Weld Heat-affected Zone Research Articles

Laser welding of FeCoCrNiMnAl x (x = 0, 0.75) high-entropy alloys fabricated by additive manufacturing

In the present study, the laser melting deposition (LMD) technology was adopted to fabricate FeCoCrNiMn and FeCoCrNiMnAl0.75 high entropy alloys (HEAs). Then, laser welding method was used to join the HEAs in forms of similar (FeCoCrNiMnAl/FeCoCrNiMnAl and FeCoCrNiMnAl0.75/FeCoCrNiMnAl0.75) and dissimilar (FeCoCrNiMnAl0/FeCoCrNiMnAl0.75) combinations, respectively. Ultra-depth field microscope and electron backscatter diffraction detection were used to observe the macro-morphology and microstructure, respectively. It was found that the width of the weld bead and heat-affected zone with higher aluminium content was larger. In both base metals and welded joints, aluminium promoted the face-centered cubic (FCC) phase transfer into body-centered cubic (BCC), significantly refined the grain and the dislocation density of HEA is also increased, which increased strength and hardness, and decreased ductility. Highlights The FeCoCrNiMn/FeCoCrNiMn, FeCoCrNiMn/FeCoCrNiMnAl0.75, FeCoCrNiMnAl0.75/FeCoCrNiMnAl0.75 joints were produced by laser welding. The widths of the weld bead and heat-affected zone increased with higher Al content. The weld bead with higher content of Al exhibited higher strength and hardness, but lower ductility.

Characterization of the local mechanical properties of 5083-5383 MIG welded joints

act. Due to the heat input effect, the weld seam and heat-affected zone (HAZ) are strength weakened phases in 5xxx aluminum welded joints. Therefore, the local mechanical properties of the 5xxx aluminum welded joint are worth studying for structural design. In this paper, the local mechanical properties of 5083-5383 MIG joints were studied. Through instrumented indentation and tensile tests with digital image correlation (DIC), the yield strength of the same area of the weld center, heat-affected zone, and the base metal (BM) was respectively characterized. The two methods show good consistency in the characterization of the yield strength in each region. The tensile strength of the weld zone and BM characterized by two methods also represent good consistency. The HV0.1 and HV10 Vickers hardness distribution of welded joints was studied, and the differences in the characterization of local mechanical properties of 5083-5383MIG welded joints by instrumented indentation test, tensile test with DIC and Vickers hardness are analyzed. The instrumented indentation test can be used for approximate non-destructive quantitative characterization of the local mechanical properties of 5083-5383 MIG welded joints.

Effects of microstructure heterogeneity on tensile properties and failure mechanism of GTAW joint of as-cast Ti2531

In this study, as-cast dual-phase titanium alloy Ti2531 was welded by Gas Tungsten Arc Welding, and the effects of microstructure heterogeneity on tensile properties and failure mechanism was analyzed. Tensile test results showed that the specimens fractured in the base metal region, and the tensile strength R m of the welded plate was 855 MPa ~ 859 MPa, which was almost the same as that of the base metal. It was found that, compared with the base metal region, the fine and basketweave phase in the weld zone and heat-affected zone resulted in higher hardness and yield strength. Therefore, plastic strain concentration occurred in the base metal region and a large number of kink bands were found, which accounts for the relatively good plasticity with the fracture strain of 0.073–0.09. In addition, by means of intergranular orientation analysis, it was demonstrated that [0001] α and [101] β were the rotation axes of kink bands in the α and β phases, respectively. Furthermore, by observing the high-resolution electron microscopy, it was found that these kink bands were formed by the arrangement of edge dislocations. As a consequence, when the lattice distortion was severe, the unstable expansion of kink bands occurred and cracks were formed in widmanstätten colonies, inducing the failure of the specimen in the base metal region and great tensile strength equivalent to that of base material. • The weld joint of Ti2531 had good tensile strength close to that of base material. • Plastic deformation was concentrated in base metal region rather than other regions. • Kink bands were formed to coordinate severe plastic deformation in base metal region. • The instable expansion of kink bands resulted in the fracture of the welded specimen.

