Dissimilar Weld Joints Research Articles

Effect of Heat Input on Microstructure and Properties of Laser-Welded 316L/In601 Dissimilar Overlap Joints in High-Temperature Thermocouple.

Heat input, a crucial factor in the optimization of high-temperature thermocouple laser welding, has a significant impact on the appearance and mechanical properties of dissimilar welded joints involving stainless-steel- and nickel-based alloys. This study focuses on laser overlay welding of austenitic stainless steels and nickel-based alloys. The findings indicate that an increase in heat input has a more pronounced effect on the penetration depth and dilution rate. Under high heat input, the weld has cracks, spatter, and other defects. Additionally, considerable amounts of chromium (Cr) and nickel (Ni) elements are observed outside the grain near the crack, and their presence increases with higher heat input levels. Phase analysis reveals the presence of numerous Cr2Fe14C and Fe3Ni2 phases within the weld. The heat input increases to the range of 30-35 J/mm, and the weld changes from shear fracture to tensile fracture. In the center of the molten pool, the Vickers hardness is greater than that of the base metal, while in the fusion zone, the Vickers hardness is lower than that of the base metal. The overall hardness is in a downward trend with the increase of heat input, and the minimum hardness is only 159 HV0.3 at 40 J/mm. The heat input falls within the range of 28-30 J/mm, and the temperature shock resistance is at its peak.

Numerical investigation of the impact of thermoelectric effect on electron beam welding of dissimilar materials

Electron beam welding of GH4169 and Ni is required in the manufacture of the regenerative cooling system of the liquid rocket motor. The thermoelectric effect is observed during the welding of dissimilar metals; however, there has been a lack of investigation into the influence of this effect on electron beam welding joint formation and its dependence on test plate thickness. The thermoelectric effect of electron beam welding between GH4169 and Ni with varying thicknesses, as well as the influence of induced magnetic fields on electron beam trajectories, are investigated through the establishment of a numerical model incorporating thermal-electric-magnetic coupling.The results show that when the test plate increases from 2.5 mm to 10 mm the peak current density increases from 5.1 × 106 A/m2 to 7.6 × 106 A/m2, and the maximum magnetic flux density increases from 1.49× 10−2 T to 1.77 × 10−2 T. The increase in magnetic flux density results in a greater displacement of the electron beam spot away from the interface between the two materials, thereby causing incomplete fusion defects in the joints. This study elucidates the fundamental physical principles underlying the occurrence of incomplete fusion defects in electron beam welding joints, thereby furnishing essential theoretical underpinnings for enhancing the quality of dissimilar metal electron beam weld joints.

Microstructural and mechanical behaviour of friction welded SS316L components fabricated by selective laser melting

The research study on solid state welding, especially rotary friction welding (FW) on the selective laser melted (SLM) components is limited. The present study is performed to deduce the scope of FW on SLM stainless steel (SS) 316 L parts and also to understand the plastic deformation effect on SLM components. The obtained results can be considered as a reference for the dissimilar welding joints of SS316L with other metallic systems in future studies. The microstructural analysis revealed significant changes in microstructural features like grain morphology and grain orientation. Also, it showed the conventional three distinct zones during the FW process, viz., base metal (BM), heat affected zone (HAZ) and weld zone (WZ). The columnar grains in the BM change into elongated deformed grains while moving towards the WZ. The findings also confirmed the existence of homogeneous equiaxed grains due to complete recrystallization in the WZ. The refined grains, resulted in improved hardness by 23 % at the WZ, when compared with SLM sample. Tensile test results demonstrated an enhancement of yield strength of about 190 MPa, however by sacrificing the ductility. WZ has achieved higher hardness and strength than the SLM component, even though the dislocation density is very high in later one. To understand this coupled effect, work hardening calculations and strengthening contributions were evaluated. The results from strengthening mechanisms confirmed that Hall-Petch strengthening is the dominant strengthening contribution in the welded samples and in case of as built parts it was due to dislocation strengthening.

