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The paper presents the results of investigations of the quality of electroslag welded joints of 100 mm plates from VT6 titanium alloy. Investigations included X-ray inspection, chemical and gas analysis, optical metallography, mechanical tensile and impact toughness tests, as well as fractographic analysis. X-ray inspection and optical metallography of the welded joint showed absence of surface and inner defects in the weld metal and HAZ. Gas analysis of the weld metal demonstrated its correspondence to standard requirements to VT6 alloy. Ultimate strength of weld metal was equal on average to 90 % of base metal strength, and impact toughness (KCU) was 1.6 times higher than in the base metal. Fractures of metal of the weld and HAZ were of transcrystalline mode of a mixed type, with areas of both ductile and brittle fracture. It is shown that the welded joint mechanical properties are determined, primarily, by the size of grains and microstructure of the weld metal and HAZ, forming under the conditions of a low cooling rate and a high heat input, characteristic for electroslag welding process. [ABSTRACT FROM AUTHOR]

One of the promising ways to solve the problem of increasing the service life of welded structures is the development of welding methods based on the use of pulsed control of energy parameters of the process. The pulsed mode of welding allows performing a regulated heat input in the welded butt joint zone, controlling the mode of melting the electrode metal, forming the structure of weld metal and heat-affected zone (HAZ). It was found that with an increase in the frequency of pulsed-arc welding, it is possible to reduce the width of the HAZ and the region of a coarse grain. Thus, in the case of welding low-alloy steels, due to the use of technology with a pulsed process, there is a prospect of reducing the width of the overheating region, which is important for the cases of repair of pipe wall thinning during remelting of defects in the operating pipeline using a mechanized method. [ABSTRACT FROM AUTHOR]

Mechanical properties were determined and features of destruction of welded joints on single-crystals of high-temperature nickel alloys at tensile testing in the range of temperatures close to working temperatures were studied. Two characteristic temperature ranges of destruction were found: 500-800, 800-1200 °C. In the first temperature range welded sample destruction occurs in the base metal at mixed fracture mode: brittle, quasibrittle and ductile. In the second range destruction takes place in the weld metal, fracture is multicenter, predominantly brittle with presence of secondary cracks. The considered features are related, mainly, to changes of the initial structure of the single-crystal, as a result of solidification and at cooling of the weld metal. These mainly are formation of a multilevel substructure, refinement of dendrites, γ- and γ-phases, eutectic formations and carbides at reduction of dendrite liquation of the weld metal. [ABSTRACT FROM AUTHOR]

The article considers the problem of welding duplex steels: state-of-the-art of the problem and prospects for further development. Welds made in air and under water using coated electrodes, are characterized by a similar structure and properties. Intensive cooling provided by the water environment does not increase the content of ferrite in the weld and HAZ as compared to its content in the joints made in the air. Butt joints produced under water at an unstable arc burning are characterized by a tendency to cold crack formation in the weld metal, but in the HAZ cracks were not detected. In the article the analysis of hardness distribution in the studied joints was presented, which did not reveal significant differences between the values determined in the welds made in air and in water. The size of austenitic phases in dry welding was larger than in wet welding under the same conditions of heat input. In wet welding, the share of γ-phase increased significantly at increase in input energy from 27.31 to 39.46 % for the weld center and from 35.01 to 44.9 % for the weld metal adjacent to the fusion line. All the studied variants of chemical composition of the weld metal were insensitive to local corrosion due to high values of PREN. The weld metal adjacent to the fusion line showed optimal resistance to local corrosion, and the weld metal also showed better resistance to local corrosion than did the heat-affected-zone. 17 Ref., 1 Table, 8 Figures. [ABSTRACT FROM AUTHOR]

During designing and manufacture of aircraft structures from modern thermomechanically strengthened aluminium alloys, there is a problem of producing welded joints with satisfactory mechanical properties without post heat treatment of large-sized products. In the work the formation of joints of thermomechanically strengthened 2219-T87 alloy during flash butt welding was investigated. It was found that a low-temperature resistance heating in combination with a shortterm heating by flashing provide the formation of defect-free welded joints. Metallographic examinations showed that joints are formed through a thin layer of melt, which is a necessary condition for a high-quality welding of aluminium alloys. The influence of intense plastic deformation during upsetting with a forced formation on the morphology of θ-phase (CuAl2) particles was studied. A decrease in the values of hardness in the joint area as a result of dissolution and coagulation of a strengthening θ'-phase was established. The strength of welded joints both along and across the rolled metal lines amounts to 76 % of the strength of the base metal. 20 Ref., 2 Tables, 7 Figures. [ABSTRACT FROM AUTHOR]