Assessment of the Effect of Residual Stresses Arising in the HAZ of Welds on the Fatigue Life of S700MC Steel

Fine-grained steels, which belong to the HSLA (High-Strength Low-Alloy) group of steels, are increasingly used for parts of statically and dynamically loaded constructions. Due to the thermal effect of welding, combined with the inherent stiffness and clamping stiffness of the part, residual stresses are generated in the HAZ (heat-affected zone) which affect the fatigue life of the sub-weld and the entire construction. In this article, a specific temperature cycle measured during welding is used, which, together with a defined clamping stiffness, produces residual stresses of a defined shape and value in the sample. Subsequently, the effect of these stresses on the fatigue life on the change of the S–N curve compared to the annealed material, is assessed. Temperature cycles were applied using a Gleeble 3500 and the residual stresses were analyzed by X-ray diffraction (XRD). It was found that the effect of residual stresses decreased the fatigue strength by 33% compared to the annealed material. It was further found that by using annealing to reduce the residual stresses, it is possible to restore the fatigue life of S700MC steel to the original value of the base material.

Microstructural characteristics and mechanical properties of Ti–6Al–2Nb–2Zr–0.4B alloy welded joint using tungsten inert gas welding

Ti–6Al–2Nb–2Zr–0.4B alloy plates were welded using tungsten inert gas welding with a new matching welding wire, and the chemical composition, microstructure, and mechanical properties of the defect-free welded joint were investigated. Furthermore, the influence mechanism of the TiB phase on the mechanical properties of the welded joint was analyzed. The results indicated that the B content in the weld metal is only 0.0145% with trace TiB phase. A large amount of TiB phases precipitate in the fusion zone and aggregate at the grain boundary. The TiB phases in the heat-affected zone are distributed diffusely. The microhardness of the weld metal (295 HV) is the lowest, followed by the heat-affected zone (331 HV), and the fusion zone (341 HV) is the highest. The ultimate tensile strength and elongation of the welded joints are 782 MPa and 12.3%, which are about 93.3% and 77.8% that of the base metal, respectively. The impact toughness of the fusion zone is 22 J, which is 53.7% that of the base metal (41 J) and lower than that of the weld metal (56 J) and heat-affected zone (36 J).

Comparing the fatigue performance of Ti-4Al-0.005B titanium alloy T-joints, welded via different friction stir welding sequences

Ti–4Al-0.005B titanium alloy T-joints were produced with two different friction stir welding (FSW) sequences, and its effect on the low-cycle fatigue performance was investigated. Results show that hysteresis loop became a straight line with no significant fatigue damage occurring at low strain amplitudes (0.2% and 0.4%). As the strain amplitude increased to 0.6%, the area enclosed by the hysteresis loop increased for both T-joints and the base material (BM) due to fatigue damage accumulation. As the stress amplitude decreased gradually with increasing number of cycles, the fatigue life followed this decreasing trend. The fatigue life of single-weld T-joints is close to that of the double-weld T-joints, with a cyclic strain hardening index of the BM being in-between of the two T-joints. However, cyclic strength coefficient of BM is the lowest, and that of the double-weld T-joint is larger than that of the single-weld T-joint. The single-weld T-joint breaks at the heat affected zone (HAZ) on the advancing side, where the double-weld T-joint breaks at the HAZ of the second weld.

Microstructure Evolution of AZ91 Magnesium Alloy Welded Joint under Magnetic Field and NiCl2 Activated Flux

As the lightest engineering materials, magnesium alloys have been widely used. Because of the specific chemical and physical characteristics, the weldability of magnesium alloy is poor. Adopting suitable welding technology and improving the quality of magnesium alloy welded joints is key to their successful application. According to previous research data, it was found that the combined action of magnetic field and activated flux has a positive effect on improving-welding efficiency and improving the properties of a welded joint, butanalysis of microstructure evolution is insufficient. In this paper, AZ91 magnesium alloy was welded by TIG welding with activated flux and external longitudinal AC magnetic field. The phase composition and microstructure evolution were investigated. The experimental results revealed that the phase composition of welded joint was not changed due to the introduction of the magnetic field and activated flux, the growth patterns of grain in the weld seam and heat-affected zone were different. When the activated flux amount was 3 mg/cm2 with the effect of the magnetic field, the grain size of the weld seam was the finest, which was 18.96 μm. However, the grain size of the weld seam was larger than that of base metal. The crystallographic characteristics of grain boundaries in the weld seam and base metal were both LAGBs. The microstructure of the weld seam was messier than the base metal due to the larger misorientation angle. Under the combined action of the magnetic field and activated flux, the crystallization nucleation condition of the molten pool was changed, the formation of twins was promoted, and the crystal could selectively grow parallel with the (0001) basal plane.