Creep, fatigue and creep-fatigue behaviour of martensitic/bainitic steels and nickel-based alloys and their welded joints at the temperature range 500°C–750°C

ABSTRACT The aim of the paper is to investigate experimentally the fatigue and creep-fatigue material behaviour of improved materials and welded joints for the application in flexible future power plants. These materials promise a reduction in manufacturing costs as well as an increase in flexibility by providing enhanced creep strength thorugh a wall thickness reduction. At the temperature range between 500°C −550°C, the investigation focusses on the creep and low-cycle fatigue behaviour of dissimilar welded joints from conventional materials (bainitic and martensitic materials T24 and T92) to nickel-based alloys (A617B and HR6W) fabricated as tubes. At the temperature range between 700°C and 750°C, it focusses on the creep, low-cycle fatigue and creep-fatigue behaviour of similar and dissimilar welded joints from nickel-based alloys (A740H, A617B and A263) fabricated as tubes and as pipes. Metallographic investigations after testing provide support for understanding the influence of temperature, strain amplitude and dwell time on the microstructure change and the fatigue strength.

Dissimilar welding of UNS S31803 and UNS S30400 tubes superiority and adverse in rotary friction welding

Solid-state welding provides a distinct state of the art to joining various metal tubes. In contrast to other types of welding, dissimilar joining by solid-state welding maintains the integrity of its joints. Dissimilar joints of UNS S31803 and UNS S30400 tubes were carried out using rotary friction welding process. Three combinations of tube joints fabricated were, ASS to ASS, DSS to DSS and ASS to DSS joint. The tensile tests showed dissimilar weld joint achieved the minimum strength of ASS similar joint. Fractography for similar and dissimilar tube joints showed a ductile pattern of fracture with dimples and voids in the dissimilar tube weld. Microstructure analysis showed that diffusion bond line for similar and dissimilar joints confirms the sound weld tube joints. Corrosion test showed that among three combinations, ASS to DSS dissimilar joint had lesser corrosion rate than ASS to ASS or DSS to DSS similar joints.

Influence of Butter Layer Thickness on Microstructure and Mechanical Properties of Underwater Wet 16Mn/304L Dissimilar Welded Joint.

Butter layers of different thicknesses were successfully deposited on ferritic steel by using the tungsten arc welding (TIG) process. The effects of butter layer thickness on the microstructural characteristics, elemental distribution, and mechanical properties of underwater wet 16Mn/304L dissimilar welded joints were investigated. The results showed that the butter layer significantly changed the microstructure and elemental distribution of 16Mn/304L joints. As the thickness of butter increased, the heat-affected zone (HAZ) at the ferritic steel side changed from the original 16Mn steel to the ERNiCrMo-3 butter layer. The martensite content in HAZ also exhibited a downward trend. When the thickness of the butter layer exceeded 6 mm, the microstructure of HAZ at the ferritic steel side was composed of ferrite and pearlite, instead of quenched martensite. The microhardness of underwater dissimilar steel welded joints significantly reduced due to the absence of martensite. The addition of the butter layer increased the ultimate tensile strength from 515 MPa to 565 MPa. The results of this work could provide a robust basis for future applications of dissimilar steel structures.

Analysis of Crack Propagation Behaviors in RPV Dissimilar Metal Welded Joints Affected by Residual Stress.

In severe service environments, the presence of high local residual stress, significant organizational gradient, and nonlinear changes in material properties often leads to stress corrosion cracking (SCC) in dissimilar metal welded (DMW) joints. To accurately predict the crack growth rate, researching the initiation and propagation behavior of SCC cracks in DMW joints under residual stress (RS) is one of the most important methods to ensure the safe operation of nuclear power plants. Using the extended finite element method (XFEM), the crack propagation behaviors in DMW joints under different RS states are predicted and compared. The effects of RS, crack location, and initial crack length on crack propagation behavior are investigated. The crack in a DMW joint without RS deflects to the material of low yield strength. High residual stress urges the crack growing direction to deflect toward the material of high yield strength. Young's modulus has little impact on the crack deflection paths. The distance between the specimen symmetric line and the boundary line has little effect on the crack initiation and propagation within the RS field. A long initial crack is more likely to initiate and propagate than a short crack. To a long crack and the crack that is far from the interface of two materials, the impact of residual stress on the crack propagation path is significant when it is located in a material with high yield strength, while when the initial crack is located in the material with low yield strength, RS has a great influence on the deflection of a short crack growth direction on the condition that the crack is adjacent to the interface.

