In the offshore industry, welding-induced distortion and tensile residual stresses have become a ... more In the offshore industry, welding-induced distortion and tensile residual stresses have become a major concern in relation to the structural integrity of a welded structure. Particularly, the continuous increase in size of welded plates and joints needs special attention concerning welding induced residual stresses. These stresses have a negative impact on the integrity of the welded joint as they promote distortion, reduce fatigue life, and contribute to corrosion cracking and premature failure in the weld components. This paper deals with the influence and impact of welding method on the welding induced residual stresses. It is also investigated whether the assumption of residual stresses up to yield strength magnitude are present in welded structures as stated in the design guidelines. The fatigue strength for welded joints is based on this assumption. The two welding methods investigated are hybrid laser-arc welding (HLAW) and submerged arc welding (SAW). Both welding methods ar...
The transfer of metal droplets during shielded metal arc welding was studied. Cellulose, rutile, ... more The transfer of metal droplets during shielded metal arc welding was studied. Cellulose, rutile, basic electrodes and a rutile covered stainless steel electrode were used. The transfer behavior was characterized by analysis of the arc signal, by plotting the welding voltage histogram, and by calculating the frequency response of the welding voltage. Some nonfusion welds were made using rutile electrodes. The size distribution of the droplets could be correlated with the arc signal. The metal transfer behavior generally changed significantly as the electrode was consumed. These changes were larger if the welding current was higher. The transfer behavior of the stainless steel electrode has the lowest sensitivity to changes in the welding current.
Increasing concerns regarding environmental contamination is driving the soldering research commu... more Increasing concerns regarding environmental contamination is driving the soldering research community to develop lead-free solder alloys. Previous studies have shown that Sn-based alloys such as Sn-3.5Ag, Sn-0.7Cu, Sn-9Zn, and Sn-3.2Ag-0.8Cu have promising mechanical properties, and can be considered as serious candidates to replace the Sn-Pb alloy. However, for joint life and reliability predictions, information about the interaction between these alloys and the most used substrates is needed. In that sense, the formation and growth of intermetallic compounds at the interface between the Cu-plated substrates and Sn-3.5Ag, Sn-0.7Cu, Sn-3.2Ag-0.8Cu, and Sn-9Zn have been studied. Coupons of joints prepared with each solder alloy on a Cu-plated circuit board were subjected to thermal aging test for 20, 100, 200, 500 hours at 70, 100 and 150 degrees Celsius. Each sample was analyzed using metallographic techniques, light microscopy, SEM and EDS. The results indicate that the formation o...
Shielded metal arc wet welding, due to its flexibility and ease of mobilization, is one of the mo... more Shielded metal arc wet welding, due to its flexibility and ease of mobilization, is one of the most attractive methods for repair of underwater structures. However, the quality of the weld metals deposited by this process is detrimentally affected by the direct contact of the welding arc with the aqueous environment. Oxygen and hydrogen generated by the decomposition of water in the arc are responsible for the main problems related to this specific process: loss of deoxidizers, oxygen pickup, increase in oxide inclusions content, hydrogen-induced cracking, and porosity. Rutile electrodes are recognized in the literature as being able to deposit welds with adequate mechanical properties but with high hydrogen content. Oxidizing electrodes, on the other hand, are able to deposit welds with lower hydrogen content but higher oxygen content. Welds deposited by rutile electrodes presented approximately 90 ml/100g of diffusible hydrogen while oxidizing electrodes produced welds with diffus...
Science and Technology of Welding and Joining, 2014
Abstract Low transformation temperature welding (LTTW) consumables have been reported to reduce t... more Abstract Low transformation temperature welding (LTTW) consumables have been reported to reduce the tensile residual stresses in weldments. Martensitic transformation induces compressive residual stresses and improves the fatigue resistance of welded joints. Several of these LTTW consumables have been developed at the Colorado School of Mines. This research work presents the comparisons of the experimentally and Sysweld calculated measurements for distortions and residual stresses for different plate thicknesses. In addition, residual stress evolution with time graphs were plotted to determine the amount of martensite required to promote compressive residual stresses and to calculate the time required to induce compressive residual stresses. The main aspect of this research is to analyse the behaviour of LTTW consumables in terms of distortion and residual stresses on various plate thicknesses.
