Weld Microstructure Research Articles

Effect of different heat inputs on the microstructure and mechanical properties of the laser welded joint of CLF-1 steel

Abstract In this study, we examined the effects of various heat inputs on the microstructure and mechanical properties of the laser-welded joints of CLF-1 low-activation ferritic/martensitic steel medium-thick plates, which are used in the Test Blanket Module (TBM). The results indicate that under four different welding heat inputs (2727 J/cm, 3000 J/cm, 3563 J/cm, and 4500 J/cm), the weld microstructure is primarily composed of a large amount of lath martensite and a small amount of δ-Fe. As the heat input increases, the average width of lath martensite in the weld microstructure progressively increases, while the average volume fraction and width size of δ-Fe experience a significant increase. When the heat input surpasses 3563 J/cm, δ-Fe exhibits a dense aggregation. The tensile properties of the joints created under different heat inputs are superior to those of the base material. At the lowest heat input, the maximum impact toughness of the weld reaches 40 J.

تأثير الاكاسيد النشطة باستخدام طريقة لحام(TIG) على جودة شكل وابعاد وصلة اللحام للصلب الاوستنيتى المقاوم للصدأ

Active flux welding (A-TIG) is a method that effectively enhances performance and improves penetration in TIG welding by applying a layer of activated flux to the workpiece before welding. The addition of flux results in higher temperatures in the welding arc, leading to increased penetration without the need for multiple passes and groove preparation, thereby significantly boosting productivity. This research explores the impact of various active fluxes (MoO3, Cr2O3, Fe2O3, Al2O3, and CaF2) in A-TIG welding on 6mm thick austenitic stainless steel 304L plates. The investigation focused on surface appearance, weld bead geometry quality, hardness, microstructure, and angular distortion. The findings revealed that utilizing A-TIG welding with Cr2O3, MoO3, and Fe2O3 fluxes notably improved the penetration depth and aspect ratio as well as reduced angular distortion compared to conventional (TIG) welding method. The application of fluxes had a minimal impact on the hardness and microstructure of A-TIG weld metal. Keywords: Activated fluxes (A-TIG), Weld Penetration, Angular distortion, Weld Bead Geometry

Effect of rotational speed on friction stir welding microstructure and properties of cast and rolled (ZrB2 + Al3Zr) particle-reinforced aluminum matrix composites

Effect of rotational speed on friction stir welding microstructure and properties of cast and rolled (ZrB2 + Al3Zr) particle-reinforced aluminum matrix composites

Correlation between heterogeneous micromechanical properties and fracture toughness in X80 girth weld

The safety accidents caused by the service of pipelines will cause huge economic losses due to the deterioration of the fracture toughness of the girth weld. To clarify the fracture behaviors of girth weld, X80 girth welds with heterogeneous microstructure consisted acicular ferrite (AF) and grain boundary ferrite (GBF) with different micromechanical properties were investigated. The results show that the typical microstructure of X80 girth weld is heterogeneous, which is consist of high strength AF and low strength GBF. With the decrease of the difference in micromechanical properties between AF and GBF, the crack tip opening displacement of three girth welds is 0.13 ± 0.04 mm, 0.18 ± 0.04 mm and 0.29 ± 0.05 mm. Meanwhile, the type of microcracks gradually changed from secondary cracks with GBF aggregation to micro-voids without obvious aggregation, which means the fracture mechanism transforms from cleavage fracture to micro-voids aggregation fracture. The finite element analysis indicates that the change of fracture mechanism is mainly due to the reduction of the gap between the micromechanical properties of AF and GBF, the stress and strain distribution are homogenized, resulting the fracture toughness is significantly improved.

Microstructural Characterization of Friction Stir Welds of Aluminum 6082 Produced with Bobbin Tool.

