Weld Fusion Zone Research Articles

Liquation cracking in Inconel 617 alloy by Laser and Laser-Arc Hybrid welding

ABSTRACT The present study investigates susceptibility of Inconel 617 to liquation cracking in laser-based welding techniques such as autogenous laser welding (ALW) and laser-MIG hybrid welding (LHW) with variation in heat input. Advanced characterization techniques such as high-speed Nano-Indentation testing and micro X-ray diffraction techniques were utilized to analyze microstructural variations in correlating mechanical behavior of low-melting eutectics formed in partially melted zone (PMZ). Results indicated that the liquation cracking in PMZ was associated with the constitutional liquation reaction between intermetallic carbides and austenite matrix. With increase in heat input, its susceptibility reduced, although with enhancement in grain-boundary liquid film formation and was associated with the constitutional liquation of (Cr, Mo)-rich M23C6 carbides and γ matrix. Combined effect of induced thermal stress with presence of low-melting eutectics in partially melted zone was found to greatly influence liquation-cracking susceptibility in both the welding processes. Indeed, ternary eutectic comprising metallic carbides of Cr and Mo and austenite-matrix with low nano-hardness values compared to that of hard carbides present in base metal and weld fusion zone re-confirmed their influence on cracking susceptibility. Increase in heat input enhanced dissolution of Mo-rich M6C carbides that attributed to stress-relaxation and thereby reduce cracking propensity.

Investigation on mechanical and microstructure characteristics of nickel based C-2000 super alloy using laser beam welding

The main aim of the research is to investigate the microstructure and mechanical properties of advanced corrosion resistant alloy C-2000 welded with Laser Beam Welding (LBW) process. Laser welding is a high-power-density fusion-welding process that produces high aspect ratio welds with a relatively low heat input compared with other arc-welding processes. Dinolite macro analyzer was used to determine the aspect ratio and other defects in the weld joint. The micro structural characteristics of the weldment are analyzed with Optical and Scanning Electron Microscope (SEM). The micro segregation of alloying element in interdendritic regions is quantified by Energy dispersive X-ray spectroscopy (EDS). Microstructure examination shows that mild copper microsegregation is observed near the interdendritic region. The strength, ductility, hardness and toughness of weld joints are evaluated by tensile, Vicker’s hardness and Charpy impact test respectively. The result outcome shows that mechanical properties are slightly lower than base metal due to the combined existence of columnar and equiaxed grains in the weld fusion zone.

Assessment of Mechanical and Metallurgical Properties of Thermally Aged Electron Beam Welded AISI 321 Stainless Steel

Electron beam welding produces very narrow and deep penetration therefore it finds application where welding of thick materials is required. AISI 321 is susceptible to intergranular corrosion when it is used in high temperature and harsh conditions, owing to the Titanium depletion in the weld zone. However, the heat affected zone formed in electron beam welding extends to a narrow region across the weld pool. In the present study electron beam welding of austenitic 321 stainless steel is done to examine the mechanical and metallurgical properties of the joints. Microhardness tests along and across the weld bead were carried out. Tensile and impact tests were performed to analyze mechanical properties. The microstructures of the weld zone, fusion zone and base metals were also captured. Skeletal ferrites were seen in the weld metal. The aging treatment of 700°C for 24 hours which resulted in a change in morphology of the grains from skeletal to vermicular and promoted the formation of Ti-rich carbides on the grain boundaries. The maximum impact toughness at sub-zero temperature i.e. -40°C was recorded as 129.3 J in as-welded samples and it got reduced to 119.5 J after aging treatment. The average ultimate tensile strength was 582 N/mm2 and it got decreased to 481 N/mm2 after aging treatment.

