Stainless Steel Weld Research Articles

Effect of pre-strain on thermal aging of austenitic stainless steel weld metal

Austenitic stainless steel welds (ASSWs) suffer from severe pre-strain during assembly process, which threatens the long-term operation safety of pipelines in nuclear power plant. In this work, the 316L weld metals (WMs) with 0 % and 8 % pre-strain were thermally aged at 400 °C for up to 39000 h to investigate the pre-strain effect on thermal aging of ASSWs. The results showed that the pre-strain caused work hardening and further promoted the hardening of thermally aged ferrite. After thermal aging for 39000 h, the nano-hardness increment of ferrite with 8 % pre-strain was about 1.6 GPa more than that without pre-strain. By microstructure characterization, it is found that the high dislocation density induced by pre-strain promoted spinodal decomposition and G-phase precipitation. The spinodal decomposition morphology and corresponding element concentration fluctuations were more obvious in the WM with 8 % pre-strain. Moreover, the size and density of G-phase along dislocations were larger in the ferrite with 8 % pre-strain than those without pre-strain.

The SAM-Krom biomonitoring study shows occupational exposure to hexavalent chromium and increased genotoxicity in Denmark.

Hexavalent chromium (Cr(VI)) is a carcinogen. Exposure to Cr(VI) may occur in different industrial processes such as chrome plating and stainless steel welding. The aim of this study was to assess occupational exposure to Cr(VI) in Denmark. This cross-sectional study included 28 workers and 8 apprentices with potential Cr(VI) exposure and 24 within company controls, all recruited from six companies and one vocational school. Use of occupational safety and health (OSH) risk prevention measures were assessed through triangulation of interviews, a questionnaire and systematic observations. Inhalable Cr(VI) and Cr-total were assessed by personal air exposure measurements on Cr(VI) exposed participants and stationary measurements. Cr concentrations were measured in urine and in red blood cells (RBC) (the latter reflecting Cr(VI)). Genotoxicity was assessed by measurement of micronuclei in peripheral blood reticulocytes (MNRET). At announced visits, a consistent high degree of compliance to OSH risk prevention measures were seen in 'chromium bath plating' for both technical devices (e.g. ventilation, plastic balls, sheet coverings) and in the use of personal protective equipment (e.g. gloves, respirators), yet a lesser degree of compliance was observed in 'stainless steel welding'. The geometric mean of the air concentration of Cr(VI) was 0.26μg/m3 (95% confidence interval (CI): 0.12-0.57) for the Cr(VI)-exposed workers and 3.69μg/m3 (95% CI: 1.47-9.25) for the Cr(VI)-exposed apprentices. Subdivided by company type, the exposure levels were 0.13μg/m3 (95% CI: 0.04-0.41) for companies manufacturing and processing metal products, and 0.81μg/m3 (95% CI: 0.46-1.40) for bath plating companies. Workers with occupational exposure to Cr(VI) had significantly higher median levels of urinary Cr (2.42μg/L, 5th-95th percentile 0.28-58.39), Cr in RBC (0.89μg/L, 0.54-4.92) and MNRET (1.59 ‰, 0.78-10.92) compared to the within company controls (urinary: 0.40μg/L, 0.16-21.3, RBC: 0.60μg/L, 0.50-0.93,MNRET: 1.06 ‰, 0.71-2.06). When sub-dividing by company type, urinary Cr (4.61μg/L, 1.72-69.5), Cr in RBC (1.33μg/L, 0.95-4.98) and MNRET (1.89μg/L, 0.78-12.92) levels were increased for workers with potential Cr(VI) exposure in bath-plating companies, and when subdividing by work task, workers engaged in process operation had increased levels of urinary Cr (8.51μg/L, 1.71-69.5), Cr in RBC (1.33μg/L, 0.95-4.98) and MNRET (1.89μg/L, 0.82-12.92) levels. This biomonitoring study shows that bath platers were highly exposed to Cr(VI), as suggested by relatively high levels of urinary Cr, Cr in RBC and increased levels of micronuclei. The urinary Cr concentrations were high when compared to the French biological limit value of 2.5μg Cr/L, corresponding to the Danish occupational exposure limit of 1μg/m3. This, in turn, indirectly suggests that additional exposure routes than via air may contribute to the exposure. For welders, no statistically significant increases compared to within company controls were observed, however, the observed urinary Cr levels were similar to the levels observed in a European study (HBM4EU), and were higher than the levels observed for welders in Sweden (SafeChrom). In spite of a high degree of self-reported and observed compliance to OSH risk prevention measures during announced visits, the biomarkers of exposure reflecting recent exposure (urinary Cr) or exposure during the last four months (Cr in RBC) may point to variation in compliance to OSH risk prevention measures in general. Reduced occupational exposure to Cr(VI) may be achieved by applying the hierarchy of controls in eliminating or substituting Cr(VI), and the use of more effective technical solutions (e.g. automation).

