Zone Of Welded Joints Research Articles

Анализ материалов и технологий нанесения изоляционного покрытия на наружную поверхность зоны сварного стыка труб с заводским покрытием

Анализ материалов и технологий нанесения изоляционного покрытия на наружную поверхность зоны сварного стыка труб с заводским покрытием

Experimental studies of heat treatment influence on the welded connections properties in working mechanisms of road building

Introduction. The experimental studies of the heat treatment effect on the properties of welded joints in working mechanisms of road-building machines are carried out in the work. Studying the structures of the metal itself, as well as welded joints and considering their heterogeneity, the author analyzes the strength characteristics of these objects.Materials and methods. By means of metallographic analysis, as well as using boron-containing steel 30MnB5, which is used for the manufacture of structures for construction machines, as a research material, the author examined its microstructure, which took place in certain zones of welded joints. In particular, welded jointss, fusion zones with an overheating area, a complete recrystallization area and the base metal were studied. We also studied the features of cold plastic deformation of the specified steel sample.Results. It was determined that the mechanical inhomogeneity of the steel at these joints is the cause of the structural inhomogeneity of the welded joints. As a result of this process, some dangerous zones of acting voltages concentration are formed. These conclusions predetermine the need to identify some certain zones that concentrate stresses in themselves, while it is mandatory to strengthen the metal in such zones to standard indicators. An increase in the strength properties of the steel under study is possible by applying cold plastic deformation and subsequent thermal cycling (STC). This is achieved by obtaining a fine-grained metal structure with higher strength. The author defines the welded joints and the zone of its fusion with the base metal and the overheating area as the most dangerous areas subject to loading. To control this process, it is recommended to use the passive fluxgate method in the work, while the fusion zone with the overheating section should be inspected first, and then the weld.Discussion and conclusion. The author comes to the conclusion that the experimental studies carried out can contribute to an increase in the efficiency of the process of reducing the stress concentration (SC) in the elements of construction machines made of steel and subjected to intensive operation by reducing the structural and mechanical inhomogeneity of welded joints.

Stress rupture initiated by the carbides in the grain boundaries of the multi-pass weld metal

The weld metal (WM) was generally regarded as one of the weakest zones in the dissimilar welded joints. The microstructure and fracture mechanism of the multi-pass WM are systematically probed in the present study. The scanning electron microscopy (SEM) results show more voids in the equiaxed grain zone (EGZ) adjacent to the fracture than those in the columnar grain zone (CGZ). The transmission electron microscopy (TEM) results reveal that the precipitates are mainly Cr-rich M23C6 and Mo-rich M6C phases. The voids were initiated by the mismatch deformation between the precipitates and matrix during the stress rupture test. Moreover, the voids could easily extend and converge to form the macro cracks in the EGZ.

Влияние направления проката АМг5 на микроструктуру и свойства сварных соединений, полученных сваркой трением с перемешиванием

Introduction. Heat emission and plastic deformation during friction stir welding (FSW) cause profound changes in the microstructure and structural properties of weld joints. The grain size, crystallographic texture evolution and second-phase precipitate are the most important microstructural changes during welding of aluminum alloys, which largely influence the strength properties of weld joints. In addition to process-dependent parameters (instrument sump force, its rotation frequency, and travel rate) of the FSW process, a significant factor, determining the properties of the obtained weld joints, is also a mutual orientation of structural elements of the weld material and the direction of the instruments impact on the material during welding. In this regard, the purpose of the work is to analyze the combined influence of the direction of the initial rolling and the instrument pressure during FSW on the structure and properties of weld joints from the AA5056 aluminum alloy. Methods. Research methods are mechanical tests for statistical tension, microhardness as well as metallographic analysis of the structure of welded joints. Results and discussion. As a result, it is established that at low values of the axial force on the instrument (7 kN), defects such as the joint line and voids are observed in welded joints both rolling and transverse directions. When the load increases from 8 kN to 12 kN, defect-free weld joints with enhanced mechanical properties form. It is determined that the rolling direction of AA5056 during FSW does not influence the structure and tensile strength of the weld joints, but it influences the relative elongation and microhardness. It is shown that in the stir zone of the weld joint, obtained by FSW in the transverse direction of AA5056 flats, the relative elongation is 1.3-2 times greater, and the microhardness is by 4-10% greater than that in the stir zone of weld joints, obtained by FSW in the rolling direction of AA5056 flats.

