Weld Region Research Articles

Influence of HAZ microstructure on RCF under twin-disc test of a flash-butt welded rail

A new twin-disc test was performed using discs containing all microstructures of the heat-affected zone (HAZ) of flash-butt welded rails. It was observed that the lower hardness regions (spheroidized cementite in a ferritic matrix) at the HAZ boundary underwent a local deformation, generating valleys and reproducing a common defect type observed in rail welds: double squat-like defect. Longer crack lengths or crack clusters were observed in the HAZ boundary and central weld regions. The cross-section metallography showed that these cracks are directly related to the microstructure of spheroidized cementite at the HAZ edges or pro-eutectoid ferrite at the central region. The decrease in surface roughness before the cracks, the presence of oxide on the bottom crack surface, and superior spheroidized cementite microstructure in the upper crack region suggest that these larger/cluster cracks are predominated by extrusion of the softer material above the harder material (pearlitic/base metal).

Characterization of As-Welded Microstructure in a P91 Steel

The microstructure of the heat affected zone (HAZ) and fusion zone (FZ) in the as-welded condition of a single-pass weld performed by the flux-cored arc welding (FCAW) process was studied in a P91 steel using microhardness measurements, field-emission scanning electron microscopy, transmission electron microscopy, and x-ray diffraction. The evolution of precipitates in each region of the single-pass weld was analyzed, and particular attention was paid to the presence of retained austenite (RA). Experimental observations indicated that M23 C6 carbide played a major role in the thermal cycle associated with the weldment. On one hand, the dissolution of M23 C6 led to the precipitation of spherical NbCN in the finegrained HAZ (FGHAZ) near the coarse-grained HAZ (CGHAZ). On the other hand, the total or partial dissolution of M23 C6 carbides changed the chemical composition of the initially formed austenite. In the regions where the M23 C6 carbides were completely dissolved (i.e., the CGHAZ and FZ), retained austenite was observed as a thin, continuous film along primary austenite grains and lath boundaries. Instead, a shell of retained austenite was observed around some partially dissolved M23 C6 of the intercritical HAZ (ICHAZ) and FGHAZ.

Polypropylene for material extrusion: Evidence that flow-enhanced crystallization restricts welding

We present a comprehensive investigation into the effect that both the crystallization kinetics and the molecular weight of polypropylene feedstock have on the welding properties in material extrusion 3D-printing (MatEx). As sufficient welding at the interfaces between printed layers may be restricted by the onset of crystallization, there is a delicate balance between polymer interdiffusion and the development of spherulites within the weld region. We monitor these processes during a cooling cycle using a well-established theoretical model that requires full characterisation of the rheology and crystallization. The model shows that the largest effect of increasing molecular weight is a reduction in interdiffusion; this mechanism leads to a reduction in the weld strength as demonstrated by mechanical testing. For the highest molecular weight feedstock, we find that the fracture pattern changes from plastic deformation to brittle mode. Furthermore, we observe that the spherulites within the weld are about an order of magnitude smaller than in other samples. These observations cannot be described by the quiescent crystallization kinetics alone. Our findings suggest that it is a flow-enhanced crystallization mechanism that accelerates nucleation leading to smaller spherulites developing in the weld earlier in the cooling process. This significantly restricts interdiffusion at the welds.

Yakma Alın Kaynağıyla Birleştirilmiş S355jr Yapı Çeliklerinde ITAB’ın Ansys ile Analizi

In this study, we focus on predicting the HAZ, which is a region whose mechanical properties are not clearly known, by modeling factors such as temperature input and heat turbulence, which may have different properties in the welding region. This is important for the safety of welded structures, because if the mechanical and thermal properties of these structures, which are used in many areas, can be determined in advance, they can be used more safely. In the study, flash butt welding method was preferred and holes were opened at regular intervals in the samples that were brought to appropriate dimensions for the welding process, and temperature values were measured and recorded using thermocouples and data loggers during the welding process. Additionally, the maximum temperature reached in the welding area was measured using a thermal camera during welding. Microstructural changes occurring in the joining regions of the welded test pieces were examined using light microscopy and scanning electron microscopy (SEM). Micro hardness measurements were made to determine mechanical properties. Using the ANSYS program, three-dimensional models were created using the finite element method under the same experimental conditions and compared with the experimental results. As a result of this comparison, it was seen that the findings were compatible with the actual results. For this reason, it is emphasized that the use of simulation programs is important to predict the properties of welded structures and possible problems.

