Search Results (82)

To address the issues of hydrogen embrittlement, creep, and fatigue that commonly occur in the welds of hydrogen production reactor operating under hydrogen exposure, high temperature and high pressure, this study proposes adding Si and Mo as reinforcing elements to the welding materials to enhance weld performance. Given the varying performance requirements of different weld layers in the stacked weld, a gradient performance optimization method for the stacked weld of hydrogen production reactors based on the response surface methodology (RSM)–genetic algorithm (GA) is proposed. Using tensile strength, the hydrogen embrittlement sensitivity index, fatigue strain strength, creep rate and weld performance evaluation indices, a high-precision regression model for Si and Mo contents and weld performance indices was established through RSM and analysis of variance (ANOVA). A multi-objective optimization mathematical model for gradient improvement of the stacked weld was also established. This model was solved using a GA to obtain the optimal element content combination added to the welding wire and the optimal weld thickness for each weld layer. Finally, submerged arc welding experiments of the stacked weld were conducted according to the optimization results. The results show that the tensile strength of the base layer, filling layer and cover layer of the stacked weld increased by 5.60%, 6.16% and 4.53%, respectively. Hydrogen embrittlement resistance increased by 70.56%, 52.40% and 45.16%, respectively. The fatigue and creep resistance were also improved. The experimental results validate the feasibility and accuracy of the proposed optimization method. Full article

Reasonable welding methods are of great significance for optimizing the microstructure and ensuring the mechanical properties of welded joints. In this study, ultra-narrow gap welding (UNGW) and submerged arc welding (SAW) were employed to weld Q355E high-strength low-alloy (HSLA) steel thick plates, and the microstructure and mechanical properties of the welded joints were systematically characterized. The UNGW welded joint exhibits superior comprehensive mechanical properties: a room-temperature tensile strength of 664 MPa with 43.1% elongation at fracture, along with higher microhardness and enhanced impact performance at −40 °C, all of which significantly outperform SAW welded joints. This advantage primarily stems from the faster cooling rate during UNGW, which promotes the formation of beneficial acicular ferrite in the joint microstructure. This study provides theoretical support and technical guidance for welding HSLA steel thick plates. Full article

The mechanical properties of surfacing layers are significantly affected by the precipitation and evolution of carbides in nickel-based alloys. At present, the study of carbide precipitation in a Ni-Cr-B-Si surfacing layer is described by using the phase field method. In this paper, the true Gibbs free energy of the M₂₃C₆ carbide phase in Ni-Cr-C ternary alloy was established by the CALPHAD method and thermodynamic database. The growth and coarsening process of M₂₃C₆ carbide was simulated based on phase field method. The microstructure of M₂₃C₆ carbide of Ni-Cr-C alloy at 1373 °C isothermal aging time was observed by scanning electron microscope (SEM). The results show that the growth and coarsening of the precipitated M₂₃C₆ carbide phase are undergone through multiple processes during isothermal aging. First, a single precipitate core is formed, and then the single precipitate continues to coarsen and grow, forming a lamellar structure. Two precipitates contact to form a single rod-like structure, and multiple precipitates form slender rod-like structures. Finally, the contacting elongated rod-like structures grow, forming a typical layered eutectic carbide. The precipitation behavior, growth, and coarsening process of M₂₃C₆-type carbides in Ni-Cr-B-Si series alloys are explored through phase field simulation and experimental research in this paper. A theoretical basis is provided for the rational control and distribution of carbides in surfacing layers. A reference is also offered for optimizing the nickel-based superalloy materials used for surfacing the surface of descaling rolls. Full article

Fracture toughness is an important index related to the service safety of marine risers, and weld is an essential component of the steel catenary risers. In this paper, microscopic structure characterization methods such as scanning electron microscopy (SEM) and electron back scatter diffraction (EBSD), as well as mechanical experiments like crack tip opening displacement (CTOD) and nanoindentation, were employed to conduct a detailed study on the influence of the microstructure characteristics of multi-wire submerged arc welded seams of steel catenary riser pipes on CTOD fracture toughness. The influence mechanisms of each microstructure characteristic on fracture toughness were clarified. The results show that the main structure in the weld of the steel catenary riser is acicular ferrite (AF), but there is also often side lath plate ferrite (FSP) and grain boundary ferrite (GBF). With the increase in the proportion of FSP and GBF in the weld microstructure, the CTOD fracture toughness of the weld decreases gradually. The weld AF is a braided cross arrangement structure, and most of the grain boundary orientation difference is higher than 45°. The effective grain size refinement of AF can effectively prevent crack propagation and significantly improve fracture toughness. GBF is distributed along proto-austenitic grain boundaries PAGB, and the large hardness difference between the GBF and the AF matrix weakens the grain boundary. Cracks can easy be initiated at the interface position of the two phases and can propagate along the GBF grain boundary, resulting in the deterioration of toughness. Although the hardness of FSP is between that of GBF and AF, it destroys the continuity of the overall weld microstructure and is also unfavorable to toughness. Full article

