Steel Weld Research Articles

Effects of stabilized heat treatment on stress rupture properties of high Si-bearing austenitic stainless steel weld metal

The 15Cr-9Ni-Nb austenitic stainless steel weld metal with a Si content of 3.5 wt% was prepared via gas tungsten arc welding and then held at 900 °C for 3 h for the stabilized heat treatment (SHT). The stress rupture properties of the as-welded (AW) and SHT weld metals at 550 °C were evaluated via the Larson-Miller parameter. The microstructure evolution was discussed during the 550 °C stress rupture process. The coarse σ-phase and relatively fine G-phase formed on the δ-ferrite during aging at 550 °C. In the AW weld metal, the continuous δ-ferrite with a large amount of coarse σ-phase led to the formation and expansion of cracks during the stress rupture process, which accelerated the eventual rupture and damaged the stress rupture properties. The SHT decreased the δ-ferrite content and formed a large amount of nanoscale NbC precipitated in the matrix. The decreased δ-ferrite content avoided the rapid formation and expansion of cracks and the nanoscale NbC blocked the dislocation movement during the stress rupture process, which improved the stress rupture properties.

Temperature Effect on Deformation Mechanisms and Mechanical Properties of Welded High-Mn Steels for Cryogenic Applications.

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.

Experimental Investigation of Mechanical Properties and Characterization of Mild Steel Weldment Fabricated Using Pulse/Robotic Pulse Metal Inert Gas Welding Processes

Experimental Investigation of Mechanical Properties and Characterization of Mild Steel Weldment Fabricated Using Pulse/Robotic Pulse Metal Inert Gas Welding Processes

Microstructural changes in the welding of titanium-stabilized steels

Abstract At the Central Institute for Engineering, electronics, and Analytics (ZEA-1 by its acronym in German) of the Jülich Research Center GmbH, a cryostat was developed for the European Spallation Neutron Source (ESS) and manufactured from a titanium-stabilized austenitic stainless steel alloy (EN 1.4571). After tungsten inert gas welding, the welds exhibited a black, patchy discoloration. After materialographic preparation, the phenomena were examined using microscopic methods to assess their impact on the strength of the weld and thus on the usability of the cryostat. Not only could the impact on the cryostat operation be assessed, but the formation mechanism could be elucidated and suitable measures could be outlined to avoid the black, patchy discoloration.

Study on molten pool flow and hot cracking of narrow gap laser welding of 316LN stainless steel for fusion reactor

In this paper, narrow-gap laser welding (NGLW) of 316LN stainless steel was studied. The results indicated that continuous laser welding with filler wire (CLWFW) and pulsed laser welding with filler wire (PLWFW) can obtain good weld formation under the transition of the wire bridge, and when the pulsed laser was a trapezoidal wave, the hot cracks of the filling layer can be greatly inhibited. The intermittent output of the pulsed laser reduced the temperature gradient of the molten pool and enhanced the morphology of the caudal region of the molten pool. Meanwhile, timely liquid backfilling effectively relieved the stress concentration of the weld, thus inhibiting the generation of hot cracks. Besides, the intermittent pulse energy input had a stirring effect on the molten pool, which disturbed the growth direction of the dendrite grain and refined the grain; consequently, the impurity elements were fully diffused, and the distribution of elements in the weld center area was more uniform.

Local shear fracture properties in heat-affected zone of resistance spot-welded advanced high-strength steel

In the process of resistance spot welding of advanced high-strength steel (AHSS), the development of heat-affected zones (HAZs) considerably modifies the mechanical properties of the weld region. However, the limited reporting in the study of shear behavior in the HAZ hinders the accurate prediction of joint fracture and failure behavior. This study focused on the shear fracture behavior of resistance spot-welded AHSS. Given the limited extent of the HAZ, a miniature shear test was designed and shear fracture tests were conducted on JSC590, JSC980, and JSC1180. These tests facilitated the acquisition and compilation of data regarding the shear mechanical properties of diverse steel grades and their respective HAZs. A hardness-based empirical model for the strength coefficient and the strain-hardening exponent in Hollomon's law was introduced, and this model was subsequently integrated into finite element method calculations. The accuracy of the model was validated by shear strength reproductions, exhibiting errors within the range of 5.4%–13.5% and the averaged error was less than 10%. Further analyses confirmed that stress triaxiality at critical positions varied from 0 to 0.33, indicative of shear-dominant stress conditions. Moreover, the evolution of stress states revealed a notable association between the fracture surfaces across different stress states and steel grades. These findings fill the gap regarding the shear behavior of localized HAZs and expand the understanding of their mechanical behavior under various stress states. It will contribute to accurate fracture prediction by stress triaxiality based fracture criteria, such as Modified Mohr-Coulomb (MMC) model, applied to AHSS.

