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Abstract
An experimental study was conducted to determine effects of welding parameters and to optimize those parameters that have the most influence on eliminating or reducing the extent of hard zone formation at dissimilar metal welds (DMWs). Preheat, base metal thickness and welding electrode composition were found to have the most influence. Maintaining an optimum preheat for a given base metal thickness and controlling the maximum interpass temperature throughout welding resulted in drastic reduction and often complete elimination of hard zones at DMWs fabricated with ENiCrFe-3 electrodes, but not those welds fabricated with E309 stainless steel electrodes. This finding indicates that depending on the cooling rate and composition of the welding electrode, hard zones in DMWs can be eliminated. The cooling rate must be slow enough to avert formation of hard allotropic structures (i.e., martensite) and fast enough to avoid precipitation of hard intermetallic phases. The optimum welding electrode composition is one that will retard formation and precipitation of intermetallic phases during welding while the preheat needed to prevent the formation of allotropics is being maintained. Unfortunately, this unique characteristic is not available in most, if not all, austenitic stainless steel electrodes; nickel-based welding electrodes have been demonstrated to be more receptive.
... O conceito original de soldagem de aços dissimilares (SAD) se refere à união de dois sistemas de ligas diferentes, isto é, a união de dois metais de base (MB) de composições químicas significativamente diferentes -utilizando-se um metal de adição devidamente selecionado -resultando numa junta de aços dissimilares (JAD). (1)(2)(3) Em geral, os MB a serem unidos são aços ferríticos e austeníticos e os metais de adição empregados são os aços inoxidáveis austeníticos ou ligas de Níquel. Por razões econômicas, este tipo de soldagem vem sendo utilizado na fabricação de juntas de transição numa variedade de equipamentos e aplicações. ...
... Na Indústria de Petróleo e Gás JAD são algumas vezes utilizadas ao invés de juntas flangeadas em ambientes corrosivos de elevadas pressões e temperaturas. (1) Outro tipo de aplicação de SAD são os revestimentos metálicos depositados por soldagem em substratos menos nobres a fim melhorar a resistência à corrosão destes substratos. De modo análogo as JAD, geralmente os revestimentos são depositados através de soldagem ao arco elétrico com metais de adição de aços inoxidáveis austeníticos ou de ligas de Ni. (1,4) Na Indústria Petroquímica estes revestimentos metálicos podem ser aplicados em equipamentos submetidos a meios agressivos contendo sulfeto de hidrogênio tais como vasos de pressão, reatores, tubulações, entre outros. ...
... (1) Outro tipo de aplicação de SAD são os revestimentos metálicos depositados por soldagem em substratos menos nobres a fim melhorar a resistência à corrosão destes substratos. De modo análogo as JAD, geralmente os revestimentos são depositados através de soldagem ao arco elétrico com metais de adição de aços inoxidáveis austeníticos ou de ligas de Ni. (1,4) Na Indústria Petroquímica estes revestimentos metálicos podem ser aplicados em equipamentos submetidos a meios agressivos contendo sulfeto de hidrogênio tais como vasos de pressão, reatores, tubulações, entre outros. (1,5,6) Uma aplicação muito comum na indústria de petróleo e gás é o revestimento de substratos de aço carbono com aço inoxidável. ...
... Fig. 14(b) shows a distinct intermediate zone with a composite appearance of base and weld metals that characterizes a partially mixed zone (PMZ) [47]. Omar [50] reported such regions as beaches of martensite and peninsulas possessing base metal constitution. Both aforementioned intermediate zones are classified as macrosegregation in the literature [47,51] because the compositions have a gradient over a bulky span (100-200 μm), whereas in microsegregation the compositions differ over the span of a dendrite arm or cell spacing [51]. ...
... Another form of macrosegregation with resemblance to islands that illustrates the base metal structure [50] was found along the fusion boundary of WS 9, as clearly seen in Fig. 16. Kou et al. [51] explained the formation of segregated islands as occurring as a result of the difference in liquidus temperature of the base (~1530°C) and weld metal (~1400°C). ...
... As previously explained, macrosegregation in the intermediate zone can move the composition toward the martensitic range. It has been presented that as the Ni content increases, the segregation band declines, and the band no longer exists where Ni content is high enough to permit primary-γ solidification [48,50,55]. An increase in the concentration gradient of Ni can be reasonably implied from EDS analysis of WS 7.1, shown in Fig. 22. ...
... For economical reasons, this type of application has been utilized as transition joints in a variety of equipments. For instance, in the oil and gas industry the transition joints are sometimes used instead of flanged joints in wet and high temperature corrosive environments containing hydrogen sulfide and in high-pressure and temperature sour services (Omar, 1998;Doody, 1992). The same as transition joints, weld claddings -that are deposited by arc welding processes -are also quite common applications in the oil and gas industry, and the filler metals commonly used are also either austenitic stainless steels or nickel alloys. ...
... One of metallurgical drawbacks during dissimilar welding between austenitic stainless steel and carbon steel is the dilution level resulted from the welding process and parameters. The lower the dilution the lower the likelihood of forming brittle microstructures susceptible to corrosion and/or the hydrogen embrittlement (Wainer et al., 1992;Omar, 1998). On the other hand, due to differences between the chemical composition of austenitic stainless steel and carbon steel, and welding conditions, hard zone (HZ) -with hardness above 300HV -can form along the fusion line of the substrate side. ...
... with composition between the base metal (BM) and the bulk weld metal (WM) which can occur with several shapes and sizes. In the literature, these hard zones are also mentioned as partially diluted zones, transition zones, unmixed zones or intermediate mixed zones, which can consist of martensite, precipitates and/or intermetallic constituents such as Sigma e Chi phases (Doody, 1992;Wang, 1993;Omar, 1998;Kejelin et al., 2005). ...
The aim of this study was to characterize the metallurgical features and impact toughness of the interface between AISI 317L weld cladding and ASTM A516 Gr 60 steel. The weld cladding were carried out using the Twin Wire GMAW process and AWS E317L wire as filler with an interpass temperature of 423K. Two levels of heat input (H = 1170kJ/m and H = 1530kJ/m) and a mixture of argon and oxygen (95% Ar and 5% O 2) as shielding gas were used. The specimens were submitted to microtructure and microhardness analysis, and Charpy impact tests at room temperature and 273K. The results showed an increase in dilution and heat affect zone(HAZ) width when the heat input increased. Moreover, there was also the formation of hard zones (HZ) along the fusion line, presenting values above 300HV mainly for higher heat input levels.. The effect of heat input on Charpy energy specific values was more remarkable for the temperature of 273k and ranged from 1090 to 1480kJ/m 2 .
... A soldagem de revestimento em materiais menos nobres apresenta alguns pontos de atenção. Quando da elevada dissimilaridade (pela diferença química), a soldagem de aços dissimilares (SAD) trata-se da união de dois materiais diferentes, geralmente empregados em diversos processos de soldagem ao arco elétrico com metais de adição (Avery, 1991;Doody, 1992;Omar, 1998). Além disso, mostra-se de suma importância o estudo da influência dos parâmetros e do processo de soldagem na microestrutura, consequente propriedades, como também da morfologia do cordão e diluição (Nouri et al., 2007). ...
... O estudo dessas estruturas, principalmente para revestimento, torna-se de suma importância, pela segregação inerente de soluto durante a solidificação do processo (Kou e Yang, 2007). Além disso, essas regiões frágeis podem ser constituídas de fases intermetálicas (Chi e Sigma), precipitados e até martensita (Omar, 1998 podem ser identificadas por meio de uma variação de dureza abrupta no local, normalmente aumento de dureza, na qual é região preferencial de nucleação e propagação de trincas. As ZPD costumam estar presentes na região de interface entre metal de base e metal de adição, ainda mais problemático na região de sobreposição horizontal, na qual foi analisado no presente trabalho. ...
A análise das regiões de soldagem em revestimento, principalmente nas sobreposições de cordões, é de suma importância. Essas regiões apresentam muitas vezes comportamento diferente na zona sobreposta, apresentando uma região as vezes refundida, como também ausência de uma agitação adequada para revestir o material menos nobre, surgindo as zonas parcialmente diluídas (ZPD), que são regiões que alteram a dureza e características dos materiais, sendo normalmente regiões de nucleação e propagação de trincas, problemas catastróficos quando visto no revestimento. Com isso, torna-se necessário estudos que visam analisar as ZPD. A adequação dos parâmetros de soldagem e ajuste do processo pode reduzir ou tornar não presente essas zonas. Por meio de soldagem TIG-P com adição de arame frio (AWS A5.9 ER385), em substrato de ASTM A36, com tecimento, foram analisadas as regiões nas zonas sobrepostas, na sobreposição horizontal de dois cordões. Notou-se uma maior dureza nas zonas sobrepostas, analisados por meio do uso de perfil vertical de microdureza, e a presença de zonas parcialmente diluídas do tipo praia e ilha. O estudo serviu para o melhor entendimentos dessas regiões sobrepostas dos cordões aplicados a revestimento, com dois materiais dissimilares à base de ferro pouco visto na literatura.
