNiVR.
文摘Based on the offshore standard DNV-OS-F101-2010,girth welding tests and girth weldability evaluations were carried out for the X65 and X70 UOE submarine pipelines of 3 wall thickness gauges,in which semi-automatic gas metal arc welding （GMAW） was adopted matched with metal powder flux cored wire. The girth welding procedure specification （WPS） was optimized to obtain good quality and cold-crack-free girth weld joint without preheating and post-weld heat treatment. At the same time, porosities, inclusions and incomplete fusion defects were avoided. Girth weld joints were evaluated for tensile strength, bending, Vickers hardness, charpy impact toughness and crack tip opening displacement （CTOD） fracture toughness. Results show that all the girth weld joints have good mechanical performances,indicating that the irth weldabilitv of Baosteel＇ s UOE submarine pipelines is excellent in the case of semi-automatic GMAW.
文摘High entropy alloys usually show good weldability.The weldability problems of high entropy alloys are segregation,cracks,and hardening or softening of weld,etc.When an Al_(x)CoCrFeNi alloy is welded,Al and Ni will segregate to the interdendritic region in the weld,but the degree of segregation is less than that of the base metal.When an Al_(x)CoCrCu_(x)FeNi alloy or a CoCrCu_(x)FeNi alloy is welded,Cu tends to segregate to the interdendritic region in the weld.Increasing the cooling rate of the welding process,such as with laser welding,is conducive to reducing the segregation in the weld.The segregation in the weld and the heat affected zone,especially the segregation of Cu,will lead to the generation of hot cracks.Hot cracking is the main form of cracking in high entropy alloys joints.Welding will lead to changes in the hardness of the weld.The main factors affecting the hardness change are the grain sizes and the precipitations.With laser welding,if the base metal is cold rolled,the hardness of the weld will decrease.If the base metal is hot rolled and annealed or cast,the hardness of the weld will increase.With TIG welding,the hardness of the weld is usually lower than that of the base metal,unless the grain of the base metal is particularly coarse before welding.With friction stir welding,recrystallization and grain refinement occur in the stir zone,and the hardness of the stir zone will be significantly improved no matter the original base metal is cold rolled or cast.
基金Sponsored by National Key Technology Research and Development Program in 11th Five-Year Plan of China (2006BAE03A08)Special Program for Key Research of National Basic Research Program of China (2011CB606306-2)Fundamental Research Funds for Central Universities of China (N090607003)
文摘CO2-shielded welding experiments of newly developed, 780 MPa super-high strength heavy-duty truck crossbeam steel were conducted, and the microstructure, microhardness, mechanical properties, and impact tough- hess of the welded joint were studied. The evolution of the microstructure of the welded joint occurred as follows.. welding seam （acicular ferrite＋proeutectoid ferrite）→fusion zone （granular bainite-long strip M/A island）→coarse grain zone （granular bainite-long strip or short bar M/A island）→fine grain zone （ferrite＋ pearlite＋ blocky M/A is- land）→mixed grained zone （ferrite＋granular bainite＋blocky M/A island）→base metal （proeutectoid ferrite＋gran- ular bainite-hlocky or granular M/A island）. Increasing the density of the grain boundaries can effectively improve the impact toughness, and the blocky M/A island hindered crack propagation more effectively than the long strip M/A island. The new hot-rolled 780 MPa super-high strength steel had excellent weldability. The welding technology was applied under the following conditions： welding voltage was 20 to 21 V, welding current was 200 to 210 A, and the gas flow rate was 25 L/rain.
基金National Natural Science Foundation of China (50671061)the China-Belgium Bilateral Project (2001-242)Shanghai Leading Academic Discipline Project (T0101)
文摘Transformation induced plasticity （TRIP） steel exhibited high or rather high carbon equivalent （CE） because of its chemical composition, which was a particularly detrimental factor affecting weldability of steels. Thus the weldability of a TRIP steel （grade 600） containing （in mass percent, %） 0.11C-1. 19Si-1.67Mn was extensively studied. The mechanical properties and impact toughness of butt joint, the welding crack susceptibility of weld and heat affected zone （HAZ） for tee joint, control thermal severity （CTS） of the welded joint, and Y shape 60° butt joint were measured after the gas metal arc welding （GMAW） test. The tensile strength of the weld was higher than 700 MPa. Both in the fusion zone （FZ） and HAZ for butt joint, the impact toughness was much higher than 27 J, either at room temperature or at -20 ℃, indicating good low temperature impact ductility of the weld of TRIP 600 steel. In addition, welding crack susceptibility tests revealed that weldments were free of surface crack and other imperfection. All experimental results of this steel showed fairly good weldability. For application, the crossmember in automobile made of this steel exhibited excellent weldability, and fatigue and durability tests were also accomplished for crossmember assembly.
基金financial support of MAPNA Group under contract No.RD-THD-89-02
文摘A new procedure was proposed for evaluating the weldability of nickel-base superalloys. The theory is on the basis of two microstructural patterns. In pattern I, the weld microstructure exhibits severe alloying segregation, many low-melting eutectic structures, and low weldability. The weld requires a weaker etchant and a shorter time for etching. In pattern Ⅱ, the weld microstructure displays less alloying segregation, low quantity of eutectic structures, and high weldability. The weld needs a stronger etchant and a longer time for etching. Five superalloys containing different amounts of Nb and Ti were designed to verify the patterns. After welding operations, the welds were etched by four etchants with different corrosivities. The weldability was determined by TG-DSC measurements. The metallography and weldability results confirmed the theoretic patterns. Finally, the etchant corrosivity and etching time were proposed as new criteria to evaluate the weldability of nickel-base superalloys.