This study utilized a bobbin tool to friction stir weld aluminum 6082 workpieces under two sets of process parameters: a tool rotation speed of 280 rev/min with a weld velocity of 280 mm/min (280/280) and a tool rotation speed of 450 rev/min with a weld velocity of 450 mm/min (450/450). The weld microstructures were characterized through optical microscopy utilizing polarized light and through transmission electron microscopy (TEM) and scanning electron microscopy (SEM) coupled with chemical analysis by energy dispersive spectroscopy and electron back scatter diffraction. The microstructural studies were supplemented by hardness measurements (Vickers) performed on the same sections as the metallographic examinations. The produced weldments were free from cracks and any discontinuities. Fine, equiaxed grains that were several microns in size characterized the stir zones (SZs), and the advancing (AS) and retreating (RS) sides revealed distinct microstructural features. On the AS, the transition from the thermo-mechanically affected zone to the SZ was well defined and sharp, but on the RS, the transition appeared as a continuous, gradual change in microstructure. The lower weld energy (280/280) produced lower hardness in the stir zone than the higher energy weld (450/450), ~95 HV1 versus ~115 HV1; however, the 280/280 welds showed higher tensile strengths than the 450/450 welds, ~238 MPa as opposed to ~172 MPa. These behaviors in mechanical performance correlated with the temperature histories produced by each set of weld parameters in relation to the precipitation behavior of the alloy. The fracture characteristics of the weldments were notably different with the 450/450 sample fracturing in a quasi-brittle manner with slight plastic deformation and the 280/280 sample fracturing ductilely. A numerical simulation supported the investigation by elucidating the temperature and material flow behavior during the joining process.

Extrusion Benchmark 2023: Effect of Die Design on Profile Speed, Seam Weld Quality and Microstructure of Hollow Tubes

The Extrusion Benchmark 2023 was focused on the evaluation of different die design strategies for the manufacturing of AA6082 hollow tubes (40 mm external diameter and 4 mm thickness) through a porthole die with 3 openings. The extrusion process was monitored in industrial environment in terms of press load, profiles speed, profiles exit temperature, and die temperatures under different processing conditions (air quenching, water quenching, nitrogen die cooling). Extruded profiles were then analyzed in terms of seam weld quality, charge weld extension and microstructure evolution for both air/water quench and presence/absence of nitrogen cooling. The results of the study are aimed at validating FEM simulation outputs in the context of the International Conference on Extrusion and Benchmark (ICEB).

Welding Characteristics of Medium Titanium Plates with Autogenous Laser Welding and Narrow-Gap Laser Filling Welding Modes.

Titanium and titanium alloys with a medium thickness of 5 to 12 mm are widely used for ocean platforms, military equipment and in other fields because of their light weight, appropriate strength and corrosion resistance. In this study, autogenous laser welding and narrow-gap laser welding processes were researched and compared, and the welding characteristics, weld microstructure and joint strength were analyzed. The results showed that autogenous laser welding had higher efficiency, narrower weld width and higher microstructure uniformity. Autogenous laser welding can achieve the single pass weld penetration at laser keyhole mode. The weld width of narrow-gap laser welded joint was 12.5 mm, which was nearly three times than that of autogenous laser welding. The grain size of autogenous laser welding was obviously smaller and more uniform in depth than that of narrow-gap laser welding. In the weld zone, the coarse columnar α grains grew from the fusion line, while in the heat-affected zone, equiaxed α grains with needle and sawtooth α morphologies were presented. The microhardness of the heat-affected zone was higher than in the weld zone and the base metal due to the denser needle microstructure. The tensile samples all fractured at the base metal, indicating the welded joint strength efficiency was greater than 1.

Effect of Cr Element in Gas-Shielded Solid Wire for Oil and Gas Long-Distance Pipeline on Microstructure and Low Temperature Toughness of Weld.

In this paper, the influence of Cr element on the mechanical properties of welded joints of gas-shielded solid wire used in oil and gas long-distance pipelines was studied by means of tensile test, impact test, and hardness test, and the microstructure and crack propagation path of weld were characterized by means of an optical microscope, scanning electron microscope, and electron backscattering diffraction. The results show that with the addition of Cr, the strength and toughness of the weld are significantly improved, in which the tensile strength is increased from 607 MPa to 656 MPa, and the impact toughness is increased from 126.37 J to 223.79 J. The proportion of the ferrite side plate in the weld structure is reduced by about 20%, and the effective grain size of acicular ferrite is reduced by about 15%. The reason is that the addition of the Cr element improves the hardenability of the weld structure, inhibits the formation of the ferrite side plate, and promotes the effective refinement of acicular ferrite, which increases the proportion of high-angle grain boundaries in the weld, effectively hindering the crack propagation, improves the crack propagation work, and thus improves the strength and toughness of the weld.