Exploring the Potential of Weld Slag as Aggregate Replacement in Concrete for Sustainable Construction: A Review Paper

Concrete is the most globally used material in the construction industry, with over ten billion tons produced annually, and its aggregates making 70 to 80% of its quantity. The aggregates production leads the natural sources of these aggregates to deplete in a high rate and with a significant carbon footprint. Consequently, industries are generating waste output in a large quantity which is posing problems to the environment and leading to economic challenges. This review explores the potential of using industrial waste such as weld slags, steel slags, and glass powder as substitutes to traditional concrete aggregates. The integration of these wastes solves the problems of waste disposal, resource depletion and environmental pollution. The review is to also to encourage the reuse, recycling and reduction of waste production to reduce pollution. This practice will help ensure resource conservation, environmental protection and enhanced sustainability. Furthermore it underscores the importance of further research on the durability and practical applications of concrete containing industrial slags such as steel slags, weld slags, glass powder etc. to establish effective and sustainable construction practices.

Study on Microstructure and Properties of LZ50 Axle Steel Repaired by Laser Additive Remanufacturing

ER308L stainless steel welding wire was used for laser repair of LZ50 train axle steel sample. A large number of defects, such as microcracks, pore shrinkage and porosity, can be found in the re-manufacturing sample. A wave-like structure was formed at the boundary of the fusion zone between the augmented repair material and the base material, and the structure in this zone was consist of about 83% martensite and about 17% austenite, In the ER308L stainless steel welding wire repair zone, columnar equiaxed crystals with different lengths and morphology were formed, all of which pointed to the center of the molten pool. After repair, the tensile strength of the specimens decreased from 601.34MPa to 427.81MPa, and the elongation decreased from 16% to 5%, The fracture mode was a combination of ductile fracture and brittle fracture.

Evolution of phase ratio and its effect on residual stress for 2205 duplex stainless steel multipass welded joints by thermo-metallurgical-mechanical model

The control of phase ratio and residual stress is a crucial subject for the structural integrity of duplex stainless steel welded components. Therefore, this paper aims to clarify the evolution of phase ratio and its effect on residual stress for duplex stainless steel multipass welded joints by a thermo-metallurgical-mechanical coupled welding model, alongside the crucial experiments which contribute to the development and validation of the coupled model. The developed model takes both the precipitation and dissolution behavior of austenite under repeated thermal cycles into consideration, thereby demonstrating a remarkable ability to predict the distribution of phase ratio and residual stress. The influencing mechanism of solid-state phase transformation on residual stress is discussed extensively. The results reveal that, for the duplex stainless steel welded joints by gas tungsten arc welding, excessive austenite is often formed within the welding zone particularly for the middle passes, while it is the occurrence of ferritization at the heat affected zone. The effect of phase transformation on residual stress is mainly presented by the change of mechanical properties and phase volume. The overtransformation from ferrite to austenite tends to induce a higher tensile residual stress, vice versa, compressive stress. In addition, it is challenging to achieve phase balance through heat input alone. However, a smaller heat input is recommended to minimize residual stress while ensuring welding penetration. This paper serves as a theoretical foundation for controlling the phase ratio and mitigating residual stress during the welding of duplex stainless steel, thereby contributing to the enhancement of weld quality and structural reliability.