Study of microstructural transition in dissimilar weld joint from as-welded to PWHT condition using electron backscattered imaging

Transition occurring in microstructures of heat affected zone (HAZ) of a P91-316LN SS dissimilar weld joint was studied using electron backscattered diffraction (EBSD). Kernel misorientation angle and grain boundary character distribution maps were used to study local strain accumulation and evolution of low angle grain boundaries in the HAZ regions. Two microstructural conditions i.e. as-welded and post weld heat treated (PWHT) were investigated. It could be seen that PWHT reduced the strain gradient in the P91 steel’s HAZ which was formed during welding and that localised softening occurred within this region after PWHT.

Evaluation of Microstructure, Microhardness, and X-Ray Elastic Constants for Simulated Heat-Affected Zones in Q1N Steel

Reliable assessment of residual stresses in critical structures using x-ray diffraction techniques requires determination of an accurate x-ray elastic constant (XEC) to accurately calculate residual stress state from measured crystallographic elastic strain. Experimental derivation of the XEC is the most reliable approach. This study examines whether experimental XECs derived for quenched and tempered Q1N steel are still accurate to quantify stress in the heat-affected zones (HAZ) of welded joints. A GleebleTM thermal simulator is used to generate coarse-grained, fine-grained and intercritical HAZ microstructure in Q&T Q1N steel. Thermal simulation conditions (grip separation, thermal cycles and cooling rate) were optimized to produce the desired coarse-grained HAZ microstructure at a peak temperature of 1300 °C in large Q1N steel samples. While thermal conditions produced HAZ microstructure and microhardness values that were characteristic of real weld HAZs, there is no measurable effect on bulk elastic properties or the XECs. The bulk elastic modulus has an average value of 204.0 ± 1.3 GPa for the base metal and the selected peak temperatures used for the three different HAZ regions. The XECs have an average value of 176.6 ± 3.6 GPa for the {211} crystallographic planes of bcc Fe for all samples. Results instil confidence in use of base metal XECs for residual stress analysis within actual or real weld HAZ of Q&T Q1N steel on submarine pressure hulls.

Study on Relationship between Material Vickers Hardness and Yield Stress of A508 Nuclear Material

It is difficult to directly obtain the mechanical properties of local materials of actual engineering structure (such as welded joints) by traditional mechanical test. Indentation test and ABAQUS finite element test were used in this paper, the relativity between Vickers hardness and yield stress of nuclear material A508 were studied, and a new method of using material surface Vickers hardness to acquire material properties was established. It can be used in the welded lines of nuclear dissimilar metal welded joints to obtain material parameters of mechanical property uneven zone of welded joints, and this new method was supported for complex engineering structure material mechanical parameters.

Effects of Preheating and Cooling Rate on the Microstructure and Mechanical Properties of Tungsten Inert Gas Welded Joints of AA5083-H321 Aluminum Alloy

Various preheating treatment and cooling rates conditions were carried out in Tungsten Inert Gas welding to study mechanical behavior and microstructural evolution of AA5083-H321 aluminum alloy welded joints. The microstructural analysis illustrated the diverse grain size during welding at different preheating and cooling rate. The highest preheat temperature caused to enlarge dendritic grains and during the fastest cooling rate formed the smaller grains. Also, the texture and grain size impressed on tensile behavior and hardness welds. Grain structure of the heat-affected zone, partially melted zone, and weld metal appeared to have a tangible relationship with preheating and cooling rate conditions. The microhardness of these regions increased by increasing the cooling rate and decreasing the preheating temperature. The high preheating had a negative effect on the hardness and width of different zones of welded joints. The results showed that the cooling rate has remarkable effects on the mechanical properties of the welded specimen.

Impact Toughness of Welded Joints on 34KhN2MA Steel Produced from Electrodes with Various Phase Compositions

We determine the brittle-fracture resistance of the metal taken from various zones of welded joints of 34KhN3MA steel produced from electrodes with different phase compositions or their combinations. It is shown that, regardless of the zone of welded joint in which a notch is made in the specimen, the highest values of impact toughness are observed for the weld metal obtained from the austenitic electrode. At the same time, the lowest value of impact toughness are observed for the combination of austenitic (weld root) and ferrite-pearlite electrodes. For any applied electrode, the lowest values of impact toughness were always observed for the metal of the heat-affected zone. Therefore, this zone determines the serviceability of welded joints under dynamic loads. The results of fractographic investigations demonstrate that austenitic electrodes are optimal for the purpose of welding of sheets made of high-strength steels because they guarantee the highest fracture energy of the joints under the action of dynamic loads.