Effect of PWHT on metallurgical and mechanical characterization of dissimilar welded joint of P91 and P92 steels

P91 and P92 steels are widely used in nuclear and thermal power plant’s high-temperature (650–700 °C) operating components. The welding procedure, base plate composition, filler material composition, and post-weld heat treatment (PWHT) significantly affect the metallurgical characterization of weldments at room temperature. This work focuses on joining P91 and P92 steel by the TIG welding with filler ER90S-B9. The study analyzes the materialization of coarse-grained HAZ (CGHAZ), inter-critical HAZ (ICHAZ), and fine grained HAZ (FGHAZ) under welded and PWHT. PWHT was conducted at 840 °C for 2, 4 and 6h. An optical microscopic (OM) scanning electron microscope (SEM) was employed to characterize the welded and PWHT samples. It was perceived that the tensile strength of PWHT increased as the heat treatment times increased from 2 to 6 h, while the hardness value decreased accordingly. The maximum tensile strength (594.71 MPa) was observed in PWHT_6 h, while the minimum tensile strength (537.52 MPa) was perceived in the as-welded sample. The PWHT_6h reveals the minimum hardness values (271.12 HV) at the fusion zone among all the conditions. The WFZ consisted of an untampered lath martensitic grain structure, demonstrating an average hardness value of 314.15 HV in the PWHT_2h condition. The hardness value in CGHAZ samples for as-welded, PWHT_2h, PWHT_4h, and PWHT_6h was observed at 456.85, 436.81, 368.63, and 327.41 HV, respectively.

APPLICATION OF ACOUSTIC EMISSION METHOD FOR DETECTING DIFFUSION INTERLAYERS IN DIFFERENT WELDED JOINTS

The paper investigates the possibility of detecting specific structural defects of dissimilar welded joints by the method of acoustic emission (AE). Carbide and decarburized interlayers are formed in dissimilar welded joints of austenitic and pearlitic steels during welding and subsequent operation. Diffusion interlayers, as a structural defect, are usually small in size and cannot be detected by traditional non-destructive testing (NDT) methods, while the AE method is promising for detecting such defects. In the present work, we studied the AE data obtained during testing of defect-free specimens of a welded joint and specimens with diffusion interlayers. It has been established that the AE parameters for defective and defect-free welded joints have significant differences, which makes it possible to identify the presence of diffusion interlayers in dissimilar welded joints.

Component test of nickel-based alloys and their welded joints under long-term creep loading

The aim of the paper is to investigate experimentally the creep behavior of improved materials and welded joints at component scale under near-to-service operating conditions, which are promising for the application in highly efficient and flexible future power plants.It focusses on the creep behavior under multiaxial loading of similar and dissimilar welded joints of high temperature resistant nickel-based alloys (A740H, A617B and HR6W) in the temperature range between 650 °C and 750 °C by means of thick-walled-component tests. In this case, the temperature, the external axial load and the internal pressure remain constant during testing.Numerical simulations are used for the estimation of the component axial load in order to induce a meaningful damage evolution without causing a total component failure. The metallographic investigation on the welds A740H/A740H and A617B/A740H indicated no test-related damage. Small cracks in circumferential direction were found on the welds HR6W/HR6W and HR6W/A617B after having reaching 2% local creep strain. The damage mechanism could be classified as a typical creep damage with carbides formation in the grain boundaries and thus grain boundary separations occur, which ultimately lead to the crack formation.In general, the FEM calculation underestimates the axial creep strain on the investigated welds, especially the initial creep strain evolution is not accurately predicted. However, the long-term creep strain evolution could be well predicted by FEM. In this case, the material parameters for the creep law should be further optimized in order to minimize the underestimation.