Clarifying the effect of irradiation and thermal treatment on the austenitic microstructure and austenitic hardening in austenitic stainless steel weld metal

The weld cladding on the inner surface of nuclear pressure vessels due to irradiation damage and thermal effect presents to a safety issue. Unfortunately, the effect of irradiation and long-term thermal treatment on the austenitic microstructure and austenitic hardening in austenitic stainless steel weld metals (ASSWMs) remains poorly understood. In this study, the effects of irradiation and thermal treatment on the austenitic microstructures and austenitic hardening of 308L ASSWMs were investigated using nanoindentation, atom probe tomography and transmission electron microscopy. The results suggested that irradiation resulted in the formation of Ni/Si-rich clusters, voids, and Frank loops in austenite, thereby inducing austenitic hardening. Subsequently, thermal treatment decreased the size and the number of Frank loops in irradiated austenite, which had a minor effect on austenitic hardening. However, thermal treatment promoted the growth of Ni/Si-rich clusters and void formation, which have a primary effect on austenitic hardening, thereby enhancing the hardening of irradiated austenite. Furthermore, thermal treatment has little effect on the microstructure and hardening of austenite. Then, irradiation promoted the formation of Ni/Si-rich clusters, voids, and Frank loops in thermally treated austenite, resulting in austenitic hardening. The interaction of irradiation and thermal treatment can promote the formation of voids. The austenitic hardening was mainly due to the contribution of Frank loops, voids, and Ni/Si-rich clusters, which acted as short-range barriers by pin-moving dislocations.

Effect of Ultrasonic Treatment on Residual Stress and Mechanical Properties of AISI 304 Stainless Steel Welding

Abstract AISI 304 stainless steel has low thermal conductivity and a high linear expansion coefficient; conventional welding with this material produces coarse grains and poor joint tensile properties. To address the problems inherent in conventional 304 stainless steel welding, an ultrasonic transducer was brought into contact with a base metal and treated with ultrasonic vibration during welding. The residual stress distribution, microstructure, and mechanical properties of the welded joint were then analyzed. The results showed that under the combined action of thermodynamics and the dynamics caused by ultrasonic treatment, the flow performance of the molten pool was enhanced, heat was transferred from the high-temperature region to the low-temperature region, and the metal elements were constantly diffused during the crystallization of the molten pool. Thus, the transformation rate of columnar crystals to equiaxed crystals was accelerated, the proportion of equiaxed crystals increased, and the grains became refined. Compared with conventional welding, the microstructure of the 304 stainless steel welded joints was better after the introduction of ultrasonic vibration, and its tensile residual stress was significantly lower. The improvement in the microstructure of the weld improved its mechanical properties, and the hardness of the weld zone increased significantly, which was close to that of the base metal. After the ultrasonic treatment, the increase in the equiaxed crystals and the refinement in the grains effectively improved the quality of the welded joints so that the tensile strength of the welded joints was higher than that of conventional welded joints. Under the condition of the same ultrasonic vibration frequency and power, the tensile strength of welded joints with 2-mm steel plate exhibited a notable increase, which was 13 %.