Arc Characteristics and Welding Process of Magnetic Field Assisting Plasma-GMAW-P

Low-carbon steel Q235B was successfully joined by plasma-pulsed gas metal arc welding (plasma-GMAW-P) with an external magnetic field. The arc profile, temperature field, electrical signal, microstructure, and mechanical properties of this method were analyzed. The results indicated that the coupling degree of the two arcs increased with the strengthening of the magnetic field current. However, when the magnetic field current was greater than 1 A, the arc pro-file changed slightly with the increase of the magnetic field current. Fixed on the magnetic field current, the coupling degree first increased and then decreased with the increase of the plasma welding current, GMAW-P welding current, plasma gas flow rate, and nozzle height, respectively. The maximum temperature had no obvious influence on joint penetration at different magnetic field cur-rents. However, the average temperature had an inverse effect on joint penetration at different magnetic field currents. The weld fusion zone joint tensile test results showed that the ratio of depth to width increased with the application of magnetic field currents. Moreover, tensile strength on the upper and lower part of the tensile samples were 521 and 488 MPa, respectively, which were 4.6% and 3.2% higher than those without the magnetic field. The microhardness of the weld joints was higher than that without the magnetic field.

Microstructure and mechanical behavior of P91 steel dissimilar welded joints made with IN718 filler

The paper presents the detailed microstructure study and mechanical behavior of P91 welded joint produced by gas tungsten arc welding process (GTAW) using the dissimilar nickel grade superalloy Inconel 718 filler (ERNiFeCr2). The microstructural changes in the weld fusion zone (WFZ) and heat-affected zone (HAZ) were also studied for varying heat treatment conditions. The effect of the Inconel 718 filler on the tensile properties, hardness and Charpy impact toughness (CIT) of the welded joint was also studied for as-welded and heat-treated conditions. The post-weld heat treatment (PWHT) was performed in a temperature range of 650–1060 °C. The microstructure study showed the formation of an unmixed zone at the interface of the HAZ and weld metal and remain unaffected during the PWHT. The region of weld metal near the boat fusion line showed the cellular and columnar dendrites. The center region of the bulk weld metal was solidified as the columnar dendrites and cellular dendrites along with segregation of the elements at inter-dendritic boundaries. The dendrite core showed the segregation of the Ni, and Cr; however, at dendrite boundaries, major segregation was observed for the elements Nb, Mo and Ti. The heat treatment up to a temperature of 810 °C has observed a negligible effect on the WFZ microstructure; however, a significant change in microstructure was observed for the P91 HAZ region. A significant change in the microstructure of the WFZ was measured after the normalizing at 1060 °C, followed by tempering at 760 °C for 2 h (complex heat treatment). The tensile strength of the welded joint was measured 817 MPa with a joint efficiency of 146% for as-welded condition and a maximum of 901 MPa with a joint efficiency of 161% for complex heat treatment. The welded joint CIT was measured a maximum of 48 J in as-welded condition and get reduced after the PWHT and measured a minimum of 35 J after complex heat treatment. A hardness variation was observed along the welded joint for as-welded and PWHT condition. In the as-welded condition, the hardness of the WFZ was measured about 417 ± 21 HV and showed a minute change with an increase in tempering temperature. The minimum hardness was measured in the inter-critical HAZ region for the as-welded joint and produce a significant level of heterogeneity in hardness variation along the P91 HAZ. PWHT has observed a considerable reduction in the hardness value of the P91 HAZs except for ICHAZ. A negligible level of hardness variation along P91 HAZ was measured after PW 4.

Effects of heat treatment and Nd: YAG laser repair welding parameters on the microstructure and properties of a Cu–Ni–Si–Cr mold alloy

The novel Cu–Ni–Si–Cr alloy (Cu-6.7Ni-1.6Si-0.3Cr) has good prospects for substitution with toxic Be–Cu alloy. This study used a Nd: YAG laser process with a variety of heat treatment processes and repair welding parameters to investigate the effects of heat treatment and repair welding parameters on the microstructure and properties of the Cu–Ni–Si–Cr mold alloy. To eliminate the disadvantages of the laser welding process for the Cu–Ni–Si–Cr mold alloy, such as high thermal conductivity and high thermal expansion coefficients, many improved approaches have been used, including pre-weld heat treatments (expected to reduce thermal conductivity), control of the laser shape, and preheating (to slow down the cooling rate and avoid excessive expansion and contraction). The results showed that after the pre-weld heat treatment and preheating, deeper penetration and defect-free welds were obtained. However, continuous Ni/Si phase precipitates were observed along the grain boundaries in the welding fusion zone (WFZ), which may have harmful effects on the mechanical properties of the welds. This problem was improved by post-weld heat treatment (PWHT). The repair welds (including WFZ and HAZ) after PWHT showed a good combination of hardness, tensile strength, and thermal properties. The high hardness or tensile strength in the weld was attributed to the formation of a nano-sized Ni/Si phase, which was identified via a transmission electron microscope.