Fast high-temperature gas-phase reactions occurring in the limited space of the arc cavity in the submerged arc welding (SAW) process limit the study of specific gas-phase behaviours. A low-temperature experimental method is applied to investigate gas-phase reactions in the reaction of oxy-fluoride slag with Al-Fe-Ni metal powders. The presence of nano-strands in the slag cavities confirms the vaporisation and re-condensation of gasses. Ti is the main element in nano-strands, although some nano-strands also contain Al-Mg-Si-Na oxy-fluoride. Nano-strand end-caps contain Mn-Fe-Si fluoride, and some contain Ni. The Ni in nano-strand end-caps is sourced from the added Ni powder and indicates gas-phase transfer. The Ti in the nano-strands is sourced from the flux. Themochemistry calculations identify KAlF₄, TiF₃, NaAlF₄, SiF₄, AlF₃, SiF₃, and Na in the gas phase. Increased Al reaction results in decreased TiF₃ in the gas phase, likely due to the displacement of Ti from TiF₃, resulting in the gas-phase transfer of Ti from the flux. Comparative diffusion flux calculations support Ti nano-strand formation via the vaporisation of TiF₃ and the re-condensation of Ti. The low-temperature simulation experiment applied here can be used to study the gas reaction behaviour in the reaction of oxy-fluoride flux with metal powders. Full article

This study investigates the effects of heat input on the microstructure and fracture toughness of SAW (Submerged Arc Welding) joints with K-groove and X-groove weld preparations using S460NL steel. Microstructural analysis focused on acicular ferrite, grain boundary ferrite, and MA (Martensite–Austenite) constituents to assess their influence on CTOD (Crack Tip Opening Displacement). The results indicate that the K-groove achieved a higher CTOD value of 0.82 mm compared to 0.13 mm for the X-groove, attributed to differences in microstructural composition and cooling rates. The findings highlight the impact of groove geometry and heat input on weld performance. Full article

Forging additive hybrid manufacturing integrated the high efficiency of forging and the great flexibility of additive manufacturing, which has significant potential in the construction of reactor pressure vessels (RPVs). In the components, the heat-affected zone (HAZ, also called as bonding zone) between the forged substrate zone and the arc deposition zone was key to the final performance of the components. In this study, the Mn-Mo-Ni welding wire was deposited on the 16MnD5 substrate with a submerged arc heat source. The in situ reheat cycle effect of the submerged arc heat source on the microstructure and mechanical properties of the HAZ were studied. The results showed that the HAZ underwent four heat treatment processes, including two full austenitizing stages, one high-temperature stage, and continuous low-temperature tempering, which formed a homogenized microstructure in the HAZ and was mainly composed of tempered sorbite (Tempered-S). The HAZ microhardness is around 278.7 HV, which is about 150 HV lower than the microhardness only conducted by one thermal cycle. Furthermore, the effects of preheating the substrate and adjusting the heat inputs on the HAZ were studied. The results indicated that the clustered cementite was precipitated, which destroys the low-temperature impact toughness of the HAZ after preheating. A suitable heat input not only homogenized the microstructure within the HAZ but also promoted the transformation of grains into equiaxed grains. The −60 °C impact toughness of the HAZ was significantly increased from 96.7 J to 113 J. Full article

