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In this study, finite element (FE) simulation by the software Abaqus was relied on to investigate the roll forming process of a wheel rim made of an innovative dual-phase steel, i.e., DP590, after flash butt welding (FBW). In the simulation, an FE model was generated, including the design of the dies for flaring, three-roll forming, and expansion, and detailed key processing parameters based on practical production of the selected DP590. Combined with the microstructures and properties of the weld zone (WZ) and heat-affected zones (HAZs) after FBW, the distribution of stress/strain and the change in thickness of the base metal (BM), WZ and HAZs were analyzed, and compared in the important stages of roll forming. Theoretically, the variation in the microstructure and the corresponding stress–strain behaviors of the BM, WZ, and HAZs after FBW have led to the thickness reduction of DP590 that originated from softening behaviors occurring at the region of subcritical HAZs (SCHAZs), and a small amount of tempered martensite has evidently reduced the hardness and strength of the SCHAZ. Meanwhile, the distribution of stress/strain has been influenced to some extent. Further, the study includes the influence of the friction coefficient on the forming quality of the wheel rim to guarantee the simulation accuracy in practical applications. In sum, the dual-phase steel has to be carefully applied to the wheel rim, which needs to experience the processes of FBW and roll forming, focusing on the performance of SCHAZs. [ABSTRACT FROM AUTHOR]

The article presents the results of studying the choice of temperature-time and energy-force parameters in flash butt welding (FBW) of the railway crosspiece core (110G13L steel) with rail (K76F steel) through an intermediate chrome-nickel austenitic insert (08Kh18N10T steel). Using an algorithm of numerical solution of the three-dimensional heat conduction equation under the initial and boundary conditions corresponding to the real conditions of welding of the specimens, thermal cycles in fBw of k76f steel with austenitic 08khl8n10t steel and 110g13l steel with austenitic 08khl8n10t steel and temperature distribution in welded joints (in the heat-affected zone for both steels) were obtained. Ranges of varying the main technological parameters of the FBW process have been determined, in which during flashing of rails from K76F, 110G13L and 08Khl8N10T steels, their uniform heating across the cross-section and length is provided, sufficient for achieving deformation to the specified extent during upsetting. [ABSTRACT FROM AUTHOR]

The article presents the results of studying the choice of temperature-time and energy-force parameters in flash butt welding (FBW) of the core of railway crossings (110G13L steel) with rail steel (K76F) through an intermediate chrome-nickel austenitic insert (08Kh18N10T). Using an algorithm of numerical solution of the three-dimensional heat conduction equation under the initial and boundary conditions corresponding to the real conditions of welding of the specimens, thermal cycles in FBW of K76F steel with 08Kh18N10T austenitic steel and 110G13L steel with 08Kh18N10T austenitic steel and temperature distribution in welded joints (in the heat-affected zone for both steels) were obtained. Ranges of varying the main technological parameters of the FBW process have been determined, in which during flashing of rails from K76F, 110G13L, and 08Kh18N10T steels, their uniform heating across the cross-section and length is provided, sufficient for achieving deformation to the specified extent during upsetting. 13 Ref., 4 Tabl., 11 Fig. [ABSTRACT FROM AUTHOR]

In this study, finite element (FE) simulation by the software Abaqus was relied on to investigate the roll forming process of a wheel rim made of an innovative dual-phase steel, i.e., DP590, after flash butt welding (FBW). In the simulation, an FE model was generated, including the design of the dies for flaring, three-roll forming, and expansion, and detailed key processing parameters based on practical production of the selected DP590. Combined with the microstructures and properties of the weld zone (WZ) and heat-affected zones (HAZs) after FBW, the distribution of stress/strain and the change in thickness of the base metal (BM), WZ and HAZs were analyzed, and compared in the important stages of roll forming. Theoretically, the variation in the microstructure and the corresponding stress–strain behaviors of the BM, WZ, and HAZs after FBW have led to the thickness reduction of DP590 that originated from softening behaviors occurring at the region of subcritical HAZs (SCHAZs), and a small amount of tempered martensite has evidently reduced the hardness and strength of the SCHAZ. Meanwhile, the distribution of stress/strain has been influenced to some extent. Further, the study includes the influence of the friction coefficient on the forming quality of the wheel rim to guarantee the simulation accuracy in practical applications. In sum, the dual-phase steel has to be carefully applied to the wheel rim, which needs to experience the processes of FBW and roll forming, focusing on the performance of SCHAZs.