Science and Technology of Welding and Joining, 2001
Abstract The use of a filler metal to facilitate the gas tungsten arc (GTA) welding of ferrous al... more Abstract The use of a filler metal to facilitate the gas tungsten arc (GTA) welding of ferrous alloys to titanium alloys has been investigated. Semi-empirical rules have been applied to identify alloying elements that would resolve the important problems of brittle intermetallic formation and weld cracking. Vanadium was found appropriate. The GTA welds between a low carbon steel and Ti–15V–3Cr–3Sn–3Al made with a vanadium filler wire resisted cracking better than comparable autogenous welds. However, the presence of a hard, brittle eutectic microconstituent along the ferrous side of the fusion boundary drastically limited the gain in weldability. As anticipated, analysis of GTA welds produced with vanadium filler wire suggested the presence of a ternary (Fe,Ti,V) single phase. Although cracking was reduced with vanadium, the practical benefit of a vanadium filler wire for GTA welding is small because the weld metals remain very hard and brittle.
Porosidade é um defeito comum em soldagem subaquática molhada. Vários estudos têm sido realizados... more Porosidade é um defeito comum em soldagem subaquática molhada. Vários estudos têm sido realizados com o objetivo de avaliar os mecanismos que controlam sua formação e assim encontrar soluções para minimizá-la ou eliminá-la. Este trabalho tem como objetivo avaliar o efeito da variação dos teores de carbono do metal de base e da alma do eletrodo sobre a porosidade do metal de solda. Dois diferentes metais de base, com variações apenas no teor de carbono (C2 - 0,1% e C7 - 0,7%), foram utilizados para deposição das soldas feitas à 50 metros de profundidade, utilizando eletrodos comerciais E6013 com diferentes teores de carbono na alma (E2 - 0,002% e E6 -0,6%), em polaridade direta (DCEN). O método macrográfico de análise de imagens foi utilizado para a quantificação da porosidade. Utilizando os metais de base C2 e C7, observou-se que a porosidade aumentou significativamente com o aumento do teor de carbono da alma do eletrodo. Em contrapartida, observou-se uma redução da porosidade com ...
An increase of nitrogen content in a 0.02 wt% Ti-containing carbon-manganese steel resulted in a ... more An increase of nitrogen content in a 0.02 wt% Ti-containing carbon-manganese steel resulted in a low coarsening rate of TiN particles in the heat-affected zone (HAZ), which led to an accelerated ferrite transformation instead of ferrite side plates during weld cooling cycle. The mixed microstructure of ferrite side plate, acicular ferrite and grain boundary polygonal ferrite in the simulated HAZ produced higher toughness. However, the increase of nitrogen content gradually increased the free nitrogen content in the HAZ and deteriorated HAZ toughness. Impact energy of the simulated HAZ (with Δt8/5 ∼60 s) at –20 °C deteriorated by about 97 J per 0.001 wt% free nitrogen, in the free nitrogen range from 0.0009 wt% to 0.0034 wt%, even though the HAZ has the tough mixed microstructure. Cooling time after welding influenced the HAZ microstructure and toughness as well, and maximum toughness was obtained when cooling produced the tough mixed microstructure. Therefore, for a high HAZ toughness, both nitrogen content and cooling time should be controlled to obtain the tough mixed microstructure and to keep the free nitrogen content low. The optimal nitrogen content and cooling time from 800 °C to 500 °C were 0.006 wt% and between 60 s and 100 s, respectively, in this experiment.
PurposeThe purpose of this research is to develop closed‐loop control of robotic welding processe... more PurposeThe purpose of this research is to develop closed‐loop control of robotic welding processes.Design/methodology/approachThe approach being developed is the creation of three‐dimensional models of the weld pool using stereo imagining. These models will be used in a model‐based feedback control system. Fusion of more than one sensor type in the controller is used.FindingsThree‐dimensional images can be produced from stereo images of GMAW‐p weld pools. This requires coordinating the image capture with the arc pulse to allow observation of the pool.Research limitations/implicationsThis is a work in progress. The imaging is not being done in real time at this point in time. Future work will address this issue. Also, how the image information is to be used to make corrections within the controller is future work.Practical implicationsClosing the loop on GMAW welding will allow robotic automation of welding to proceed to a much broader degree of application.Originality/valueThis pape...