Effect of microstructure and low cycle fatigue deformation on tensile properties of P91 steel

AbstractIsothermal furnace heat treatments were carried out to simulate the microstructures of inter‐critical, fine grain and coarse grain heat‐affected zones of P91 steel weld joint at different soaking temperatures ranging from just above AC1 (837 °C) to well above AC3 (903 °C). Interrupted low cycle fatigue tests were performed on the specimens of P91 steel up to 5 %, 10 %, 30 %, and 50 % of the total fatigue life at the strain amplitude of ±0.6 %, strain rate of 0.003 s−1 and temperatures of 550 °C and 600 °C. Subsequently, tensile tests were conducted on the interrupt tested specimens at the same strain rate and temperatures. Soaking at the inter‐critical temperature region reduces / deteriorates the tensile and yield strengths of base metal compared to fine grain and coarse grain regions. The inter‐critical heat‐affected zone accounted higher damage contribution towards the overall tensile behavior of the actual P91 steel weld joint. Substructural coarsening during strain cycling at elevated temperatures attributes to the rapid reduction in the initial yield strength up to 10 % of fatigue life of P91 steel. A higher amount of plastic strain accumulation during low cycle fatigue deformation resulted in a decrease in fatigue life of the inter‐critical heat‐affected zone of P91 steel.

Effect of change in microstructures due to simulation temperatures on the low cycle fatigue behavior of P91 steel

In this study, the microstructures of the three principal heat-affected zones (HAZs) of the P91 steel weld joint were simulated using appropriate heat treatments at different soaking temperatures ranging from 865 °C to 1200 °C. Low cycle fatigue tests were conducted on the samples of each microstructural zone of the weld joint at 550 °C employing a constant strain amplitude of ±0.6% and strain rate of 3 × 10−3 s−1. In the weld joint’s microstructures, the weld metal exhibits the lowest fatigue life, followed by the inter-critical (IC). However, the actual weld joint specimen failed at the interface between the ICHAZ and the base metal.

The microstructure and weldability in welded joints for AA 5356 aluminum alloy after adding modified trace amounts of Sc and Zr

Abstract Different AA5356 alloy filler metals containing various amounts of Sc and Zr are obtained and applied to join the 5083 aluminium plate with 2.8 mm thickness. A significant grain refinement can be observed in the fusion zone (FZ) of welded joints after the additions of Sc and Zr. The filler metal modified with 0.2 wt.% Zr+0.1 wt.% Sc obtained the smallest grain size with 29 μm, and the filler metal with 0.2 wt.% Sc+0.1 wt.% Zr additions got the similar grain size with 30 μm. The 0.2 wt.% Sc addition can effectively modify the microstructure of filler metal and improve the mechanical properties. The grain size of fusion zone for AA5356 + 0.2 wt.% Sc+0.1 wt.% Zr filler metal decreased by 75.8 % and the highest ultimate tensile strength (UTS) increases by 15 % compared with the unmodified alloy joints. However, individual 0.2 wt.% Zr addition cannot effectively modify the filler metal. The improvement of mechanical properties can attribute to the presence of refined grains.

Tensile and fatigue behavior of resistance spot-welded HSLA steel sheets: Effect of pre-strain in association with dislocation density

In the automotive applications, sheet metals are inevitably subjected to pre-straining during stamping operation prior to spot welding. The integrity of vehicles is governed by the static and fatigue strengths of the joints. However, the effect of pre-strain on the tensile and fatigue properties of the spot-welds on the high strength low alloy (HSLA) steel sheets has not been well studied. To abridge this gap, steel sheets of 1.2 mm thickness in as-received condition as well as after pre-straining to three different levels of 5%, 10%, and 15% were spot-welded in the form of lap-shear joints. With an increase in pre-strain, the load-bearing capacity of the joints monotonically increased, while there was no significant effect of pre-strain on the fatigue behavior and endurance limit of the joints. This difference in tensile-shear and fatigue behavior of the joints for pre-strained samples is attributed to the variation in the location of the failure, which has been explained in terms of the difference in failure mechanisms involved with the tests. The crack initiated at the base metal in case of tensile-shear tests, whereas under cyclic loading, fatigue cracks initiated between fine-grained heat affected zone (FGHAZ) and coarse grain heat affected zone (CGHAZ) located near the interfacial notch between the two welded sheets. While the location of failure in tensile-shear test is dictated by its lower strength across the joint, that in fatigue test is governed by the stress concentration. The magnitude of dislocation density has been evaluated quantitatively in the base metal, heat affected zone (HAZ), and fusion zone of weld joint using X-ray diffraction (XRD), and the dislocation substructures have been examined by transmission electron microscopy (TEM). The increase in tensile-shear load-bearing capacity is due to increased dislocation density in base metal with pre-strain. As most of these dislocations generated due to the pre-straining are annihilated at the HAZ during welding, there was no significant effect of pre-strain on the fatigue strength of the joints. These results were corroborated by microstructural examination and micro-hardness measurements across the weld joints in as-received and pre-strained conditions.