P23-19 Cell-specific responses to mild and stainless steel welding particles in bronchial epithelial and macrophage-like cells

P23-19 Cell-specific responses to mild and stainless steel welding particles in bronchial epithelial and macrophage-like cells

Postweld Heat Treatment of 15Cr-6Ni-2Mo-1Cu Supermartensitic Stainless Steel Welds

Supermartensitic stainless steels with 15Cr-6Ni- 2Mo-1Cu and 135 ksi minimum yield strength (15Cr- 135 SMSS) offer high strength and good toughness through a complex hierarchical microstructure of nanoscale precipitates, tempered martensite, and reverted austenite. Upon welding and postweld heat treatment, substantial changes to heat-affected zone microstructure and hardness may occur. Here, we reveal spatially heterogeneous microstructure and microhardness in the HAZ of 15Cr-135 SMSS; correlate these changes to measured phase transformation temperatures; and demonstrate that HAZ hardness changes depend strongly on postweld heat treatment (PWHT) temperatures. Furthermore, we demonstrate that PWHT may lead to undesired reductions in base metal yield strength and formulate a design guide for PWHT that quantifies the trade-offs in desired reductions of HAZ hardness with undesired changes to base metal yield strength. These findings have important practical implications for welding procedure design and qualification.

Optimization of TIG welding parameters for enhanced mechanical properties in AISI 316L stainless steel welds

Optimization of TIG welding parameters for enhanced mechanical properties in AISI 316L stainless steel welds

Metallurgical and Corrosion Characterization of Austenitic Stainless Steel Welds during Post Weld Heat Treatment

Metallurgical and Corrosion Characterization of Austenitic Stainless Steel Welds during Post Weld Heat Treatment

Effect of oscillation parameters on weld surface morphology during laser beam oscillation welding of stainless steel

During laser beam oscillation welding (LBOW), the weld surface morphology is important because it influences the appearance of the workpiece and reflects the welding quality, and the oscillation parameters have an important effect on the weld surface morphology. Therefore, a combination of experimental research and numerical simulation is conducted to investigate the influence of oscillation parameters, including oscillation mode, oscillation frequency, and oscillation amplitude, on the weld surface morphology during LBOW. The calculation encompasses the oscillation trajectory, combined velocity, and energy distribution on the weld surface, varying with different oscillation parameters. A three-dimensional heat transfer and fluid flow model with the oscillation heat source is established to simulate the temperature and fluid flow behavior inside the weld pool. When the heat input is constant, an increase in oscillation frequency results in a decrease in weld width and a smoother surface. As the oscillation frequency increases, the weld width decreases, the surface becomes smooth, and the energy distribution on the weld surface becomes more uniform. The fact that the period of the surface pattern is almost equal to the oscillation period indicates a direct correlation between the formation of weld surface pattern and the oscillation trajectory in LBOW. Among all the oscillation modes, the minimum combined velocity which is equal to the welding velocity occurs at the inflection point in the linear oscillation mode, and the variation in combined velocity of the laser beam is the smallest for circular oscillation mode. The surface pattern is primarily influenced by the oscillation trajectory and fluid flow within the weld pool. Under conditions of lower oscillation frequencies or larger oscillation amplitudes, the fluid flow is weaker, and the surface pattern is primarily influenced by the oscillation trajectory. Conversely, when the fluid flow is stronger, the surface pattern is mainly determined by the fluid flow within the weld pool under conditions of higher oscillation frequencies or smaller oscillation amplitudes. This study explains the formation mechanisms of weld surface patterns and provides insights and guidance for selecting optimal oscillation parameters in LBOW.