Microscopic characterisation of brittle fracture initiation in irradiated and thermally aged low-alloy steel welds of a decommissioned reactor pressure vessel

Microstructure has a significant effect on material's integrity and in a heterogeneous weld microstructure the discontinuities affect the brittle fracture initiation and propagation and determine the fracture toughness. The knowledge of brittle fracture initiation mechanisms in high-Mn/high-Ni welds is limited. The brittle fracture initiation behaviour of the decommissioned Barsebäck Unit 2 reactor pressure vessel (RPV) welds of high-Mn/high-Ni weld metal from three different locations, the RPV head and the beltline regions, were investigated and compared with specimens from the surveillance program with high fluence. Systematic fractography has been performed on impact and fracture toughness specimens and the main features of the brittle fracture initiation in the component weld are presented and discussed. Two main types of initiators are identified as the weakest links to initiate the cleavage fracture and the initiation mechanism is found independent from the operation condition. The high-fluence surveillance specimens have a larger amount of intergranular cracking. The cleavage fracture initiation appears to be independent of the operation conditions but dependent on the welding process and metallurgical features. The findings aid in the development of improved material-property correlations which will result in better computational tools for predicting aging of welds based on microstructure.

Characterization and optimization of TIG welding parameters for AISI 304 and AISI 316 stainless steel dissimilar joints

This study explores the impact of tungsten inert gas (TIG) welding parameters on the mechanical properties and microstructure of dissimilar welds between AISI 304 and AISI 316 austenitic stainless steels. Given the growing industrial demand for these materials, the research focuses on optimizing welding current, shielding gas flow rate, and voltage to enhance tensile strength, hardness, and impact toughness. Using the L9 orthogonal array based on Taguchi’s methodology, the experiments revealed that Relatively highs currents and voltages significantly improved the ultimate tensile strength (up to 673.67 MPa) and impact energy absorption (up to 36.5 J). Microstructural analysis indicated refined grain structures in the heat-affected zones, with pronounced grain growth in AISI 316 due to its thermal sensitivity. The micro-hardness analysis revealed that the highest hardness occurred in the HAZ of AISI 304, with samples 5 and 6 exhibiting the optimal hardness profile, reflecting the most favorable welding parameters. The study concludes that a current range of 80-90 A and a voltage range of 10-11 V and a shielding gas flow rate of 12-16 L/min provide optimal welding conditions, offering robust guidelines for industrial applications requiring high-performance dissimilar welds.

Effect of grain boundary ferrite morphologies on impact toughness of X80 girth weld

The X80 girth weld microstructure formed by high-strength acicular ferrite and low-strength grain boundary ferrite was studied to investigate the effect of grain boundary ferrite morphologies on impact toughness. The results show that due to the difference in direction of heat loss caused by the narrow groove, the grain boundary ferrite morphology of the weld metal center and the weld metal edge are continuous network structure and parallel layered structure, respectively. The continuous network structure grain boundary ferrite causes strain localization, resulting in the formation of a large number of secondary cracks in the crack propagation process, which seriously deteriorates the toughness.

Mechanical Properties and Microstructure Analysis of Mild Steel Welding Made by GTAW

This work discusses the effect of gas tungsten arc welding (GTAW) variables on the welding transverse tensile strength and hardness of S 235JR at different groove configurations. The welding microstructure and numerical fracture mechanism are also discussed. GTAW is increasingly emerging in the local industry due to its advantages over conventional shielded metal arc welding (SMAW). The properties of steel welding have always concerned manufacturers and researchers. Since steel structures experience forces such as tensile, it’s vital that good welding has increased tensile strength. It was reported that the hardness of welding affects the welding properties and, therefore, the integration of welded structures. The groove shape of the joining ends determines the size of the FZ and affects the dilution; thus, it is important to study the groove shape due to its effect on the final properties of welding. The results showed an increased welding traverse tensile strength (251 MPa) at higher welding speeds (150 mm/min) and V-shaped groove welding. The V-shaped groove welding that obtained higher tensile strength (251 MPa) has shown higher grain boundary ferrite and PF volume friction in the FZ and finer PF in the HAZ due to its higher interpass heat input. Higher traverse tensile strength welding has shown increased bainite and lower bainite volume friction in FZ and a finer grain structure in HAZ. The failure due to tensile force starts at the welding root, according to numerical analysis, and a double V-shaped groove has shown deformation balance at the tensile test.

