Regions Of Welded Joint Research Articles

A comparative study of creep crack growth behaviour amongst the dissimilar P91-IN182-SS316LN and similar P91 weld joints

ABSTRACT Towards ensuring the structural integrity of the high-temperature components, it is essential to evaluate the creep crack growth (CCG) behaviour, especially for the weaker creep regions of the components. In this study, the CCG behaviour was investigated in the modified 9Cr-1Mo (P91) and Inconel (IN182) buttered layer interface regions of dissimilar metal weld (DMW) joints of P91 and type 316LN SS at 798 K and 898 K. For a quantitative assessment, the CCG rates were compared with the heat-affected zone (HAZ) of similar metal P91 welds (P91HAZ). The CCG rate was characterised using the creep fracture C* parameter as per ASTM E1457–17. The CCG rate in the P91/IN182 interface region was found to be higher than the P91HAZ, viz. 3.5 times and 4 times at 798 K and 898 K, respectively. This could be attributed to the propensity for creep cavitation in the interface region of the DMW joint.

Thermal aging effects on Tensile and Metallurgical characteristics of Stainless steel weld joint

A girth austenitic stainless steel (say, SS) weld joints are invariably used for joining piping components in typical light water based nuclear power reactor. To avoid hot cracking during the welding of SS, some 5-8% delta ferrite is required in the filler material, which remains in the metastable phase in weld pool. Under prolonged exposure at operating temperature (300 ℃), these delta ferrite which remains in weld metal may get transformed to brittle phases that leads to reduction in its ductility and toughness. Hence, for prolonged safe operation of these piping components in power reactors, it is important to quantify the amount of degradation in toughness and ductility because of thermal aging. Therefore, present work aims at quantifying the reduction in toughness in SS weld joint by carrying out accelerated thermal ageing and thereafter carrying out micro-structural examinations, hardness and tensile tests on specimens machined from different regions of weld joint. Austenitic stainless steel (SA312 Type 304LN) pipe weld joints have been prepared using Gas Tungsten Arc Welding (GTAW) for root passes and Shielded Metal Arc Welding (SMAW) for filling passes. Full-scale pipe weld were subjected to thermally ageing for 10,000 and 20,000 hours at temperature 400 ℃. The effects of thermal aging on the structural morphology, hardness at macro and micro-scale and tensile characteristics of different zones of these joints have been quantified. Micro-structural examination reveals vermicular and lathy morphology in the ferrite and austenite phase. It has been found that, thermal aging leads to significant increase in ferrite hardness and reduction in ductility for the weld specimen from SMAW compared to that of the GTAW and no effect in heat affected zone.

Spatiotemporal variations of creep damage in dissimilar welded joints

The influence of high-temperature creep on local microstructural, physical and mechanical performance for different regions of dissimilar welded joints of two kinds of martensitic heat-resistant steels F92 and Co3W2 is studied, under 873 K and 150 to 200 MPa. The rupture location is located in F92 for all testing specimens under various creep conditions and the fracture morphology exhibits a transgranular plastic fracture. Analysis on creep rupture data yields a 100,000 h creep rupture stress of 93.5 MPa, and a creep damage tolerance of 4.93. Creep damage micromechanisms like external cross section loss, microcavities’ nucleation and growth and microstructural deterioration are observed, and creep damages are more complicated in the crept dissimilar welds compared to single material because they are not only location dependent but also time dependent. Nanoindentation technique was implemented to acquire local nanohardness, reduced modulus, plasticity index, strain rate sensitivity and activation volume of different welding microzones with various degrees of creep damage. Co3W2 side displays better local physical and mechanical properties after creep compared to uncrept state due to the positive impact of creep, while the properties of F92 side improve for short creep and are decreased after longer creep, which are consistent with their microstructural evolution during creep.