Low transformation temperature welding (LTTW) consumables are characterized by a low martensite s... more Low transformation temperature welding (LTTW) consumables are characterized by a low martensite start temperature and a large fraction of martensite forming in the weld. It can efficiently reduce the tensile residual stress because the volume expansion associated with the martensitic transformation compensates for the thermal contraction during cooling. In this work, a LTTW wire, designated as EH200B, was created for the arc welding of advanced high-strength steel thin plates. In comparison to conventional ER70S-3 wires, this LTTW wire generated an opposite distortion pattern. Neutron diffraction measurements along the center thickness of the welded plates showed the maximum residual stress along the longitudinal direction (LD) in the weld region, and the heat-affected zone (HAZ) immediately adjacent to the weld region was reduced from ~330 MPa to below 240 MPa by using the LTTW wire. A finite element (FE) model was developed to predict the residual stress distributions of the plate...
Grain refinement can significantly improve the mechanical properties of freeform-fabricated Ti6Al... more Grain refinement can significantly improve the mechanical properties of freeform-fabricated Ti6Al-4V alloy, promoting increased strength and enhanced isotropy compared with coarser grained material. Large β-grains can lead to a segregated microstructure, in regard to both αphase morphology and α-lath orientation. Beam modulation, which has been used in conventional fusion welding to promote grain refinement, is explored in this study for use in additive manufacturing processes including electron beam freeform fabrication (EBF3) and gas-tungsten arc (GTA) deposition to alter solidification behavior and produce a refined microstructure. The dynamic molten pool size, induced by beam modulation causes rapid heat flow variance and results in a more competitive grain growth environment, reducing grain size. Consequently, improved isotropy and strength can be achieved with relatively small adjustments to deposition parameters.
In the offshore industry, welding-induced distortion and tensile residual stresses have become a ... more In the offshore industry, welding-induced distortion and tensile residual stresses have become a major concern in relation to the structural integrity of a welded structure. Particularly, the continuous increase in size of welded plates and joints needs special attention concerning welding induced residual stresses. These stresses have a negative impact on the integrity of the welded joint as they promote distortion, reduce fatigue life, and contribute to corrosion cracking and premature failure in the weld components. This paper deals with the influence and impact of welding method on the welding induced residual stresses. It is also investigated whether the assumption of residual stresses up to yield strength magnitude are present in welded structures as stated in the design guidelines. The fatigue strength for welded joints is based on this assumption. The two welding methods investigated are hybrid laser-arc welding (HLAW) and submerged arc welding (SAW). Both welding methods ar...
The transfer of metal droplets during shielded metal arc welding was studied. Cellulose, rutile, ... more The transfer of metal droplets during shielded metal arc welding was studied. Cellulose, rutile, basic electrodes and a rutile covered stainless steel electrode were used. The transfer behavior was characterized by analysis of the arc signal, by plotting the welding voltage histogram, and by calculating the frequency response of the welding voltage. Some nonfusion welds were made using rutile electrodes. The size distribution of the droplets could be correlated with the arc signal. The metal transfer behavior generally changed significantly as the electrode was consumed. These changes were larger if the welding current was higher. The transfer behavior of the stainless steel electrode has the lowest sensitivity to changes in the welding current.
Increasing concerns regarding environmental contamination is driving the soldering research commu... more Increasing concerns regarding environmental contamination is driving the soldering research community to develop lead-free solder alloys. Previous studies have shown that Sn-based alloys such as Sn-3.5Ag, Sn-0.7Cu, Sn-9Zn, and Sn-3.2Ag-0.8Cu have promising mechanical properties, and can be considered as serious candidates to replace the Sn-Pb alloy. However, for joint life and reliability predictions, information about the interaction between these alloys and the most used substrates is needed. In that sense, the formation and growth of intermetallic compounds at the interface between the Cu-plated substrates and Sn-3.5Ag, Sn-0.7Cu, Sn-3.2Ag-0.8Cu, and Sn-9Zn have been studied. Coupons of joints prepared with each solder alloy on a Cu-plated circuit board were subjected to thermal aging test for 20, 100, 200, 500 hours at 70, 100 and 150 degrees Celsius. Each sample was analyzed using metallographic techniques, light microscopy, SEM and EDS. The results indicate that the formation o...