In a hydrogen production reactor based on the principle of coal-to-hydrogen, the welds, which are considered the weak points, must exhibit a good impact resistance property and high hardness under special operating conditions. This paper investigates the influence of submerged arc welding (SAW) process parameters on the hardness and the impact resistance property of welds in the steel used for a hydrogen reactor. It establishes the relationship between the microstructure of the welds and their hardness and impact resistance property under varying welding parameters. Based on orthogonal welding experiments and a comprehensive balance method, the welding parameters were optimized to obtain the best combination of parameters. The results indicate that as the current and voltage increase, the average hardness of the welds first decreases and then increases, while the impact resistance property initially improves before declining. As the welding speed increases, the average hardness of the welds initially increases and then decreases, while the impact resistance property gradually declines. After optimization under specific experimental conditions, the best welding parameters are determined to be a current (I) of 320 A, a voltage (U) of 34 V, and a welding speed (v) of 33 cm/min. Compared to the base metal, the hardness of the weld increased by 36.1%, and the impact resistance property improved by 71.5%. Full article

To reduce manufacturing costs, energy companies aim to maximize the deposition rate during welding operations by increasing the interpass temperature (IT), thereby minimizing the cooling time. However, IT can significantly affect weldment performance, particularly its Charpy V-notch (CVN) impact energy (toughness). The present study investigates the effect of increasing IT beyond the limit specified by the ASME B31.3 (315 °C) on the CVN impact energy (−30 °C) of the simulated coarse-grained heat-affected zone (CGHAZ) of a 2.25Cr-1Mo steel submerged arc welded (SAW). The CGHAZ thermal cycles were obtained through finite element method simulations and physically replicated using a Gleeble machine. The increase in IT beyond the ASME-specified limit significantly reduces the CVN impact energy of the CGHAZ. However, the values obtained remained above the minimum required threshold (NORSOK M630, 42 J). The main effect of increased IT was grain coarsening. Additionally, an inverse linear relationship was observed between effective grain size (EGS) and CVN impact energy. The steel’s microstructure showed non-significant sensitivity to variations in IT within the studied range. These findings suggest that, under the conditions studied, increasing IT could be a viable option for optimizing production by reducing welding time and potentially lowering costs. Full article

Super duplex stainless steel UNS S32750 is widely used in marine industries, pulp and paper industries, and the offshore oil and gas industry. Welding manufacturing is one of the main manufacturing processes to make material into products in the above fields. It is of great importance to obtain high-quality welded UNS S32750 joints. The austenite content and ferrite content in UNS S32750 play an important role in determining UNS S32750 properties such as mechanical properties and corrosion resistance. However, the phase proportion between the ferrite phase and austenite phase in the welded joint will be changed during welding. Lots of research has been done on how to weld UNS S32750 and how to obtain welded joints with good quality. In this work, the recent studies on welding UNS S32750 are categorized based on the welding process. The welding process for UNS S32750 will be classified as gas tungsten arc welding, submerged arc welding, plasma arc welding, laser beam welding, electron beam welding, friction stir welding, and laser-MIG hybrid welding, and each will be reviewed in turn. The microstructure and properties of the joints welded using different welding processes will also be discussed. The critical challenge of balancing the two phases of austenite and ferrite in UNS S32750 welded joints will be discussed. This review about the welding process for UNS S32750 will provide people in the welding field with some advice on welding UNS S32750 super duplex stainless steel. Full article

Welding current is an essential parameter for submerged arc welding process. In submerged arc welding, the enormous heat generated by the current promotes the decomposition of the oxides in the flux, releasing oxygen and increasing the oxygen level in the metal, which further affects the microstructure and mechanical properties of the weld joint. Although previous studies have developed various models to evaluate oxygen content, the thermodynamic mechanism by which current influences oxygen levels in metal remains inadequately understood. This study integrates CALPHAD technology with welding thermodynamics to predict and simulate the impact of the welding current on oxygen content in metals. By combining experimental data with thermodynamic modeling, the research investigates how different current settings affect oxygen content in the metal across various welding zones, specifically when using CaO-Al₂O₃ fluxes with low and high basicity indices for the welding of typical carbon steel. This study selected two current values, 300 A and 600 A, for modeling analyses of the welding process, along with two typical fluxes with basicity indices of 1.6 and 0.4. The results indicate that the proposed method outperforms the BI model and can predict the metallurgical effects of current on oxygen content in the droplet and molten pool zones. The thermodynamic mechanisms that govern the metal oxygen level are also evaluated. These findings aim to enhance the understanding of the thermodynamic mechanism that governs oxygen behavior under different current conditions, thereby contributing to the optimization of submerged arc welding process. Full article