Dynamic constitutive model of U75VG rail flash-butt welded joint and its application in wheel-rail transient rolling contact simulation

Rail welded joint is one of weak links in high-speed railway, and its dynamic performance has important effects on the safety, stability, and comfort of the high-speed train. In this work, the dynamic mechanical responses at different regions of U75VG rail flash-butt welded joint were investigated. The results show that the base metal (BM), welding zone (WZ), and heat-affected zone (HAZ) of U75VG rail flash-butt welded joint has an obvious strain rate effect, i.e., the material strength increases with increasing the loading strain rate. The strength of WZ is similar to that of BM, but its toughness is much lower than that of BM. The toughness of HAZ is the same as that of WZ, but its strength is much lower than that of BM and WZ. Based on the experimental results, an improved dynamic constitutive model was established to reasonably simulate the stress–strain curves of different regions from quasi-static loading to dynamic loading. Finite element (FE) analysis of transient rolling contact between rail welded joint and wheel under different conditions was performed. Compared with the results from quasi-static wheel-rail contact simulation, the equivalent plastic strain at each region of rail welded joint increases significantly and presents non-uniform distribution after considering the dynamic effect. When the wheel contacts the junction between different regions, the impact will cause a significant stress concentration at the rail welded joints. The maximum wheel-rail load by the implicit dynamic analysis is about 4 ∼ 12 times that obtained by the quasi-static analysis. Moreover, the maximum contact pressure, equivalent stress and equivalent plastic strain of each area of rail welded joints gradually increase with the increase in axle load and driving speed.

Underwater wet welding of S1300 ultra-high strength steel

An expected tendency in marine and offshore structures is an increasing share of steels with high mechanical properties. The necessity to perform the welding work under water leads to a decreasing of the weldability of the steel. It results from the increased susceptibility to form cold cracks, especially in welded structures made of high-strength steel. A potential method, which may improve the problem of limited weldability of steel under water is the use of temper bead welding (TBW) technique. In this paper, the possibility of underwater wet welding by covered electrode S1300 ultra-high strength steel of different thickness (4 mm and 10 mm) has been investigated. The visual, metallographic macro- and microscopic tests, and Vickers HV10 measurements of samples with two nonparallel beads were performed. On the basis of the performed tests, the effectiveness of TBW technique was quantitatively verified. It was proved that TBW leads to positive microstructural changes and reduces the number of cracks in different regions of welded joints. Moreover, it was found that the proposed technique allows to decrease the hardness of S1300 steel joint by 30–80 HV10 in the weld metal and 40–100 HV10 in heat-affected zone. Finally, it was stated that the thickness of the base material does not affect the effectiveness of the TBW technique.

Effect of titanium alloy powder reinforcement on the mechanical properties and microstructural evolution of GMAW mild steel butt joints

Despite its well-reported application in a few welding processes, the use of reinforcing powders in weld joints to improve weld integrity has not garnered ample research attention for Gas Metal Arc Welding (GMAW) process. In this study, the adoption of Titanium alloy powders as metallic reinforcement for mild steel butt welds was investigated. By adopting Taguchi’s L4 orthogonal array, process optimisation for titanium-reinforced mild steel butt welds were first carried out. In the second phase of welding, the optimum parameters were used to create and compare two sets of weldments; one set was reinforced with titanium alloy powder and the other set left unreinforced. It was observed that in the Weld Metal (WM) region, the titanium-reinforced samples had higher micro-hardness values than their unreinforced counterparts with an average of 285.62 HV and 211.6 HV respectively. However, there was no substantial improvement in the ultimate tensile strength of the mild steel butt welds due to titanium powder reinforcements. Interestingly, the formation of acicular ferrite microstructure was more prevalent in the titanium-reinforced weldments and this was attributed to the presence of titanium inclusions in the weld metal. This prevalence of acicular ferrite suggests improved toughness properties in the weld joint region. While the higher hardness values in the Weld Metal of the reinforced sample indicates improved wear resistance.