Lean manufacturing of dissimilar weld joints using Taguchi method

The lean manufacturing concepts and tools are presented as a good alternative to increase production efficiency, promoting cost reduction and increasing the quality of manufactured products. Tungsten inert gas (TIG) welding is a kind of metal joining processes that has found widespread usage across the industries; it involves the employment of a non-consumable conductive tungsten electrode in a shield of inert gas. A204GRB alloy steel and UNS 317 stainless steel have been used extensively in high pressure vessel fabrication and in similar applications, owing to their great strength and corrosive resistiveness. Further, the quality of the weldments is sturdily depending upon the input process variables, and finding their optimum combination is quite important. In the present investigation, the optimized quantities of the TIG welding variables namely, current, voltage level and the weld speed were identified with the aid of the Taguchi’s method for the dissimilar weld joints created with the aforementioned materials.

P92 steel and inconel 617 alloy welds joint produced using ERNiCr-3 filler with GTAW process: Solidification mechanism, microstructure, mechanical properties and residual stresses

The objective of the current study was to analyse the microstructure, mechanical characteristics, and residual stresses of a dissimilar welded joint (DWJ) made of P92 steel and the Inconel alloy 617 (IN617) using the gas tungsten arc welding (GTAW) method. The ERNiCr-3 filler was selected to produce the conventional V groove (VG) and narrow V groove (NVG) butt joint. The filler deficient zones in the weldments, such as the filler deficient beach, i.e. unmixed zone (UZ), peninsula, and island, as well as the distinct heat-affected zone (HAZ), were visible near the interface of ERNiCr-3 filler weld and P92 steel due to the distinct differences in the chemical composition, microstructure, and mechanical properties between the filler and P92 base metal (BM). A very narrow partial melted zone (PMZ) and almost negligible UZ and HAZ were noticed at the interface of IN617 and ERNiCr-3 weld metal and it occurred mainly due to the similarity in microstructure and melting point. The austenitic microstructure of ERNiCr-3 filler weld was accompanied by precipitates enriched with Ti and Nb along with the inter-dendritic space. At room temperature, the mechanical properties of both the groove joints were evaluated, and the test results indicated that the welded joint satisfied the standard requirements for AUSC power plants' boiler applications. The tensile test results showed the failure from ERNiCr-3 filler weld with a tensile strength of 627 ± 2 MPa and 636 ± 3 MPa for VG and NVG welded joints, respectively. A poor weld metal impact toughness in comparison to the BMs was attributed to the presence of the brittle Ti(C, N) and Nb(C) particles in the interdendritic space. The impact toughness for the NVG weld joint was measured higher than for the VG weld joint. A significant hardness deviation was measured along the weldments that might be due to heterogeneous microstructure, i.e. UZ, HAZ, delta ferrite, and weld metal. To impart the ductility and temper the martensite in P92 HAZ, post-weld heat treatment (PWHT) was also performed, and a studied their effect on microstructure evolution across the weldments and mechanical properties. Groove design also showed a significant effect on residual stress variation. The work highlights the groove geometry, welding procedure, evolution of the microstructure along the weldments, mechanical characteristics, and residual stress variation of DWJ of P92 steel and IN617 alloy. In comparison to conventional VG joints, the NVG joints exhibited superior mechanical properties and lower residual stress values.

Effect of post weld heat treatments on microstructure and mechanical properties of dissimilar P92 steel-AISI 304H ASS A-TIG weld joint

In present work, the efficacy of post weld heat treatment (PWHT) on microstructure and mechanical properties of dissimilar P92 steel-AISI 304H austenitic stainless steel (ASS) activated flux-tungsten inert gas (A-TIG) weld joint was studied. Based on the time temperature cycle, the post weld heat treatment was performed in two ways: (a) PWHT-1 (760 °C, 2 h) and (b) PWHT-2 (1160 °C, 2 h and 760 °C, 2 h). After PWHTs, the microstructure and mechanical properties (micro-hardness, tensile behavior and impact toughness) of weld joint were tested and compared with as-welded condition. PWHT-1 resulted in coarsening of existing precipitates and formation of new precipitates in weld zone. The average size of precipitates along the PAGB and inside the grain matrix was measured to be 294 ± 50 nm and 153 ± 50 nm, respectively. After PWHT-2, the microstructure of P92 FGHAZ, P92 CGHAZ and weld zone were observed to be quite similar due to the re- austenitisation during this PWHT regime. The hardness distribution shows the non-uniformity even after PWHT-1 however; PWHT-2 shows negligible variation in hardness of P92 side HAZs and weld zone. In tensile testing, the failure location has been changed to P92 steel base metal from AISI 304H ASS which suggests that P92 steel becomes weak after the post weld heat treatments. An increase in elongation % (PWHT-1: 37% and PWHT-2: 45%) was also obtained after PWHTs. Upon PWHTs the weld zone impact toughness also improved (PWHT-1: 59 ± 2 J and PWHT-2: 132 ± 2 J) and satisfy the minimum average impact toughness as per standard EN 1559:1999.