... Figure 2 shows the schematic representation of stainless steel and copper dissimilar laser welding. Secondly, aluminum alloys are generally preferred in vehicle applications as they are effective in reducing vehicle weight and thus increasing fuel efficiency, as shown in Fig. 3 [13]. At this point, friction stir welding provides an adequate joining technology that can be used in joining aluminum alloys [13]. ...
... Secondly, aluminum alloys are generally preferred in vehicle applications as they are effective in reducing vehicle weight and thus increasing fuel efficiency, as shown in Fig. 3 [13]. At this point, friction stir welding provides an adequate joining technology that can be used in joining aluminum alloys [13]. The possibility of hot cracking should be considered during welding of nickel-based alloys and stainless steels, which are generally used in power plants [14]. ...
Recently, the welding of dissimilar metals has attracted great interest due to its widespread use in engineering building applications. In this article, welding methods of dissimilar metal joints containing different metal types with different chemical compositions are examined and their fatigue behavior is evaluated. In dissimilar metal welds, the difference in chemical composition affects the weldability and mechanical properties of the joints. In this study, the factors affecting the fatigue strength of dissimilar welded joints are described. Since welded structures can be used in sensitive and risky places, welding quality and mechanical properties of the weld are extremely important. In the research, a detailed literature review was presented by evaluating the latest studies on the mechanical properties of dissimilar welded joints such as fatigue strength, tensile strength, hardness, and the latest developments in the welding of different metals were reviewed. This study, which deals with the latest developments in the joining of different metal alloy combinations, is expected to increase the interest of the researchers in the future.
... Em termos da interface dissimilar, muitos são os artigos científicos que abordam o estudo da zona parcialmente misturada (ZPM) ao longo da zona de ligação, com destaque para Omar [5], DUPONT & KU-SKO [6] e KEJELIN et al. [7]. Segundo estes autores, um dos problemas mais usuais na interface austenítica/ferrítica está associado à formação de uma zona martensítica (Zona M) adjacente à linha de fusão e situada na ZPM que, analogamente a ZAC, também é susceptível as trincas por hidrogênio. ...
... Para DUPONT & KUSKO [6], a formação da Zona M pode ser minimizada com a substituição de consumíveis de aço inoxidável por ligas de níquel. OMAR [5] complementa afirmando que estas regiões podem ser eliminadas com o uso do consumível correto e de uma combinação adequada de pré-aquecimento. Para KEJELIN et al. [7], a formação dessas regiões tem uma ligação direta com a corrente de soldagem. ...
An adequate procedure for dissimilar welding must use the buttering of the bevel through the temper-bead technique, in order to establishing a thermal barrier capable to minimize the joint embrittlement. The buttering interface in these welds is indicated as the most critical region of the joint due to the presence of hard phases, which are often found in the coarse region of the heat affected zone (HAZ) and near the fusion line. The present work aims to investigate the feasibility of the Higuchi and Modified Higuchi techniques for the selection of operational parameters for controlled welding by the temper-bead technique, concerning the tempering the HAZ with coarse grains of the first layer deposited on an HSLA (High Strength Low Alloy) steel. The weld overlays were deposited by the combination of two wires, the ER NiCrMo-3 and the ER 316L, which used the GMAW (Gas Metal Arc Welding) process with pulsed current and with conventional current, respectively. The ASTM A182 F22 HSLA steel was used as base metal. The results showed a reduction in the microhardness level of the first layer HAZ by using the temper-bead technique. However, the tempering level achieved is still insufficient to eliminate the use of postweld heat treatment (PWHT).
Key-words
Dissimilar welding; temper-bead technique; Higuchi’s test
... A combinação desses dois materiais diferentes pode causar a formação de microrregiões com composição química, microestrutura e propriedade mecânica diferentes do metal de base (MB) e do metal de solda (MS). Sendo identificadas como zona parcialmente misturada (ZPM) e zona não misturada (ZNM), podendo ainda serem subclassificadas em ilhas, baias e praias [9,[12][13][14][15][16][17][18][19][20]. ...
... A borda externa da zona não misturada limita uma região parcialmente misturada na interface de solda. Essas microrregiões ainda podem ser influenciadas pelas temperaturas liquidus do MS e do MB, com possível influência das velocidades de resfriamento que cada microrregiões sofre, sendo localizadas no MS [9,[12][13][14][15][16][17][18][19][20][21]. De acordo com a literatura, as zonas parcialmente misturadas podem falhar quando submetidas à esforços de tensões [9]. ...
Resumo: Aços carbono são revestidos com Inconel 625® para atender os requisitos de projeto no Pré-Sal. Entretanto, isso gera microrregiões conhecidas como a zona não misturada (ZNM) e a zona parcialmente misturada (ZPM) sendo a sua formação relacionada a dissimilaridade entre o metal de base e o metal de adição. O objetivo desse artigo é analisar o efeito da diluição, da ZPM e da ZNM e do reaquecimento dessas microrregiões sobre a resistência ao arrancamento do aço 9%Ni revestido com a liga Inconel 625®. A ZNM tem direções cristalográficas similares a ZAC e é CCC igual a ZAC. A ZPM apresenta direções cristalográficas mais heterogêneas quando comparadas ao metal de solda e é CFC igual ao metal de solda. A nanodureza da ZPM é similar a ZAC e até 42,5% maior que o metal de solda. A nanodureza da ZNM é até 14,9% menor que ZPM, até 48,2% menor que o metal de solda e até 15% menor que a ZAC. Todos os corpos de prova tiveram a propagação da trinca no metal de solda e atendem o requisito de 140 MPa mínimo para a tensão de cisalhamento. A diluição apresenta uma correlação com a tensão de cisalhamento.
... In this respect, there is a great concern about the metallurgical aspects of the fusion line, mainly in regard to the formation of very small, brittle and hard zones along the fusion line, referred to as partially diluted zones (PDZs) ( Ref 24). These zones are usually associated with the presence of high-hardness martensite (400-550 HV) (22,(24)(25)(26)(27)(28) and can promote a deleterious influence on the corrosion resistance of dissimilar metal welds for sour service. Although the occurrence of PDZ has been observed (Fig. 2), no evidences of cracking or disbonding were verified at the overlay obtained by GMAW process. ...
... As expected ( Ref 22,[24][25][26][27][28], martensite was the microstructural constituent observed at this region, being important to notice its different morphology in comparison with the martensite observed close to the fusion line (Fig. 4). Indeed, an intense carbide precipitation due to the multiple passes was observed at the CGHAZ (Fig. 4). ...
The use of superaustenitic stainless steels (SASS) as an overlay replacement for nickel-based alloys can be an interesting alternative for the oil and gas industries, due to its lower cost, when compared to superalloys. Usually, the deposition is made with several welding passes by using conventional arc welding processes, such as gas tungsten arc welding (GTAW) or gas metal arc welding (GMAW) processes. In this respect, electro-slag welding (ESW), which promotes high heat inputs and low dilution of the welds, can also be attractive for this application, as it provides a higher productivity, once only one layer is needed for the deposition of the minimum thickness required. The present work evaluates the behavior of an AISI 904L SASS weld overlay deposited on a carbon steel ASTM A516 Grade 70 by ESW and GMAW processes. Both as-welded and heat-treated conditions were evaluated and compared. A multipass welding by GMAW process with three layers and 48 passes was performed on 12.532003250 mm steel plates with average welding energy of 1.0 kJ/mm. For ESW process, only one layer was deposited on 5034003400 mm steel plates with average welding energy of 11.7 kJ/mm. After welding, a post-weld heat treatment (PWHT) at 620 �C for 10 h was performed in half of the steel plate, in order to allow the comparison between this condition and the as-welded one. For both processes, the austenitic microstructure of the weld deposits was characterized by optical microscopy and scanning electron microscopy with electron backscatter diffraction.
