This study investigates the impact of welding heat input on weldments of modified 9Cr-1Mo(P91)steel,a high-strength material that requires high-energy welding processes like submerged arc welding.In the as-welded cond...This study investigates the impact of welding heat input on weldments of modified 9Cr-1Mo(P91)steel,a high-strength material that requires high-energy welding processes like submerged arc welding.In the as-welded condition,P91 steel welds primarily consist of untempered martensite,which transforms into tempered martensite during post-weld heat treatment(PWHT).Electron spectro-scopy analysis reveals the presence of M_(23)C_(6) and MX carbonitride precipitates at grain boundaries.Increasing the heat input leads to greater quantities of precipitates in the prior austenite grain boundaries,which can affect material properties.Weldment hardness profiles exhibit modest improvements,while ultimate tensile strength and toughness decrease with higher welding heat input,poten-tially due to the formation of a ferritic phase.Residual stress distributions are noticeably influenced by the welding heat input level.展开更多
The effects of Ti/N ratio on the number densities of nano particles,the size of the prior austenite grain(PAG)and the toughness of the heat-affected zone(HAZ)of Mg-deoxidized steels were studied after high heat input ...The effects of Ti/N ratio on the number densities of nano particles,the size of the prior austenite grain(PAG)and the toughness of the heat-affected zone(HAZ)of Mg-deoxidized steels were studied after high heat input welding of 400 kJ/cm.With increasing the Ti/N ratio from 2.7 to 5.7,the cuboid nano-sized particles are formed,and their number density increases.The area fractions of ductile intragranular acicular ferrites(IAFs)have the highest value and the area fractions of brittle microstructures of ferrite side plates and upper bainites have the lowest value in TN30 steel.With the Ti/N ratio of about 3.0,the HAZ of steel plate has the best low-temperature toughness.With increasing the Ti/N ratio from 2.7 to 5.7,the PAG sizes after the high-temperature laser scanning confocal microscopy observation decrease linearly with increasing the number densities of nano-sized particles.The PAG size of TN30 steel is between 100 and 150μm,which is conducive to the nucleation of IAFs.展开更多
In order to study the latest designed large heat input welding material of marine engineering extra-thick plate,EH36 steel was joined by using twin-wire submerged arc welding with heat inputs of 85,100 and 115 kJ/cm s...In order to study the latest designed large heat input welding material of marine engineering extra-thick plate,EH36 steel was joined by using twin-wire submerged arc welding with heat inputs of 85,100 and 115 kJ/cm separately.Meanwhile,the microstructure and mechanical properties were evaluated to explore the toughening mechanism of weld metal.Results show that a lot of active inclusions are obtained in the weld metal due to the design idea of low carbon and oxide metallurgy,which contributes to the generation of numerous fine and interlocking acicular ferrite.The acicular ferrite volume ratio of weld metal exceeds 60%.Moreover,the impact energy at-40℃ surpasses 115 J and the crack tip opening displacement value at-10℃ is more than 0.2 mm under three heat inputs owing to the role of acicular ferrite,of which 85 kJ/cm is the best.The martensite-austenite constituents are minor in size and the microstructure of the weld metal in reheated zone is dominated by small massive equiaxed ferrite,without impairing the toughness.As the heat input increases,the content of acicular ferrite drops and then rises;the impact toughness and fracture toughness first worsen consequently and then stabilize on account of the dramatic expansion of the proeutectoid ferrite size.展开更多
The welding interface is crucial to the service safety of dissimilar metal weld(DMW)joints between stainless steel(SS)and low alloy(LA)steel.Different status of welding interfaces was prepared by cladding SS consumabl...The welding interface is crucial to the service safety of dissimilar metal weld(DMW)joints between stainless steel(SS)and low alloy(LA)steel.Different status of welding interfaces was prepared by cladding SS consumables to LA steel substrates with different heat inputs via tungsten inert gas arc welding(TIG),followed by a series of microstructural characterizations and hardness tests.Results showed that a hardening and transition layer(TL)would be generated along the welding interface,and the width and hardening degree of the TL would increase with the heat input.Meanwhile,heavy load hardness tests showed that highly severe inhomogeneous plastic deformation and the microcrack would be generated in the interfacial region and the welding interface respectively in the highest heat input sample(1.03 kJ/mm).These results indicate that the increase in heat input would deteriorate the bonding performance of DMW joints.Further microstructural observations showed that the higher hardening degree of the highest heat input sample was mainly attributed to the stronger grain boundary,solution,and dislocation strengthening effects.展开更多
The evolution of microstructure and local properties near the welding interface is essential for the service safety of dissimilar metal welded joints between nickel-based alloy(NA) and low-alloy steel(LA).In this work...The evolution of microstructure and local properties near the welding interface is essential for the service safety of dissimilar metal welded joints between nickel-based alloy(NA) and low-alloy steel(LA).In this work,NA filler metal was deposited on LA substrate under different heat inputs by tungsten inert gas(TIG) welding.Microstructural characterization and microhardness tests were carried out near the prepared cladding interfaces.Optical and scanning electron microscopes show the lack of evident hardening transition layer along the welding interface.As the heat input increases,the mean hardness of the deposited layer also increases remarkably due to the rising dilution rate.Microstructural characterization shows a significant composition gradient across the cladding interface,but the diffusion gradient is limited to a small range.Under high heat input,a planar grain zone is generated along the interface due to the large temperature gradient across the interface region.展开更多