The problem of general evaluation of technical condition of main longitudinal beams of the E.O. Paton Bridge was considered based on the results of selective non-destructive testing of truss elements. It is shown that the main cause of damage to the elements of the main beams is corrosion of the nodal welded joints in the places of debris accumulation. High quality of welded butt joints made by automatic and semi-automatic submerged arc welding was noted. [ABSTRACT FROM AUTHOR]

The results of studying the influence of the modifier of the Al--Ti--C system, obtained by high-voltage electric discharge treatment in a hydrocarbon liquid, on the structure and properties of the cast AK7pch (A357) alloy are presented. The prospects for the use of a modifier produced by the method of a high-voltage electric discharge treatment of metal powders to improve the structure of cast alloys and weld metal are shown. [ABSTRACT FROM AUTHOR]

In the work the results of studies of corrosion and mechanical resistance of welded joints of B1341T alloy with a thickness of 1.2 mm, depending on the technology of manual argon arc welding using free and constricted arc are presented. The strength coefficient of welded joints is 0.79 and 0.8, respectively. Potentiometric measurements established an electrochemical heterogeneity between the base metal and the welded joints produced using free and constricted arc, which is equal to 100 mV and 86 mV, respectively. More positive potential is inherent to the region of a weld with a smaller area, which is safe to operation. Accelerated corrosion tests determined that the shape of the arc column during manual welding does not affect the resistance of welded joints to exfoliating corrosion and a corrosion-mechanical resistance under the conditions of a constant deformation. The level of resistance of the metal to exfoliating corrosion of the joints produced by both types of arc welding technology, was estimated by the point 2-3. The fracture time of the specimens welded by free arc welding, decreased on average to 20 days as compared to the base metal (73 days). The similar results were obtained for the joints welded by a constricted arc. At the same time, it was revealed that the use of constricted arc for welding, causes a decrease in the resistance of the joints to intercrystalline corrosion. The maximum fracture depth of the boundaries' grains is 0.350 mm for the joints produced by a free arc and 0.460 mm for the joints made by a constricted arc. 15 Ref., 3 Tables, 11 Figures. [ABSTRACT FROM AUTHOR]

A set of procedures, mathematical models and tools for their finite-element realization were developed to solve typical practical tasks of expert analysis of the technological condition and residual safe operating life of welded elements of the main and technological pipelines with defects of corrosion-erosion metal loss detected during diagnostics. In order to lower the conservativeness of analysis, the interrelated processes of thermal deformation at assembly and repair welding, as well as initiation and propagation of subcritical damage of the defective structure material in the ductile mode in operation under complicated temperature-force conditions of external impact, were taken into account. Procedures of statistical analysis of fracture susceptibility of welded pipelines were developed on the base of Weibull and Monte-Carlo methods, and adequacy of the developed computational methods was confirmed. Peculiarities of the effect of welding on the reliability and serviceability of the main and technological pipelines with detected defects of corrosion-erosion metal loss were determined, in order to develop minimally conservative recommendations as to the possibility of safe operation of the pipelines. 18 Ref., 2 Tables, 12 Figures. [ABSTRACT FROM AUTHOR]

We propose a procedure of accelerated corrosion testing of welded joints for modeling the long-term effect of the most significant climatic factors of moderate climate atmosphere (temperature and relative humidity) on them. Duration of accelerated testing of welded joints in the humidity chamber to obtain corrosion damage, which is characteristic for welded joints of metal structures after approximately 12 years of operation, is substantiated. Fatigue testing of butt and tee welded joints of 15KhSND steel after preliminary exposure to 2 mln cycles at maximum stresses of 150 MPa, corrosion testing under the conditions of higher temperature and relative humidity without strengthening and with further strengthening by the technology of high-frequency mechanical peening, were performed. It is found that strengthening by the technology of high-frequency mechanical peening improves 10 times the cyclic fatigue life of butt and tee welded joints with accumulated fatigue and corrosion damage. 23 Ref., 5 Figures. [ABSTRACT FROM AUTHOR]

The paper presents the main technical means and methods of pulsed control of the process of consumable electrode gas-shielded arc welding, developed over the recent years at PWI and Admiral Makarov National University of Shipbuilding. A lot of attention is given to methods using systems of pulsed impact on the processes of electrode metal transfer, weld formation and deposited metal structure. Good prospects for application of systems with pulsed dozed feed of electrode wire are shown, and results of effective control of welding and surfacing processes are given. Methods of arc welding with pulsed feed of shielding gas and with two-jet gas shielding are considered, and problems are indicated, which prevent extensive application of these processes. The paper gives the results of some studies of the influence of external electromagnetic impact on electrode metal transfer, weld formation and crystallization, and presents some examples of effective application of this method of welding process control. Analysis of the methods of mechanical impact on the welding process using different oscillator systems was performed. The possibility is shown of combined control of electrode metal transfer, deposited bead formation and its metal structure, depending on the scheme of oscillation application and oscillation process parameters. The good prospects for this method application for surfacing operations are pointed out. [ABSTRACT FROM AUTHOR]