A low proportion of secondary phases were observed in all conditions, and the PWHT did not promote significant changes on the hardness profile. Martensite for GMAW process and bainite for ESW process were the microstructural constituents observed at the coarse grain heat-affected zone, due to the different cooling rates. For ESW process, no
evidences of partially diluted zones were found. As a consequence of the microstructural findings, the hardness results for ESW were lower than those usually observed for other
electric arc welding processes. In addition, specimens subject to bending tests performed in accordance with the current standards used for qualification of welding procedures were approved. These evidences allow the conclusion that the ESW process can provide deposits with high quality despite the high welding energy levels, in order to achieve the desired productivity, being an interesting alternative for AISI 904L weld overlays.
... Najzad, prirubničke veze se razmatraju gde je to moguće, ali zahtevaju detaljan pristup izbora materijala za vijke i navrtke u takvoj aplikaciji visokog pritiska/temperature. Dodatni materijali na bazi Ni preporučuju se za DMW zbog njihove metalurške kompatibilnosti, srednje granice puzanja do loma i visoke duktilnosti, kao i za njihovog srednjeg termičkog koeficijenta ekspanzije. Dodatni materijali na bazi Ni ograničavaju migraciju ugljenika koja je inherentna razlikama sadržaja Cr sadržaja obe komponente usled manje rastvorljivosti i carbide layer (type I) formed at the fusion line of the martensitic component may initiate microvoiding and premature creep failures [6]. Using a Ni-alloy transition piece does not avoid this phenomenon. ...
... koeficijenta difuzije [5]. Međutim, vrlo tanak sloj Crkarbida (tip I) koji se formira na liniji stapanja martenzitne komponente može pokrenuti mikropraznine i preuranjene lomove usled puzanja [6]. Korišćenje prelaznog komada od Ni-legure ne izbegava ovu pojavu. ...
... In this work, the investigations of the transition zone were primarily carried out by transmission electron microscopy (TEM) on thin foils prepared by FIB (Focus Ion Beam). Though the microstructure of the transition zone between Inconel 625 overlaid on steel has been already described in the literature [3][4][5][6][11][12][13][14][15], those investigations pertained to Inconel 625 coatings produced by arc welding methods like gas metal arc welding (GMAW). There are no thorough studies concerning microstructure and chemical composition of a transition zone in weld overlay coating produced by CMT. ...
... The presence of martensite in the transition zone is undesirable, therefore the width of this area should preferably be as small as possible. Appearance of martensite in the transition zone of weld overlays made of Ni alloys deposited by a variety of overlay welding methods on an unalloyed or low-alloy steel is widely discussed in relevant publications [3][4][5][6][11][12][13][14], and rather unavoidable according to the Schaeffler diagram [20]. The authors of this text, however, are not aware of publications that would discuss and prove the presence and width of the martensite area in weld overlays made of Inconel 625 deposited by the CMT method. ...
... In this work, the investigations of the transition zone were primarily carried out by transmission electron microscopy (TEM) on thin foils prepared by FIB (Focus Ion Beam). Though the microstructure of the transition zone between Inconel 625 overlaid on steel has been already described in the literature [3][4][5][6][11][12][13][14][15], those investigations pertained to Inconel 625 coatings produced by arc welding methods like gas metal arc welding (GMAW). There are no thorough studies concerning microstructure and chemical composition of a transition zone in weld overlay coating produced by CMT. ...
... The presence of martensite in the transition zone is undesirable, therefore the width of this area should preferably be as small as possible. Appearance of martensite in the transition zone of weld overlays made of Ni alloys deposited by a variety of overlay welding methods on an unalloyed or low-alloy steel is widely discussed in relevant publications [3][4][5][6][11][12][13][14], and rather unavoidable according to the Schaeffler diagram [20]. The authors of this text, however, are not aware of publications that would discuss and prove the presence and width of the martensite area in weld overlays made of Inconel 625 deposited by the CMT method. ...
The aim of this work was to investigate the microstructure and chemical composition of the transition zone between 16Mo3 steel and Inconel 625 weld overlay coating produced by the Cold Metal Transfer (CMT) method. Investigations were primarily carried out through transmission electron microscopy (TEM) on thin foils prepared by FIB (Focus Ion Beam). The chemical analysis demonstrated that the amount of certain elements (Fe, Ni, Cr, Mo, Nb) in the transition zone between
the base material and the weld overlay changes quickly, from the composition of the steel to the composition of the composite zone. STEM and TEM investigations revealed that two areas are clearly visible in the transition zone. In the narrow band close to the fusion boundary where plates are clearly visible and the Ms temperature is higher than room temperature, electron diffraction analyses show reflections of martensite and austenite. Moreover, the crystallographic relations between martensite and austenite can be described by the Kurdjumov-Sachs (K-S) relationship. The microstructure of the part of the transition zone with an Ms temperature lower than room temperature as well as that of the composite zone is austenite. The investigations proved that the width of the martensitic area can be significantly limited by using the CMT technique for weld overlaying.
... In this respect, there is a great concern about the metallurgical aspects of the fusion line, mainly in regard to the formation of very small, brittle and hard zones along the fusion line, referred to as partially diluted zones (PDZs) (Ref 24). These zones are usually associated with the presence of high-hardness martensite (400-550 HV) (22,(24)(25)(26)(27)(28) and can promote a deleterious influence on the corrosion resistance of dissimilar metal welds for sour service. Although the occurrence of PDZ has been observed (Fig. 2), no evidences of cracking or disbonding were verified at the overlay obtained by GMAW process. ...
... As expected ( Ref 22,[24][25][26][27][28], martensite was the microstructural constituent observed at this region, being important to notice its different morphology in comparison with the martensite observed close to the fusion line (Fig. 4). Indeed, an intense carbide precipitation due to the multiple passes was observed at the CGHAZ (Fig. 4). ...
The use of superaustenitic stainless steels (SASS) as an overlay replacement for nickel-based alloys can be an interesting alternative for the oil and gas industries, due to its lower cost, when compared to superalloys. Usually, the deposition is made with several welding passes by using conventional arc welding processes, such as gas tungsten arc welding (GTAW) or gas metal arc welding (GMAW) processes. In this respect, electro-slag welding (ESW), which promotes high heat inputs and low dilution of the welds, can also be attractive for this application, as it provides a higher productivity, once only one layer is needed for the deposition of the minimum thickness required. The present work evaluates the behavior of an AISI 904L SASS weld overlay deposited on a carbon steel ASTM A516 Grade 70 by ESW and GMAW processes. Both as-welded and heat-treated conditions were evaluated and compared. A multipass welding by GMAW process with three layers and 48 passes was performed on 12.5 × 200 × 250 mm steel plates with average welding energy of 1.0 kJ/mm. For ESW process, only one layer was deposited on 50 × 400 × 400 mm steel plates with average welding energy of 11.7 kJ/mm. After welding, a post-weld heat treatment (PWHT) at 620 °C for 10 h was performed in half of the steel plate, in order to allow the comparison between this condition and the as-welded one. For both processes, the austenitic microstructure of the weld deposits was characterized by optical microscopy and scanning electron microscopy with electron backscatter diffraction. A low proportion of secondary phases were observed in all conditions, and the PWHT did not promote significant changes on the hardness profile. Martensite for GMAW process and bainite for ESW process were the microstructural constituents observed at the coarse grain heat-affected zone, due to the different cooling rates. For ESW process, no evidences of partially diluted zones were found. As a consequence of the microstructural findings, the hardness results for ESW were lower than those usually observed for other electric arc welding processes. In addition, specimens subject to bending tests performed in accordance with the current standards used for qualification of welding procedures were approved. These evidences allow the conclusion that the ESW process can provide deposits with high quality despite the high welding energy levels, in order to achieve the desired productivity, being an interesting alternative for AISI 904L weld overlays.
... Essas zonas são muito finas, de camadas descontínuas, tipicamente de 0,025 mm. Podem apresentar dezenas de mícrons de largura, diversas morfologias e composição química de baixa liga, ou seja, uma composição intermediária entre o metal de base (substrato) e o metal de solda (4,5,6,7,8) . Devido a estas características, as ZPD tornam-se susceptíveis a ataques corrosivos por pitting, fragilização por hidrogênio e corrosão sob tensão (6) . ...
... Podem apresentar dezenas de mícrons de largura, diversas morfologias e composição química de baixa liga, ou seja, uma composição intermediária entre o metal de base (substrato) e o metal de solda (4,5,6,7,8) . Devido a estas características, as ZPD tornam-se susceptíveis a ataques corrosivos por pitting, fragilização por hidrogênio e corrosão sob tensão (6) . No revestimento de tubulações com ligas de Ni aplicados por soldagem, o surgimento destas zonas na interface e o nível de dureza na superfície do revestimento podem ser fortemente influenciados pelo nível de diluição que por sua vez dependerá dos parâmetros de soldagem. ...