A low-cost vision-based weld-line detection and measurement technique for robotic welding

ABSTRACT To make robotic welding more flexible and intelligent, artificial intelligence-based systems are one of the most important developments. This paper introduces a computer vision-based algorithm for weld path detection, gap measurement, and weld length calculation. The proposed innovative approach employs various image processing techniques and mathematical operations, accurately determining weld attributes at seam points. Using the YOLO-based object detection algorithm, the model attains a remarkable average precision of 99.5% in identifying atypical weld regions. The study also introduces an efficient boundary line elimination method based on the Probabilistic Hough transform and mathematical logic. Methodology for classifying weld lines with or without significant gaps has been proposed, followed by adapting distinct set of algorithms for weld line identification and gap measurement. Rigorous testing on butt joints of diverse shapes (e.g., straight, zig-zag, and curve) and sizes verifies the robustness of the algorithm, with errors well within ±1 mm for length measurements. In testing conducted at three different points along the individual weld profile, the maximum error in estimating the weld gap was observed to be 0.11 mm. Weld seam information can be extracted effectively with the proposed algorithm, which proves its viability for industrial applications.

Effect of rotational speed and penetration depth on Al-Mg-Si welded T-joints through underwater and conventional friction stir welding

The present work deals with the effect of penetration depth on welding T-joints through conventional friction stir welding (FSW) as well as underwater friction stir welding (UFSW). Various set of parameters have been used such as tool rotational speeds of 1000, 1400, and 1800 rpm, and depths of penetration, such as 6, 7, and 8 mm. In UFSW, lower heat generation prevents the development of complex intermetallic compounds and defects in welding. Additionally, in the weld region, a rapid cooling rate in UFSW generates fine microstructural particles. Mechanical and microstructural characteristics has been compared in both UFSW and FSW. There was a substantial grain size effect on mechanical properties. The stir zone shows comparatively finer grains with average grain size of 49.76 µm at 1800 rpm and 7 mm depth of penetration. It was seen that the tensile strength of UFSW was 189.9 MPa and the nugget zone hardness was 70 VHN, compared to the FSW that has 175.2 MPa and 62 VHN, respectively, obtained at a rotation speed of 1800 rpm and a travel speed of 60 mm/min. The joints tested at various penetration depths show a significant number of uniform and equiaxed dimples. The presence of ductile rupture and the formation of dimples suggest that the joints were effectively bonded and tested at different strain rates.

Low cycle fatigue behavior of Incoloy 800H weld joint at 800 °C

The fatigue behavior of the 800H weld joint at the temperature of 800 °C was investigated, taking into account the effects of residual stress and microstructure. To model the residual stress in the welded joint, a finite element method was employed and its accuracy was verified using a hole drilling method, which was also used to study the evolution of residual stress during cutting and heating processes. Additionally, the weld region was characterized by measuring the distributions of elements and micro-hardness via energy dispersive X-ray spectroscopy and Vickers hardness tester. Fatigue lives, curves of displacement versus the number of cycles were obtained, and the fracture morphology was analyzed. The results reveal that the calculated residual stress in the weld region agrees well with the experimental results, and the transverse residual stress reduces in magnitude due to cutting and heating. Element distribution and micro-hardness exhibit obvious variations from the base metal to the weld metal. The micro-hardness has a minor effect on residual stress but a significant impact on local stress amplitudes at the weld toe. Furthermore, fatigue fractures primarily occur at the weld toe when the maximum cyclic stress exceeds 200 MPa, while the fracture location varies within the middle weld metal under smaller loads.