Analysis of the Creep Failure of P92/HR3C Dissimilar Steel Welded Joint

Harsh service environments, such as high temperature and pressure, cause many unforeseen premature failures, especially for welded joint structures, whose heat-affected zones have been in service. Cases of pressure vessel damage caused by premature cracking in the process often occur. In this paper, the finite element model of dissimilar welded joints of P92/HR3C steel was established to simulate the actual service process, and the variation law of maximum principal stress, equivalent stress, and stress triaxiality on the inner and outer surfaces of the joint and both sides of the welding were analyzed. The results show that in the long-term use of welded joints, the stress concentration occurs in the weld fusion zone; with the increase in service time, the creep strength of the HR3C weld interface is much higher than the P92 weld interface, the structural shape changes and the stress concentration is transferred from the HR3C-weld to the P92-weld.

Improving the strength-ductility synergy and corrosion resistance of Inconel 718/316L dissimilar laser beam welding joint via post-weld heat treatment

Inconel 718/316L dissimilar welding is widely used in nuclear power plants, which suffers from the deterioration of mechanical properties and corrosion resistance after welding, attributed to the formation of brittle phase and the existence of residual stress. In this paper, the impact of post-weld heat treatment (PWHT) on Inconel 718/316L welding joints is systematically investigated. By conducting PWHT after welding, notable reductions in residual stress in as-welded joints are significantly reduced and the microstructure is improved, resulting in an enhanced strength-ductility synergy and corrosion resistance. The as-welded joints exhibit the generation of brittle Laves phase and welding residual stress in the fusion zone. After PWHT at 650 °C, a substantial increase in the quantity of fine-scale γ″ strengthening phases with a uniform dispersion distribution in weldment is observed, along with the release of residual stress. This combination yields an optimal strength-ductility synergy and corrosion resistance of the joint. However, the δ phase precipitates along in Laves phase boundary after PWHT at 850 °C, which exhibits a semi-coherent interface with γ matrix, and a non-coherent interface with the Laves phase, leading to severe stress concentration at the δ phase interface. This severe stress concentration could be a preferred location for crack initiation and propagation, resulting in a substantial loss in mechanical behavior. Additionally, the increase in the phase boundary of γ/γ″, γ/Laves, Laves/δ and γ/δ reduces the corrosion resistance of the joint. The findings of this study provide an effective strategy for improving the performance of Inconel 718/316L dissimilar laser beam welding joint.

Mitigating the influence of industrially relevant disturbances on LME severity of dissimilar resistance spot welded advanced high-strength steels

The third generation of advanced high-strength steels (3G-AHSS) has been developed to provide high strength and high ductility, which attract automakers. To protect these materials from corrosion during service, these materials are typically coated with zinc. During resistance spot welding (RSW), the zinc coating can melt, allowing it to penetrate into the grain boundaries (GBs), and lead to liquid metal embrittlement (LME) phenomena. Concerns regarding LME susceptibility have impacted the industrial application of 3G-AHSS; therefore, its mitigation has become a top focus for automakers. Several possible strategies for lowering LME severity by altering welding parameters have been proposed to mitigate LME in similar spot weld joints. However, these strategies were not tested on a dissimilar spot weld joint. Therefore, in this work, 1.4 mm gauge thickness galvanized (GI-coated) 3G-980 AHSS was joined with 0.6 mm thick Interstitial Free (IF) steel. In this work, current pulsation and ultra-short hold time were proposed to minimize LME severity. The robustness of the developed welding schedule was then tested on welds made with industrial disturbance factors such as pre-strained sheets (between 0 to 80% of 3G-980 material yield strength) and electrode misalignment (between 0° to 10° misalignment) compared to baseline parameters. In severe circumstances of disturbance factors, the resulting optimized welding schedule decreased LME cracking and showed improved resistance to LME, lowering LME severity by 41% for the extreme pre-strain condition and 27% for the extreme misalignment angle.