The objective of this work was to evaluate the influence of welding parameters on microhardness, microstructure and dilution level of nickel-based alloys cladding deposited on API 5L Gr B steel using MIG process with AWS ER NiCrMo-3 (Inconel 625) wire and pure Ar (Argon) as consumable. For this welds without and with preheat 423 K (150 °C), 22 V and 24 V tension, 5 an d 7 m/min wire feed speed resulting in welding current range from 123 to 150 A were done. The results indicated the presence of regions at the interface between the base and weld metal with microhardness values above 300 HV and dilutions varying from 5, 2 to 12, 8%.
... A ausência de porosidades ou bandeamento representa fator relevante junto às juntas soldadas, pois reduzem drasticamente a presença de elementos concentradores de tensões e associações com pites de corrosão que podem comprometer a vida em fadiga em aplicações dinâmicas [2,11,12]. O comportamento macroestrutural encontrado no metal de solda e ZTA foi similar, não detectando-se segregações ou macroestrutura dendrítica [13]. ...
The welding of dissimilar steels such as duplex and superaustenitic stainless steels is often used in industrial applications. The effect of welding energy on the heat-affected zone (ZTA) and fusion zone (ZF) presents knowledge gaps to be researched in relation to the metallurgical and mechanical properties of these steels. Variations in the application of welding energy can favor the presence of a greater volume of the ferritic or austenitic phases, and in more critical cases, cause the formation of precipitates harmful to corrosion. This work aims to evaluate the metallurgical, mechanical properties and corrosion resistance of dissimilar welding composed of duplex stainless steel S32205, as base metal, and superaustenitic stainless steel as weld metal, verifying the effects on microstructural, sensitization and anisotropies with the application of different heat inputs. In the microstructural analysis, the formation of first phase constituents, such as grain boundary austenite (GBA), witmanstatten austenite (WA), intragranular austenite (IGA) and secondary austenite (γ2) was verified. The microhardness values found were higher than those reported in the literature. In the corrosion tests, in environments with oxidizing chlorides, the samples showed pitting corrosion, with a high loss of mass in the specimens being detected. It is concluded that in the ZTA the metallurgical characteristics were maintained after the variation of the thermal input and in the ZF there was an increase in the loss of mass in the corrosion test in the analyzed samples.
Keywords
Duplex stainless steel; Superaustenitic stainless steel; Welding
... As fases presentes nas ligas de aços inoxidáveis correspondem a descontinuidades no aço como os óxidos, sulfetos, carbetos, nitretos, ferrita derivada da solidificação e fases intermetálicas decorrentes dos processos de soldagem ou tratamentos térmicos (FEDELE, 2004). Segundo Omar (1998) (SATHIYA et al., 2010;ANBURAJ et al., 2012;KOUTSOUKIS, 2013;MADALENA, 2013;JORGE et al., 2017;MEIRA et al., 2017;LEE et al., 2018). ...
Os vasos de pressão conhecidos como separadores trifásicos são equipamentos essenciais à separação do petróleo bruto na etapa de processamento primário em uma planta de extração petrolífera, sendo responsável pelo isolamento das três principais fases da mistura homogênea do produto extraído: óleo, gás e água. Tais separadores são usualmente fabricados maciçamente de aços inoxidáveis devido ao ambiente agressivo e corrosivo ao qual são submetidas as paredes internas do equipamento, constantemente em contato com o petróleo bruto, ricos em cloretos e sulfetos em sua composição. Como alternativa ao alto custo associado à fabricação de equipamentos de grande porte completamente fabricados em aço inoxidável, tem- se o revestimento de materiais nobres sobre substratos de aço carbono. O presente trabalho estudou o processo de eletroescória com fita de Inconel 625 em chapas cladeadas de aço carbono A516 Gr. 70 e aço inoxidável superaustenítico AISI 904L. O trabalho se propôs a estudar o comportamento metalúrgico da soldagem dissimilar por meio de análises estruturais e microestruturais, ensaios não destrutivos, análise de dureza por microindentações e ensaio de corrosão da junta soldada. As análises microestruturais destacaram a presença de importantes regiões denominadas de zonas parcialmente diluídas nas interfaces próximas as linhas de fusão, as quais são associadas ao aumento brusco de dureza na região e formação de precipitados e fases deletérias às propriedades mecânicas e à resistência à corrosão. Apesar da formação de tais regiões nas interfaces, a junta fabricada foi aprovada nos ensaios de tração, dobramento, líquido penetrante, radiografia e, o topo da junta, em ensaio de corrosão por voltametria cíclica, capacitando a fabricação da junta dissimilar proposta como uma excelente alternativa na fabricação de separadores de petróleo por apresentar uma melhor relação entre custos e propriedades ao processo usual de fabricação, além de agregar uma maior vida útil pela otimizada resistência à corrosão alcançada devido a soldagem dissimilar realizada entre o aço 904L e o metal de adição à base de níquel Inconel 625.
... As fases presentes nas ligas de aços inoxidáveis correspondem a descontinuidades no aço como os óxidos, sulfetos, carbetos, nitretos, ferrita derivada da solidificação e fases intermetálicas decorrentes dos processos de soldagem ou tratamentos térmicos (FEDELE, 2004). Segundo Omar (1998) (SATHIYA et al., 2010;ANBURAJ et al., 2012;KOUTSOUKIS, 2013;MADALENA, 2013;JORGE et al., 2017;MEIRA et al., 2017;LEE et al., 2018). ...
Os vasos de pressão conhecidos como separadores trifásicos são equipamentos essenciais à separação do petróleo bruto na etapa de processamento primário em uma planta de extração petrolífera, sendo responsável pelo isolamento das três principais fases da mistura homogênea do produto extraído: óleo, gás e água. Tais separadores são usualmente fabricados maciçamente de aços inoxidáveis devido ao ambiente agressivo e corrosivo ao qual são submetidas as paredes internas do equipamento, constantemente em contato com o petróleo bruto, ricos em cloretos e sulfetos em sua composição. Como alternativa ao alto custo associado à fabricação de equipamentos de grande porte completamente fabricados em aço inoxidável, tem- se o revestimento de materiais nobres sobre substratos de aço carbono. O presente trabalho estudou o processo de eletroescória com fita de Inconel 625 em chapas cladeadas de aço carbono A516 Gr. 70 e aço inoxidável superaustenítico AISI 904L. O trabalho se propôs a estudar o comportamento metalúrgico da soldagem dissimilar por meio de análises estruturais e microestruturais, ensaios não destrutivos, análise de dureza por microindentações e ensaio de corrosão da junta soldada. As análises microestruturais destacaram a presença de importantes regiões denominadas de zonas parcialmente diluídas nas interfaces próximas as linhas de fusão, as quais são associadas ao aumento brusco de dureza na região e formação de precipitados e fases deletérias às propriedades mecânicas e à resistência à corrosão. Apesar da formação de tais regiões nas interfaces, a junta fabricada foi aprovada nos ensaios de tração, dobramento, líquido penetrante, radiografia e, o topo da junta, em ensaio de corrosão por voltametria cíclica, capacitando a fabricação da junta dissimilar proposta como uma excelente alternativa na fabricação de separadores de petróleo por apresentar uma melhor relação entre custos e propriedades ao processo usual de fabricação, além de agregar uma maior vida útil pela otimizada resistência à corrosão alcançada devido a soldagem dissimilar realizada entre o aço 904L e o metal de adição à base de níquel Inconel 625.
... These regions of elevated hardness may be found in the interface with different morphologies and extensions. The development of these regions is attributed [25][26][27][28][29][30][31][32] to the formation of a laminar flow zone near the weld pool dissimilar interface. These regions are critical because they have an intermediate chemical composition to steel base metal and nickel filler metal alloy, which with the welding thermal cycle, can lead to the formation of fragile zones, even after PWHT. ...
... This band presented a solidification pattern type II as explained by Nelson, et al. 10 Metal inert gas (MIG) welding with filler metals ER2209/ Alloy 625 appears to be suitable for dissimilar metal welds of SDSS and HSLA, as martensite band is not formed. 11 McPherson, et al., experimented submerged arc welding (SAW) of stainless steel to carbon steel plate and a filler metal of 2205. A single "V" groove preparation with central positioning of consumable resulted in acceptable hardness levels of welds in the absence of martensite. ...