Shielded metal arc wet welding, due to its flexibility and ease of mobilization, is one of the mo... more Shielded metal arc wet welding, due to its flexibility and ease of mobilization, is one of the most attractive methods for repair of underwater structures. However, the quality of the weld metals deposited by this process is detrimentally affected by the direct contact of the welding arc with the aqueous environment. Oxygen and hydrogen generated by the decomposition of water in the arc are responsible for the main problems related to this specific process: loss of deoxidizers, oxygen pickup, increase in oxide inclusions content, hydrogen-induced cracking, and porosity. Rutile electrodes are recognized in the literature as being able to deposit welds with adequate mechanical properties but with high hydrogen content. Oxidizing electrodes, on the other hand, are able to deposit welds with lower hydrogen content but higher oxygen content. Welds deposited by rutile electrodes presented approximately 90 ml/100g of diffusible hydrogen while oxidizing electrodes produced welds with diffus...
Science and Technology of Welding and Joining, 2014
Abstract Low transformation temperature welding (LTTW) consumables have been reported to reduce t... more Abstract Low transformation temperature welding (LTTW) consumables have been reported to reduce the tensile residual stresses in weldments. Martensitic transformation induces compressive residual stresses and improves the fatigue resistance of welded joints. Several of these LTTW consumables have been developed at the Colorado School of Mines. This research work presents the comparisons of the experimentally and Sysweld calculated measurements for distortions and residual stresses for different plate thicknesses. In addition, residual stress evolution with time graphs were plotted to determine the amount of martensite required to promote compressive residual stresses and to calculate the time required to induce compressive residual stresses. The main aspect of this research is to analyse the behaviour of LTTW consumables in terms of distortion and residual stresses on various plate thicknesses.
Science and Technology of Welding and Joining, 2001
Abstract The use of a filler metal to facilitate the gas tungsten arc (GTA) welding of ferrous al... more Abstract The use of a filler metal to facilitate the gas tungsten arc (GTA) welding of ferrous alloys to titanium alloys has been investigated. Semi-empirical rules have been applied to identify alloying elements that would resolve the important problems of brittle intermetallic formation and weld cracking. Vanadium was found appropriate. The GTA welds between a low carbon steel and Ti–15V–3Cr–3Sn–3Al made with a vanadium filler wire resisted cracking better than comparable autogenous welds. However, the presence of a hard, brittle eutectic microconstituent along the ferrous side of the fusion boundary drastically limited the gain in weldability. As anticipated, analysis of GTA welds produced with vanadium filler wire suggested the presence of a ternary (Fe,Ti,V) single phase. Although cracking was reduced with vanadium, the practical benefit of a vanadium filler wire for GTA welding is small because the weld metals remain very hard and brittle.
Porosidade é um defeito comum em soldagem subaquática molhada. Vários estudos têm sido realizados... more Porosidade é um defeito comum em soldagem subaquática molhada. Vários estudos têm sido realizados com o objetivo de avaliar os mecanismos que controlam sua formação e assim encontrar soluções para minimizá-la ou eliminá-la. Este trabalho tem como objetivo avaliar o efeito da variação dos teores de carbono do metal de base e da alma do eletrodo sobre a porosidade do metal de solda. Dois diferentes metais de base, com variações apenas no teor de carbono (C2 - 0,1% e C7 - 0,7%), foram utilizados para deposição das soldas feitas à 50 metros de profundidade, utilizando eletrodos comerciais E6013 com diferentes teores de carbono na alma (E2 - 0,002% e E6 -0,6%), em polaridade direta (DCEN). O método macrográfico de análise de imagens foi utilizado para a quantificação da porosidade. Utilizando os metais de base C2 e C7, observou-se que a porosidade aumentou significativamente com o aumento do teor de carbono da alma do eletrodo. Em contrapartida, observou-se uma redução da porosidade com ...