Microstructure and Performance Analysis of Welded Joint of Spray-Deposited 2195 Al-Cu-Li Alloy Using GTAW

High-strength aluminum alloy fabricated using spray deposition technology possesses many advantages, such as fine crystal grains, low component segregation, uniform microstructure, and small internal stress. In this study, spray-deposited 2195 Al-Cu-Li alloy in forged state was used and welded using the gas tungsten arc welding (GTAW) process to test and verify the features of the fusion joint. Quantitative analysis was carried out to evaluate the relationship between the local microstructures and performances of the fusion joint, which was composed of four zones: weld metal, fusion zone, heat-affected zone, and base metal. The characteristic quantities of each zone, including recrystallized grain fraction, grain sizes, grain misorientation angle, and Vickers hardness, and their distributions were considered as the key factors affecting the performance of the joint because of welding thermal cycle impact on the fusion joint. To recognize the metallurgical characteristics of spray-deposited alloy 2195, a statistical algorithm based on the concept of the Hall–Petch relationship was proposed to validate the actual test results, which include the correlation effects of both the filler wire and welding process. The correlation between the microstructures and performances of several characteristic quantities were evaluated by integrating the above characteristic information of the fusion joint under the strong coupling of multiple factors. Thus, the advantages of weldability of spray-deposited alloy 2195 using GTAW could be understood in detail.

Role of dissimilar IN617 nickel alloy consumable on microstructural and mechanical behavior of P91 welds joint

This paper investigates the metallurgical behavior and mechanical properties of the P91 steel welds joint. The joint of heat-resistant P91 steel has been welded by the gas tungsten arc welding (GTAW) process using the dissimilar Inconel grade 617 filler. The P91 welds joints have been subjected to varying heat treatment regimes in the temperature range of 650–810 °C for 2 h. The normalizing-based tempering was also performed for the welded joint. The weld fusion zone (WFZ) with austenitic structure and heat-affected zones (HAZs) with martensitic structure was characterized using the optical microscope and scanning electron microscope (SEM). The detailed characterization of the weld metal and HAZ interface has also been performed for as-welded and post-weld heat treatment (PWHT) conditions. For mechanical properties of the welds joint, tensile testing and hardness testing were performed. The relationship between mechanical behavior and microstructure of the welded joint has been evaluated for as-welded and heat treatment conditions. The microstructure studies revealed the formation of an unmixed zone (UZ) close to the fusion line, and it was characterized as peninsula and island. The WFZ showed the complete austenitic mode of the solidification and revealed the austenitic structure with cellular and equiaxed grains in the center of the weld metal. The columnar and cellular dendrites were seen near the boat fusion line, i.e., interface of the weld metal and HAZ. The soft δ ferrite patches were observed near the fusion line in the area of HAZ and remain undissolved up to tempering temperature of 810 °C (PW 3). The dissolution of the ferrite patches was noticed for PW 4. The maximum and minimum tensile strength of the welds joint was measured 731 MPa and 502 MPa for PW 3 and PW 2, respectively. A uniform hardness variation in the transverse direction of the welded joint was observed for PW 3 and PW 4 conditions. The optimum combination of strength and ductility was obtained for the PW 3 condition.

Role of heat-treatment and filler on structure-property relationship of dissimilar welded joint of P22 and F69 steel