Effect of initial microstructure on irradiation induced microstructure evolution in δ-ferrite in an austenitic stainless steel weld

The irradiation induced microstructure evolution of δ-ferrite in an austenitic stainless steel weld was investigated. To simulate long-term service in light water reactor (LWR) at operating temperature, accelerated thermal aging at 400 °C up to 30,000 h was performed. Then, proton irradiation up to 10 displacement per atom (dpa) was subsequently conducted for unaged and aged samples. For the unaged samples, formation of Cr-rich (α’) phase by spinodal decomposition increased with irradiation dose. Meanwhile, formation of G-phase was promoted after 1 dpa, but decreased after 10 dpa. For the aged samples, after 1 dpa irradiation, Cr-rich (α’) phase formed by spinodal decomposition during thermal aging was destroyed while population of G-phase increased. After further irradiation up to 10 dpa, α’ phase was re-precipitated and coarsened significantly, but the degree of which was significantly less compared to the unaged samples. Meanwhile, with increase of irradiation to 10 dpa, G-phase population increased for the aged samples. The difference in the evolution of microstructural features during irradiation were discussed in view of the initial microstructure of δ-ferrite.

Flux-cored arc welding of 316L austenitic stainless steel: the effect of different shielding gas mixtures on microstructural features and weld performance

ABSTRACT Double-pass flux cored arc welding (FCAW) of 316 L austenitic stainless steel was performed using different shielding gas mixtures. Microstructural features and weld performance were evaluated. Based on the Creq/Nieq ratio of fusion zone and cooling rate, different morphologies of ferrite (skeletal, lathy, and dendritic) and austenite with various volume fractions were produced. An increase in Creq/Nieq ratio can increase the strength level because the presence of ferrite in the weld metal acts as a second-phase strengthening agent. On the other hand, ferrite is a suitable place for sigma phase precipitation. Highest joint efficiency resulted in the specimen welded via GTAW. The ductility of welds was ranked as CO2 +Ar shielded FCAW > GTAW > CO2 shielded FCAW > self-shielded FCAW. At room temperature, variation of delta-ferrite content (Creq/Nieq ratio) does not affect toughness. However, an increased amount of CO2 in shielding gas will result in decreased toughness values because of the enhanced formation of oxide inclusions. Increasing CO2 content of shielding gas from 0% to 18% and finally to 100% will result in decreasing toughness values from the highest value of 76J to 40 J and finally the lowest value of 38J.

A Comparative Study on the Performance and Microstructure of 304NG Stainless Steel in Underwater and Air Laser Welding.

In order to facilitate the application of underwater laser welding technology in in situ repairs of nuclear power plants, this study conducted comparative experiments between local dry underwater laser welding and laser welding in air on 304NG nitrogen-controlled stainless steel. The aim was to explore its microstructural evolution and mechanical properties in underwater environments. It was found that, near the fusion line of laser welding in air, columnar dendrites gradually evolved into cellular dendrites toward the weld center, eventually disappearing, resulting in a skeletal ferrite and serrated austenite structure. The underwater laser welding joints exhibited similar characteristics yet with more pronounced alternation between columnar and cellular dendrites. Additionally, the size of cellular dendrites decreased significantly, and needle-like ferrite was observed at the weld center. The hardness of underwater laser welded joints was slightly higher than that of in-air laser welded joints. Compared to laser welding in air, the strength of underwater laser welding joints increased from 443 MPa to 471 MPa, and the displacement increased from 2.95 mm to 3.45 mm, both types of welded joints exhibited a mixed mode fracture characterized by plasticity and brittleness.

Enhancing NDE Reliability for Grade 91 Steel Welds: Ultrasonic Imaging and Microstructural Correlations

Ensuring the integrity of Grade 91 (9Cr-1Mo-V) steel welds is vital for the safe and reliable operation of fossil fuel–fired and nuclear power plants. This study applies an imaging technique for the ultrasonic characterization of two Grade 91 steel welds created with cold metal transfer and flux-cored arc welding processes. Ultrasonic immersion testing in the through-transmission configuration was employed to generate shear waves, which helped identify the weld metal, heat-affected zone, and base metal regions. These weld microstructures were also correlated to their ultrasonic images using metallography, ultrasonic amplitude, hardness measurements, and grain size. The findings from this study can assist practitioners in developing new nondestructive evaluation technologies, improving the inspection reliability of creep strength–enhanced ferritic steel welds by potentially identifying weld microstructure regions susceptible to creep-type failures.