Stress Distribution in Pipe Samples of Gas Pipelines with Welded Joints

Напряжения в зоне термического влияния и сварного соединения связаны с наличием внутренних напряжений, возникновение которых связано с различными причинами. Основными из них являются неравномерность нагрева и усадки сварного шва, а также структурные изменения металла и околошовной зоны в процессе сварки. Эти напряжения могут складываться с эксплуатационными напряжениями, что в свою очередь приводит к ускорению скорости зарождения трещин в зоне сварного соединения. Произведена оценка двухосных напряжений в основном металле и в зоне сварных соединений магистральных трубопроводов на основе явления акустоупругости с использованием трех типов волн различных поляризаций (продольной и двух поперечных с ортогональной поляризацией) и электромагнитно-акустического преобразования ввода-приема ультразвуковых волн.В осевом направлении ближе к краям вырезки значения напряжений ниже, чем по центру, что объясняется уменьшением напряжений при удалении связей. Похожая картина наблюдается для окружного σ2 направления. В образцах со сварным соединением наблюдается резкое уменьшение значения относительных напряжений в зоне термовлияния сварного соединения по сравнению с напряжениями в области основного металла.

Mechanical and surface morphology study of Monel – Copper joint by rotary friction welding

The demand for of dissimilar metal joints is increasing day by day in many industrial applications like automobile, aero space, boiler accessories, defence and structural components. Recently many of researchers have focussed on monel base dissimilar weld joints because, it has played a main role in the fabrication of hydraulic, boiler components such as valve, pump, casing, fin, pipe and shaft. So, the present experimental work is to join Monel (K-500) – Copper (ETP) by rotary friction welding technique under a spindle speed of 1500 rpm for boiler heat exchanger applications. Totally 16 joints were prepared with varied process parameter like frictional pressure (20, 25, 30 and 35 bar), Upset pressure (15, 20, 25 and 30 bar) and constant feed rate (9 mm/s) was maintained. Finally, all the joints were evaluated to find its mechanical and micro structural properties such as micro hardness, yield and ultimate strength as per ASTM standards. The interface (inertial bonding structure) and Heat Affected Zone (HAZ) of weld joint were examined by scanning electron beam microscope and its level of monel – copper layer was identified through X-ray diffraction technique.

Causes of the field flowline weld joint rust-through damage

The paper presents results of the flowline pipe analysis in order to determine the causes of the butt weld joint rust-through damage (wormhole). Using Baumann sulfur print technique, the presence of iron sulfides scale on the inner pipe surface was studied. Using X-ray diffraction technique, the phase composition of the corrosion products was determined. It was found that chemical composition and mechanical properties of the metal from the studied flowline fragment comply with standard requirements. The resulting hardness values including those in the weld joint zones indicate that the metal has a certain corrosion-cracking resistance. Results of metallographic studies of longitudinal polished samples with full product thickness show that the residues of the weld capping pass remained on the bottom of the corrosion pit in the area of the observed rust-through hole. They have multiple pores up to 3 mm diameter. The corrosion pit surface is covered with iron sulfide layer 1–3 mm thick. The sulfide layer thickness in the area of the corrosion pit is 10+ times higher than on the rest pipe surface; this indicate that the corrosion process progressed faster here. The authors concluded that the cause for the weld joint rust-through damage was the pit corrosion that occurred under the impact of H2S-containing fluids on the lower generating line of the pipeline in the area of the weld startstop, where the weld root side suckback was observed. Probably, there was a flaw in the first weld pass within the corrosion pit area (shrinkage cavity, incomplete fusion, pore, or other), and the accelerated corrosion was the consequence of H2S-containing liquid slug here. This suggests that there was a flaw in the first weld pass within the area of the corrosion pit that has propagated along the first weld pass start-stop line.