This paper investigates the microstructural features and mechanical behavior of the dissimilar welded joint (DWJ) of lean duplex A 182 F 69 steel and 2.25Cr-1Mo (P22) steel. The multi-pass DWJ has been prepared using the Gas Tungsten Arc Welding (GTAW) process employing the Inconel 617 filler material. The DWJ has been subjected to post-weld heat treatment (PWHT) in a temperature range of 760 °C (PW 1)-810 °C (PW 2). The tensile testing and metallographic testing sample have been cross-sectioned from the DWJ for different heat treatment conditions of the welded joint. Each zone of the DWJ was characterized using the optical and scanning electron microscope (SEM). Cellular and columnar dendrites have been observed near the interface of weld fusion zone (WFZ) and heat-affected zone (HAZ) while equiaxed structure in center of the WFZ. The WFZ showed the austenitic structure with dendritic core and inter-dendritic boundaries. The inter-dendritic boundaries showed the presence of secondary phase particles, mainly enriched with Cr, Mo and Ti. Unmixed zone and compositional variation across the WFZ and HAZ interface have been observed on both the sides of DWJ. For as-welded condition, tensile fracture surface revealed the mixed mode of the fracture with tensile strength higher than that of the base P22 and F69 steel. The fracture location was in the center of the WFZ. For PW 1 condition, the crack initiation zone showed the mixed-mode while the final fracture showed the brittle fracture with cleavage facets. In PW 1, the fracture has been observed in HAZ of P22 side with strength lower than that of the base metal of F69. In PW 2 condition, complete brittle mode of the fracture has been observed and fracture surface showed the cleavage facets with river marking.

A microstructural and mechanical behavior study of heterogeneous P91 welded joint

The current work has been performed to characterize the heterogeneous P91 welded joint. The gas tungsten arc welded (GTAW) P91 welds joint has been prepared using the dissimilar Inconel 617 filler. The P91 welded plates have been subjected to post-weld normalizing and tempering (PWNT) heat treatments for varying normalizing temperature in the range of 950–1150 °C. To homogenize the microstructure across the welded joint, tempering has been performed at 760 °C for 2 h for each normalized conditions. The tensile and microhardness tests have been conducted to determine the mechanical properties of the welded joint in as-welded and heat-treated conditions. The microstructure characterization has been performed for the weld fusion zone (WFZ) and efforts have been made to develop a relation between microstructure evolutions and mechanical behavior of the welded joint. Microstructure analysis was carried out with optical and field scanning electron microscope (FESEM). The optimum combination of strength and ductility was obtained for the sample heat-treated at 1050 °C for 40 min (normalized)+760 °C/2 h (tempering). The lower strength was obtained for the Inconel 617 filler as compared to P91 filler, while ductility obtained for Inconel 617 filler was higher than that of P91 filler.

Microstructural Characterization and Mechanical Properties of Fiber Laser Welded CP-Ti and Ti-6Al-4V Similar and Dissimilar Joints

In this research, the microstructures and mechanical properties of similar and dissimilar autogenous joints of 3 mm thick commercially pure titanium (CP-Ti) and Ti-6Al-4V welded by ytterbium fiber laser (Yb:YAG) were investigated. Two sets of laser power and welding speed were selected in such a way that the heat input remained constant. Microstructural characterization of the joints was investigated by an optical microscope, and mechanical properties were determined by hardness and tensile tests. The only defects found were porosity and underfill, and no signs of lack of penetration and solidification cracks were observed in any of the joints. Microstructural evaluation of the fusion zone (FZ) showed that in similar Ti-6Al-4V joint, a supersaturated nonequilibrium α′ martensite was formed due to rapid cooling associated with laser welding. In similar CP-Ti, coarse equiaxed grains were observed in the FZ. Unlike the similar joints, a clear interface was observed between the heat-affected zone (HAZ) and the FZ in both the CP-Ti and Ti-6Al-4V sides in dissimilar joints. Among all the joints with different weld parameters, similar Ti-6Al-4V showed the highest strength and the lowest ductility. In similar CP-Ti and dissimilar joints, fractures took place in the CP-Ti base metal, but all the Ti-6Al-4V similar joints failed in the FZ. Significant changes in the strength and hardness with varying laser power and welding speed implied that the mechanical properties of the weld fusion zones were not entirely governed by the heat input but were also affected by individual welding parameters.