This study investigated the effect of pre-friction surfacing heat treatment of consumable rods and heat input during friction surfacing on the microstructure,mechanical properties,and wear resistance of hypereutectic ...This study investigated the effect of pre-friction surfacing heat treatment of consumable rods and heat input during friction surfacing on the microstructure,mechanical properties,and wear resistance of hypereutectic Al-Si alloy deposited on a commercially pure aluminum substrate.The results show that regardless of the consumable rod’s heat treatment conditions,the coating’s efficiency has increased with the increase in heat input,so the coating efficiency increases by 20%and 30%in the solid solution-treated rod and the artificially aged rod,respectively.By increasing the heat input,the average grain size in the coating fabricated by solid solution-treated rod and artificially aged rod increased from 0.1 to 0.9μm and from 0.2 to 1.3μm,respectively.At constant heat input,the average hardness and wear resistance of the coating created in the solid solution-treated rod are lower than those of the artificially aged rod.By decreasing heat input,the wear loss in the coating fabricated by solid solution-treated rod and artificially aged rod decreased by 10%and 20%,respectively,reaching 0.1 and 0.03μg/m.展开更多
The microstructure and hardness of the stir zone （SZ） with different welding heat inputs were investigated for friction stir-welded 2024-T3 aluminum by transmission electron microscopy, differential scanning calorim...The microstructure and hardness of the stir zone （SZ） with different welding heat inputs were investigated for friction stir-welded 2024-T3 aluminum by transmission electron microscopy, differential scanning calorimeter and Vickers micro-hardness test. The results show that welding heat input has a significant effect on the hardness of the SZ. Under high welding heat input condition, a higher welding speed is beneficial for improving the hardness of the SZ. However, when the welding heat input is low, the hardness of the SZ elevates with increasing the rotation speed. The hardness of the SZ decreases after post-welded heat treatment due to overaging. The joints welded at 500 r/min and 100 mm/min show a high resistance to overaging. The reduction of hardness in the SZ is only 3.8%, while in other joints, the reduction is more than 10%. The morphology of strengthening precipitates plays important roles for the improvement of hardness.展开更多
Aging treatment and various heat input conditions and mechanical properties of TIG welded 606I-T6 alloy joints were adopted to investigate the microstructural evolution by microstructural observations, microhardness t...Aging treatment and various heat input conditions and mechanical properties of TIG welded 606I-T6 alloy joints were adopted to investigate the microstructural evolution by microstructural observations, microhardness tests, and tensile tests. With an increase in heat input, the width of the heat-affected zone （HAZ） increases and grains in the fusion zone （FZ） coarsen. Moreover, the hardness of the HAZ decreases, whereas that of the FZ decreases initially and then increases with an increase in heat input. Low heat input results in the low ultimate tensile strength of the welded joints due to the presence of partial penetrations and pores in the welded joints. After a simple artificial aging treatment at 175℃ for 8 h, the microstructure of the welded joints changes slightly. The mechanical properties of the welded joints enhance significantly after the aging process as few precipitates distribute in the welded seam.展开更多
The influence of Nb on microstructure, mechanical property and the transformation kinetics of the coarse grain heat affected zone （CGHAZ） in HSLA steels for different heat inputs, has been investigated. When welded ...The influence of Nb on microstructure, mechanical property and the transformation kinetics of the coarse grain heat affected zone （CGHAZ） in HSLA steels for different heat inputs, has been investigated. When welded at higher heat inputs （100-60 kJ/cm）, impact toughness values of the steel without Nb are much higher than those of the steel with Nb, and the lowest span is 153 J at 60 kJ/cm. But only a little higher values are observed at lower heat inputs （40-30 kJ/cm）, and the highest span is 68 J at 30 kJ/cm. Dilatation studies indicate that continuous cooling transformation starting temperatures （Ts） of CGHAZ for the steel with Nb are approximately 15-30℃ which are lower than those of the steel without Nb at all heat inputs. For higher heat inputs, Nb in solid solution suppresses ferrite transformation and promotes the formation of granular bainite which has detrimental effect on impact toughness. For lower heat inputs higher Charpy impact energy values in the steel with Nb are associated with the formation of low carbon self-tempered martensite.展开更多
As a new type of low cracking suscepbility high strength steel,07MnCrMoVR steel has excellent weldability,with low carbon equivalent and cold cracking susceptibility coefficient.However,there are still some problems w...As a new type of low cracking suscepbility high strength steel,07MnCrMoVR steel has excellent weldability,with low carbon equivalent and cold cracking susceptibility coefficient.However,there are still some problems when this steel is on the outdoor actual welding condition,such as having some extend cold cracking suscepbility and embrittlement of heat affected zone.Currently, researching works for the welding of this steel mostly focus on the evaluation the weldability of it,only few works are concentrated in how the heat input affecting the embrittlement of HAZ.The goal of this research is to study the effect of heat input on the embrittlement of the heat affected zone so as to get the optimal welding heat input range for it.In this paper,38 mm 07MnCrMoVR