Statistical Assessment of Fracture Toughness Results from the HAZ of X80 Pipeline FCAW Girth Weld.

Due to the wide application of flux-cored arc welds (FCAW) susceptible to significant scatter in weld and Heat Affected Zone (HAZ) fracture toughness, there is an interest in methods for evaluating the reliability of welds containing defects. The mechanical properties of the FCAW girth weld of an X80 pipeline are tested and then analyzed. By obtaining fracture toughness results from a statistically significant number of SENB specimens, with notches positioned in different HAZ locations, the effect of variation within the results can be evaluated. The results of the fracture toughness tests were analyzed using statistical methods, to compare both the difference in behavior between HAZ microstructures and the variation when a similar microstructure has been sampled. The range of different characteristic toughness values was analyzed using a postulated ECA case to illustrate the sensitivity of the results to how toughness is defined. The analyses supported recommendations to be made on the optimum approach to characterizing HAZ fracture toughness for reliable pipeline assessments in multi-pass girth welds with complex HAZ microstructure distributions.

Wear and Corrosion Resistance of FeCoCrxNiAl High-Entropy Alloy Coatings Fabricated by Laser Cladding on Q345 Welded Joint

High-entropy alloy (HEA) coatings on the surface of low-alloy steel by laser cladding can improve the corrosion and wear resistance, and the performance can be further improved by adding the Cr element. However, the effect of Cr content on the microstructure, hardness, wear and corrosion resistance of the coatings on the welded joint has not been completely understood in the literature. This paper aims at revealing the influence of Cr content on the microstructure and properties of laser-cladded FeCoCrxNiAl HEA on different regions of Q345 welded structure. The results indicate that FeCoCrxNiAl HEA coating has good metallurgical bonding with the Q345 welded surface. The increase of Cr element content in the powder plays an important role in energy absorption of powder and substrate, affecting the dilution rate and diffusion of Fe from the substrate to HEA coating. The HEA coating is mainly composed of the face-centered cubic phase (FCC) and body-centered cubic phase (BCC). When x = 1.5, the actual Cr element content of coating is the highest, which promotes the formation of hard brittle phase BCC, and subsequently affects the hardness and wear resistance of the sample. Meanwhile, the corrosion resistance increases and then decreases, and reaches the highest when x = 1.5. Due to the existence of Cr and other elements with good corrosion resistance in the HEA coating, a dense oxide film can be formed in 3.5 wt.% NaCl solution and neutral salt spray environment to prevent the corrosion from continuing, which can effectively improve the corrosion resistance of each region of the welded joint, and the protective efficiencies on the weld bead (WB), heat-affected zone (HAZ) and base metal (BM) are 99.1, 98.4 and 96.6%, respectively.

Local microstructure and mechanical characteristics of HAZ and tensile behavior of laser welded QP980 joints

Microstructural evolution of the heat-affected zone (HAZ) seriously affects the mechanical properties of the welded joints. In this paper, QP980 steels were butt-welded by fiber laser. The thermocouple and Gleeble1500 system were used to achieve the thermal simulated HAZ specimens of laser welded joints, which solved the problem that it was difficult to evaluate the mechanical properties due to the narrow HAZ of the laser welding. Large amounts of granular carbides were precipitated in the block martensite of the sub-critical HAZ (SCHAZ). Carbides were not found in lath martensite, but there were dislocation tangles in the lath martensite of the SCHAZ. In addition, the number of dislocations in the ferrite of the SCHAZ was significantly reduced. The SCHAZ had the lowest strength but the highest elongation owing to the tempering. The fine-grain strengthening resulted in the highest tensile strength in the fine-grained HAZ (FGHAZ). The tensile fracture morphologies indicated a brittle fracture mechanism in coarse-grained HAZ (CGHAZ) and FGHAZ, and exhibited a ductile fracture mechanism in the inter-critical HAZ (ICHAZ) and SCHAZ. According to the overview of the joint and the local mechanical characteristics of HAZ, the numerical model of the tensile test was performed by ABAQUS. And the simulation results showed good agreement with the experimental results, which both illuminated the constraint effect of SCHAZ and made the strain concentration transferred from SCHAZ to the BM with the increase of stress.