Effect of inhomogeneous microstructure on the deformation and fracture mechanisms of 316LN stainless steel multi-pass weld joint using small punch test

The local microstructural effect on the deformation behavior and fracture mechanisms in different zones of 316LN stainless steel multi-pass weld joint of the nuclear power plant was investigated by using small punch test. The results indicated that microstructure of the weld joint was highly inhomogeneous from region to region. The microstructure of base metal (BM) and heat affected zone (HAZ) was austenitic cellular crystal with twins, while that of as-deposited weld metal (WM) was duplex austenite-ferrite. By inducing multi-pass thermal cycles, at least five distinct morphologies of ferrite were identified in the WM. On the other hand, the deformation and fracture mechanisms in different zones of the multi-pass weld joint were strongly influenced by the inhomogeneous microstructure. The WM showed lower deformability than the BM and HAZ due to the deformability mismatch between ferrite and austenite. In BM and HAZ, the cracks tended to initiate at the slip bands and propagate along the slip bands. However, in WM, the cracks tended to initiate at the ferrite and ferrite-austenite interface and preferentially propagate along the needle-like ferrite. In the fusion zone (FZ), the plastic deformation always first occurred in the HAZ followed by the deformation of the WM near the fusion boundary. And the crack initiated at the region adjacent to the fusion boundary but did not propagate along the fusion boundary. Fractographic analysis demonstrated that the fracture model of all the specimens was ductile fracture except a few quasi-cleavage fracture features were observed in the HAZ.

Identification Plastic Properties of Spot Welded Joints Using the Instrumented Indentation Technique

The parameters of elastic-plastic material and fracture of materials can be readily determined when standard specimens are available, however, for a spot welded joint, standard testing is not applicable to characterize the HAZ and nugget due to their complex structure and small size. This has opened up the possibility to characterize material properties based on the Indentation method to inversely characterize the parameters of the constitutive material laws for the nugget, HAZ and the base metals. In a mixed numerical-experimental approach, the load-deformation data of the material is used as input data to a numerical finite element (FE) model that simulate the geometry and boundary conditions of the experiment. The numerical approach based on the Finite Element (FE) model has been developed and validated. The established formulation is used for reverse (inverse) prediction of the nature of constitutive material (ie yield stress (σ y), strain hardening coefficient (n)) for the welded joint zone namely the nugget, HAZ and parent metals (base). Then able to predict the effect of the nugget size and the thickness of the sheet metal on the strength of the spot welded joint with dissimilar material.

The impact of deformation in the zone of welded joints on the force action of the rolling stock on the track

The causes of deformation in the zone of welded joints are considered. Authors experimentally studied changes in hardness on the rolling surface of the rail in the longitudinal and transverse profiles within the thermally affected zone of the welded joint. It is established that the hardness of the rolling surface of the rail in the longitudinal direction in the thermally affected zone of the joint is uneven and is determined by the structures arising from the effects of the thermal cycles of welding and the quality of the local heat treatment. In this case, two "low spots" are clearly traced with a decrease in hardness to 290...300 HB and with a higher hardness up to 350 HB right in the welded joint. Experimentally investigated the change in the depth of the welded joint from the implemented tonnage. At the same time with strain gauge method, using the force method developed by N. N. Kudryavtsev, continuous changes in vertical forces when the wheels move along the welded joint zone were recorded. Average values of vertical forces from loaded cars were established. Experimental distributions of vertical forces were approximated by theoretical laws according to the Kolmogorov — Smirnov matching criterion. Recommendations are given on minimizing the harmful impact of rolling stock on the track in areas of lowering welded joints.The following conclusions were made.1. Geometry of the joint irregularity is in the form of a W-shaped deformation with an influx of metal on the receiving rail and lowering on the directing rail. The width of the upper part of the deformation varies between 160...200 mm along the axis of the rail.2. Deformation zone of the welded joint is a source of increased dynamic impact from the wheels of the rolling stock on the elements of the upper track structure. According to the results of experimental studies it was found that the greatest increase in dynamic effects was observed from locomotive wheels up to 45.. . 70 kN, maximum values reached 180...210 kN, from the wheels of loaded freight cars the values of vertical forces increased by 35.. .45 kN, maximum values reached 145...170 kN, from the wheels of empty cars increase dynamic impacts amounted to 14...16 kN, maximum values reached 32...36 kN.

Исследование возможности применения ультразвуковой обработки для снижения остаточных напряжений и деформаций в сварных соединениях

This work explores the possibility of using ultrasonic vibrations as a method for eliminating residual and intrinsic stresses, as well as improving the quality of welded joints. Based on the experiments carried out on three steel grades of various classes, it was found that ultrasonic treatment of welds contributed to the elimination of such defects as deformations, intrinsic and residual stresses, as well as increasing fatigue strength and certain mechanical properties of welded joints. An analysis of existing methods of removing residual and intrinsic stresses was conducted. It was shown that the treatment of the welded joint zone by ultrasound reduced the degree of deformation over time by more than two times. A method for determining stresses in welded joints was developed. Ultrasonic processing modes were optimized to determine the energy and power in the welded zone. The shape and the material of the waveguide tool with a spherical percussion mechanism were selected.