The paper presents the results of examination of the structure and properties of samples of rail metal produced by laboratory melting (in slightly deformed and cast state), which were obtained by electroslag remelting after flash-butt welding of rails. Examination showed that the microstructure of weld metal and heat-affected zone in both the cases features a homogeneous dense structure. Fracture of the samples took place mainly in the heat-affected zone. Strength of welded joints from metal in the cast state is lower, than that of slightly deformed one, which is apparently caused by coarse grains, the size of which can be reduced using heat treatment. Electroslag remelted rail steel in the cast and slightly deformed state has a level of mechanical properties in the range of requirements made to nonthermostrengthened rails K76 in GOST R 51045 and DSTU 4344 that reveals the prospects for application of electroslag remelting for manufacture of rails, including rail tongues, applied in as-cast state. 25 Ref., 3 Tables, 7 Figures. [ABSTRACT FROM AUTHOR]

There was investigated an effect of modes of high-frequency mechanical peening on increase of fatigue resistance of butt welded joints of steel St3sp (killed). Different technology of sample preparation for investigation allowed determining that a quantitative contribution in rise of fatigue limit of welded joints of residual compression stresses, deformation hardening of surface layer of a groove formed after peening of a narrow zone of weld fusion with base metal, and change of stress concentration after high-frequence mechanical peening makes 57, 37 and 6 %, respectively. It is shown that there is a correlation between the groove depth and depth of plastically deformed layer of material. The procedure was proposed for determination of the fatigue limits of butt welded joints after different modes of peening on groove depth and plastically deformed layer of material, using the experimental data of microhardness measurement as well as the change of amplitude of working tool oscillation in the investigated range. A depth of groove was determined depending on rate of high-frequency mechanical peening and amplitude of working tool oscillations as well as change of sample fatigue limit due to different technology of their manufacture. It is shown that increase of peening rate independent on the working tool oscillation amplitude promotes decrease of efficiency of improvement of welded joint fatigue resistance and at 0.4 m/min rate the fatigue limit from deformation hardening and total effect of all factors typical for high-frequency mechanical peening rises by 11 and 26 %, respectively. [ABSTRACT FROM AUTHOR]

A work proposes a comparative analysis of the diagrams of cycle limiting stresses in welded joints of low-carbon and low-alloy steels of different strength under condition that they have the same level of steady residual stresses. By the example of testing of St3sp (killed), 09G2S and 14KhMNDFR steel butt welded joints it is shown that the welded joints with larger mechanical properties have higher endurance limits in all investigated range of change of the limiting steady residual stresses. It was found that the welded joints of stronger steels have also higher values of endurance limit at the same relative value of cycle average stress. They rise more intensively with increase of the relative values of cycle average stress. [ABSTRACT FROM AUTHOR]

The efficiency of selection of non-damaging modes of vibration treatment of welded elements of low-carbon steel metal structures with the purpose of reducing residual stresses in them without danger of fatigue fracture at the stage of technological treatment is shown. The comparative fatigue investigations showed an increase in the service life of vibrotreated welded joints and an increase in their fatigue limit at the increase of test base. A method for determination of fatigue limits for butt welded joints of low-carbon steel after different modes of high-frequency mechanical peening, using experimental data of groove depth measurement, was proposed. The efficiency of increasing their fatigue limit is shown depending on the speed of high-frequency mechanical peening and the amplitude of oscillations of the working tool. The results of experimental investigations of increasing fatigue resistance of welded joints of low-alloy and low-carbon steels under harmonic and repeated impact loading at the temperature of -60 °C after high-frequency mechanical peening, argon-arc, explosive, and mechanical treatments were analyzed and a comparative analysis of their efficiency was presented. 23 Ref., 4 Tables, 10 Figures. [ABSTRACT FROM AUTHOR]

Results of experimental studies of the influence of the ratio of static and dynamic stresses on limit stresses and second critical brittleness temperature of butt welded joints with a crack on 09G2 and 12GN2MFAYu steels under the conditions of room and low (to -80 °C) temperatures are analyzed. It is found that at the specified temperature the dynamic component of critical stress decreases linearly with increase of static stress. It is shown that decrease of limit stresses and increase of the second critical brittleness temperature take place at increase of the dynamic factor. Critical brittleness temperatures of welded joints of steel with higher mechanical properties are significantly lower. It is found that ignoring the dynamic stresses leads to underestimated values of limit stress and overestimated values of second critical brittleness temperature. Presented analysis of research allows a more substantiated approach to assessment of brittle fracture resistance of structural elements made from the studied materials, and determination of their safety margins. [ABSTRACT FROM AUTHOR]