steel made by Shougang is welded by manual arc welding technology,and the effect of heat input on the microstructure and mechanical properties of weld joints is also investigated by use of optical microscope（OM）,scanning electron microscope（SEM）,mechanical properties testing machines and Viker hardness tester.The microstructure and fractography observation results and the mechanical properties testing results indicate that the 07MnCrMoVR steel made by Shougang has a wide adaptable range for heat input,and when the heat input is in the range of 15-42 kJ/cm,the toughness of the weld joints is well.With the increase of heat input,the impact toughness of weld zone and heat affected zone decrease,whereas the tensile strength of the weld joints does not change at all.The microstructure of the weld is acicular ferrite with small amount of proeutectoid ferrite,and with the increase of heat input,the ratio of proeutectoid ferrite and the amount of M-A constituent increase,as well as the grain size and the width of the bainite lath in coarsened grain heat affected zone. Fractography results show that with the increase of heat input,the number of dimples in impact fracture specimens decreases,and the cleavage patterns increase,inducing the fracture from ductility to embrittlement.This research provides a theory support for guiding the penstock constructor how to use 07MnCrMoVR steel in actual welding.展开更多
AA5083 friction stir welds were produced using systematic experimental design, the process forces and heat input with varying parameters were studied. Helpful empirical models were developed in designing friction stir...AA5083 friction stir welds were produced using systematic experimental design, the process forces and heat input with varying parameters were studied. Helpful empirical models were developed in designing friction stir welding （FSW） tools and FSW welders. These models may be further helpful for making process parameter choice for this sort of alloy, defining welding program and control of process parameters by using computer numerical control friction stir welding welders. The results show that tool rotational speed, welding speed and tool shoulder diameter are most significant parameters affecting axial force and heat input, while longitudinal force is significantly affected by welding speed and probe diameter.展开更多
The high corrosion resistance of duplex stainless steel （DSS） is due to elements such as Cr, Mo and N, hut also depends on the microstructure. The best general properties are obtained with approximately equal amount...The high corrosion resistance of duplex stainless steel （DSS） is due to elements such as Cr, Mo and N, hut also depends on the microstructure. The best general properties are obtained with approximately equal amounts of austenite and ferrite and the absence of third phases such as σ（sigma） and Cr2N. In the present work the effect of heat input variations on the microstructure and corrosion resistance of a DSS UNS S32760 in artificial sea water media were studied. The corrosion resistance in 3.5 % of NaCl solution was evaluated by potentiostatic polarization tests at room temperature. It is found that the presence of sigma phase and Cr2N decreases the corrosion potential. The specimen with heat input of approximately 0.95 kJ/mm have the best corrosion characteristics, which is the result for the lack of deleterious phases such as sigma and Cr2 N and balanced ferrite austenite proportion.展开更多
The effect of heat input on martensite formation and impact properties of gas metal arc welded modified ferritic stainless steel （409M） sheets （as received） with thickness of 4 mm was described in detail in this w...The effect of heat input on martensite formation and impact properties of gas metal arc welded modified ferritic stainless steel （409M） sheets （as received） with thickness of 4 mm was described in detail in this work. The welded joints were prepared under three heat input conditions, i.e. 0.4, 0.5 and 0.6 kJ/mm using two different austenitic filler wires （308L and 316L） and shielding gas composition of Ar ＋ 5% CO2. The welded joints were evaluated by microstructure and charpy impact toughness. The dependence of weld metal microstructure on heat input and filler wires were determined by dilution calculation, Creq/Nieq ratio, stacking fault energy （SFE）, optical microscopy （OM） and transmission electron microscopy （TEM）. It was observed that the microstructure as well as impact property of weld metal was significantly affected by the heat input and filler wire. Weld metals prepared by high heat input exhibited higher amount of martensite laths and toughness compared with those prepared by medium and low heat inputs, which was true for both the filler wires. Furthermore, 308L weld metals in general provided higher amount of martensite laths and toughness than 316L weld metals.展开更多
The effects of welding heat input and post-weld heat treatment on the mechanical and microstructural aspects of dissimilarfriction stir welds of age-hardened AA7075-T6and strain hardenable AA5086-H32aluminium alloys w...The effects of welding heat input and post-weld heat treatment on the mechanical and microstructural aspects of dissimilarfriction stir welds of age-hardened AA7075-T6and strain hardenable AA5086-H32aluminium alloys were investigated.X-raydiffraction(XRD)residual stress analysis and tensile testing together with optical metallography and transmission electronmicroscopy(TEM)were performed to assess the effects of process parameters on welded joints.It was discovered that jointsproduced without heat sink exhibited more homogeneous stir zones than other joints.Of the natural aging time studied,higheramount of solid solution during rapid cooling of welds produced higher driving force for increase in hardness in the AA7075sideduring natural aging.Natural aging within stirring zone and thermo-mechanical affected zone of AA7075side resulted in a10to25MPa reduction in the residual stress in these zones;its effect decreased considerably in the welds performed without heat sink.Inaddition,natural aging had no noticeable effect on the joint strength.展开更多