Influence of filler metal and arc pulsation on P91 steel weldments developed by activated TIG welding and its effect on stress corrosion cracking

This study examines the influence of arc pulsation and ErNiCrMo-3 filler metal on stress corrosion cracking (SCC) in P91 steel weld joints using activated tungsten inert gas (A-TIG) welding. The constant current joint without filler showed the lowest resistance to SCC, while the pulsed current joint with filler exhibited the highest SCC resistance. Arc pulsation reduced chromium carbide precipitates, enhancing microstructural refinement and crack growth thereby increasing tensile strength and SCC resistance. Filler introduced minor austenitic phases inside martensitic microstructure with reduced hydrogen content contributed to increased SCC resistance. The joint fractography among all welds revealed a complete transgranular fracture.

Effect of cobalt on Microstructure and toughness properties of 9Cr-1.8W-0.4Ni-xCo weld metal

In this research, microstructural characterization and mechanical properties of 9%Cr, 0.4%Ni (including W and Mo) steel weld metal with alloyed cobalt were investigated. Due to their strong creep resistance, oxidation resistance, and low thermal expansion, 9%Cr steels are used in nuclear power plants, petrochemical industries, and fossil fuel-powered power plants that operate in high temperature conditions. In this context, weld metals comprising 0.5 %, 1 % and 1.5 % cobalt and cobalt-free weld metal were produced by SMAW (shielded metal arc welding) technique. Microstructure of the weld metals were characterized with optical microscope (OM), scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). Also, XRD analysis was performed on the bulk samples and precipitated carbide/nitride phases extracted from the weld metals. In addition, differential scanning calorimetry (DSC) was used to determine the phase transformations. Thermo-Calc modeling study was also performed. Hardness, tensile and Charpy-V impact tests were carried out to determine the mechanical properties. The hardness did not change significantly when cobalt up to 1.5 % in the weld metal. However, with the increase of cobalt, the yield and tensile strength increased without affecting the elongation value too much. In the Charpy impact tests performed at different temperatures (−40 °C, −20 °C, +20 °C, +40 °C, +60 °C), the amount of cobalt increased toughness, especially at +40 and + 60oC temperatures. Ductile brittle transformation temperature (DBTT) of the weld metal with 1.5 % Co decreased from 29 °C to 15 °C compared to cobalt free weld metal. It is thought that this may be caused by the further separation of C, Cr and W from the matrix through forming precipitate by the cobalt effect. Besides the mechanical properties, microstructure was also affected by adding Co with inhibition of delta ferrite formation which decrease the toughness. Curie temperature increased with increasing cobalt content detected by DSC.

Predicting Weld Quality in Duplex Stainless Steel Butt Joints During Laser Beam Welding: A Hybrid DNN-HEVA Approach

Duplex stainless steel (DSS) welding is critical for producing structures and components in a variety of industries. Because traditional optimization approaches cannot manage the complexity of welding, additional solutions must be investigated. This study addresses the need for a systematic exploration of the welding parameters affecting the quality and performance of DSS butt joints, specifically employing fiber laser welding. This study focuses on butt joints in UNS S32304 and 304L using a fiber laser. Welding process parameters were systematically varied, including laser power, scanning speed, beam diameter, and focal position. To efficiently examine the parameters in the design space, the response surface methodology (RSM) with Box–Behnken design (BBD) was used. The combination of the specific parameter values used in the 7th run (Laser Power: 1600 W, Scanning Speed: 2000 mm/min, Beam Diameter: 1.5 [Formula: see text]m, Focal Position: 30 mm) led to better yield point stress (YPS), maximum tensile stress (MTS), break stress (BS) and reduction in area (RA). ANOVA and lack of fit analysis confirmed the significance of the experiment. In particular, the selected welding parameters significantly influenced all responses. A hybrid machine learning method of deep neural network (DNN) and human eye vision algorithm (HEVA) was used for predicting weld quality during laser beam welding (LBW). The hybrid DNN-HEVA consistently outperformed other optimization methods (RSM-BBD, FNN, CNN, and RNN) across key welding quality parameters. High [Formula: see text]2 values (0.9922, 0.9962, 0.9983, and 0.9907) indicated a strong correlation between predicted and actual values for all calculated responses. Lower RMSE, MSE, and MAE values were also highlighted in the precision of predicted values to the experimental data.