A new technological process of postweld treatment of welded joints is presented, namely the electrodynamic treatment by pulses of high-density electric current. The carried out complex of experimental investigations on specimens of aluminium alloy AMg6 at different parameters of electric current pulses and inductance of power source showed that electrodynamic treatment influences the structure of treated metal and allows a significant reduction in residual stresses in welded joints, increasing their resistance to fatigue and brittle fracture, and also eliminating buckling deformations of thin-walled structural elements. The developed technologies and equipment provided the possibility of performing electrodynamic treatment of welded joints of ship-building structures and repair welds of intermediate casing of aircraft engine, which facilitated their increased operational reliability and service life. 8 Ref., 18 Figures. [ABSTRACT FROM AUTHOR]

Earlier investigations showed that treatment of welded joints of reactor vessel steel 15Kh2NMFA with alternating magnetic field of commercial frequency significantly improves a complex of mechanical properties under conditions of uniaxial tension that is accompanied by decrease of a level of thermal stresses in a weld zone. Aim of the present work is study of the effect of magnetic treatment on magnetic characteristics, structure, level and distribution of residual stresses in the welded joint. Changes of stress-strain state in different areas of the welded joint were evaluated on data of X-ray diffraction and electron-microscopic examinations. It is shown that effect of alternating magnetic field results in decrease of a level of microstresses in a transition layer and balancing of spectrum of these stresses in all area of heat affect. Correlation of changes of initial magnetic susceptibility and microstresses in the transition layer and formation of expressed magnetic texture in the weld central part is noted. The mechanisms of changes of magnetic properties and structure at magnetic treatment of welded joint, which are related with activation of plastic microdisplacements and defect redistribution, were considered. Given method of magnetic treatment can be observed as magnetic tempering, providing rise of homogeneity of stress-strain state of welded joints. This promotes increase of their resistance to nucleation and propagation of cracks. [ABSTRACT FROM AUTHOR]

To improve the service reliability of products and welded structures in the conditions of corrosive environment, the methods of surface plastic deformation of metal are applied, which impart the physical-mechanical properties to the hardened layer, differed from the base metal. The technical progress contributes not only to the development of new methods of surface plastic deformation (for example, surface fusion using a nanopulsed laser), but also to the continuous improvement of conventional methods (shot blasting, pressure treatment, etc.), the efficiency of which was proved in practice. The aim of this review is to evaluate the current state of use of surface plastic deformation methods to increase the corrosion fatigue resistance and durability of steels and welded joints. The analysis of literature data showed that the experimental investigations of recent years are mainly devoted to the determination of efficiency of hardening the stainless steels and their joints applying these methods for subsequent application in such areas as medicine (implants), nuclear power engineering (reactors) and shipbuilding. For the treatment of welded metal structures, the most promising is ultrasonic impact treatment due to compactness and mobility of the equipment, ecological compatibility of the technological process, high efficiency, capability of strengthening the welded joints in any spatial positions in the field conditions. [ABSTRACT FROM AUTHOR]

A work, based on a complex diagram of cycle limit stresses, proposes a method for selection of vibrotreatment undamaging modes for the elements of metal structures in order to gain effective decrease of their residual stresses without a risk of fatigue damage during technological treatment. This method was approved by the example of testing of the structural elements of steel 20 and end pivot of steel 20GFL of span bolster of eight-axis rail tank car. Comparative fatigue tests showed 2.5 times increase of fatigue life of treated welded specimens and rise of their endurance limit by 40 %. In process of vibrotreatment of a circular element of steel St.3, decrease of residual stresses is accompanied by rise of its damping capacity. Growth of maximum cycle stresses promotes for increase of vibration decrement to larger value and its stabilizing in time matches with residual stress stabilizing. This allows assessing completion of a process of change and further stabilizing of the vibration decrement. Determined decrease of damping capability of the investigated sample after vibrotreatment indicates its strain aging, showing plastic strain during treatment. Rise of cycle stress amplitude reduces sample deformation after vibrotreatment at further aging to 1500 h and decrease of initial residual tensile stresses to 0.51 of yield limit of the material results in its geometry stability. [ABSTRACT FROM AUTHOR]

The residual welding stresses negatively affect the fatigue limit of welded joint, being the main cause for brittle fracture of metal, i.e. corrosion cracking. Therefore, the development of effective methods for control of welding stresses, characterized by low energy consumption and relatively simple realization, is traditionally an urgent problem for modern production. At the present time the methods for reducing welding stresses became widespread, based on the influence of pulses of electric current and magnetic field. Moreover, each of the methods has its advantages and disadvantages, and evaluation of their efficiency in the control of residual welding stresses represents an urgent problem. In the work the comparative evaluation of efficiency of control of residual stresses of AMg6 alloy of welded plates was carried out at treatments by pulsed electromagnetic field (TPEMF) and pulsed current (EDT), applying planar inductors. Using the method of electron speckle interferometry it was revealed that TPEMF and EDT reduce the initial level of welding stresses in the zone of pulsed effects to 100 %. 16 Ref., 1 Table, 4 Figures. [ABSTRACT FROM AUTHOR]