Heterogeneous microstructure-induced mechanical responses in EH420 shipbuilding steel welded joint by electro-gas welding processed have been systematically studied by scanning electron microscopy,electron backscatter...Heterogeneous microstructure-induced mechanical responses in EH420 shipbuilding steel welded joint by electro-gas welding processed have been systematically studied by scanning electron microscopy,electron backscatter diffraction and mechanical testing.Comparing with the coarse-grained heat-affected zone(CGHAZ),the weld metal presents higher toughness(129.3 J vs.37.3 J)as it contains a large number of acicular ferrites with high-angle grain boundaries(frequency 79.2%)and special grain boundary∑3(frequency 55.3%).Moreover,coarse austenite grains in CGHAZ and slender martensite–austenite constituents between bainite laths may likely facilitate crack propagation.Polygonal ferrites and tempered pearlites formed at the junction of the fine-grained heat-affected zone and the intercritical heat-affected zone induced a softened zone with an average hardness of 185 HV0.5,which is the main reason for the occurrence of tensile fracture.展开更多
The non-heat-treatable AA3003-H18 plates were joined by friction stir welding（FSW） to achieve a proper joint by optimizing the welding parameters.For this purpose,the effects of heat input on microstructure and mech...The non-heat-treatable AA3003-H18 plates were joined by friction stir welding（FSW） to achieve a proper joint by optimizing the welding parameters.For this purpose,the effects of heat input on microstructure and mechanical properties of the welded samples were investigated by changing the ratios of rotational speed（800-1200 r/min） to travel speed（40-100 mm/min）（w/v）.It was revealed that the grain growth rate was strongly increased with the increase of the heat input by rotational speed at constant travel speed,while the grain growth rate was slightly increased with the increase of the heat input by travel speed at constant rotational speed.Subsequently,hardness reduction was observed in the stir zone at higher rotational speed compared with that at lower one.An interesting observation was that various welding parameters do not have noticeable effect on the tensile strength of the FSW joints.Also,it has been observed that the fracture location of tensile test specimens was placed in the heat-affected zone（HAZ）on the advancing side at lower travel speed,while at higher travel speed,it was placed at the HAZ/thermomechanical affected zone（TMAZ） interface on the retreating side.展开更多
The influence of Ti on weld microstructure and mechanical properties in large heat input welding of high strength low alloy steels is investigated. The results indicate that a moderate amount of Ti is still effective ...The influence of Ti on weld microstructure and mechanical properties in large heat input welding of high strength low alloy steels is investigated. The results indicate that a moderate amount of Ti is still effective for grain refinement even under larger heat input and a large amount of acicular ferrite （AF） is formed in the weld metal when Ti content is within 0. 028%--0. 038%. With increasing Ti content, proeutectoid ferrite in the weld metal decreases, whereas bainite and M-A constituent increase. The type of inclusion in the welds varies from Mn-Si-AI-O to Ti-Mn- A1-O and finally to Ti-A1-O as Ti content increases from 0 up to 0. 064%. As for adding 0. 028%--0. 038% Ti, high weld toughness could be attained since most inclusions less than 2 tim which contain Ti20s provide the effective nu- clei for aeicular ferrite formation. However, the toughness of the weld metals severely reduces when Ti content is over the optimum ranRe of 0. 028%--0. 038%.展开更多
The primary purpose of this study was to determine the effects of gas tungsten arc welding heat input on the high-temperature tensile properties, toughness, and microstructural features of titanium alloy Ti-3A1-2.5V. ...The primary purpose of this study was to determine the effects of gas tungsten arc welding heat input on the high-temperature tensile properties, toughness, and microstructural features of titanium alloy Ti-3A1-2.5V. The secondary objective was to examine the effect of the repeated repair welding on the properties of the alloy. It was also found that the mechanical properties progressively decreased with increasing the repair welding cycles, especially in the case of the weldment after the first welding repair. It was observed that the sizes of the acicular and prior β grain boundaries as well as the volume fraction of the acicular phases increased with increasing the welding heat input. In addition, the amount and size of the acicular a1 phases were found to increase with increasing the repair welding cycles.展开更多
SAW308L submerged arc welding wire and SJ601A submerged arc welding flux were selected to weld the 12 mm 08Cr19MnNi3Cu2N low nickel and high nitrogen austenitic stainless steel plates with three different welding heat...SAW308L submerged arc welding wire and SJ601A submerged arc welding flux were selected to weld the 12 mm 08Cr19MnNi3Cu2N low nickel and high nitrogen austenitic stainless steel plates with three different welding heat input,and microstructure,tensile properties,microhardness and corrosion properties of the welded joints were studied.The results show that no defects are found in the three groups of welded joints,and the welded joints have better performance.The tensile strength of 08Cr19MnNi3Cu2N stainless steel welded joints with different heat input is slightly lower than that of the base metal,and fracture occurs in the weld zone,and the hardness of the weld zone is lower than that of the base metal.The weld microstructure of stainless steel welded joints with different heat input is composed of austenite+δferrite,and ferrite is uniformly distributed in austenite.With the increase of the welding heat input,the ferrite content in the weld zone decrease gradually,the grain size in the thermal affected zone increase gradually,and the impact toughness reduce.展开更多