Effects of irradiation plus thermal aging on the phase boundary microstructure of austenitic stainless steel welds

Irradiation damage and thermal aging greatly affect the phase boundary microstructure and stress corrosion cracking of austenitic stainless steel weld metals (ASSWMs) in water-cooled nuclear reactors. However, the effects of irradiation plus thermal aging (I + A) on the phase boundary segregation and phase changes remain unclear. Phase changes and elemental segregation at the carbide and carbide-free phase boundaries of 308 L ASSWMs after I + A treatment were investigated using atom probe tomography and transmission electron microscopy. The I + A treatment induced Si depletion at the phase interfaces of δ-ferrite/austenite (δ/γ) and δ-ferrite/carbide (δ/C) and also induced Ni enrichment and Cr depletion with concentrations having the order Ni/Cr(δ/γ) > Ni/Cr(δ/C) > Ni/Cr(γ/C). The solute-defect binding model and the vacancy mechanism were applied to explain the phase boundary segregation. Furthermore, the I + A treatment affected microstructural evolution near the phase boundaries; this reduced spinodal decomposition and inhibited G-phase and Ni/Si-rich-cluster formation. The phase separation of δ-ferrite near δ/γ and δ/C phase boundaries differed with the distance from the boundary, forming a gradient microstructure from phase boundaries to δ-ferrite internally. The gradual precipitation of the G-phase was observed beyond about 15 and 10 nm from the δ/γ and δ/C interfaces, respectively; moreover, the growth of α'-phase in the δ-ferrite was accelerated with increasing distance from the δ/γ and δ/C interfaces.

Microstructure and mechanical characterization of weldments of titanium alloy plates joined using different welding techniques

Microstructure and mechanical characterization of weldments of titanium alloy plates joined using different welding techniques

Optimization of gas metal arc welding parameters for dissimilar steel welds: A case study on duplex stainless steel 2205 and stainless steel 316L

The significance of welded connections in steel structures necessitates precise structural designs and processing adaptations to ensure robust mechanical strength and durability. Gas metal arc welding (GMAW) employing controlled curves presents advantages over conventional methods, offering enhanced weld bead properties, improved aesthetics, and reduced thermal inputs. This research investigates the impact of GMAW parameters using controlled curves on the microstructure and geometry of welds between dissimilar structural steels—duplex stainless steel 2205 and stainless steel 316L grade 50—commonly employed in construction. The aim is to optimize the GMAW welding process with controlled curves and surface tension transfer between these dissimilar steels. Through a 23-factorial experimental design encompassing feed speed (Va), arc focus (FC), and peak-to-base amplitude (APB), the study examines welding energy, geometry, deposition efficiency, microstructure, microhardness, tensile strength, and corrosion properties. Optimal welding energy fosters refined microstructures and uniform hardness, aiding in predicting weld throat area. Higher energy levels expand the heat-affected zone and coarse grains, while lower energies escalate variability. Predictive models facilitate fine-tuning welding energy and throat area for desirable properties and penetration while minimizing disruptions. This process optimization can be achieved by employing derived equations that limit welding energy and curve parameters, striking a desired balance between cost, structural integrity, and reliability.

Dynamic behavior regulation of droplet transfer based on arc-bubble control by ultrasound-induced during underwater wet welding

In comparison to welding in air, the periodic formation of unstable arc bubbles is a significant factor contributing to the unstable mass transfer process during underwater wet welding (UWW). Up to now, there is no ideal method to control droplet transfer and improve arc stability. In this study, the ultrasound-induced method (UIM) was used to regulate the droplet transition behavior and improve the process stability. The behavior features and key mechanisms of arc-bubble and droplet transfer induced by ultrasound were revealed with the employment of highspeed camera and X-ray observation, respectively. The incident angle of ultrasound was taken as a variable to reveal its effects and mechanism of action on the behaviors of arc bubble and droplet transfer, weld formation quality, microstructure, and property of weld joint. The results show that ultrasound-induced a new rising mode of arc bubble, which can significantly reduce the repulsive resistance that come from the bubble rising on the droplet transfer process. Compared with underwater wet welding without ultrasound, the average diameter of molten droplets reduces from 3.2 mm to 1.7 mm, and the droplet transfer frequency increases from 7.8 Hz to 13 Hz as the incident angle of ultrasound increases to 60°. In addition, the weld seam without obvious defects could be produced by UWW with UIM, of which the Variation coefficient of weld reinforcement is reduced from 21.3 to 11.6 and 17.4 at an ultrasonic incident angle of 30° and 45°. With increasing of ultrasound incident angle, it showed that the microhardness of the weld joint has a slight increase. In the heat-affected zone, the microhardness for the joint increased from 290 HV to 320 HV while the incident angle increased to 60°. This research shows that an appropriate incident angle of ultrasound can obtain good-quality joints which has a stable metal transfer process in underwater wet welding.