Effects of post-weld heat treatment on the microstructure and properties of the matching SMAW filler metal for weld joints in MarBN steel

AbstractA detailed investigation has been carried out of the matching composition filler metal for welding MarBN steel to explore the influence of welding procedure and post-weld heat treatment (PWHT) on the microstructure and properties of the weld metal and a MarBN steel weld joint. The filler metal was in the form of a shielded metal arc welding (SMAW) electrode. With different interpass temperatures and PWHT procedures applied, the microstructure and mechanical properties, particularly toughness, of the all-weld metal deposits and welded MarBN alloy joints were examined. The differences in microstructure (grain structure, precipitates, etc.) were evaluated to provide a better understanding of how the PWHTs influence the starting conditions of the matching weld metal and welded MarBN steel joints before service. The current work found that for a 30-mm-thick all-weld metal coupon, reasonable impact toughness was achieved after PWHT of 735 °C × 8 h; longer heat treatment durations (16 h and 36 h) did not further increase the toughness. For thicker cast blocks, a PWHT of 735 °C × 16 h was needed for weld toughness comparable to the base metal, hence was considered more appropriate for actual engineering applications. Evenly distributed Laves phase precipitation was observed after 735 °C × 8 h; the precipitates gradually increased in size and area fraction as the duration increased, and appeared to be stable when approaching 36 h. Differences in the precipitation were observed between different weld regions. The weld cap region had a lower density of Laves precipitates compared to the lower weld area. From the current investigation, aspects for further investigation are also identified.

Polysilazane-derived SiON coating on stainless steel weld for corrosion resistance

In this study, SiON coatings were created using perhydropolysilazane (PHPS) on the weld region and the base stainless steel region with different microstructure and composition. The influences of the weld and base steel compositions and microstructures on coating formation, composition, microstructure, mechanical properties, and corrosion resistance are discussed. The SiON coatings show a higher N content and a lower O content on the base metal than on the weld metal. Salt spray tests show that the differences in mechanical properties and compositions on the weld and base steel substrates do not significantly affect the function of the corrosion-protective coatings. However, when the coating thickness is high, the corrosion resistance decreases. This study provides important guidance regarding the desirable SiON coating and thickness for best corrosion prevention.

Distribution and Characteristics of Residual Stresses in Super Duplex Stainless Steel Pipe Weld

This paper explores the distribution and features of residual stresses formed by super duplex stainless steel pipe welding. Experimental investigations, which encompass an elevated temperature tensile test and metallographic observation along with a hardness test and residual stress measurement, were first conducted to obtain the mechanical properties at high base metal temperatures and to confirm whether or not the duplex stainless steel undergoes martensitic phase development during the welding process. Finally, experiments were performed to scrutinize the residual stress evolution through the metallurgical phase transformation in the weld region and its vicinity. A sequentially coupled 3D thermal, mechanical and metallurgical finite element (FE) model capable of incorporating the experimental consequences was established next. A 3D FE simulation of the girth welding process was conducted, and the axial and hoop residual stress profiles along the girth were evaluated. The results substantiate that martensitic phase evolution occurs in the process of cooling during the welding of super duplex stainless steel, and they also highlight the significance of taking the metallurgical phase transformation into account in the numerical reproduction of the girth welding process for the accurate expression of weld-induced residual stresses, which is especially important for precisely predicting hoop residual stresses.

A novel approach to suppression of reverted austenite in aerospace grade thick maraging steel weldments using the turbo-TIG welding process

This research examines aerospace grade-maraging steel weldments produced by the novel Turbo-TIG welding technique. The vital challenge in welding maraging steel is the development of reverted austenite in the weld region and HAZ. This reverted austenite degrades the mechanical characteristics of weldments. MDN 250 maraging steel with a 12 mm thick plate was welded at a high speed of 300 mm/min with consistent quality using the Turbo-TIG welding technique. The objective of the present work is to suppress the reverted austenite in the 12 mm thick plate of MDN 250 using the Turbo-TIG welding technique. Three different postweld heat treatments were applied, namely, (i) aging heat treatment (AT), (ii) solutionizing + aging (ST), and (iii) homogenization + solutionizing + aging (HT). The microstructure and X-ray diffraction analysis of the weld zone under AT and ST conditions demonstrate the existence of reverted austenite in the grain boundary regions. The SEM/EDS analysis of the weld zone of welded, AT, and ST conditions indicated Ni, Mo, and Ti microsegregation from the center matrix to the grain boundary regions. In contrast, neither microsegregation nor austenite reversion occurred in the HT condition. The tensile test demonstrates a maximum strength of 1797 MPa (UTS) under HT conditions. Likewise, the microhardness of the HT conditions exhibits a higher hardness of 552 HV in the fusion zone. In light of the metallurgical and mechanical characteristics of the weld, the HT heat treatments provide better weld performance in the case of Turbo-TIG welding of maraging steel grade MDN 250.