Abstract This work focuses on studying the effect of welding heat input within the range from 1 to 5 kJ/mm on the microstructure and the corresponding mechanical and corrosion properties of dissimilar joint between su...Abstract This work focuses on studying the effect of welding heat input within the range from 1 to 5 kJ/mm on the microstructure and the corresponding mechanical and corrosion properties of dissimilar joint between superaustenitic stainless steel （UNS S31254） and Incoloy 28 （UNS N08028）. The two materials were butt-welded with ER NiCrMo3. The metallurgical changes associated with welding of SASS and Incoloy 28 were studied using optical microscope, SEM, and EDX. The mechanical and corrosion properties were investigated using tensile test, Vickers hardness test, and pitting and crevice corrosion tests. The weld metal microstructure showed precipitates with needle-like shape at 3 and 5 kJ/mm. Also, the microstructure showed unmixed zone （UMZ） at the fusion line of both SASS and Incoloy 28 sides at all the investigated heat inputs. The Mo microsegregation within UMZ at Incoloy 28 side increased as the heat input increased from 1 to 5 k J/ram but that in SASS increased with increasing heat input from 1 to 3 kJ/mm and then decreased with increasing from 3 to 5 kJ/mm. The ultimate tensile strengths for all specimens at all the investigated heat inputs are acceptable. The average hardness noticeably changed in weld metal as the heat input increased from 1 to 5 kJ/mm. Other zones such as HAZ or UMZ did not demonstrate marked changes in the average hardness. The pitting and crevice corrosion rates of the weld joint were found significant at l and 3 kJ/mm but insignificant at 5 kJ/mm according to ASTM G48.展开更多
文摘This study investigates the impact of welding heat input on weldments of modified 9Cr-1Mo(P91)steel,a high-strength material that requires high-energy welding processes like submerged arc welding.In the as-welded condition,P91 steel welds primarily consist of untempered martensite,which transforms into tempered martensite during post-weld heat treatment(PWHT).Electron spectro-scopy analysis reveals the presence of M_(23)C_(6) and MX carbonitride precipitates at grain boundaries.Increasing the heat input leads to greater quantities of precipitates in the prior austenite grain boundaries,which can affect material properties.Weldment hardness profiles exhibit modest improvements,while ultimate tensile strength and toughness decrease with higher welding heat input,poten-tially due to the formation of a ferritic phase.Residual stress distributions are noticeably influenced by the welding heat input level.
基金financially supported by the National Natural Science Foundation of China(52474361).
文摘The effects of Ti/N ratio on the number densities of nano particles,the size of the prior austenite grain(PAG)and the toughness of the heat-affected zone(HAZ)of Mg-deoxidized steels were studied after high heat input welding of 400 kJ/cm.With increasing the Ti/N ratio from 2.7 to 5.7,the cuboid nano-sized particles are formed,and their number density increases.The area fractions of ductile intragranular acicular ferrites(IAFs)have the highest value and the area fractions of brittle microstructures of ferrite side plates and upper bainites have the lowest value in TN30 steel.With the Ti/N ratio of about 3.0,the HAZ of steel plate has the best low-temperature toughness.With increasing the Ti/N ratio from 2.7 to 5.7,the PAG sizes after the high-temperature laser scanning confocal microscopy observation decrease linearly with increasing the number densities of nano-sized particles.The PAG size of TN30 steel is between 100 and 150μm,which is conducive to the nucleation of IAFs.
基金the Major Science and Technology Innovation Project of Shandong Province(No.2019JZZY020239)。
文摘In order to study the latest designed large heat input welding material of marine engineering extra-thick plate,EH36 steel was joined by using twin-wire submerged arc welding with heat inputs of 85,100 and 115 kJ/cm separately.Meanwhile,the microstructure and mechanical properties were evaluated to explore the toughening mechanism of weld metal.Results show that a lot of active inclusions are obtained in the weld metal due to the design idea of low carbon and oxide metallurgy,which contributes to the generation of numerous fine and interlocking acicular ferrite.The acicular ferrite volume ratio of weld metal exceeds 60%.Moreover,the impact energy at-40℃ surpasses 115 J and the crack tip opening displacement value at-10℃ is more than 0.2 mm under three heat inputs owing to the role of acicular ferrite,of which 85 kJ/cm is the best.The martensite-austenite constituents are minor in size and the microstructure of the weld metal in reheated zone is dominated by small massive equiaxed ferrite,without impairing the toughness.As the heat input increases,the content of acicular ferrite drops and then rises;the impact toughness and fracture toughness first worsen consequently and then stabilize on account of the dramatic expansion of the proeutectoid ferrite size.
文摘The welding interface is crucial to the service safety of dissimilar metal weld(DMW)joints between stainless steel(SS)and low alloy(LA)steel.Different status of welding interfaces was prepared by cladding SS consumables to LA steel substrates with different heat inputs via tungsten inert gas arc welding(TIG),followed by a series of microstructural characterizations and hardness tests.Results showed that a hardening and transition layer(TL)would be generated along the welding interface,and the width and hardening degree of the TL would increase with the heat input.Meanwhile,heavy load hardness tests showed that highly severe inhomogeneous plastic deformation and the microcrack would be generated in the interfacial region and the welding interface respectively in the highest heat input sample(1.03 kJ/mm).These results indicate that the increase in heat input would deteriorate the bonding performance of DMW joints.Further microstructural observations showed that the higher hardening degree of the highest heat input sample was mainly attributed to the stronger grain boundary,solution,and dislocation strengthening effects.