The paper deals with features of joint formation in complex high-strength (α + β)-titanium alloy in vacuum electron beam welding. Investigations were performed on samples of alloy of Ti-Al-Mo-V-Nb-Cr-Zr system produced by electron beam remelting. Influence of thermal cycle of welding and subsequent heat treatment on structural-phase transformations in the metal of weld and welded joint HAZ has been studied. A structure with prevalence of metastable β-phase forms in the metal of weld and HAZ, which promotes lowering of ductility and impact toughness values. Postweld heat treatment is required to improve the structure and properties of EB-welded joints. The best combination of strength and ductility of studied welded joints was achieved after performance of furnace heat treatment (annealing at T = 900 °C for 1 h and cooling in the furnace), which promotes producing a practically uniform structure and metastable phase decomposition in the weld and HAZ. [ABSTRACT FROM AUTHOR]

The resistance butt welding finds new areas of application. The aim of the work is the development of technology for RBW of T-joints of rods and eyelets of hydraulic cylinders of dissimilar steels 45 and 17GS in the range of diameters from 16 to 60 mm. The tasks of investigations were the selection of optimal technological scheme of RBW process of large cross-section parts, testing of technological methods, providing localization of heating and deformation of metal in the contact zone. The RBW process and the structure of joints of these dissimilar steels produced with preliminary preparation of welded edges and using the composite inserts were investigated. It was found that in RBW of T-joints of steels 45 and 17GS with optimum preparation of welded edges and programmable change in welding force at the stage of heating it is succeeded to localize the heat generation in welding zone, to avoid the formation of defects and to provide the high mechanical properties of welded joints. During mechanical tests of welded rods on bending the fracture occurs in the base metal of the rod. The technology for RBW of T-joints of dissimilar steels using the composite inserts was developed. The technology of RBW of rods of hydraulic cylinders of 16-60 mm diameter was realized in specialized welding machine K1040, designed and manufactured at the PWI. [ABSTRACT FROM AUTHOR]

During long service of the tanks, manufactured of stainless steel, the pits are formed on the surface contacting with periodically preheated aggressive liquid, mainly in welded joints, and the danger of through fracture of wall arises. The aim of the work was to increase the reliability and longevity of tanks for storage of aggressive liquid, first of all, by increasing the resistance of welded joints against pitting formation. The specimens, being untreated and mechanically treated in different ways with penetration of the untreated surface and polished sheet steel 12Kh18N10T were subjected to accelerated tests for resistance against pitting corrosion at room temperature and preheatings of FeCl3 solution similar to the technological ones. The resistance against pitting corrosion of welded joints is significantly increased after abrasive treatments, surface peening to a lesser extent and is independent of the surface roughness. The pitting resistance is also increased by replacing the indirect preheating of solution through the specimen to its direct preheating by the immersed heater. The results of the work are advisable for using in manufacture, repair and service of chemical, petrochemical, food and other equipment. 9 Ref., 2 Tables, 5 Figures. [ABSTRACT FROM AUTHOR]

It is shown that process of CO2 arc surfacing with pulse feed of electrode wire in contrast to its continuous feed is characterized by increased stability, lower loss of electrode metal for spattering and improved characteristics of wear resistance of 30KhGSA deposited metal. determined was an optimum range of parameters of electrode wire pulse feed, namely frequency 10-30 Hz and relative pulse duration 3-5 units. It is shown that reduction of penetration depth of base metal is achieved due to current decrease at stage of droplet growth in elementary cycle of electrode metal transfer. Comparative examination of microstructure of deposited metal and HAZ was carried out employing scanning electron microscopy at continuous and pulse feed of electrode wire at ?(500-2000) magnifications. 18 Ref., 2 Tables, 10 Figures. [ABSTRACT FROM AUTHOR]