SPT analysis of hydrogen embrittlement in CrMoV welds

In this paper Small Punch Tests (SPT) are used to determine the mechanical properties of the heat affected zone (HAZ) of CrMoV welded joints and to evaluate the embrittlement caused by the presence of internal hydrogen. Hydrogen permeation tests were carried out to determine the effective diffusion coefficients of the different regions of welded joints, whose hydrogen contents were measured using a hydrogen analyser.The paper demonstrates that SPTs can be used to estimate the tensile properties and the toughness of small areas, such as the subzones of a welded joint which are not thick enough for machining standard specimens. In cases where it is not possible to determine the fracture toughness of brittle regions using standard SPT samples, tests using longitudinally notched SPT samples were conducted. The normalized energy at failure, W/t2, was selected as the most appropriate SPT parameter to estimate the fracture toughness regardless of the fracture behaviour of the material (ductile or brittle). It was seen that the fracture toughness of the fine grained HAZ (FG-HAZ) is similar to that of the Base Metal (BM), while the fracture toughness of the coarse grained HAZ (CG-HAZ) is more similar to that of the Weld Metal (WM). The effect of hydrogen on BM and FG-HAZ is low, with embrittlement indexes of about 20%. However, a strong effect of hydrogen was observed in CG-HAZs and WMs, with embrittlement indexes of 60–80%. and a clear change from ductile to brittle behaviour in their fracture surfaces.

Surface effect of environmentally assisted corrosion growth of automotive welded steel performance

Failure of steel in automobile industries due to environmentally assisted medium in service is alarming. In this study an effort has been made to investigate critically the corrosion induced performances of automotive welded part. The experimental correlation on the effect of corrosive media (NaCl and HCl solutions) on the base metal, heat affected zone (HAZ) and weld metal formed were examined using linear potentiodynamic polarization technique. The hardness, microstructural and phase rationale of the studied joint was evaluated using, diamond base indenter, Scanning electron microscope and x-ray diffractograms respectively. The results revealed that the base metal has no detrimental phase transformation unlike the HAZ and the weld joint region. The hardness value of 185 HV welded joint was obtained compared to 235.95 HV of base region. The corrosion propagation in the 3.5NaCl and 1 M HCl shows that pitting deterioration occurs at the welded position in all case as a result of the shift in grain refinement and micro-straining during welding process.

Characterization of Microstructure and Stress Corrosion Cracking Susceptibility in a Multi-pass Austenitic Stainless Steel Weld Joint by Narrow-Gap TIG

In the present study, correlation of the microstructure and stress corrosion cracking (SCC) susceptibility in the top, middle and root regions of a multi-pass austenitic stainless steel weld joint fabricated by narrow-gap tungsten inert gas welding (NG-TIG) was investigated by slow strain rate tests (SSRT) following a microstructure characterization. The results show that from the top to root regions in both the heat-affected zone (HAZ) and weld metal (WM), the dislocation density and length fraction of the Σ3 boundaries present a decreased trend, while the grain size, length fraction of LAB and residual strain all increase. By comparing the microstructure of WM with HAZ, δ-ferrite in WM is excessive and continuous while that in HAZ is island-shaped and discontinuous. In addition, larger grain size, lower dislocation density, higher residual strain, lower length fraction of Σ3 boundaries and higher length fraction of RGB are observed in WM. As a result, the SCC susceptibility in various regions of the weld joint follows the order of root regions > middle regions > top regions and WM > HAZ.

Effect of forging pressure on microstructural characteristics and tensile properties of linear friction welded Ti-6Al-4V alloy joints