文摘The evolution of microstructure and local properties near the welding interface is essential for the service safety of dissimilar metal welded joints between nickel-based alloy(NA) and low-alloy steel(LA).In this work,NA filler metal was deposited on LA substrate under different heat inputs by tungsten inert gas(TIG) welding.Microstructural characterization and microhardness tests were carried out near the prepared cladding interfaces.Optical and scanning electron microscopes show the lack of evident hardening transition layer along the welding interface.As the heat input increases,the mean hardness of the deposited layer also increases remarkably due to the rising dilution rate.Microstructural characterization shows a significant composition gradient across the cladding interface,but the diffusion gradient is limited to a small range.Under high heat input,a planar grain zone is generated along the interface due to the large temperature gradient across the interface region.
文摘This study investigated the effect of pre-friction surfacing heat treatment of consumable rods and heat input during friction surfacing on the microstructure,mechanical properties,and wear resistance of hypereutectic Al-Si alloy deposited on a commercially pure aluminum substrate.The results show that regardless of the consumable rod’s heat treatment conditions,the coating’s efficiency has increased with the increase in heat input,so the coating efficiency increases by 20%and 30%in the solid solution-treated rod and the artificially aged rod,respectively.By increasing the heat input,the average grain size in the coating fabricated by solid solution-treated rod and artificially aged rod increased from 0.1 to 0.9μm and from 0.2 to 1.3μm,respectively.At constant heat input,the average hardness and wear resistance of the coating created in the solid solution-treated rod are lower than those of the artificially aged rod.By decreasing heat input,the wear loss in the coating fabricated by solid solution-treated rod and artificially aged rod decreased by 10%and 20%,respectively,reaching 0.1 and 0.03μg/m.
基金Project(61901110301)supported by the Aircraft Science Foundation,China
文摘The microstructure and hardness of the stir zone （SZ） with different welding heat inputs were investigated for friction stir-welded 2024-T3 aluminum by transmission electron microscopy, differential scanning calorimeter and Vickers micro-hardness test. The results show that welding heat input has a significant effect on the hardness of the SZ. Under high welding heat input condition, a higher welding speed is beneficial for improving the hardness of the SZ. However, when the welding heat input is low, the hardness of the SZ elevates with increasing the rotation speed. The hardness of the SZ decreases after post-welded heat treatment due to overaging. The joints welded at 500 r/min and 100 mm/min show a high resistance to overaging. The reduction of hardness in the SZ is only 3.8%, while in other joints, the reduction is more than 10%. The morphology of strengthening precipitates plays important roles for the improvement of hardness.
基金financially supported by the Natural Science Foundation Project of Chongqing City (No.cstc2012jjA50002)
文摘Aging treatment and various heat input conditions and mechanical properties of TIG welded 606I-T6 alloy joints were adopted to investigate the microstructural evolution by microstructural observations, microhardness tests, and tensile tests. With an increase in heat input, the width of the heat-affected zone （HAZ） increases and grains in the fusion zone （FZ） coarsen. Moreover, the hardness of the HAZ decreases, whereas that of the FZ decreases initially and then increases with an increase in heat input. Low heat input results in the low ultimate tensile strength of the welded joints due to the presence of partial penetrations and pores in the welded joints. After a simple artificial aging treatment at 175℃ for 8 h, the microstructure of the welded joints changes slightly. The mechanical properties of the welded joints enhance significantly after the aging process as few precipitates distribute in the welded seam.
文摘The influence of Nb on microstructure, mechanical property and the transformation kinetics of the coarse grain heat affected zone （CGHAZ） in HSLA steels for different heat inputs, has been investigated. When welded at higher heat inputs （100-60 kJ/cm）, impact toughness values of the steel without Nb are much higher than those of the steel with Nb, and the lowest span is 153 J at 60 kJ/cm. But only a little higher values are observed at lower heat inputs （40-30 kJ/cm）, and the highest span is 68 J at 30 kJ/cm. Dilatation studies indicate that continuous cooling transformation starting temperatures （Ts） of CGHAZ for the steel with Nb are approximately 15-30℃ which are lower than those of the steel without Nb at all heat inputs. For higher heat inputs, Nb in solid solution suppresses ferrite transformation and promotes the formation of granular bainite which has detrimental effect on impact toughness. For lower heat inputs higher Charpy impact energy values in the steel with Nb are associated with the formation of low carbon self-tempered martensite.
文摘As a new type of low cracking suscepbility high strength steel,07MnCrMoVR steel has excellent weldability,with low carbon equivalent and cold cracking susceptibility coefficient.However,there are still some problems when this steel is on the outdoor actual welding condition,such as having some extend cold cracking suscepbility and embrittlement of heat affected zone.Currently, researching works for the welding of this steel mostly focus on the evaluation the weldability of it,only few works are concentrated in how the heat input affecting the embrittlement of HAZ.The goal of this research is to study the effect of heat input on the embrittlement of the heat affected zone so as to get the optimal welding heat input range for it.In this paper,38 mm 07MnCrMoVR steel made by Shougang is welded by manual arc welding technology,and the effect of heat input on the microstructure and mechanical properties of weld joints is also investigated by use of optical microscope（OM）,scanning electron microscope（SEM）,mechanical properties testing machines and Viker hardness tester.The microstructure and fractography observation results and the mechanical properties testing results indicate that the 07MnCrMoVR steel made by Shougang has a wide adaptable range for heat input,and when the heat input is in the range of 15-42 kJ/cm,the toughness of the weld joints is well.With the increase of heat input,the impact toughness of weld zone and heat affected zone decrease,whereas the tensile strength of the weld joints does not change at all.The microstructure of the weld is acicular ferrite with small amount of proeutectoid ferrite,and with the increase of heat input,the ratio of proeutectoid ferrite and the amount of M-A constituent increase,as well as the grain size and the width of the bainite lath in coarsened grain heat affected zone. Fractography results show that with the increase of heat input,the number of dimples in impact fracture specimens decreases,and the cleavage patterns increase,inducing the fracture from ductility to embrittlement.This research provides a theory support for guiding the penstock constructor how to use 07MnCrMoVR steel in actual welding.