A NOVEL DOUBLE-SIDE LASER WELDED THICK PLATE: MICROSTRUCTURE AND NUMERICAL PREDICTION OF TENSILE TEST

The study aims to provide firsthand knowledge on finite element simulation (FES) of double-side laser welded (LW) stainless steel 304 (SS-304) thick plates used for automobile application. Double-side welding technique is an idea of achieving complete penetration with minimal heat input. The microstructural evaluation revealed the presence of dendritic growth that results in the enhancement of tensile strength (TS) for the welded sample. There is a slight increase in the delta ferrite content in weldment. The change in microstructure is due to thermal history during solidification. The TS of base metal (BM) was [Formula: see text][Formula: see text]MPa whereas the welded sample exhibited strength of [Formula: see text][Formula: see text]MPa. FES was successfully employed to simulate TS with error percentage less than 1.

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.

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.

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.

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.

Frequencies of chromosomal aberrations and related biochemical parameters in welders

Stainless steel welders are exposed to heavy filler metals. We evaluated the concentration of these metals in whole blood and urine, and the relevant biochemical parameters in relation to the total chromosomal aberrations (CAs), chromatid-type (CTA-type, CTAs) and chromosome-type (CSA-type, CSAs), in 117 welders and control individuals. Statistically higher concentrations of the total Cr, Ni and Mn were observed in whole blood and urine of welders, and the concentrations were higher in welders who smoked. On the contrary, concentrations of urinary heavy metals Cr and Mn adjusted for creatinine were significantly higher in the control groups. A statistically higher frequency of total CAs was observed in the whole group of welders, and also in the non-smoking welders, as compared to controls. The frequency of total CAs significantly correlated with the concentration of Cr, Ni and Mn in whole blood (R=0.61, P˂0.0001, R=0.33, P˂0.0001 and R=0.66, P˂0.0001, respectively), with urinary concentrations of Ni and Mn (R=0.27, P=0.003 and R=0.28, P=0.003, respectively) and with urinary concentrations of Cr, Ni and Mn adjusted for creatinine (R=0.22, P=0.029, R=0.26, P=0.005 and R=0.20, P=0.030, respectively). Likewise, the frequency of CTA-types significantly correlated with the concentration of Cr and Mn in whole blood (R=0.31, P=0.0007 and R=0.34, P=0.0002). The frequency of CSA-types significantly correlated with concentrations of Cr, Ni and Mn in whole blood (R=0.43, P˂0.0001, R=0.38, P˂0.0001 and R=0.46, P˂0.0001, respectively). The statistically higher values of serum creatinine and total bilirubin were detected in all welders, as well as in smokers when compared to the corresponding controls. The exposure to heavy metals in welders increased the frequencies of CAs and altered the balance between urinary excretion of heavy metals and their possible accumulation.

Long-term thermal aging of austenitic stainless-steel weld: Microstructure evolution in δ-ferrite and δ / γ phase boundary and apparent recovery of mechanical properties

This study aimed at investigation of thermal aging effects on evolution of microstructure and mechanical properties of ER316L austenitic stainless-steel weld (ASSW). The ASSW was subjected to thermal aging at 400 °C for up to 30,000 h. Initially, thermal aging triggered spinodal decomposition of δ-ferrite and clustering of Ni. Thermal aging up to 20,000 h further enhanced spinodal decomposition and G-phase formation. After 30,000 h of aging, precipitation of Mo-rich χ-phase occurred adjacent to the G-phase. Concurrently, thermal aging induced segregation of different elements and formation of nickel depletion zone was observed at the ferrite/austenite (δ/γ) phase boundary. The consequence of these microstructure changes was the hardening of δ-ferrite and loss of fracture toughness of ASSW. However, after 30,000 h of aging at 400 °C, degraded fracture toughness and tensile properties were partially recovered. This recovery in fracture toughness was attributed to the evolution of microchemistry and the formation of a softer shell in the δ/γ phase boundary region.

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” [...]