The paper deals with the features of producing joints of an alloy based on γ-TiAl intermetallics at resistance butt welding with application of interlayers in the form of foil, differing by thickness, composition and structural state. Investigations were performed on samples of Ti—47Al—2Cr—2Nb (at.%) alloy, produced by electron beam remelting, both in as-delivered (cast) condition, and after heat treatment (1250 °C, 6 h). Used as interlayer was titanium foil with microcrystalline structure 100, 200 and 400 μm thick, and nanostructured multilayered foils Ti/Al (52Ti—48Al, at.%) and Ti/Co (75Ti—25Co, at.%) of 30—160 μm thickness. Experiments were performed in K802 system, welding mode parameters were varied in the following ranges: 5—20 MPa pressure at heating, 20—100 MPa upset pressure, hand 5—15 mm upset value. Joint microstructure and composition were studied by optical and scanning electron microscopy and X-ray microprobe analysis. Metal strength properties in the joint zone were assessed by microhardness distribution and rupture testing. It is established that the zone of Ti—47Al—2Cr—2Nb alloy joints made with application of solid titanium foil demonstrates structural inhomogeneity in the form of a continuous titanium interlayer and diffusion zone between the interlayer and alloy being welded, containing linear porosity. Application of nanostructured Ti/Al and Ti/Co foils ensures formation of defect-free joints. Metal structure in the joint zone is fine-grained bimodal γ/γ+ α2, irrespective of base metal initial structure. Remains of nanostructured foils of Ti/Al system are present in the joint zone in the form of an interlayer of dispersed γ-TiAl intermetallic, not containing any chromium or niobium. At application of foil of Ti/Co system of eutectic composition, no chemical inhomogeneity in the form of foil transformation products is found in the butt. At rupture testing of the joints, fracture runs through the base metal of Ti—47Al—2Cr—2Nb alloy. Joint region of higher hardness in all the considered cases coincides with the zone of structural changes resulting from thermodeformational impact of the welding process. [ABSTRACT FROM AUTHOR]

The work describes the results of investigation of microstructure and impact toughness of metal of welded joints of gas-and-oil pipeline pipes of steel category X65-X80 with different content of niobium and molybdenum. Investigated were welded joints of longitudinal pipes of 820-1420 mm diameter with 17.5-36.0 mm wall thickness, manufactured by using the traditional technology with applying the double-sided submerged multiarc welding. Optical and electron scanning metallography, as well as standard impact bend tests were used. The negative effect of increased content of niobium on structural characteristics of metal of HAZ and weld was found, which was intensified in the presence of molybdenum. Taking into account the niobium susceptibility to segregation at the grain boundaries, the additional alloying with molybdenum, decreasing the temperature of transformation, leads to the formation of unfavorable structural constituents and phases in the metal of welded joints, and also their clustering along the grain boundaries, in particular in reheating regions. To provide high impact toughness and crack resistance of welded joints of pipes of high-strength microalloyed steel, it is necessary to limit in it, in addition to carbon, the content of niobium (±0.05 %) and molybdenum (±0.20 %), as well as to use the welding consumables, providing the mass share of molybdenum in weld of not more than 0.30 %. Results of the work were applied in industrial production of pipes of category X65-X80 at pipe welding enterprises of Ukraine and Russia. [ABSTRACT FROM AUTHOR]

Proposed is a new structure of fastening of slabs of ballast-free bridge deck to T-girders of railway bridges, which provides for change of thread studs to welded ones. Arc-contact welding allows for stud positioning directly over vertical wall of T-girder that does not result to angular deformation of girder upper flange typical in application of thread studs. Aim of present work was evaluation of possibility of application of welded studs for fastening of slabs of ballast-free bridge deck in construction and repair of railway bridges. For that, fatigue tests of welded joints of stud to upper flange of girder from the most wide-spread steels St3sp (killed) and 09G2S were carried out at different ranges of loading, which are realized in stud preliminary tightened with 6 tf force during rolling stock movement. It is determined that cyclic life of such joints exceeds 5⋅106 cycles of stress alternation at loading range ΔP ≤ 3 tf. Numerical simulation showed that application of oak board and rubber band as spacing layer between slab of ballast-free bridge deck provides for cyclic life of welded stud not less than 5⋅106 cycles of stress alternation, since loading range exceeds ΔP = 3 tf. However, application of fast hardening nonshrinking mixtures (cast-in-place concrete) as spacing layer allows reducing range of loading to ΔP = 1 tf, that guarantees welded stud life not less than 5⋅106 cycles of stress alternation. [ABSTRACT FROM AUTHOR]

Cyclic fatigue life of butt welded joints of low-alloyed steel 09G2S, strengthened by the technology of high-frequency mechanical peening (HFMP) at different stages of fatigue fracture: in as-welded state, after accumulation of 70 % of fatigue damage, at formation of surface fatigue cracks, was studied. The objective of these studies is establishing the effectiveness of application of HFMP treatment of butt welded joints after long-term service at alternating loading. It is shown that strengthening of butt welded joints by HFMP right after welding increases the endurance limit (2 mln cycle base) by 50 % - from 180 up to 270 MPa, and cyclic fatigue life - by 5 to 10 times. It is experimentally confirmed that the effectiveness of strengthening welded joints with 70 % accumulated fatigue damage depends on the levels of applied maximum stresses before strengthening. So, residual cyclic fatigue life of samples, tested in the range of maximum 240-260 MPa stresses, falls within the scatter band of experimental data for welded joints in unstrengthened condition, and for those tested in the range of maximum stresses of 280-300 MPa it is within the scatter band of experimental data for welded joints strengthened by HFMP technology in as-welded condition. It is established that application of HFMP technology improves the residual cyclic fatigue life of welded joints with surface fatigue cracks (down to 2 mm deep) 2.5 times compared to fatigue life before crack formation. [ABSTRACT FROM AUTHOR]