文摘AA5083 friction stir welds were produced using systematic experimental design, the process forces and heat input with varying parameters were studied. Helpful empirical models were developed in designing friction stir welding （FSW） tools and FSW welders. These models may be further helpful for making process parameter choice for this sort of alloy, defining welding program and control of process parameters by using computer numerical control friction stir welding welders. The results show that tool rotational speed, welding speed and tool shoulder diameter are most significant parameters affecting axial force and heat input, while longitudinal force is significantly affected by welding speed and probe diameter.
文摘The high corrosion resistance of duplex stainless steel （DSS） is due to elements such as Cr, Mo and N, hut also depends on the microstructure. The best general properties are obtained with approximately equal amounts of austenite and ferrite and the absence of third phases such as σ（sigma） and Cr2N. In the present work the effect of heat input variations on the microstructure and corrosion resistance of a DSS UNS S32760 in artificial sea water media were studied. The corrosion resistance in 3.5 % of NaCl solution was evaluated by potentiostatic polarization tests at room temperature. It is found that the presence of sigma phase and Cr2N decreases the corrosion potential. The specimen with heat input of approximately 0.95 kJ/mm have the best corrosion characteristics, which is the result for the lack of deleterious phases such as sigma and Cr2 N and balanced ferrite austenite proportion.
文摘The effect of heat input on martensite formation and impact properties of gas metal arc welded modified ferritic stainless steel （409M） sheets （as received） with thickness of 4 mm was described in detail in this work. The welded joints were prepared under three heat input conditions, i.e. 0.4, 0.5 and 0.6 kJ/mm using two different austenitic filler wires （308L and 316L） and shielding gas composition of Ar ＋ 5% CO2. The welded joints were evaluated by microstructure and charpy impact toughness. The dependence of weld metal microstructure on heat input and filler wires were determined by dilution calculation, Creq/Nieq ratio, stacking fault energy （SFE）, optical microscopy （OM） and transmission electron microscopy （TEM）. It was observed that the microstructure as well as impact property of weld metal was significantly affected by the heat input and filler wire. Weld metals prepared by high heat input exhibited higher amount of martensite laths and toughness compared with those prepared by medium and low heat inputs, which was true for both the filler wires. Furthermore, 308L weld metals in general provided higher amount of martensite laths and toughness than 316L weld metals.
文摘The effects of welding heat input and post-weld heat treatment on the mechanical and microstructural aspects of dissimilarfriction stir welds of age-hardened AA7075-T6and strain hardenable AA5086-H32aluminium alloys were investigated.X-raydiffraction(XRD)residual stress analysis and tensile testing together with optical metallography and transmission electronmicroscopy(TEM)were performed to assess the effects of process parameters on welded joints.It was discovered that jointsproduced without heat sink exhibited more homogeneous stir zones than other joints.Of the natural aging time studied,higheramount of solid solution during rapid cooling of welds produced higher driving force for increase in hardness in the AA7075sideduring natural aging.Natural aging within stirring zone and thermo-mechanical affected zone of AA7075side resulted in a10to25MPa reduction in the residual stress in these zones;its effect decreased considerably in the welds performed without heat sink.Inaddition,natural aging had no noticeable effect on the joint strength.
基金the National Natural Science Foundation of China(Grant Nos.U20A20277,51861130361,51861145312,51850410522,5201101443,and 52011530180)the Newton Advanced Fellowship by Royal Society(Grant No.RP12G0414)+5 种基金the Royal Academy of Engineering(No.TSPC1070)the Special Fund for Key Program of Science and Technology of Liaoning Province(Grant No.2019JH1/101000014)the Research Fund for Central Universities(Grant Nos.N172502004 and N2025025)the Xingliao Talents Program(Nos.XLYC1807024 and XLYC1802024)the Regional Innovation Joint Fund of Liaoning Province(No.2020-YKLH-39)funded in part by the National Research Foundation of South Africa(No.BRICS171211293679)。
文摘Heterogeneous microstructure-induced mechanical responses in EH420 shipbuilding steel welded joint by electro-gas welding processed have been systematically studied by scanning electron microscopy,electron backscatter diffraction and mechanical testing.Comparing with the coarse-grained heat-affected zone(CGHAZ),the weld metal presents higher toughness(129.3 J vs.37.3 J)as it contains a large number of acicular ferrites with high-angle grain boundaries(frequency 79.2%)and special grain boundary∑3(frequency 55.3%).Moreover,coarse austenite grains in CGHAZ and slender martensite–austenite constituents between bainite laths may likely facilitate crack propagation.Polygonal ferrites and tempered pearlites formed at the junction of the fine-grained heat-affected zone and the intercritical heat-affected zone induced a softened zone with an average hardness of 185 HV0.5,which is the main reason for the occurrence of tensile fracture.