An increase of nitrogen content in a 0.02 wt% Ti-containing carbon-manganese steel resulted in a ... more An increase of nitrogen content in a 0.02 wt% Ti-containing carbon-manganese steel resulted in a low coarsening rate of TiN particles in the heat-affected zone (HAZ), which led to an accelerated ferrite transformation instead of ferrite side plates during weld cooling cycle. The mixed microstructure of ferrite side plate, acicular ferrite and grain boundary polygonal ferrite in the simulated HAZ produced higher toughness. However, the increase of nitrogen content gradually increased the free nitrogen content in the HAZ and deteriorated HAZ toughness. Impact energy of the simulated HAZ (with Δt8/5 ∼60 s) at –20 °C deteriorated by about 97 J per 0.001 wt% free nitrogen, in the free nitrogen range from 0.0009 wt% to 0.0034 wt%, even though the HAZ has the tough mixed microstructure. Cooling time after welding influenced the HAZ microstructure and toughness as well, and maximum toughness was obtained when cooling produced the tough mixed microstructure. Therefore, for a high HAZ toughness, both nitrogen content and cooling time should be controlled to obtain the tough mixed microstructure and to keep the free nitrogen content low. The optimal nitrogen content and cooling time from 800 °C to 500 °C were 0.006 wt% and between 60 s and 100 s, respectively, in this experiment.
PurposeThe purpose of this research is to develop closed‐loop control of robotic welding processe... more PurposeThe purpose of this research is to develop closed‐loop control of robotic welding processes.Design/methodology/approachThe approach being developed is the creation of three‐dimensional models of the weld pool using stereo imagining. These models will be used in a model‐based feedback control system. Fusion of more than one sensor type in the controller is used.FindingsThree‐dimensional images can be produced from stereo images of GMAW‐p weld pools. This requires coordinating the image capture with the arc pulse to allow observation of the pool.Research limitations/implicationsThis is a work in progress. The imaging is not being done in real time at this point in time. Future work will address this issue. Also, how the image information is to be used to make corrections within the controller is future work.Practical implicationsClosing the loop on GMAW welding will allow robotic automation of welding to proceed to a much broader degree of application.Originality/valueThis pape...
Low transformation temperature welding (LTTW) consumables are characterized by a low martensite s... more Low transformation temperature welding (LTTW) consumables are characterized by a low martensite start temperature and a large fraction of martensite forming in the weld. It can efficiently reduce the tensile residual stress because the volume expansion associated with the martensitic transformation compensates for the thermal contraction during cooling. In this work, a LTTW wire, designated as EH200B, was created for the arc welding of advanced high-strength steel thin plates. In comparison to conventional ER70S-3 wires, this LTTW wire generated an opposite distortion pattern. Neutron diffraction measurements along the center thickness of the welded plates showed the maximum residual stress along the longitudinal direction (LD) in the weld region, and the heat-affected zone (HAZ) immediately adjacent to the weld region was reduced from ~330 MPa to below 240 MPa by using the LTTW wire. A finite element (FE) model was developed to predict the residual stress distributions of the plate...
Grain refinement can significantly improve the mechanical properties of freeform-fabricated Ti6Al... more Grain refinement can significantly improve the mechanical properties of freeform-fabricated Ti6Al-4V alloy, promoting increased strength and enhanced isotropy compared with coarser grained material. Large β-grains can lead to a segregated microstructure, in regard to both αphase morphology and α-lath orientation. Beam modulation, which has been used in conventional fusion welding to promote grain refinement, is explored in this study for use in additive manufacturing processes including electron beam freeform fabrication (EBF3) and gas-tungsten arc (GTA) deposition to alter solidification behavior and produce a refined microstructure. The dynamic molten pool size, induced by beam modulation causes rapid heat flow variance and results in a more competitive grain growth environment, reducing grain size. Consequently, improved isotropy and strength can be achieved with relatively small adjustments to deposition parameters.
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