基金Item Sponsored by State Key Lab of Mechanical Transmissions,Chongqing University
文摘The NiSix based alloy typically has poor weldability due to its lower ductility. A limited amount of work has been performed on the weldability of NiSix based alloys. Therefore, the effect of heat treatment and welding parameters on weldability of the alloys, and the relationship between the weldability and microstructure were studied. The results show that the as-cast Ni-Si-Nb-B alloy （Ni 76. 5%, Si 20%, Nb 3%, and B 0. 5%） could be successfully welded after preheating at 600 ℃. The welding procedure should be performed on the alloys before any heat treatment and a preheating at 600 ℃ should be used. The fusion zone is harder than the matrix due to a large amount of 7 phase and a finer microstructure. The cracks are predominantly intergranular in heat affected zone and associated with the needle-like ）, phase. The heat treatment before welding increases the tendency of cracking in the fusion zone.
文摘Based on API STD 1104-2005 and CSA Z662-2007, field girth welding tests and girth weldability evaluations were executed for three types of wall thickness X70 UOE pipeline, in which the most popular main line girth welding method, single-wire automatic gas metal arc welding （GMAW）, was used. The welding procedure specification was optimized to achieve a good quality and cold-crack-free girth weld joint without preheating or post-weld heat treatment. In addition ,porosities ,inclusions ,and incomplete fusion defects were avoided. The tensile strength,bending ,Vickers hardness,Charpy V-notch impact toughness, and crack tip opening displacement fracture toughness of the girth weld joint were evaluated, and the field girth weldability of Baosteel＇ s X70 UOE pipeline is joint exhibited good mechanical performance. Thus, the excellent for automatic GMAW.
基金Item Sponsored by National Science and Technology Support Plan Project of China(2007BAE51B07)
文摘Maximum hardness test in weld heat-affected zone（HAZ）,oblique Y-groove cracking test and mechanical property test of welding joint of 1 000 MPa grade ultra-low carbon bainitic steel were carried out,so as to research the weldability of the steel.The results show that the steel has lower cold cracking sensitivity,and preheating temperature of 100 ℃ can help completely eliminate cold cracks,generating good process weldability.The increase of preheating temperature can reduce the hardening degree of heat-affected zone.The strength of welding joint decreases and hardness reduces when heat inputs increase,and excellent mechanical properties can be obtained when low welding heat inputs are used.Fine lath bainites of different orientations combined with a few granular bainites that effectively split the original coarse austenite grains are the foundation of good properties.
文摘Understanding the weldability of steel in relation to the use of carbon equivalent is very necessary </span><span style="white-space:normal;font-family:"">for</span><span style="white-space:normal;font-family:""> the welding industry. The study was poised to unearth the fundamentals of carbon equivalent as applied in evaluating the weldability of steel. The study used </span><span style="white-space:normal;font-family:"">a </span><span style="white-space:normal;font-family:"">two-stage design approach to address the problem of carbon equivalence weldability of steel, thus, survey and experimental. Two different steels were tested to ascertain their chemical composition which could inform carbon equivalent calculation, and the results revealed microalloy and low alloy steels respectively. In subjecting the microalloy steel to carbon equivalent analyses of the AWS and IIW coefficients;revealed a value (CEV) = 0.11 each, suggesting that this microalloy steel has excellent weldability;no preheat</span><span style="white-space:normal;font-family:"">ing</span><span style="white-space:normal;font-family:""> is required. A successful welding operation on this steel does not depend on preheat</span><span style="white-space:normal;font-family:"">ing</span><span style="white-space:normal;font-family:"">.<b> </b>Also</span><span style="white-space:normal;font-family:"">,</span><span style="white-space:normal;font-family:""> the average results of the low alloy steel revealed a value (CEV) = 0.37 and 0.32 respectively, suggesting that this type of steel has very good weldability and may require </span><span style="white-space:normal;font-family:"">to </span><span style="white-space:normal;font-family:"">preheat. It is recommended that welders have </span><span style="white-space:normal;font-family:"">a </span><span style="white-space:normal;font-family:"">general idea about the weldability of steel with regard to carbon equivalent calculation. In addition</span><span style="white-space:normal;font-family:"">,</span><span style="white-space:normal;font-family:""> they should understand the chemical compositions of steels they are dealing with.
文摘The weldability of copper-bearing aging steel is evaluated using calculated cracking susceptibility index Pcm,oblique Y-groove cracking test,heat-affected zone （HAZ） maximum hardness measurement,submerged arc welding （SAW） test and gas metal arc welding （GMAW） test.The results show that this copper-bearing aging steel has low hardenability and cold cracking susceptibility.SAW test of 40 mm thick plate with WS03 wire matched by CHF101 flux reveals that the welded joints obtain high strength and good impact toughness at low temperature.The HAZ has no hardening but there exists a slightly softening phenomenon.Thus,line energy should be limited or controlled strictly to avoid softening behavior in HAZ during SAW.GMAW tests of 12mm and 24mm thick plates using WER70NH wire show that the tensile strength of joints reaches 720MPa,higher than the stipulated strength requirement of base metal.The average impact energy at-40℃ in the welded joints is more than 140J exceeding minimum stipulated requirement by a wide margin.There are no hardening and softening behaviors in the heat-affected zones of GMAW.All weld metals exhibit acicular ferrite （AF） plus small amount of proeutectoid ferrite （PF） structure,of which the former can significantly improve impact toughness of weld metal.The predominant microstructure in coarse grain HAZ is bainite.