Metallurgical Factors Affecting the Tensile Properties of Weld Heat-Affected Zone in Medium Mn Transformation-Induced Plasticity Steel

The role of retained austenite in the mechanical property changes in the medium Mn transformation-induced plasticity (TRIP) steel heat-affected zone (HAZ) was elucidated throug a comparison with conventional TRIP steel. The two steel grades had similar microstructures consisting of ferritic phases with a high fraction of retained austenite in the as-received state; however, the difference in properties after welding was significant. The microstructures of both steels were dramatically changed to a martensitic matrix in the coarse-grained HAZ region. The medium Mn TRIP steel HAZ can have a higher retained austenite fraction than the conventional one; hence, an excellent combination of tensile strength and elongation can be obtained. The decisive difference between the two steels was determined in terms of austenite stability and the initial grain size.

Dissimilar joining of the martensitic grade P91 and Incoloy 800HT alloy for AUSC boiler application: Microstructure, mechanical properties and residual stresses

The presented study intends to analyze the microstructure and corresponding mechanical characteristics of P91 and Incoloy 800HT dissimilar welded joint (DWJ). The thermo-physical property differences between P91 and Incoloy 800HT arise due to their complex alloying composition, making their weldability difficult. Incoloy 800HT is difficult to weld due to its high susceptibility to solidification cracking. The recommended nickel-based filler metals for welding Incoloy 800HT were employed to weld P91 and Incoloy 800HT using conventional gas tungsten arc welding (GTAW). The welded joint morphology and characteristics were analyzed in as-welded (AW) and post-weld heat treatment (PWHT) conditions. The PWHT was performed to observe changes in microstructural inhomogeneity and residual stress relaxation in weld after the heat treatment. An electron probe microanalyzer (EPMA) was utilized to observe the distribution and segregation of elements in different weld regions. The deep hole drill technique was employed to find the distribution of bi-axial residual stresses in the weld fusion zone (WFZ) and heat-affected zone (HAZ) of base metals in both AW and PWHT conditions. The two nickel-based fillers, ERNiCr-3 and ERNiCrMo-3, were employed, and their weld characteristics were compared. The mechanical strength of ERNiCr-3 filler-based DWJ was found superior to ERNiCrMo-3 filler-based DWJ. The standard AW and PWHT ERNiCr-3 filler-based DWJ tensile specimen failed from Incoloy 800HT base metal with an ultimate tensile strength (UTS) of 570 ± 4 MPa and 650 ± 4 MPa, respectively. The ERNiCrMo-3 filler-based DWJ obtained the highest UTS of 679 MPa after PWHT in a subsize specimen. The microhardness for ERNiCrMo-3 WFZ was found to be higher than ERNiCr-3 WFZ microhardness, and PWHT successfully tempered the P91 HAZ. Further, the impact toughness for the ERNiCr-3 WFZ in AW condition was 86 ± 3 J and PWHT did not provide any significant improvements, while ERNiCrMo-3 WFZ had an impact toughness of 47 ± 10 J in AW state and 41 ± 10 J in PWHT state. Thus, a successful weld characteristic study of defect-free P91 and Incoloy 800HT DWJ was completed, and ERNiCr-3 filler was concluded to be an optimum choice of filler to make the DWJ between P91 and Incoloy 800HT.