The effect of weld passes and single V grove designs, on the corrosion resistance of dissimilar welds of a low alloy steel and a super-duplex stainless steel, was studied in synthetic brine. Welds were manufactured in argon by gas tungsten arc (GTA) technique and joined by a high nickel wire of super-duplex stainless steel. Samples of weld regions were characterized by composition scans, electrochemical measurements, micro-hardness and scanning electron microscopy. In X52/ER2594, a transition region (TR) of grain boundaries type II and a band of martensite were formed. The base metal of X52 underwent the highest corrosion rate and localized corrosion occurred in the heat affected zone. Interface ER2594/25Cr7Ni and 25Cr7Ni showed the presence of pitting near intermetallics.
... By observation, crystal structure and the microstructure while defining the structure of a substance have been differentiated clearly. The word 'crystal structure' is being used to characterise the typical locations of atoms inside the atom cell and is described entirely in the atomic lattice form and nominal co-ordinates [13] (as calculated by radiation diffraction, for example). The molecular structure shows the material's personality on the atomic (or Å) length scale. ...
Austenitic stainless steels (ASS) grades have strong corrosion resistance in mildly corrosive acid, industrial and marine environments than other materials such as brass, bronze or galvanised steel. Among the ASS grades, AISI 316 stainless steel is safe to seawater. This paper describes the efficiency and enhancement of the performance of stainless steel in a marine environment. Plasma arc welding has been used for joining AISI 304 and 316 stainless steels and observed the microstructures of the welded joints. Corrosion resistance test has been used to determine the corrosion rate of the welded steels. Using Tafel plot curve the corrosion rate has been analysed, for the three types of samples for which AISI 316 has very less corrosion rate when compared to AISI 304 and the welded joint of both AISI 316 and 304.
... According to OMAR [33], these discontinuous and hard zones primarily along the fusion line can often lead to inservice failures, once they may cause the dissimilar weld to be susceptible to localized pitting corrosion attack, hydrogen embrittlement and sulfide stress cracking. These zones are usually associated with the presence of high-hardness martensite (higher than 400 HV) [8,29,30,[34][35][36] and can promote a deleterious influence on the corrosion resistance of dissimilar metal welds for sour service. Although the occurrence of PDZ ( Figure 3) and grain boundaries of Type II have been observed (Figure 4), no evidences of cracking or disbonding were verified. ...
Nickel-based weld overlays (cladding) are commonly used in oil & gas industry to extend the life of equipment under corrosive environment, as it improves the corrosion resistance without a significant increase in the manufacturing cost, when compared to a full nickel-based alloy equipment. Although there are extensive literature involving overlays applied by SMAW, GMAW or GTAW processes, works about the use of FCAW process are limited. Consequently, an investigation of the performance of the overlays deposited by this process, which provides a higher productivity in comparison to the processes usually used, can be an interesting option for this application. The present work evaluates the mechanical and microstructural properties of the nickel-based superalloy 625 weld overlay deposited on a ASTM A516 Grade 70 carbon steel plate by the flux cored arc welding process (FCAW), both in as welded and heat treated conditions. Bending and microhardness tests were performed in order to verify possible effects of welding thermal cycles on the mechanical properties. The microstructure was evaluated through both optical (OM) and scanning electron microscopy (SEM), with the use of electron backscatter diffraction (EBSD) technique. Corrosion tests were conducted on samples removed from the top layer of the weld overlay according to ASTM G 48 Method A. All results obtained with this welding process, in both as welded and heat treated samples, were considered satisfactory.
... Esse resultado é parecido ao mostrado na Figura 6a para a condição como soldado. Por se tratar de uma região de transição, resultante da mistura incompleta de materiais, a ZPD apresenta gradientes significativos de composição química [17]. A normalização não alterou a ZPD sob o ponto de vista da microestrutura. ...
Resumo O propósito deste trabalho é comparar as mudanças na microestrutura e na dureza de um tubo de aço API 5L X-52, revestido internamente por soldagem com Inconel 625, após a execução dos tratamentos térmicos de normalização a 1100 °C por 60 min. e resfriamento ao ar, e de solubilização a 1030 °C com aquecimento por indução eletromagnética por 30 s. e resfriamento em água. Foram utilizadas técnicas de microscopia ótica (MO) e eletrônica de varredura (MEV), análise por espectroscopia de energia dispersiva (EDS) e dureza Vickers. Na condição como soldada, o metal de base (MB) teve na zona termicamente afetada (ZTA) a formação de zona de grãos grosseiros (ZGG) com dureza média de 234 HV. A zona parcialmente diluída (ZPD) se apresentou clara, sem contornos de grãos, com alto teor de ferro e dureza média de 370 HV, indicando ser constituída de martensita. No revestimento, a microestrutura é austenítica dendrítica com formação de carbetos de Nb e indícios da presença da fase Laves, com dureza média de 287 HV em suas camadas. Na condição após normalização, a ZTA foi suprimida e houve refino na microestrutura do MB; a ZPD foi mantida com sua morfologia original, porém com redução de cerca de 15% em sua dureza; no revestimento, a microestrutura tornou-se granular, com indício da dissolução da fase Laves e redução de sua dureza de cerca de 26%. Na condição após solubilização, a ZTA do MB foi eliminada, a ZPD manteve sua morfologia e microestrutura original, mas reduziu sua dureza em cerca de 30%; no revestimento, a microestrutura e precipitados foram mantidos, mas houve uma redução da dureza em cerca de 20%. Por fim, este trabalho conclui que ambos os tratamentos térmicos foram considerados benéficos às propriedades do tubo de aço API 5L X-52 revestido internamente com Inconel 625. Promoveram a homogeneização da microestrutura e a redução de dureza na ZTA do MB, significativa redução da dureza na ZPD e, nas camadas do revestimento, a redução e adequação da dureza às normas técnicas pertinentes, possibilitando assim a sua utilização em ambientes agressivos, principalmente na indústria offshore de petróleo e gás.
... A descoberta dos campos do pré-sal indicou a existência de fluidos ainda mais agressivos aos materiais até então utilizados. Altas concentrações de gás carbônico e ácido sulfúrico presentes nos fluidos mostraram a necessidade de desenvolver novos materiais e novas técnicas [1]. Dentro desse contexto, a técnica de revestimento por soldagem vem sendo amplamente utilizada, pois ela é capaz de prover uma maior resistência a corrosão aliada a uma boa resistência mecânica [2]. ...
... Satyanarayana et al. [2] mentioned that joining of ferritic stainless steels was facing problem of coarse grains in weld zone and heat affected zone of fusion weld where as austenitic stainless steels are easy weld materials. Joining of dissimilar F/A materials is not an easy task; it is considered to be a challenging problem due to differences in thermal conductivities and thermal expansion which may cause crack formation interface [25,26]. ...
To study and analyze the effects of welding parameters: welding current, gas flow rate and nozzle to plate distance, on ultimate tensile strength (UTS) and Yield Strength (YS) in MIG welding of AISI409 ferritic stainless steel to AISI 316L Austenitic Stainless Steel materials. Experiments have been conducted as per L9 orthogonal array of Taguchi method. The observed data of UTS and YS have been interpreted, discussed and analyzed with use of Taguchi Desirability analyses.
... He observed base-metal-like beaches and islands on the carbon steel side of the weld. Omar [12] also welded carbon steel to stainless steel and observed beaches, peninsulas and islands on the carbonsteel side. The formation of these macrosegregation features was not understood. ...
Solute segregation on a macroscopic scale in a weld between two dissimilar metals or alloys has long been recognized, but fundamental understanding of macrosegregation in dissimilar-metal welding is still lacking. Two mechanisms for macrosegregation were proposed based on the liquidus temperature of the bulk weld metal, TLW, relative to the liquidus temperature of metal 1, TL1, and the liquidus temperature of metal 2, TL2. According to the mechanisms, two distinctly different macrosegregation features can form. A “peninsula” of an unmixed metal 1 can form if TLW < TL1. On the other hand, a “beach” of unmixed metal 2 irregular in shape can form if TLW > TL2. To verify the mechanisms, a pure Cu sheet was butt welded to a low carbon steel sheet by gas-tungsten arc welding without a filler metal. Composition measurements were conducted inside and across the weld metal. A peninsula of unmixed steel and an irregular-shaped beach of unmixed Cu were observed, which verified the mechanisms. In addition, the bulk weld metal exhibited a layered structure caused by undercooling of the bulk weld pool into a metastable miscibility gap in the Cu-Fe phase diagram. Macrosegregation in previous studies on laser- and electron-beam welding of Cu to steel or stainless steel was discussed in light of the findings in the present study.