Corrosion behavior and microstructure analysis of butt welds of Q690 high strength steel in simulated marine environment

Steel components that have served in the marine environment for extended periods often face challenges in preventing surface damage caused by corrosion protection measures. These challenges can ultimately diminish the expected service life of structures. To investigate the corrosion behavior and time-varying effects in butt welds of Q690 high strength steel in the ocean splash zone, a macroscopic morphology analysis was conducted using various corrosion times involving indoor saltwater immersion and hot-humid cycling accelerated corrosion. Quantitative analysis of corrosion pits' size and distribution range was performed in both the weld zone (WZ) and heat-affected zone (HAZ) to establish a relationship between roughness parameters and corrosion time. Experimental results were compared with corrosion parameters of regular steel. The findings reveal a gradual reduction in metallic luster with increasing corrosion time on specimen surfaces. Moreover, a greater accumulation of corrosion products is observed in the butt weld region, leading to progressive corrosion damage. High strength steel (HSS) exhibits superior corrosion resistance compared to ordinary steel. However, the corrosion damage of HSS weld joints gradually approaches that of ordinary steel in the later stage of corrosion. Microscopic scanning indicates that the accumulated corrosion layer effectively impedes the penetration of corrosive media into the matrix's interior, while the surface microstructure transitions from pitting to corrosion pits. These research findings significantly contribute to assessing the performance and analyzing the reliability of high strength steel in marine environments.

Fatigue Life Analysis of Hydrogen Production Reactor Welds Under Thermal-mechanical-chemical Coupling

Hydrogen production reactor are subject to performance degradation problems in the complex environment of high temperature, high pressure and exposed to hydrogen atmosphere. The welds, being weak parts, are susceptible to fatigue damage under the influence of loads such as temperature, pressure and hydrogen penetration. In this paper, we focus on the fatigue life analysis of welds in hydrogen production reactor, taking into account the complex working conditions of thermal-mechanical-chemical coupling. Based on the Fe-safe fatigue analysis software, the stress variation of the welds under multi-field coupling was used as a cyclic load and the fatigue life was predicted using the stress-life method. Respectively, the fatigue life variation law of the weld region was studied at different temperatures, pressures, and hydrogen penetration conditions. The results show that the lowest fatigue life of the welds are concentrated in the vicinity of the fusion zone, with hydrogen penetration and temperature variations having a larger impact on the fatigue life, followed by pressure.

Process strategies for optimizing the cooling behaviour of laser-welded Tailor Welded Blanks made of advanced high strength steels (AHSS)

AHSS with 1000 MPa tensile strength show promising properties for the use in Tailor Welded Blanks (TWBs) to locally strengthen car body parts. Challenges in laser beam welding of the sheets are hardness-drops and -peaks in the heat-affected zone (HAZ) and weld, which cause risks during cold-forming. This happens due to rapid cooling caused by laser welding. A numerical approach aiming for slower cooling rates in the weld region is presented in this article. Laser welded sheets served as reference for setting up a process simulation. Models for pre-heating and a coaxial setup with power split were set up. A correlation between cooling-rate and hardness in the joining zone was established and applied to the modelled strategy. Splitting the power led to a slightly narrower weld seam and experimental pre-heating of the sheets to 600 °C could lower total seam hardening. It achieved a homogenization of the fusion zone.