In this work, the microstructure–property relationship of the heat-affected zone (HAZ) of a FH690 ultra-heavy marine steel plate was investigated based on insight of microstructure and crystallographic features. After multi-pass welding with a heat input of ~30 kJ/cm, an ~8 mm wide HAZ was obtained with a coarse grain HAZ (CGHAZ) of ~3.8 mm, fine grain HAZ (FGHAZ) of ~3.4 mm, and intercritical HAZ (ICHAZ) of ~1 mm. High impact toughness values of ~120 and 140 J at −60 °C were obtained for coarse grain HAZ and fine grain HAZ, respectively. The microstructure of the CGHAZ and FGHAZ was fine lath bainite. Although the average prior austenite grain size for the CGHAZ was ~75 μm, which was five times that of the FGHAZ (15 μm), a high density of high-angle grain boundaries (HAGBs) with misorientation higher than 45° was obtained in the CGHAZ. This is the underlying reason for the excellent low-temperature toughness of the HAZ. Thermo-dynamic calculations indicated that the high density of HAGBs in the CGHAZ was attributed to the decreased bainitic transformation temperature due to the reduced phase transformation driving force via the high nickel addition, leading to weak variant selection. In addition, the high nickel addition offered high hardenability for high hardness in the FGHAZ. The outcome of this study could provide an experimental and fundamental basis for designing high-strength ultra-heavy steel plates with excellent weldability. Full article

In this work, the effects of the mixing water loss capacity of hydrated lime mortars with different dosages were analysed—type O (mix 1:2:9), type N (mix 1:1:6), and type M (mix 1:0.5:4.5), with additions of submerged arc welding (SAW) slag. Infrared thermography tests and optical and scanning electronic microscopy analyses of the mortars were also carried out. The experimental results showed that the mortar samples with additions of SAW slag type M, using low-cost materials, proved to be in economic and technical terms (adhesion strength) the best solution, even more so if a spatter dash layer is used, a fact that increases the adhesion strength even more. Also, the infrared thermographic results revealed that the ability of the mortar paste to yield water to the ceramic substrate in the interface regions is a relevant factor in the adhesion of these coatings. Finally, the analyses by scanning electron microscopy and optical microscopy revealed that the ability to release water to the substrate is related to the hydration of the mortar and its anchoring capacity. Furthermore, the analyses carried out demonstrated that the adhesion of the mortars is influenced and increased with the application of a layer of splashes, as the pores of the substrate become more refined and better filled with the applied mortar. Full article

High-manganese steel (high-Mn) is valuable for its excellent mechanical properties in cryogenic environments, making it essential to understand its deformation behavior at extremely low temperatures. The deformation behavior of high-Mn steels at extremely low temperatures depends on the stacking fault energy (SFE) that can lead to the formation of deformation twins or transform to ε-martensite or α′-martensite as the temperature decreases. In this study, submerged arc welding (SAW) was applied to fabricate thick pipes for cryogenic industry applications, but it may cause problems such as an uneven distribution of manganese (Mn) and a large weldment. To address these issues, post-weld heat treatment (PWHT) is performed to achieve a homogeneous microstructure, enhance mechanical properties, and reduce residual stress. It was found that the difference in Mn content between the dendrite and interdendritic regions was reduced after PWHT, and the SFE was calculated. At cryogenic temperatures, the SFE decreased below 20 mJ/m², indicating the martensitic transformation region. Furthermore, an examination of the deformation behavior of welded high-Mn steels was conducted. This study revealed that the tensile deformed, as-welded specimens exhibited ε and α′-martensite transformations at cryogenic temperatures. However, the heat-treated specimens did not undergo α′-martensite transformations. Moreover, regardless of whether the specimens were subjected to Charpy impact deformation before or after heat treatment, ε and α′-martensite transformations did not occur. Full article

With the advancement of the manufacturing industry, performing submerged arc welding subject to varying welding heat inputs has become essential. However, traditional thermodynamic models are insufficient for predicting the effect of welding heat input on elemental transfer behavior. This study aims to develop a model via CALPHAD technology to predict the influence of heat input on essential elements such as O, Si, and Mn when typical SiO₂-bearing fluxes are employed. The predicted data demonstrate that the proposed model effectively forecasts changes in elemental transfer behavior induced by varying welding heat inputs. Furthermore, the study discusses the thermodynamic factors affecting elemental transfer behavior under different heat inputs, supported by both measured compositions and thermodynamic data. These insights may provide theoretical and technical support for flux design, welding material matching, and composition prediction under various heat input conditions subject to submerged arc welding processes when SiO₂-bearing fluxes are employed. Full article