Statistics of accident rate at Ukrainian and Russian railways is an evidence of increase in the recent years of the accidents, related with failure of cast bearing elements of two-axle three-component freight car bogies. Analysis of service reliability of cast structures of side frame and bolster of 18-100 type bogie shows that appearance of fatigue cracks is the main reason of reject. It is reasonable to search an alternative application of welding technologies in manufacture of indicated parts from sheet products for the purpose of increase of their safety and survivability. It is shown that existing Norms for designing of welded joints and assemblies of railway cars significantly overstate real cyclic load resistance of welded joints in comparison with the Recommendations of the International Institute of Welding. This disadvantage is typical for number of reference documents acting in Russia and Ukraine, which regulate calculation of fatigue resistance of welded joints and assemblies. This promotes negative results in designing with respect to required life of welded elements. Development of safe and technological welded elements of freight car bogie requires application of the recent achievements in the field of fatigue strength of welded joints. [ABSTRACT FROM AUTHOR]

A work is dedicated to experimental investigation of dependencies of fatigue resistance of sheet (δ = 2-3 mm) welded joints of average and high strength aluminum alloys, which were produced using consumable-electrode pulsed-arc welding in inert gases (PMIG) as well as determination of efficiency of rise of their fatigue life through application of high-frequency mechanical peening (HFMP) by set parameters of strengthening. Efficient parameters of HFMP strengthening of sheet welded joints with the help of portable manual equipment USP-300 were determined based on measurement of microhardness, local geometry parameters of weld and angular residual lipping distortion. Influence of HFMP of zone of weld to base metal transition on measurement of stress concentration factor, welding residual stresses and structure of surface layer of butt joints of small thickness aluminum alloys was investigated. It is shown that increase of radius of weld to base metal transition and elimination of angular residual lipping distortion after HFMP treatment provides for 1.35-1.49 reduction of stress concentration factor in the joints. It is determined that life on the basis of testing 2·106cycles of stress alternation for strengthened butt joints from D16T alloy shows 5 times rise, that for AMg6 alloy makes 4 times and 7 times for 6061-T6 alloy in comparison with initial as-welded condition. The recommendations are given on efficient HFMP strengthening of sheet welded joints for increase of their fatigue life and elimination of residual welding deformations. [ABSTRACT FROM AUTHOR]

Results of investigation of the structure and properties of dissimilar metal joints made by friction stir welding (FSW) are given. Systems with unlimited (Ni-Cu) and limited (Cu-Fe) solubility, as well as absence of component solubility (Al-Fe) in the solid state were studied. FSW of copper and nickel produced a sound welded joint with metal interpenetration to 3 mm depth. Mechanical mixing of metals plays the leading role in this process, whereas diffusion processes are negligible. Structure refinement occurs in mechanical mixing bands as a result of recrystallization processes. Copper diffusion into nickel along grain boundaries proceeds down to 20 μm depth with formation of interlayers of these metals solid solution. When studying the copper to steel welded joint, it was established that metal mixing has a leading role also in this process, and the role of diffusion processes is small. During welding a considerable grain refinement takes place both in the recrystallization zone, and in thermomechanically affected and heat affected zones. FSW of aluminium to iron resulted in formation of the joint zone of a considerable volume with aluminium penetration into iron down to 2.5 mm depth. Metal interaction proceeds here, namely mass transfer, primarily, of aluminum, and subsequent formation of Fe2Al7, FeAl2 compounds. The hardest regions of welded joint zone contain intermetallics in the aluminium matrix. Such a structure has the hardness of 2870 ± 410 MPa that is more than 3 times lower than that of iron aluminides Results of the conducted investigations allow recommending this welding process to produce bimetal joints of dissimilar metals with different solubility of elements in the solid state. 20 Ref., 5 Tables, 15 Figures. [ABSTRACT FROM AUTHOR]