Near-threshold fatigue crack growth behavior of the weld metal and heat-affected zone in an ex-service CrMoV steel joint

Threshold value (ΔKth) and fatigue crack growth behavior at different temperatures and stress ratios were investigated in weld metal (WM) and heat-affected zone (HAZ) of an ex-service CrMoV steel joint. Compared with the ΔKth at 25 ℃, the ΔKth at 500 ℃ and 540 ℃ were still high, because significant oxide-induced crack closure (OICC) occurred in WM and HAZ during high-temperature tests. The high-temperature ΔKth of HAZ were higher than those of WM, due to their more severe oxidation and more significant OICC. This was owing to the lower Si and Cr content and smaller grain size in HAZ.

APPLICATION POSSIBILITIES OF THE S960 STEEL IN UNDERWATER WELDED STRUCTURES

In this paper, the application possibilities of the ultra-high strength (UHSS) Domex 960 steel in the underwater welded structures are analyzed. In the research, the investigated material has been tested in bead-on-plate wet welding conditions with the usage of different heat input values, namely 0.63 kJ/mm, 0.72 kJ/mm and 0.93 kJ/mm. Specimens were performed by the manual metal arc (MMA) welding method with the usage of rutile covered electrodes. Firstly, the nondestructive visual testing (VT) was carried out. In the next step, the metallographic macro- and microscopic tests were performed. Finally, the hardness of the weld metal and heat-affected zone (HAZ) was measured by the Vickers HV10 method. The performed experiments allow the statement that the Domex 960 steel could be welded in a water environment. It also showed that increasing heat input leads to decreasing the hardness in HAZ by 30 HV10. It may result in decreasing the susceptibility to cold cracking during butt- and filet welding in the water environment.

The effect of heat input on microstructure and HAZ expansion in dissimilar joints between API5L X80 / DSS 2205 steels using thermal cycles

In this research, the effect of the shielded metal arc welding (SMAW) process heat input upon the microstructure and development of the heat-affected zone in the dissimilar joint of API 5L X80/DS5 2205 steels was investigated by recording the thermal cycles with thermocouple implantation in the perpendicular direction of the weld line. The filler metal used (electrode) is DSS 2209. The microstructure of the base and weld metals and their interfaces at different heat inputs were investigated using the scanning electron microscopy/energy-dispersive spectroscopy analysis technique (SEM/EDS) and optical microscopy (OM). The results indicated that the interface between the base metals and the weld metal has excellent consistency and that there is no evidence of cracks at different heat inputs. By increasing the heat input, it was determined that the amount of secondary austenite in the weld metal and heat-affected zone of 2205 steel had been increased. There occurred an epitaxial growth at the interface of 2209/2205, and there were a fine transition zone and Type II boundaries at the interface of 2209/ API 5L X80. The areas containing coarse, fine, and partially fine grains were detected in the heat-affected zone of the X80 steel. The thermal cycle results determined that the temperature peak in the areas away from the fusion line had increased by increasing the heat input and that the heat-affected zone of the two base metals, particularly the X80 steel, had been extended further.

Failure analysis on weld joint of centrifugal pump diffuser for oil and gas pipeline transportation

The failure mechanism of weld joint in centrifugal pump diffuser was analyzed through scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and electron back-scattering diffraction (EBSD). Meanwhile, the strength and toughness of weld joint, heat-affected zone (HAZ), and matrix are quantitatively compared by geometrically necessary dislocation density (ρGND). The result indicated that the strength and toughness of HAZ are the highest, followed by matrix, and weld joint is the lowest. Defects such as slag inclusion and residual austenite create initial conditions for the corrosion of weld joint. Severe chloride ion corrosion resulted in micro-cracks on the weld surface. Meanwhile, corrosion reduces the surface energy of the micro-cracks. Therefore, the concentrated driving force makes the micro-cracks with reduced surface energy spread rapidly, eventually causing the rapid failure of diffuser weld joint. This study may provide a reference for petroleum engineers and centrifugal pump manufacturers.