Liquation cracking in the heat-affected zone of IN939 superalloy tungsten inert gas weldments

The main aim of this study was to investigate liquation cracking in the heat-affected zone (HAZ) of the IN939 superalloy upon tungsten inert gas welding. A solid solution and age-hardenable filler metals were further studied. On the pre-weld heat-treated samples, upon solving the secondary γ′ particles in the matrix, primary γ′ particles in the base metal grew to “ogdoadically diced cubes” of about 2 µm in side lengths. The pre-weld heat treatment reduced the hardness of the base metal to about HV 310. Microstructural studies using optical and field-emission scanning electron microscopy revealed that the IN939 alloy was susceptible to liquation cracking in the HAZ. The constitutional melting of the secondary, eutectic, and Zr-rich phases promoted the liquation cracking in the HAZ. The microstructure of the weld fusion zones showed the presence of fine spheroidal γ′ particles with sizes of about 0.2 µm after the post-weld heat treatment, which increased the hardness of the weld pools to about HV 350 and 380 for the Hastelloy X and IN718 filler metals, respectively. Application of a suitable solid solution filler metal could partially reduce the liquation cracking in the HAZ of IN939 alloy.

Unveiling the strengthening mechanism of laser welded fusion zone of dissimilar Ni-based superalloys

The strengthening mechanism of a laser welded fusion zone between two dissimilar Ni-based superalloys is studied. The microstructure of as-welded fusion zone is columnar grain featured with a micron scale dislocation cellular substructure. Strengthening component analysis of aged fusion zone at 650 °C reveals the hardening contribution of gamma prime phase (~52%), dislocation cellular substructure (~28%) and solid solution elements (~19%). Our results indicate that the formation of dislocation cellular structure endows fusion zone with higher strength particularly at 600 and 650 °C, which provides novel insights into strengthening of welded Ni-based superalloy.

Dissolution of δ-ferrite and its effect on mechanical properties of P92 steel welds

This paper reports on the dissolution of δ-ferrite in the weld fusion zone using post-weld normalizing and tempering (PWNT) and its effect on mechanical properties. The autogenous gas tungsten arc welding (GTAW) was used to prepare double-sided welded joints of P92 steel. After welding, post-weld heat treatment (PWHT) at 760 °C for 2 h and post-weld normalizing at 1050 °C for 1 h followed by tempering at 760 °C for 2 h were performed. The morphology, composition, structure, and hardness of δ-ferrite are verified. The effect of PWHT and PWNT on mechanical properties is also observed. In as-welded and PWHT conditions, the retention of δ-ferrite was observed while the dissolution of δ-ferrite was confirmed after PWNT. In the PWNT condition, uniform microhardness across the welded joint, increased ductility, and increased Charpy toughness of weld fusion zone (almost equal to as received material) were achieved. Dissolution kinetics of δ-ferrite is quantified using Thermo-Calc for Scheil's solidification calculation and DICTRA for calculating diffusion coefficients of Cr and W at 1050 °C in austenite.

A Study on Microstructure and Phase Transformation in the Weld Fusion Zone of TIG-Welded IN939 with IN625 and IN718 as Filler Metal

Microstructure and phase transformations were investigated in the weld fusion zone (WFZ) of tungsten inert gas (TIG)-welded IN939 nickel-based superalloy with IN718 and IN625 alloys used as filler metal. The optical and field-emission scanning electron microscopy (FESEM) and also energy dispersive spectroscopy (EDS) were utilized for the microstructural study of the WFZ. The microstructural examination showed that the Nb and Ti elements were microsegregated in the inter-dendrite region, causing a significant concentration gradient between the core and the inter-dendrite region within the WFZ. Observations indicated the formation of the (Nb, Ti) C carbide phases in the solidification process. With a thickness of about 0.2 μm, some plate-like δ phase was observed in the WFZ of both samples upon heat treatment at 750 °C. The results of X-ray diffraction analysis (XRD) confirmed the presence of the δ phase in the WFZ. However, the δ phase disappeared at temperatures beyond 1000 °C. The occurrence of phase transformation during the solidification process was identified by differential thermal analysis (DTA). The WFZ was seen to solidify in the temperature range of 1370°C to 1270°C.