Simulation and validation of experimental residual stresses of dissimilar AA2124 and AA7075 TIG weld joint using ANSYS APDL

Simulation and validation of experimental residual stresses of dissimilar AA2124 and AA7075 TIG weld joint using ANSYS APDL

Study on microstructure–mechanical integrity of the dissimilar gas tungsten arc weld joint of sDSS 2507/X-70 steels for marine applications

Study on microstructure–mechanical integrity of the dissimilar gas tungsten arc weld joint of sDSS 2507/X-70 steels for marine applications

Carbide evolution and its effect on the impact toughness of the 9Cr/CrMoV dissimilar welded joint during the aging treatment

The microstructure evolution in the weld metal (WM) and its effect on the impact toughness for the 9Cr/CrMoV dissimilar welded joint with various aging time was systematically investigated. With the aging time increased from 0 h to 3,000 h, the specimen aged at 470 ℃ for 1,000 h revealed the lowest impact energy (13.5 J). Moreover, the impact fracture morphology details were obtained by scanning electron microscopy (SEM). The results showed that the quasi-cleavage fracture appeared for the specimens in the original and aged (aged at 470 °C for 3,000 h) states, while the cleavage fracture could be observed for the specimen aged at 470 °C for 1,000 h. Besides, the microstructure observation exhibited that the main microstructure in the WMs for the specimens in the original and aged states were all the tempered martensite. The columnar and equiaxed grain zones formed owing to the multi-layer and multi-pass techniques. Based on the characterization analysis of the precipitates for the aged specimens, the coarsening of the carbides was determined as the crucial factors to decrease the impact energy. On the contrary, with the aging time increased, the newly precipitated fine carbides could produce the positive effects on the impact toughness. In the original state, the impact energy of the specimens was about 29.2 J. With the aging time increased to 1,000 h and 3,000 h, the impact energy became 13.5 J and 21.0 J, respectively.

High contrast corrosion mapping of dissimilar metal weld joints using alternating current scanning electrochemical microscopy: A case study with Zr-4–Ti–304L SS weld

Intermittent contact alternating current scanning electrochemical microscopy (IC-AC–SECM) has been used in the present study to image the local electrochemical activity of Zr-4–Ti–304L SS dissimilar weld joint without a redox mediator at an open circuit potential. The perturbation frequency and bias potential applied to the Pt ultramicroelectrode (UME) are found to affect the contrast of IC-AC-SECM imaging. The optimum parameters for high contrast imaging with high sensitivity were determined by performing potentiodynamic polarization and approach curves of Pt UME. The potentiodynamic polarization behaviour of Pt UME carried out in tap water revealed that the Pt UME biased with potential at −0.5 V was ideal for obtaining better sensitivity due to the maximum reduction of dissolved oxygen in the electrolyte. The effect of applied perturbation frequencies on Pt UME examined by the approach curves using the AC-SECM technique showed a transition from negative to positive feedback over 304L SS at about 10 kHz whereas for Zr-4 and Ti the transition was observed at 50 kHz but with only a minor difference in their feedback. Better contrast in mapping local current and impedance magnitude across the weld joint has been achieved by applying an optimum dc bias (–0.5 V) to the Pt tip and perturbation frequency (10 kHz). The IC-AC-SECM results have been compared with the conventional potentiodynamic polarization and electrochemical impedance spectroscopy results of Zr-4, Ti, 304L SS and the weldment in tap water, where the weld sample undergoes preferential corrosion of 304L SS region due to the galvanic coupling. The present work provides new insight into the optimal IC-AC-SECM parameters for best lateral imaging to map electrochemical activity with good contrast across a multilayer weld joint in tap water.