Numerical modeling of liquid metal embrittlement initiation during resistance spot welding of third generation advanced high strength steel – Effect of welding schedule and electrode alignment

Third generation (GEN3) advanced high-strength steels are increasingly used to reduce vehicle body structure weight for improved fuel economy. Zinc-induced liquid metal embrittlement (LME) has become a prevalent challenge when these steels are welded by resistance spot welding (RSW). In the literature, various numerical models have been developed to study LME during RSW of GEN3 steels. Those models tend to have a limited utility in predicting how various factors such as RSW parameters affect LME cracking. In this study, a novel LME calculation method has been developed by integrating an electro-thermo-mechanical finite element model of RSW process with an LME ratio for crack initiation established from hot tensile testing data. The onset of different types of LME cracking is tracked throughout the weld region over the entire course of RSW including the final cooling stage after electrode retraction. The model is validated using an existing set of literature data that involves different welding schedules, electrode geometries and electrode misalignments. The local temperature and stress conditions during RSW are calculated and used to understand how different welding parameters affect the severity of LME cracking. It is found that electrode misalignment exacerbates crack initiation on outer surfaces of the spot weld due to the tensile stress arisen from the off-centered squeeze force as well as the reduced surface cooling to electrodes. Initiation of cracks between the steel sheets, taking place mainly after electrode retraction, is not significantly affected by the welding schedule and the electrode tip diameter.

A study on the effect of weld repair on the structural margins of a solid rocket booster hardware

Cylindrical shells in one of ISRO’s solid rocket booster is fabricated from ultra-high strength steel (M250 Maraging steel) through rolled and welded construction. This steel being a fracture prone material, elastic-plastic fracture mechanics-based design is followed for the design of cylindrical shell. The no-flaw failure pressure i.e. elastic plastic failure pressure (Pb) of the cylinder is an important parameter in design. For a given diameter of cylindrical shell, Pb is a function of shell thickness and mechanical property. If any unacceptable flaw is found on welds during NDT, repairs are carried out in the weld region. Mechanical properties of weld/weld repairs are lower when compared to parent material. It is seen that, at any location, if it is repaired twice, the strength reduces by 21% when compared to the parent metal property. Thus, the mechanical properties of the weld region dictate the overall design thickness of the cylindrical shell. A study is carried out to find the effect of length of weld repair zone on the Pb. A parametric 3D FE model simulating the repair in long seam weld, cirseam weld and combination of long seam & cirseam weld in cylindrical shell is used for this purpose. It is found that the effect of parent metal property needs to be considered while estimating Pb. Further while considering the repair in long seam, the length of repair also needs to be considered. Pb is found to increase considering its effect. This study was helpful in establishing more realistic structural margins in a solid rocket booster case which had weld repair.

Investigating parametric effects during TIG welding of dissimilar metals

This paper explores the optimization of Tungsten-Inert-Gas (TIG) welding process parameters for creating a hybrid structure of Aluminium 6061 and Stainless Steel 304 using a copper filler rod (ER-Cu). The Welding of these two materials has industrial relevance owing to its weight reduction capabilities and environmental benefits. However, Aluminium and Stainless-Steel have different melting points and thermal properties. Aluminium has twice coefficient of thermal expansion and six times coefficient of thermal conductance as compared to Stainless-Steel. This difference often results in residual stresses and brittle intermetallic compounds in the weld region. We have chosen the Welding Current, Welding Speed, and Gas Flow Rate as input parameters, and Ultimate Tensile Strength (UTS) and Micro-hardness as response parameters. We have employed the Response Surface Methodology (RSM) using a Box-Behnken design to evaluate the influence of input parameters on UTS and Micro-hardness. Furthermore, an Analysis of Variance (ANOVA) is conducted to determine the input parameters' significance on the response parameters. Our surface plots demonstrate that UTS improves with increased Welding Current and reduced Welding Speed. Simultaneously, Micro-hardness increases with elevated Welding Speed and decreased current, up to a specific limit. The peak value of UTS (79 MPa) was observed with a Current range of 85-90 A, Speed range of 95-100 mm/min, and Gas Flow Rate of 14.5-15 l/min. On the other hand, maximum Micro-hardness (260HV) was obtained with a Current range of 80-85 A, Speed range of 105-110 mm/min, and Gas Flow Rate of 14.5-15 l/min. This research contributes to improving the manufacturing process of hybrid structures, specifically by optimizing the advantages of both Aluminium and Stainless Steel while addressing the challenges that arise during their combination. The study's conclusions have major consequences for sectors looking to take advantage on the mutually beneficial characteristics of different metals in welding applications.