... A descoberta dos campos do pré-sal indicou a existência de fluidos ainda mais agressivos aos materiais até então utilizados. Altas concentrações de gás carbônico e ácido sulfúrico presentes nos fluidos mostraram a necessidade de desenvolver novos materiais e novas técnicas [1]. Dentro desse contexto, a técnica de revestimento por soldagem vem sendo amplamente utilizada, pois ela é capaz de prover uma maior resistência a corrosão aliada a uma boa resistência mecânica [2]. ...
Resumo Este trabalho tem como objetivo realizar uma análise comparativa das propriedades de revestimentos soldados com a liga INCONEL 625 sobre o aço ASTM A516 grau 70 obtidos pelos processos eletrodo revestido e arame tubular. Para tanto, foram realizados ensaios de mecânicos, metalográficos e de corrosão nos revestimentos obtidos. A análise metalográfica evidenciou a presença de precipitados ao longo do metal de solda obtido pelo processo arame tubular, não sendo verificada esta ocorrência para o processo eletrodo revestido. Os ensaios mecânicos mostraram resultados satisfatórios para ambos os processos. Os ensaios de corrosão realizados em conformidade com a norma ASTM G48 não evidenciaram a ocorrência de pites e a perda de massa foi satisfatória para ambos os processos. Baseado nos resultados obtidos pode-se inferir que ambos os processos de soldagem se mostraram adequados para a deposição de revestimentos com a liga INCONEL 625. Abstract This paper aims to conduct a comparative analysis of INCONEL 625 alloy weld overlay's properties on ASTM A516 grade 70 steel obtained by flux cored arc welding (FCAW) and shielded metal arc welding (SMAW). Therefore, mechanical, metallographic and corrosion tests were performed in the studied weld overlays. Metallographic examinations revealed the presence of precipitates over the weld metal obtained by the FCAW process. Those precipitates were not observed for the SMAW process. The mechanical tests showed satisfactory results for both processes. The corrosion tests conducted in accordance with ASTM G48 showed no occurrence of pits and the loss of mass was satisfactory for both processes. Based on the results in the resent work, it can be concluded that both welding processes are suitable for the weld overlay of the INCONEL 625's alloy.
... This will affect seriously in low toughness and ductility [2,3]. It was reported [4][5] that welding of ferritic to austenitic stainless steels is considered to be a major problem due to difference in coefficient of thermal expansion, which may lead to crack formation at the interface, formation of hard zone close to the weld interface, relatively soft regions adjacent to the hard zone; large hardness difference between the hard and soft zones would also persist in this type of joints. Research work has been carried out on the dissimilar welding of ferriticaustenitic stainless steel using Electron Beam Welding (EBW), Friction Welding (FW) and GTAW processes by Reddy et al. [4], CO2 laser beam welding by Anawa et al. [7]. ...
In this present investigation, a comparative analysis is made to examine the microstructure and mechanical properties of Gas Tungsten Arc (GTA), Pulsed Current Gas Tungsten Arc (PCGTA) welded dissimilar ferritic stainless steel (AISI 430) and austenitic stainless steel (AISI 304) using E309L filler material. Tensile tests on the dissimilar weldments reveal that the fracture occurred at the parent side of AISI 430. Hardness measurements showed that PCGTA weldments show higher hardness values as compared to the GTA weldments. Cyclic hot corrosion studies were conducted on the various zones of the GTA and PCGTA weldments at 600 °C in the aggressive molten salt environment containing Na2SO4 -60% V2O5. The hot corrosion products were investigated using the combined techniques of SEM/EDAX analysis.
... Though not shown, "islands" different from the bulk weld metal in composition have been observed near the fusion boundary by other investigators (Refs. 76,77). How peninsulas and islands form has not been explained so far. ...
Fluid flow and solidification during welding dominate the fusion zone of the resultant weld, including its shape, microstructure, properties, and defects. Fundamental research conducted at the University of Wisconsin led to the first demonstrations of the following things in four different areas. The first area, fluid flow in welding, includes: 1) computer models capable of calculating the weld-pool shape and showing how weld-pool fluid flow affects the pool shape, including Marangoni flow driven by surface-tension gradients along the pool surface, 2) visualization of Marangoni flow in simulated weld pools, including its reversal by the surface-active agent and its oscillation, and 3) a theory on the effect of the surface-active agent on pool-surface deformation, pool-surface oscillation and ripple formation as well as weld penetration. The second area, solidification in the fusion zone, includes 1) quenching of the weld pool and its surroundings to reveal the microstructure development, microsegregation, and nucleation mechanisms during welding, e.g., with liquid Sn for stainless steels and water for Al alloys, and 2) suppression of solidification cracking with a wavy crack path, as demonstrated by transverse magnetic arc oscillation in welding of Al sheets. The third area, solidification in the partially melted zone (PMZ), includes: 1) weakening of the PMZ by severe grain-boundary segregation caused by planar solidification of the grainboundary liquid, as demonstrated in arc welds of high-strength Al alloys, and 2) prediction and elimination of the susceptibility of Al alloys to liquation cracking, i.e., cracking in the PMZ along grain boundaries where liquid formation (i.e., liquation) occurs. The fourth area, solidification with dissimilar filler metals, includes 1) fundamental concepts in welding with dissimilar filler metals, including non isothermal pool boundaries and quick freezing of one liquid metal in another to cause macrosegregation, and 2) macrosegregation mechanisms based on the concepts to explain the formation of beaches, peninsulas, and islands different in composition from the bulk weld metal (i.e., bulk fusion zone).
... Hence, dissimilar metal welding is the matter of interest owing to their technical and economical potentials. [4][5][6][7][8][9][10][11] In power generation applications, the boiler and heat exchangers operating at low temperature and less corrosive environment permit the use of inexpensive CS, whereas the super heaters and re-heater areas operating at high temperatures and high corrosive areas require the use of austenitic stainless steel. 10 A dissimilar metal weld (DMW) must be made at the transition region between CS to SS. ...
This research work focuses on comparison of the weld geometry, distortion, microstructure and mechanical properties of thin SS 304 L sheets (0.8 mm thickness) welded using micro-plasma arc welding and tungsten inert gas welding process. Initial experiments were performed to identify suitable processing parameters for micro-plasma arc welding and tungsten inert gas welding processes. Microstructures of welds were analysed using scanning electron microscopy, X-ray diffraction and energy dispersive spectroscopy. The results indicate that the joint produced by micro-plasma arc welding exhibited higher tensile strength, higher ductility, smaller dendrite size and a narrow heat affected zone. Samples welded by micro-plasma arc welding process had lower distortion as compared to that welded by tungsten inert gas process. Micro-plasma arc welding was shown to be the suitable process for welding of thin 304 L sheets owing to its higher welding speed and better weld properties as compared to the tungsten inert gas welding process.
... Hence, dissimilar metal welding is the matter of interest owing to their technical and economical potentials. [4][5][6][7][8][9][10][11] In power generation applications, the boiler and heat exchangers operating at low temperature and less corrosive environment permit the use of inexpensive CS, whereas the super heaters and re-heater areas operating at high temperatures and high corrosive areas require the use of austenitic stainless steel. 10 A dissimilar metal weld (DMW) must be made at the transition region between CS to SS. ...
This research aims to optimize the process parameters of plasma arc welding for welding of dissimilar metals: austenitic stainless steel SS-304 L and low carbon steel A-36. It investigates the effect of welding current and welding speed on the quality of the welded joints. The quality characteristics like bead geometry, microstructure, hardness, ferrite measurement and tensile test are considered for qualification of the welded samples. Welded specimens were prepared both with and without filler material. These specimens were mechanically tested and analyzed using metallographic techniques. Based on the results, suitable welding parameters were found to be 45 A and 2 mm/s for samples prepared with and without filler wire. An all-martensitic weld zone structure was obtained for direct fusion. However, a complex heterogeneous microstructure was obtained by using austenitic stainless steel filler wire E 309 L. Hardness of directly fused sample was observed to be significantly higher compared to filler wire sample.
... Hence, dissimilar metal welding is the matter of interest owing to their technical and economical potentials. [4][5][6][7][8][9][10][11] In power generation applications, the boiler and heat exchangers operating at low temperature and less corrosive environment permit the use of inexpensive CS, whereas the super heaters and re-heater areas operating at high temperatures and high corrosive areas require the use of austenitic stainless steel. 10 A dissimilar metal weld (DMW) must be made at the transition region between CS to SS. ...