Assessment of Weld Microstructure Through Sound Velocity Measurements for Power Plant Applications

This research study employed an immersion-based micro-resolution ultrasonic velocity measurement technique (MUVT) to evaluate Grade 91 (9Cr-1Mo-V) steel welds. This process utilized a 20 MHz focused ultrasonic beam with a spot size of 250 µm, a 6 µm laser vibrometer spot size for detection, and an automated 3-axis raster scanner to accurately collect ultrasonic velocity data from two Grade 91 steel welds fabricated using cold metal transfer (CMT) and flux-cored arc welding (FCAW) processes. By analyzing the MUVT data, the Poisson’s ratio (υ) and modulus of elasticity (E), which are important mechanical properties for weldments, were calculated. The correlation between mechanical properties and ultrasonic velocity was examined. The results indicated that longitudinal ultrasonic velocity could effectively identify base metal, heat-affected zone (HAZ), and weld metal areas, showing a strong correlation with hardness. In particular, the distinctive V-shaped dip in velocity and hardness data across the HAZ areas of both samples highlighted changes in the microstructure of creep strength–enhanced ferritic steel welds. Importantly, the immersion-based MUVT demonstrated high accuracy in small sections of the weld, surpassing the conventional contact ultrasonic testing method in spatial resolution detection.

A novel method for fully penetrated U-rib-to-deck joints: Single-sided oscillating laser arc hybrid welding

U-rib-to-deck (RTD) joints represent one of the most critical and vulnerable welding details of orthotropic steel decks. Aiming for full penetration and high-level service performance, a novel method with single-sided oscillating laser-arc hybrid welding (OLAHW) technique was proposed for the RTD joint. The weld formation, microstructure and mechanical properties were extensively investigated. The results indicated that the porosity and lack of fusion (LoF) defects effectively suppressed with the beam oscillation during LAHW process. The OLAHW technique has good spatial accessibility with larger laser beam incidence angle of 20° Beam oscillation led to an increase in acicular ferrite in the fusion zone (FZ) while simultaneously a reduction of martensite in the heat effected zone (HAZ). This was related to the cooling time, and the thermal simulation results revealed that the OLAHW sample demonstrated comparable cooling times in both the Laser-FZ and arc-FZ. Consequently, beam oscillation can generated more homogeneous microstructures and microhardness. Although the microhardness of the OLAHW sample in the FZ was increased compared to the conventional arc welding (CAW) and LAHW sample, the highest microhardness value remained within acceptable limits (380 HV). Moreover, the ultimate tensile strength of the OLAHW weld sample increased by 7 % compared to the CAW weld sample. The application of the OLAHW technique demonstrates its feasibility for engineering applications in orthotropic steel decks manufacturing.

Analyzing weld bead geometry and microstructure in ultrasonic-assisted activated flux TIG welding of ST37 steel

Analyzing weld bead geometry and microstructure in ultrasonic-assisted activated flux TIG welding of ST37 steel

Microstructures and mechanical properties of laser-arc hybrid welded high-strength aluminum alloy through beam oscillation

High-frequency beam oscillation and synchronous wire-powder feeding were adopted for the laser-arc hybrid welding of a 2219-T6 high-strength aluminum alloy. Increasing the beam oscillation frequency from 0 to 250 Hz not only reduced the weld porosity from 2.64% to 0.16% but also promoted the transformation of columnar dendrites to fine equiaxed grains. In addition, the content of precipitated Al2CuMg increased with the refined size of the weld microstructure. The length of the columnar grains and the diameter of the equiaxed grains in the weld center were reduced by 40% and 50%, respectively. Owing to these improvements, the weld microhardness increased and became more uniform, and the variance decreased by 74%. The ultimate tensile strength and elongation of the welded joint reached 238.5 MPa and 4.3%, respectively, which were 26.5% and 105% higher than those of the non-oscillating hybrid weld, respectively. The weld tensile strength and the proportion of the area of the pore were negatively correlated. The porosity and microcracks of the welded joints were the main factors affecting the tensile strength of welded joints.