Microstructure and mechanical properties of longitudinal weld in 6005A aluminum alloy profile extruded by a porthole die

Porthole die extrusion experiments were carried out on 6005A aluminum alloy under the billet heating temperatures of 420–570 °C and ram speeds of 1–120 mm/min. The effects of extrusion parameters on the microstructure and mechanical properties in the longitudinal weld of profiles were investigated. It was found that the crystal orientation of longitudinal weld region showed the characteristics of gradient arrangement with different oriented grains wrapped in layers and symmetric along the welding line. The Copper{112}<111> grains are formed at the welding line under the combined effect of shear and compression, and the Goss{110}<100> grains are formed on their both sides due to dynamic recrystallization. A shear band is formed when part of metals flow through the 45° inclination angle of port bridge due to a sudden change in velocity, causing the Goss{110}<100> texture in local region to rotate to Brass{110}<112> texture. The 6005A aluminum alloy profiles mainly contain β (Mg2Si) phase, Q (Al3Mg9Si7Cu2) phase, AlCrMnSi phase and AlFeMnCrSi phase. Appropriately increasing billet heating temperature and ram speed can promote dynamic recrystallization and the dissolution of β-phase and Q-phase, thus improving the strength and hardness of the profile. However, when the billet heating temperature is too high, the strength and hardness are reduced instead due to grain coarsening. The profile extruded at billet heating temperature of 510 °C and ram speed of 120 mm/min has the best mechanical properties, with the tensile strength in 0° direction and hardness at the welding line of 179.93 MPa and 52.2 HV, respectively.

Cold metal transfer welding of 316L/430 dissimilar stainless-steel welds

Purpose This paper aims to examine dissimilar joints for various applications in chemical, petrochemical, oil, gas, shipbuilding, defense, rail and nuclear industry. Design/methodology/approach This study examined the effects of cold metal transfer welding on stainless steel welds for 316L austenitic and 430 ferritic dissimilar welds with ER316L, ER309L and without (autogenous) fillers. The microstructural observation was done with an optical microscope. The mechanical test was done to reveal the strength, hardness and toughness of the joint. The electrochemical polarization tests were done to reveal intergranular and pitting corrosion in the dissimilar joints. Findings This microstructural study shows the presence of austenitic and ferritic phases with vermicular ferrite for ER309L filler weld, and for ER316L filler weld specimen shows predominately martensitic phase in the weld region, whereas the autogenous weld shows lathy ferrite mixed with martensitic phase. Mechanical test results indicated that filler welded specimen (ER316L and ER309L) has relatively higher strength and hardness than the autogenous weld, whereas ER316L filler weld exhibited the highest impact toughness than ER309L filler weld and lowest in autogenous weld. The electrochemical corrosion results displayed the highest degree of sensitization (DOS) in without filler welded specimen (45.62%) and lower in case of filler welded specimen ER309L (4.95%) and least in case of ER316L filler welded specimen (3.51%). The high DOS in non-filler welded specimen is correlated with the chromium carbide formation. The non-filler welded specimen shows the highest pitting corrosion attack as compared to the ER316L filler weld specimen and relatively better in ER309L filler welded specimen. The highest pitting corrosion resistance is related with the high chromium content in ER309L composition. Originality/value This experimental study is original and conducted with 316L and 430 stainless steel with ER316L, ER309 and without fillers, which will help the oil, shipbuilding and chemical industries.

A Machine Learning Approach for Prediction of Surface Temperature of the Weld Region in A-TIG Welding

A Machine Learning Approach for Prediction of Surface Temperature of the Weld Region in A-TIG Welding