... Nevertheless, when the Ni-based alloys are used as a filler metal, it is frequently suggested to use a maximum interpass temperature, which is specified according to the literature for minimizing the dilution, reducing the secondary phase precipitation, minimizing the excessive grain growth and reducing the tendency to solidification and liquation cracking, as well as other metallurgical changes that can result in the loss of corrosion resistance and also reduce the mechanical properties [4]. ...
The purpose of this study is to evaluate the effectiveness in the contribution of the interpass welding in the microstructures and properties of the dissimilar fusion zones produced with an alloy 625 and API 5L X65 steel pipes. Three multipass welded joints with v-groove, were made under the same welding parameters, therefore, changing only the interpass temperatures at: 150°C, 250°C and 450°C. The microstructural characterization was performed using the light microscopy and the scanning electron microscopy (SEM). The hardness test, charpy-V impact test and the transverse tensile test were conducted according to specific standards. The results have shown that all ruptures in the tensile tests occurred in the base metal. Both yield strengths and ultimate tensile strengths, have dropped to the 450°C interpass temperature. It was also observed a slight drop in the hardness with increasing interpass temperature. The Charpy-V impact test results showed no significant differences among the interpass temperatures. These said results indicated that the maximum interpass temperature for the alloy 625/X65 steel dissimilar welding is limited by the steel properties.
The connecting of contrasting metals, namely double stainless steel to steel made of carbon, has taken place. performed using a hybrid welding system. A TIG and MIG welding joining based hybrid joining method was designed. The microstructures of the dissimilar metal joints were studied and the grains are coarser as contrast to the use of a single the welding process process by itself. With the addition of TIG welding to the process of MIG welding, the water-holding capacity of the metal in molten state pool is significantly improved. The nominal corrosion behaviour of the weldments was found better than the single arc welding system alone. The passivation behaviour of the joints was in the similar line to that of double stainless steel base metal. The pitting resistance of the joints in 1 M NaCl solution was inferior to the base metals.
The Co-based alloy/AISI 410 stainless steel dissimilar welded joint was fabricated by the electron beam welding (EBW) technique. The anomalous microstructure containing the element transition zone (ETZ) and/or core of tail-like zone (CTLZ) is in the weld metal (WM) adjacent to the fusion line. The melting temperature difference between the WM and AISI 410 steel, melt stirring effect and element diffusion can trigger the formation of such anomalous microstructure. In particular, the larger distance of the region in WM away from the fusion line, the smaller CTLZ and larger ETZ occurred. Compared with the fine and ellipsoidal precipitates in the as-welded CTLZ, a large number of chain-type clustered precipitates were detected in the CTLZ and ETZ interface after the aging treatment at 566 °C for 1 000 h. The element diffusion under elevated temperature in WM is regarded as the crucial factor for such anomalous microstructure evolution during the aging treatment.
This study investigates the effects of ER308L butter layer on the microstructure and mechanical properties of API 5L X65/dissimilar joint. High strength low alloy API 5L X65 and AISI 304 steel grades are widely used in a wide range of industrial applications, and more specifically in the oil and gas sector. Dissimilar welds between API 5L X65 pipeline and austenitic stainless steel joints have long been used in the oil/gas and petrochemical sectors. Using buttering layer to improve properties of these types of dissimilar joints has lately received significant attentions. In the present work, the ER308L butter layer was applied on the API 5L X65 side through gas tungsten arc welding, followed by a stress-relief heat treatment at 600 °C. Buttered API 5L X65 samples were welded to AISI 304 samples through gas tungsten arc welding in 5 passes. Microstructures of joints were evaluated by scanning electron microscope (SEM) and optical microscope (OM). Mechanical properties were also assessed by tensile, impact, and Vickers micro-hardness tests. Fractography and phase identifications were carried out using SEM and energy dispersive spectroscopy (EDS). Results showed that a martensite layer on the fusion zone with a thickness of about 30 μm was observed at the interface of API 5L X65/butter layer. It appears that compositional changes played a significant role in the formation of martensitic structures and type-II grain boundaries. Results also showed that the fracture positions in both heat treated and as-welded samples were in the heat affected zone (HAZ) of API 5L X65. The implications of buttering and post-buttering stress-relief heat treatment for the microstructure and mechanical properties are comprehensively discussed.
In the recent times the power of the industry standard materials has gained a lot with the advancement in technology. To run the power plants at a required temperature and pressure, the demand for the material with high strength, high thermal conductivity and high corrosion resistance increased significantly. The large number of materials that are mostly used in power plants which are operating at high temperature and high pressure are creep strength enhanced steels, nickel based alloys and austenitic stainless steels. To fulfill and to satisfy the strength requirements, lower cost investment and service conditions, dissimilar welding between Stainless steels is required. And here we can see how important is the need joining dissimilar metals in such cases. A successful joining of two dissimilar metals is as strong as the weaker of the two metals being joined using different welding techniques, i.e., having enough and sufficient tensile strength and ductility so that the joint will not fail in the weld. These joints can be used in a variety of different metals and by several welding processes. The filler material and both metals need to be evaluated before choosing the best way to connect the metals. Here the welding process done between steels is TIG welding. Challenges in the current research are to join the different materials without disturbing the properties of parent metals. Some of the frequently occurring problems are: wider HAZ (heat affected zone), Difference in coefficient of thermal expansions, Difference in chemical composition, Multipass welds to weld high thickness materials. Current research deals with the Optimization the TIG Welding Process Parameters using RSM (Response surface Methodology) and To Understand the effect of Process Parameters on Mechanical Characteristics of the dissimilar joints and to carry out Numerical Investigation on the dissimilar welding of Ferritic Stainless Steel by joining the different materials using tungsten inert gas welding.
In this paper, the solid-state welding and fusion welding of high-entropy alloys (HEAs) were reviewed. For solid-state welding of HEAs, the influence of microstructure change and welding parameters on properties of welded joints were discussed. For fusion welding of HEAs, the application of laser welding, electron beam welding and gas tungsten arc welding was analyzed. Then relevant welding mechanisms, solidification behavior of grains, and phase formation in fusion welding of HEAs were discussed. The methods optimizing properties and microstructure of welded joints were discussed, including the adjustment of parameters, usage of pre-welding heat treatment and post-welding heat treatment, as well as the application of metallic interlayers in dissimilar welding of HEAs. The application of numerical simulation in HEAs welding could facilitate the optimization of experimental parameters. In addition, HEAs have been applied as coatings to improve the properties and life of materials based on welding methods, and the application of HEAs fillers in welding was also achieved. In the future, molecular dynamics simulation can be applied to analyze the atomic diffusion and stress distribution in HEAs welding, and there are still many aspects that need to be explored in the field of HEAs welding.
Effect of inter-pass temperature on the microstructure evolution and mechanical properties of AISI 430 ferritic stainless steel welded by autogenous tungsten inert gas (TIG) technique was investigated. The relationship between the structure and the property of the weldments with inter-pass temperature and without inter-pass temperature is elaborated in this study. Microstructure studies depicted the presence of martensite in the weld metal and some parts of the heat affected zone (HAZ). Increasing inter-pass temperature resulted in higher amount of martensite both in the weld metal and in the HAZ. In addition, high inter-pass temperatures resulted in large HAZ width and grain growth which in turn led to poor tensile strength and ductility of the weldments. An optimum inter-pass temperature of 150 °C provided the best mechanical properties. However, it was inferred that when it is not possible to have a precise control on inter-pass temperature during manufacturing AISI 430 joints, it is better to complete welding without applying inter-pass temperature in order to at least keep tensile strength and ductility of the weldments.
The purpose of the study is to predict deformation of a weldment in dissimilar laser welding process of low carbon steel and stainless steel 304 based on numerical and computation simulation approach. Different characterization of material on heat expand result influent distortion direct. The temperature rated effect of welding process direct to low carbon steel that caused heat expansion value of stainless steel 304 less than low carbon steel. Computer simulation or finite element model (FEM) used to understand the response and behavior of weldment during the welding process. Thermal expansion of weldment often leads to thermal stress in the weldment. The resulting temperature distribution, heat flux distribution and structural response under arc current welding constitute knowledge in assuring design success of welding product. The calculation results used FEM shows heat rated direct to low carbon area and high distortion occur there. Stainless steel with low expansion value has slow heat rated expansion and low distortion.