Exploring the performance of the topological energy method for object and damage detection from noisy and poor databases.

In this work, we study the performance of numerical methods based on the computation of topological energies to process data from synthetic and real experiments where only noisy limited-view data corresponding to a few frequencies are available. We show numerical experiments in two problems of practical interest. The first one corresponds to experimental measurements of the electromagnetic scattering produced by different objects extracted from the Fresnel database. The second one is related to synthetic experiments in a simplified model where steel welding joints are acoustically tested to identify possible flaws (air bubbles and inclusions) produced during the welding process. This article is part of the theme issue 'Non-smooth variational problems with applications in mechanics'.

Comparative study of fillers for welding E410 structural steel

ABSTRACT An endeavour for creating an understanding of the effect of filler wires (ER-70S6 and ER-80SG) on the mechanical performance of metal inert gas (MIG) weldments of two E410 graded structural steels that differed majorly in carbon contents i.e. 0.04 wt.%C and 0.17 wt.%C was undertaken. Improvements in yield stress (YS) with ER-80SG for MIG weldments of both investigated E410 structural steels were noticed; however, %elongation and room temperature (RT) impact toughness deteriorated as regards to ER-70S6. Almost ⁓5% increase in YS and a drop by ⁓4%, ⁓22%, and ⁓60% in ultimate tensile stress (UTS), %elongation, and toughness, correspondingly, were obtained for 0.04 wt.%C structural E410 steel with ER-80SG over ER-70S6. While moderate ⁓9% and ⁓8% increments in YS and UTS and a decrement of ⁓7% and ⁓40% in %elongation and toughness, respectively, were observed for 0.17 wt.%C steel with ER-80SG over ER-70S6. Enhancement in YS and a fall in %elongation and toughness with ER-80SG compared to ER-70S6 were due to high heat input for performing MIG welding of E410 steel, leading to thorough phase transformations providing fine Widmanstätten ferrite and acicular ferrite structures in weld metal with variable-sized inclusions and dissolved cementite and pearlite sub-structures in heat affected (HAZ) subzones of 0.04 wt.%C and 0.17 wt.%C steels, respectively.

RETRACTED: Mohan et al. Laser Welding of UNS S33207 Hyper-Duplex Stainless Steel to 6061 Aluminum Alloy Using High Entropy Alloy as a Filler Material. Appl. Sci. 2022, 12, 2849

The Applied Sciences Editorial Office retracts the article, “Laser Welding of UNS S33207 Hyper-Duplex Stainless Steel to 6061 Aluminum Alloy Using High Entropy Alloy as a Filler Material” [...]

A piece-wise linear model for modelling the tension-stiffening effect in steel-reinforced UHPC composites

This study examines the tensile behaviour of Ultra-High Performance Concrete (UHPC) specimens reinforced with varying steel fibre content and rebar diameters. An experimental campaign involving 18 reinforced UHPC specimens was conducted, following individual tensile response characterizations of UHPC and reinforcing steel. These specimens were designed and fabricated with threaded welded steel cages to transfer loads to the central measurement area. Force–displacement curves were measured to derive stress–strain curves for the UHPC component, evaluating the impact of reinforcement rebar and steel fibre content on UHPC’s mechanical response. The analysis revealed that steel fibre volume content significantly influences the tensile response of UHPC reinforcement more than the steel bar diameter and yield strength. Comparing the strain in steel bars to the average strain in reinforced UHPC specimens indicated that post-cracking deformation concentrates at the crack. At the same time, the bond between reinforcement and UHPC remains intact in uncracked sections, allowing effective load transfer. UHPC specimens reinforced with 14 mm diameter steel bars displayed a significant horizontal segment in the descending phase of the stress–strain curve. In contrast, specimens with 18 mm or 22 mm diameter bars exhibit a progressive stress reduction at a nearly constant rate. Stress–strain curves of UHPC were fitted with a five-fold piecewise empirical model applicable to UHPC with a reinforcement ratio higher than 0.09%. The resulting model can be used to model the axial behaviour in UHPC, considering the effects of steel reinforcement.