COMPARISON STUDY OF CONSTANT CURRENT AND ARC OSCILLATION TECHNIQUES ON GTA WELDED AZ31B MAGNESIUM ALLOY JOINTS

The challenges of achieving significant weight reduction in the automobile industry in the context of fuel savings, recyclability and emission reduction has promoted focus on lightweight metals such as magnesium. GTA welding technology is the main welding method adopted for magnesium alloys because of its advantages of utility and economy. Both magnetic arc oscillation and current pulsing techniques resulted in significant microstructural refinement in weld fusion zone. Hence in this investigation an attempt has been made to study the constant current and arc oscillation on tensile and microstructural characteristics of gas tungsten arc welded AZ31B magnesium alloy joints. From this investigation, it is found that the joints fabricated with magnetic arc oscillation having the superior tensile properties compared to constant current welding. The formation of fine grains and higher hardness in fusion zone are the main reasons for the superior tensile properties of these joints.

Mechanical and Metallurgical Characterization of Dissimilar P92/SS304 L Welded Joints Under Varying Heat Treatment Regimes

This work was performed to characterize the dissimilar austenitic grade SS304 L and martensitic grade creep strength of an enhanced P92 steel welded joint. The welded joint was prepared using the autogenous gas tungsten arc welding process. The welded joint was subjected to conventional heat treatment consisting of tempering at 760 °C for 2 hours, followed by air cooling and unconventional heat treatment (UHT) consisting of normalizing (1040 °C/40 min), further followed by air cooling and, finally, stabilized tempering at 760 °C for 2 hours. The heat-treated welded joint was subjected to the microstructural characterization and mechanical testing. The room temperature Charpy toughness (CT) testing for both the weld fusion zone (WFZ) and heat-affected zone, tensile testing, and hardness testing were performed to characterize the dissimilar welded joint. Stabilized microstructure associated with improved mechanical properties were observed for UHT. The CT and tensile strength were optimum for the UHT.

A study on laser beam oscillating welding characteristics for the 5083 aluminum alloy: Morphology, microstructure and mechanical properties

Laser beam oscillating welding was used to connect 5083 aluminum alloy sheets. The effect of oscillating parameters on the weld porosity and morphology was investigated. When the oscillating frequency was over 200 Hz and the oscillating diameter was over 2 mm, the weld porosity could be suppressed by laser beam oscillation. The microstructure analysis conducted by electron backscattered diffraction and an electron probe micro-analyzer revealed that the laser beam oscillation could refine grains and promote the uniform distribution of the β(Mg2Al3) phase in the weld fusion zone, thus leading to increasing micro-hardness of the weld zone. The tensile test results demonstrated that the tensile strength and the elongation of the laser oscillating welding joints were much higher than the joints without oscillation, mainly owing to the suppression of porosity.

Process parameters and mechanical properties of SAPH440 steel in pulse arc welding with different heat inputs

Thermal cycling parameters of pulse arc welding for SAPH440 steel was experimentally determined for different heat inputs. The welding thermal cycle curves of the weld fusion and heat-affected zones were successfully constructed based on the thermocouple measurements through the back drilling hole. The hardness and tensile strength variations under different heat inputs were also analyzed. This provided a database for the determination and optimization of process parameters, improvement of microstructure and properties of weld fusion and heat affected zones, and overall quality of pulse arc welding of steels.

Thermo-mechanical study of single and multi-pass welding of CSEF steel for residual stresses and deformations considering solid state phase transformation

The present study involves thermo-mechanical modelling of submerged arc welding of CSEF (Creep Strength Enhanced Ferritic) steel plate of thickness 10 mm as single pass and multi-pass welding. A square butt joint with no edge preparation and a V-butt joint with 15° included angle are considered for SAW welding. The martensitic-austenitic transformation phenomenon in P91 steel was also implemented with specific changes in the properties of the weld and base material. It is observed that SAW process with single pass demonstrates stable residual stress distribution, whereas in multi-pass weld, the residual stresses show uneven distribution across the weld. The longitudinal residual stresses are higher in magnitude comparing to transverse residual stresses for both the welding cases. The single pass SAW weld fusion zone has shown compressive stress throughout the thickness of the plate with maximum value at the top side. However, in multi pass weld, the compressive residual stresses have multiple peak values along the weld thickness. The deflection pattern is not effectively altered with multi pass with slight difference from single pass. Therefore, it is suggested that if possible, single pass weld can be preferred over multi pass weld.