The gradient microstructure occurring adjacent to fusion interface of dissimilar metal between high Cr steel and nickel-based Alloy 617 was characterized in detail, and its formation mechanism was discussed in this paper. The island-like and peninsula-like structures present various characters due to difference in elements mixing during welding process. It is found that an unmixed zone (UMZ), a partial mixed zone (PMZ) with lamellar structure and a transition zone (TZ) together make up island-like gradient microstructures. In UMZ, the tempered martensite with much finer equiaxed grains was the main microstructure. In PMZ, nickel-deficient ferrite as the dendritic core, which is separated by nickel-rich fresh lath martensite in interdendritic region, lead to the lamellar structure. The formation of fresh martensite showed phase transition happened under post weld heat treatment (PWHT), which is also verified by the higher nanohardness. In TZ, the occurrence of carbide-free ferrite indicates the carbon diffusion was inhibited by the reaustenitization of TZ. It is also found that the formation of gradient microstructure has close relationship with the angle (θ) between tangents of fusion line and the interface of multi-layer, it is easier to form gradient microstructure as θ > 0 due to complex fluid flow of steel. So, suitable design of multi-layer in weld could help in controlling the formation of this kind of gradient microstructure.
Modern and future power plants will use more complex materials to withstand the higher steam temperatures and pressures as well as thermal cycling. As such, dissimilar metal welds (DMWs) will be more widespread in new design than before and will need to demonstrate resistance to combinations of severe creep, corrosion/oxidation, and low cycle fatigue. The DMWs between different steels or alloys are an underestimated topic. Experienced and documented premature failures reveal the criticality of DMWs. This study focused on the DMWs between 9Cr martensitic creep strength enhanced ferritic steels and advanced austenitic stainless steels. Two collaborative projects related to 18%Cr and 25%Cr austenitic creep resisting stainless steel delivered data concerning base metal characterization and weldability of similar and dissimilar welding. The specific features of dissimilar welding are further approached in more detail in this analysis. Two main methodologies, i.e., direct welding and buttering techniques using different filler metals were investigated and characterized via uniaxial creep rupture testing and metallographic examination particularly focusing on the fusion line carbide formation and morphology. For the limited exposure times of 10 kh in this project, the results show that aligned and coarse type I carbide formation is occurring at the 9Cr fusion line between A617 type weld metal. The selection of P87 or A82 type filler metals demonstrated isolated to partly aligned carbides, respectively, at the fusion line. To mitigate the risk to corrosion and achieve a marginal increase in creep performance, buttering techniques are recommended.
The forged low-alloy steel and weld consumable used in this study have compositions that differ enough to create a significant concentration gradient adjacent to the weld interface following welding. The major compositional differences between base metal and weld, respectively, are 3.4 vs. 0.95 wt-% Ni, 1.75 vs. 0.1 wt-% Cr, and 0.25 vs. 1.4 wt-% Mn. This study measures the concentration gradients and models their development based on the mass transport processes during solidification and cooling of the weld, which occurs over a time period of only about 5 s. The composition of the base metal heat-affected zone is altered by diffusion adjacent to the weld interface. Nickel and chromium diffuse out, and manganese diffuses in, where the extent is predicted by a simple diffusion model. In the weld metal, local maxima in nickel and chromium are attributed to unmixed zones that detach from the base metal but are not fully dissolved into the weld pool. These compositional maxima occur within 75 μm of the weld interface and are intermittent. Both compositional and microstructural evidence exists for these localized regions. The composition in the weld adjacent to the weld interface influences the fracture behavior, where the unmixed regions are susceptible to inter-granular fracture.
Filler metals different from the base metal in composition called dissimilar filler metals, are often used to reduce cracking or develop desired weld-metal properties. Macrosegregation can occur in welds made with dissimilar filler metals and degrade the weld quality. Macrosegregation can occur near the fusion boundary. Two different mechanisms have been proposed recently for such macrosegregation: Mechanism I for TLW < TLB and Mechanism II for TLW > TLB, where TLW is the liquidus temperature of the bulk weld metal and TLB that of the base metal. These mechanisms can result in two distinctly different forms of macrosegregation. With Mechanism I, a filler-deficient beach can form along the fusion boundary, and it is often discontinuous. Filler-deficient peninsulas and islands can also form, and they are often roughly parallel to the fusion boundary. With Mechanism II, on the other hand, a filler-deficient beach can form along the fusion boundary, and it is often continuous and intruded by the weld metal. These mechanisms were verified with welds of Al-Si and Cu-Ni made with dissimilar filler metals by gas-metal arc welding.
A hard region known as the unmixed zone (UMZ) occurs during gas-tungsten arc (GTA) welding of 304 austenitic stainless steel to A36 steel using 308L filler/wire. This zone lowers the fracture toughness of the weldments, thus it should be eliminated from the weld. The formation of this zone is due to stagnant liquid film at the fusion boundary (FB) of the A36 base metal (BM) in the fusion zone (FZ). By increasing the buoyancy force (g-level) in the weld pool using a centrifuge (MGRWS), the size of the UMZ can be decreased significantly. The reduction in the size of the UMZ is due to enhanced convection in the weld pool, which produces a more efficient mixing and dilution in the FZ. In addition, the increase in the buoyancy force increases the cooling rate in the weld zone, decreases the size of the A36 heat-affected zone (HAZ), but does not affect the hardness of the UMZ. The tension test results, show that the fracture occurs in the BM/HAZ of the A36 at all g-levels.
Duplex stainless steel (DSS) SAF2205 and micro-alloyed steel X65 were welded by metal inertia gas welding (MIG) with ER2209 welding wires, and the welded joints have good mechanical properties. The type II boundary close to the fusion line at the micro-alloyed steel side was observed by SEM. Obvious concentration gradients of Ni and Cr exist in the region between the two boundaries, where the hardness is much higher. The mechanical properties of the welded joints were investigated by using smooth and notched tensile test and low temperature impact test, and the polarization curves of different weld regions were also tested in 1 mol·L-1 NaCl solution. The notched tensile strength and impact toughness of the welded metal are lower than those of DSS base metal, but the corrosion potential is higher. The mechanical properties of X65 heat-affected zone (HAZ) is as good as the base metal and the corrosion potential is higher.
Demands placed on dissimilar metals joints have increased from various viewpoints, such as, environmental concerns, energy saving, high performance, cost saving and so on. The aim of this manuscript is to predict and optimize laser welding of some economically important dissimilar materials in industry through applying a Taguchi orthogonal array design as a design of experiment (DOE) approach to design the experiments, develop mathematical models and optimize the welding operation. This was achieved by controlling selected welding parameters; laser power, welding speed and focus position, to relate the mechanical properties and weld bead geometry to the selected input welding parameters. The dissimilar materials studied in this work were low carbon steel and stainless steel. For the studied dissimilar welded material, mathematical models were developed to predict the required responses. Furthermore, the study of dissimilar were optimized by determining the best combinations of input process parameters in order to produce an excellent weld quality.
Dissimilar metal welds between ferritic and austenitic alloys are used extensively in power plants. Premature failure of such welds can occur below the expected creep life of either base metal. This article reviews microstructural evolution in dissimilar welds and describes factors that contribute to premature failure. The microstructure in the as welded condition consists of a sharp chemical concentration gradient across the fusion line. Martensite forms within this gradient due to high hardenability and rapid cooling rates from welding. Upon aging, carbon diffuses down the chemical potential gradient from the ferritic steel toward the austenitic alloy. This can lead to formation of a soft carbon denuded zone in the ferritic steel, and nucleation and growth of carbides in the austenitic steel that produce high hardness. These differences in microstructure and hardness occur over distances of about 50–100 μm. Failure is attributed to the steep microstructural and mechanical property gradients, the large difference in coefficient of thermal expansion, formation of interfacial carbides that promote creep cavity formation, and preferential oxidation of the ferritic steel. Information is also provided on available creep rupture properties, remaining life estimation techniques, current best practices and research in progress.
Dissimilar-metal welding refers to the joining of two different alloy systems. Actually all fusion welds are dissimilar-metal welds (DMWs) because the metals being joined have a wrought structure and the welds have a cast structure. Frequently the matching-composition filler metal is deliberately altered from that of the base alloys. For this discussion a dissimilar-metal weld will be that between metals of two different alloy systems. In dissimilar-metal welding, the properties of three metals must be considered: the two metals being joined and the filler metal used to join them. The development of a DMW procedure often requires more study than for a conventional, similar-metal welding procedure. The nickel-containing stainless steels, nickel- and copper-base alloys are readily fusion welded to carbon and low alloy steel and to each other. Methods are described to estimate the weld metal composition of DMWs. Knowing the composition, weld properties can be predicted for a wide range of DMWs. In establishing a DMW procedure, the more restrictive requirements for each base metal (such as preheat, temperature control, weld heat treatment, etc.) should be used. On occasion, there will be a conflict that needs special study and testing.