Ti-6Al-4V (also called as Ti64) is often used in the aerospace applications for its high strength to weight ratio. Ti64 can be welded by almost all the fusion welding processes but it led to the development of coarse-grained microstructure in the fully deformed zone, severe deformation, and high residual stresses. To reduce these complications, solid state welding processes are now adopted in the aerospace industries because it avoids total melting of materials and provides finer grain structures in the nugget region. Among different solid-state techniques, linear friction welding (LFW) is highly suitable to join the blade to disk assembly in the next generation aero engines. In order to get a joint with higher efficiency, the process parameters such as oscillating frequency, friction pressure, friction time, forging pressure and forging time are to be optimized. Hence, in the current investigation an effort has been made to study the effect of forging pressure on microstructure and tensile properties of LFW Ti64 joints. The tensile strength of the joints was evaluated as per the ASTM standards. The microstructure of various regions of welded joints was examined using optical microscopy (OM) and scanning electron microscopy (SEM). From this study, it is understood that wider interface is observed for lower forging pressure and decrease with increase in forging pressure. The tensile strength increases with increases with forging pressure and it gradually decreases over increasing the forging pressure. The microstructure shows evidence of fine structure in the weld region i.e., FDZ. The TMAZ region of the grain is plastically deformed and reoriented in the direction of the friction motion.

Sensitivity and stress analysis of serrated fin structure in plate-fin heat exchanger on cryogenic condition

The effects and interaction effects of fin height, fin space, fin thickness and fin interrupted length on flow resistance, heat transfer and stress of plate fin heat exchanger (PFHE) on cryogenic condition are analyzed quantitatively, based on computational fluid dynamics (CFD), fluid structure interaction (FSI), response surface methodology (RSM) and sobol sensitivity analysis. The stress distribution in serrated fin structure shows that the large stress is mainly distributed in the regions of keen-edged geometric structure such as weld joint region and the region connecting two rows of fin. The sensitivity analysis results reveal that j factor is the most sensitive to fin interrupted length, and f factor and maximum stress are most sensitive to fin thickness. The sobol sensitivity analysis results show that, for j factor and maximum stress, it is sufficient to investigate the first-order sensitivity indices and high-order sensitivity is weak. For f factor, it is necessary to consider the second-order sensitivity, especially for fin space and fin thickness. Based on above analyses, by combining with Multi-Objective Genetic Algorithm (MOGA), the serrated fin structure is optimized from perspective of two objectives (maximizing JF factor and minimizing maximum stress) and three objectives (maximizing j factor, minimizing f factor and minimizing maximum stress). In general, the optimization results based on two objectives are more intuitive, and they offer a smaller solution space. An original point is optimized, the results reveal that, compared with original point, JF factor of optimized point 1 increases by 17.8% without changing maximum stress, while maximum stress of optimized point 2 decreases by 50.0% without changing JF factor.

Study on The Thermal Distortion, Hardness and Microstructure of St 37 Steel Plate Joined Using FCAW

This study sets out to investigate the distortion angle, microstructure, and hardness of St 37 steel plate weld joint produced by FCAW using the welding current of 80, 110, and 140 A. By using flat position, CO 2 and E71T-1 wire were utilized as a shielding gas and electrode filler, respectively. The distortion angle measurement was done on 3 different locations of the welded sample perpendicular to weld direction by using bevel protractor. The micro Vickers tests were then applied gradually at the cross-sectional surface with a distance of 0, 5, 10 and 15 mm from weld centreline using the load of 300 g for indentation time of 15 s. A series of microstructural observations were subsequently directed on cross-sectional weld joint regions including base metal, heat-affected zone (HAZ) and weld metal to investigate the microstructural transformation. From the results, it can be observed that increasing welding current can reduce the hardness at all indentation regions as well as inducing a higher level of thermal distortion occurred on a weld joint, especially at HAZ. The microstructural transformation was also observed at sample welded using various welding current. Both heat input and cooling rate subjected to the welded sample played an important role to characterize their properties.