Evaluation of serviceability and residual life of the critical welded structures with found defect, including pipelines and pressure vessels, assumes a complex analysis of interrelated multidimensional processes, influencing their bearing capacity. At that, grounded reduction of conservatism of such an evaluation is rational that requires description of structure limiting state considering main fracture mechanisms. In particular, ductile fracture is a main mechanism of development of material damage in the main pipelines with typical surface defects of local corrosion wall thinning without accompanying sharp concentrators. Complex methodology for numerical analysis of processes of nucleation and development of ductile fracture pores of metal welded structures as well as criteria for determination of their limiting state was developed in the scope of present work. Thus, a procedure for calculation of stress-strain state in-service structure considering change of load-carrying net-section of structure areas at microporosity growth was build on the basis of Gurson-Tvergaard model. The criteria of pore nucleation as well as mathematical description of different mechanisms of their development depending on character of external force action were proposed for non-isothermal metal state, in particular, in the process of welding heating. Application of the developed approaches was shown on the example of analysis of limiting state of main pipeline element with local wall thinning defect in area of circumferential site weld. It is shown that limiting internal pressure in the pipeline with such service damage is determined by character of interaction of local stresses in zone of the weld and geometrical anomaly, i.e. the lower is the distance between them, the less is the loading necessary for formation of common zone of microdamage in which the macrodefects are formed as a consequence. Similarly, significant effect of pores on the bearing capacity in pipeline site weld is shown. Generality of the developed approaches of numerical analysis of ductile fracture processes allows applying them for evaluation of limiting state and residual life of the welded pressure vessels from high-strength steels. [ABSTRACT FROM AUTHOR]

One of the most difficult tasks in manufacture of the gas-and-oil line pipes, from the point of view of technology of their welding, is fulfillment of the requirements of normative indices on impact toughness of HAZ metal of welded joint. The aim of present work is an investigation of effect of chemical composition of microalloyed steel and cooling rate of HAZ metal of pipe welded joints on its structure-and-phase state and toughness characteristics. Specimens of Kh70 grade steel of different chemical composition varying, mainly, in carbon content and different rate cooling conditions simulating HAZ metal of the pipe welded joints were studied using modern Gleeble-3800 complex. It is determined that a structure of bainite type, i.e. lamellar ferrite with strengthening second phase martensite-austenite-carbide - MAC or carbide phase), is mainly formed in the metal of studied chemical composition in sufficiently wide interval of the cooling rates. Density of distribution of the phase, its location (orientation), dimensions and morphology are determined, in preference, by chemical composition, and, to lesser degree, by metal cooling rate of the Vcool.8/5. In this connection, the possibilities of metallurgical factor influence should be use to greater extent in order to increase HAZ metal toughness. Strict limitation of weight fractions of the elements promoting formation of coarse ferrite packages with ordered carbide phase of lamellar morphology (for example carbon, niobium, molybdenum etc.) is also reasonable for formation of optimum structure and, respectively, improvement of HAZ metal toughness together with reduction of content of the detrimental impurities in steel (sulfur, phosphor and nitrogen) to minimum possible level. The results of investigations were used in production of pipes from low-alloyed steel of Kh70 grade for main gas-and-oil pipelines. [ABSTRACT FROM AUTHOR]

The generalized data of technologies and equipment for flash butt welding of products of aluminium alloys and also types of products being welded using this method in rocket construction are given. The main directions of investigations for modernization of technologies of welding of high-strength aluminium alloys are considered: technology of welding using pulsed flashing as a method of heat intensification, and also effect of deformation degree at upsetting on the structure and properties of welded joints. The optimal degree of deformation of forming devices was determined allowing increase the elongation of welded product by 1.5 times at simultaneous preserving of high values of strength. In welding of thick-wall heat-hardened aluminium alloys the postweld thermomechanical treatment allows producing joints, equal in strength to base metal. Technology of welding of thick-wall T-profiles of high-strength hard-to-weld alloys was developed. The mechanical characteristics of welded joints of high-strength aluminium alloys are at the level of not less than 90 % of the strength of base metal. [ABSTRACT FROM AUTHOR]

Two-pass two-sided welding is widely applied to manufacture large-diameter pipes for main gas and oil pipelines. It is obvious that metal of the welds that are the first to make is subjected to repeated heating in making the subsequent pass. The study is dedicated to evaluation of the effect of repeated heating on properties of the weld metal of the two-sided welded joints on pipes made from increased-strength microalloyed steels. Investigations were carried out on the weld metal of welded joints on the pipes made from ferritic-pearlitic steels of strength category K56-K60 and of different microalloying types (10(09)G2FB, 10G2FT, 10G2T, etc.). Impact toughness, hardness and peculiarities of structural characteristics of the inside weld metal of the welded joints on pipes subjected to repeated heating in making the outside weld were evaluated. It was shown that decrease in impact toughness of test specimens of the two-pass two-sided welded joints on the pipes, the tested section of which comprises the metal of intersection of the inside and outside welds, is caused by the presence of the local embrittlement zones forming in the inside weld metal due to its heating in making the outside weld. Investigations, including by transmission electron microscopy combined with microdiffraction, detected the following two zones present in the inside weld metal: low-temperature zone (heating to 450-650 °C) caused by occurrence of the dispersion hardening processes, and high-temperature zone (heating to 950-1100 °C) related to the MAC-phase containing a substantial amount of a more stressed lath martensite and forming as a result of decomposition of non-homogenised austenite. [ABSTRACT FROM AUTHOR]