基金the research board of Sharif University of Technology for the financial supportthe provision of the research facilities used in this work
文摘The non-heat-treatable AA3003-H18 plates were joined by friction stir welding（FSW） to achieve a proper joint by optimizing the welding parameters.For this purpose,the effects of heat input on microstructure and mechanical properties of the welded samples were investigated by changing the ratios of rotational speed（800-1200 r/min） to travel speed（40-100 mm/min）（w/v）.It was revealed that the grain growth rate was strongly increased with the increase of the heat input by rotational speed at constant travel speed,while the grain growth rate was slightly increased with the increase of the heat input by travel speed at constant rotational speed.Subsequently,hardness reduction was observed in the stir zone at higher rotational speed compared with that at lower one.An interesting observation was that various welding parameters do not have noticeable effect on the tensile strength of the FSW joints.Also,it has been observed that the fracture location of tensile test specimens was placed in the heat-affected zone（HAZ）on the advancing side at lower travel speed,while at higher travel speed,it was placed at the HAZ/thermomechanical affected zone（TMAZ） interface on the retreating side.
基金Item Sponsored by National High Technology Research and Development Project of China(2009AA03Z530)
文摘The influence of Ti on weld microstructure and mechanical properties in large heat input welding of high strength low alloy steels is investigated. The results indicate that a moderate amount of Ti is still effective for grain refinement even under larger heat input and a large amount of acicular ferrite （AF） is formed in the weld metal when Ti content is within 0. 028%--0. 038%. With increasing Ti content, proeutectoid ferrite in the weld metal decreases, whereas bainite and M-A constituent increase. The type of inclusion in the welds varies from Mn-Si-AI-O to Ti-Mn- A1-O and finally to Ti-A1-O as Ti content increases from 0 up to 0. 064%. As for adding 0. 028%--0. 038% Ti, high weld toughness could be attained since most inclusions less than 2 tim which contain Ti20s provide the effective nu- clei for aeicular ferrite formation. However, the toughness of the weld metals severely reduces when Ti content is over the optimum ranRe of 0. 028%--0. 038%.
文摘The primary purpose of this study was to determine the effects of gas tungsten arc welding heat input on the high-temperature tensile properties, toughness, and microstructural features of titanium alloy Ti-3A1-2.5V. The secondary objective was to examine the effect of the repeated repair welding on the properties of the alloy. It was also found that the mechanical properties progressively decreased with increasing the repair welding cycles, especially in the case of the weldment after the first welding repair. It was observed that the sizes of the acicular and prior β grain boundaries as well as the volume fraction of the acicular phases increased with increasing the welding heat input. In addition, the amount and size of the acicular a1 phases were found to increase with increasing the repair welding cycles.
文摘SAW308L submerged arc welding wire and SJ601A submerged arc welding flux were selected to weld the 12 mm 08Cr19MnNi3Cu2N low nickel and high nitrogen austenitic stainless steel plates with three different welding heat input,and microstructure,tensile properties,microhardness and corrosion properties of the welded joints were studied.The results show that no defects are found in the three groups of welded joints,and the welded joints have better performance.The tensile strength of 08Cr19MnNi3Cu2N stainless steel welded joints with different heat input is slightly lower than that of the base metal,and fracture occurs in the weld zone,and the hardness of the weld zone is lower than that of the base metal.The weld microstructure of stainless steel welded joints with different heat input is composed of austenite+δferrite,and ferrite is uniformly distributed in austenite.With the increase of the welding heat input,the ferrite content in the weld zone decrease gradually,the grain size in the thermal affected zone increase gradually,and the impact toughness reduce.
文摘Abstract This work focuses on studying the effect of welding heat input within the range from 1 to 5 kJ/mm on the microstructure and the corresponding mechanical and corrosion properties of dissimilar joint between superaustenitic stainless steel （UNS S31254） and Incoloy 28 （UNS N08028）. The two materials were butt-welded with ER NiCrMo3. The metallurgical changes associated with welding of SASS and Incoloy 28 were studied using optical microscope, SEM, and EDX. The mechanical and corrosion properties were investigated using tensile test, Vickers hardness test, and pitting and crevice corrosion tests. The weld metal microstructure showed precipitates with needle-like shape at 3 and 5 kJ/mm. Also, the microstructure showed unmixed zone （UMZ） at the fusion line of both SASS and Incoloy 28 sides at all the investigated heat inputs. The Mo microsegregation within UMZ at Incoloy 28 side increased as the heat input increased from 1 to 5 k J/ram but that in SASS increased with increasing heat input from 1 to 3 kJ/mm and then decreased with increasing from 3 to 5 kJ/mm. The ultimate tensile strengths for all specimens at all the investigated heat inputs are acceptable. The average hardness noticeably changed in weld metal as the heat input increased from 1 to 5 kJ/mm. Other zones such as HAZ or UMZ did not demonstrate marked changes in the average hardness. The pitting and crevice corrosion rates of the weld joint were found significant at l and 3 kJ/mm but insignificant at 5 kJ/mm according to ASTM G48.