MICROSTRUCTURAL AND MECHANICAL ASPECTS OF FRICTION WELDED DISSIMILAR JOINTS FOR AERO ENGINE APPLICATION

Gas turbine engines demand material with unique properties like high-temperature oxidation and corrosion resistance, high specific strength, etc. All over the world material development to meet these requirements has led to the development of novel alloys. While Titanium base alloys are used in the low-temperature regime of the gas turbine engine, Nickel-basedsuperalloys are used for hot end components of the engine. With the increase in the temperature requirement for the turbine parts, the form of the Ni-based superalloys changed from wrought to cast superalloys. As an inherent process of investment cast superalloy blades and vanes which has serpentine passages for air cooling, these passages are required to be closed after casting. The numerous adapters also need to be joined on the cast superalloy casings for various instrumentation, lube oil ports. These cast superalloys are nonweldable and joining these pose a challenge. In this present investigation, the joining of the Nibasedsuperalloy BZL12Y and martensitic stainless steel AE961W using rotary friction welding process. The mechanical properties of the dissimilar joints were evaluated as per the ASTM standards. Microstructural features of various regions of welded joints using optical microscopy (OM) and scanning electron microscopy (SEM). The material is welded in different condition to obtain the maximum tensile strength of the weld joint. From this investigation, it was found that the combination of aging and h & t condition weld joint gives good strength and a stable hardness value. Correlation between tensile properties and microstructural features were analyzed and reported in this paper.

Enhanced Galvanic Corrosion Phenomenon in the Welded Joint of NiCrMoV Steel by Low-Cycle Fatigue Behavior

The effect of microstructural changes on the corrosion of a NiCrMoV steel welded joint induced by low-cycle fatigue behavior in chloride solution has been investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), potentiodynamic polarization curve tests and scanning vibrating electrode technique (SVET) tests. During the low-cycle fatigue tests, cyclic softening takes place in the three zones (base metal, BM/weld metal, WM/heat affected zone, HAZ) of the welded joint due to the decrease of dislocation density or the formation of low-energy structures. Compared to the as-received specimens, the corrosion potential of each zone in the low-cycle fatigue damage specimens moves to the positive direction and the corrosion current density decreases. The corrosion resistance of the individual zone increases, which is related to the reduction of dislocation density or the formation of low-energy structures. However, the difference of corrosion potential between base metal and weld metal in the low-cycle fatigue welded joints becomes lager, which means that the galvanic corrosion susceptibility of the low-cycle fatigue welded joint increases. This may be caused by the difference of microstructural changes in the various regions of welded joints during cyclic plastic deformation.

Ratcheting Behavior of Weld Joints Under Uniaxial Cyclic Loading Using Miniature Specimen

Because of the size limitation of weld joints in different regions, the traditional standard bar specimen is not suitable to investigate the mechanical properties of weld joints. In this study, miniature specimens were extracted from specific regions (base metal, weld metal, and three heat-affected zones) of API X80 and X70 weld joints. Uniaxial tensile tests were conducted to obtain the mechanical properties of different regions, and then uniaxial ratcheting tests were conducted to investigate the ratcheting behaviors of the different regions under the same peak and nominal stresses. Under both the tensile tests and ratcheting tests, the weld joints exhibit heterogeneous results, such as different mechanical properties and ratcheting behaviors, which were region dependent. Furthermore, the yield strength and yield-to-tensile strength ratio contribute differently to the ratcheting response.

Evaluation of fracture toughness in different regions of weld joints using unloading compliance and normalization method

Both unloading compliance method and normalization method specified in ASTM E1820-16 were conducted on the API 5L X70 and X80 pipeline steels. Extensive experimental measures of fracture toughness for different regions of weld joints were carried out. For comparison, the J–R curves and initiation fracture toughness determined using the normalization method are compared with those obtained by the elastic unloading compliance method for two different weld joints. The results show that good agreements exist between the two methods, and an average difference less than 10% is detected. Moreover, the comparison indicates that the J–R curves from the unloading compliance method are lower at the initial stage of crack extension, and as the crack grows, the J–R curves are higher compared with those of the normalization method. For different regions in weld joints, there is clear distinction of differences between the corresponding results from above two methods. A ductile brittle mixed fracture mechanism is found in weld metal and coarse grained heat affected zone, and a corresponding higher deviation is detected.