A Study on Heat Input Control and a Quality Evaluation Algorithm to Prevent Toughness Deterioration of the Heat-Affected Zone in the Fiber Laser Welding Process of ASTM A553-1 (9% Nickel Steel) Material

Various international organizations and governments of many countries are making efforts to prevent environmental pollution, with the IMO (International Maritime Organization) reinforcing related regulations. With these regulations, equipment related to LNG-fueled ships, which have the greatest carbon dioxide reduction effect among eco-friendly ships, are expected to increase. Although the IGC code designates the materials that can be used for LNG containers, such as 304L stainless steel and 9% nickel steel, these materials have a tendency to deteriorate the tissue around the heat-affected zone due to excessive heat input. In this study, we analyzed the effect of brittle fracture in the weld zone and heat-affected zone after fiber laser welding and found that welding quality improved with control of the heat input. SVM discriminant analysis was applied to classify the groups in which brittle fracture and ductile fracture occurred. The shape of the penetration section, hardness in the welding zone and heat-affected zone, and fracture surface were selected as factors for discrimination; these values were determined under various welding conditions. With these data, we derived a regression model and multi-objective optimization algorithm to predict mechanical properties after welding, as well as the conditions necessary to prevent brittle fracture. Finally, the prediction models were verified, as the results of welding under the derived conditions were classified as ductile fracture group.

A Study on Welding Characteristics, Mechanical Properties, and Penetration Depth of T-Joint Thin-Walled Parts for Different TIG Welding Currents: FE Simulation and Experimental Analysis

Considering the effect of heat input of tungsten inert gas (TIG) arc welding for T-joint welding of thin-walled parts of aluminum alloy 6061-T6, here, the welding characteristics are analyzed via the finite element method. The experiments are carried out using scanning electron microscope (SEM), optical microscope (OM), and tensile test of specimens to investigate the microstructure variation of the weld zone (WZ), heat-affected zone (HAZ), and base metal (BM), and the mechanical properties of the T-welded joint. The mechanical properties of the T-welded joint are explored and assessed combined with the tensile test in terms of yield strength, tensile strength, and Vickers hardness. Furthermore, the effects of different welding currents on welding penetration variation under welding deformation are thoroughly investigated, and the appearance of porosity and incomplete fusion defects of T-welded joints are clearly illustrated. The results show that the yield and tensile strength of T-welded joints, respectively, account for less than 37% and 74% of the base metal (BM) strength. Moreover, the welding penetration depth and microstructure of T-welded joints are deeply affected by the welding current. The maximum penetration depth is achieved at about 2.18 mm under the maximum welding current, and partial welding defects emerged, affecting and reducing the mechanical properties of the welded joint. It is expected that these results will provide an analysis foundation for optimization of the welding process, suppression of welding defects, and promotion of mechanical properties for thin-walled parts in the future.

Critical assessment 42: acicular ferrite formation and its influence on weld metal and heat-affected zone properties of steels

Toughness and fatigue resistance of welds and associated heat-affected zones (HAZs) in high-strength steels are important design parameters in structural applications. Acicular ferrite microstructures, which can be achieved through control of weld process and nucleant (inclusions or precipitates) characteristics, are often regarded as key to enhancing weld metal and HAZ properties of welded steels. This paper addresses the transformation characteristics of acicular ferrite related to alloying and weld processing as well as the specific role of acicular ferrite in weld performance, along with future research needs to identify weld processes suitable to specific alloying strategies.

Influence of heat input on weld integrity of weldments of two dissimilar steels

ABSTRACT The present study investigates the influence of heat input on microstructure evolution and mechanical properties of nitronic steel and super duplex stainless steel dissimilar welded joints. For this experimental purpose, carbon steel filler (ER70S–2) was employed using gas tungsten arc welding (GTAW) with two heat input conditions: lower (0.624 kJ/mm) and higher (1.01 kJ/mm). The welded joint was subjected to the microstructure of different zones, including weld metal, base metals, and heat-affected zones/interfaces were accomplished by optical microscopy, scanning electron microscope. Tensile test, Impact test, and Vickers microhardness were conducted to study the mechanical properties. Microstructural evolution in the weld metal and heat-affected zone reported the presence of Type II boundary and macrosegregation. Hardness test investigation reveals that the weld metal’s hardness rises compared to the base metals. Moreover, the weldment hardness decreases at higher heat input than lower heat input. The tensile test study reveals that the lower heat input weldment exhibits more elongation and tensile strength than the higher heat input weldment. The Charpy impact tests show that the average toughness value increases with heat input. The results also indicate that the lower and higher heat input specimen exhibited brittle fracture.