Welded joints as critical regions in pressure vessels -case study of vinyl-chloride monomer storage tank

Welded joints are analysed as critical regions in a pressure vessel in respect to structural failure due to the elastic-plastic fracture/crack growth. To assess structural integrity of pressure vessels used in chemical industry the risk based procedure has been introduced and applied in the case of a large spherical pressure vessel used as a vinyl-chloride monomer (VCM) storage tank in HIP Azotara Pancevo. The risk matrix has been used, taking into account the basic definition of risk, being the product of the probability and consequence, and applied to different regions of welded joints, having different mechanical properties, i.e. crack resistance. To estimate probability, the failure assessment diagram (FAD) has been used, as an engineering tool, defined according to the position of the operating point for different regions of the welded joint, relative to the critical point on the limit curve. Generally speaking, consequence is estimated based on pressure vessel parameters, or by detailed analysis of health, safety, business and security issues, but in the analysed case, the worst case scenario is assumed, with the highest consequence due to potential disaster for environment and fatalities.

Tensile and impact toughness properties of various regions of dissimilar joints of nuclear grade steels

Abstract Modified 9Cr-1Mo ferritic steel is a preferred material for steam generators in nuclear power plants for their creep strength and good corrosion resistance. Austenitic stainless steels, such as type 316LN, are used in the high temperature segments such as reactor pressure vessels and primary piping systems. So, the dissimilar joints between these materials are inevitable. In this investigation, dissimilar joints were fabricated by the Shielded Metal Arc Welding (SMAW) process with Inconel 82/182 filler metals. The notch tensile properties and Charpy V-notch impact toughness properties of various regions of dissimilar metal weld joints (DMWJs) were evaluated as per the standards. The microhardness distribution across the DMWJs was recorded. Microstructural features of different regions were characterized by optical and scanning electron microscopy. Inhomogeneous notch tensile properties were observed across the DMWJs. Impact toughness values of various regions of the DMWJs were slightly higher than the prescribed value. Formation of a carbon-enriched hard zone at the interface between the ferritic steel and the buttering material enhanced the notch tensile properties of the heat-affected-zone (HAZ) of P91. The complex microstructure developed at the interfaces of the DMWJs was the reason for inhomogeneous mechanical properties.

Localized creep characterization of 316LN stainless steel weld joint using Small Punch Creep test

Type 316LN stainless steel (SS) weld joints are widely used in several high temperature applications. The variations of creep properties across the microstructurally heterogeneous regions of 316LN SS weld joint such as base metal, weld metal and heat affected zone (HAZ) have been evaluated using Small Punch Creep (SPC) technique at 923K. Both the SPC rupture and deformation behaviors were investigated. The creep strength gradient across 316LN SS weld joint showed a smooth increasing trend from base metal to weld metal. However, the trend of the rupture life for weld metal shifted with change in load level. The SPC deformations of various regions of weld joint have been analyzed according to the equation,δ=δ0+δT(1−e−κt)+δ̇st+δ3e[ϕ(t−tr)]. The variations of transient, secondary and tertiary creep parameters were determined across the weld joint. The master curve for transient creep deflection was obtained for various regions of weld joint.

Failure Analysis of Dissimilar Steel Weld Cracking on High and Medium Pressure Guide Pipe

The hardness test and microstructure characterization were adopted to analyze the cracking failure of dissimilar steel weld cracking on high and medium pressure steam lead pipe. The materials of the cylinder, the guide pipe and the welding material were ZG15Cr2Mo1, 1Cr9Mo1VNbN and AWS 5. 11 ENiCrFe-1, respectively. The study showed that the hardness of the fusion line was higher than that of the adjacent base metal (ZG15Cr2Mo1) and nickel base welding, which was the weak area. The pressure pipe cracking is high temperature fatigue crack. The grains in the weld joint region were coarse, indicating that the welding specification is too broad and the time for welding remaining in the sensitized temperature zone is too long. The improper welding process was the main reason for the welding cracking of the high and medium pressure guide pipe.