The effect of cold deformation and annealing temperature on the microstructure evolution and mechanical properties is shown in this research together with a unique short strategy for manufacturing lean duplex stainless steel bars. Furthermore, the effects of post-weld heat treatment (PWHT) and cooling treatments on the microstructure and mechanical properties of LDX 2101 bars are being investigated. The results demonstrate that the austenite produces a large number of deformation twins and strain-induced martensite (SIM) as cold deformation increases, and the SIM and austenite follow the traditional K–S and N–W orientation relationships. The best mechanical properties overall are achieved in LDX 2101 bars that have been annealed at 1020 °C. Moreover, short-time PWHT improves the austenite proportion in the heat-affected zone and weld metal, and PWHT can greatly enhance the overall mechanical properties of the welded joints. Additionally, the optimal heat treatment temperature of the welded joints is 1050–1080 ℃. Furthermore, compared to those treated with air cooling, the mechanical properties of the welded joints treated with water quenching following flash butt welding are superior. As a result, it is recommended that following flash butt welding, the welded joints are given a water-quenching treatment. [ABSTRACT FROM AUTHOR]

In this study, the microstructure and performance of newly designed dual-phase steel (DP590) after joining by flash butt welding (FBW) for vehicle wheel rims was analysed and compared by two simulations, i.e., physical simulation and numerical simulation, due to the high acceptance of these two methodologies. Physical simulation is regarded as a thermal–mechanical solution conducted by the Gleeble 3500 simulator and which can distribute the heat-affected zone (HAZ) of the obtained weld joint into four typical HAZs. These are coarse-grained HAZ, fine-grained HAZ, inter-critical HAZ and sub-critical HAZ. A combination of ferrite and tempered martensite leads to the softening behaviour at the sub-critical HAZ of DP590, which is verified to be the weakest area, and influences the final performance due to ~9% reduction of hardness and tensile strength. The numerical simulation, relying on finite element method (FEM) analysis, can distinguish the temperature distribution, which helps us to understand the relationship between the temperature distribution and real microstructure/performance. Based on this study, the combination of physical and numerical simulations can be used to optimise the flash butt welding parameters (flash and butt processes) from the points of temperature distribution (varied areas), microstructure and performance, which are guidelines for the investigation of flash butt welding for innovative materials. [ABSTRACT FROM AUTHOR]

U75V rail steel is widely used in railways in China, including train tunnels in mountain and subsea projects, where it suffers from selective corrosion near welded joints. To ensure adequate railway service life, this study examines the effect of the normalisation process on the electrochemical behaviour of U75V rail-welded joints (URWJs) manufactured by flash butt welding (FBW) using potentiodynamic polarisation and electrochemical impedance spectroscopy (EIS). Corrosion morphology and elemental distribution analyses were performed to investigate the corrosion behaviour. The results show that the grains within the joints became finer and more homogeneous after normalisation, with a lower corrosion rate and higher corrosion resistance. It is demonstrated that fewer corrosion products were formed on the surface of the normalised joints after electrochemical test, and the corrosion resistance of the URWJs improved, owing to the formation of denser passivation films caused by normalisation. These mechanisms of corrosion response help explain corrosion failure in railway lines, as well as also help optimise the welding process and normalising processes to obtain a corrosion-resistant microstructure and ensure the quality of welded joints. [ABSTRACT FROM AUTHOR]

Defects would occur in the weld joint of the wheel rims during the post-flash butt welding (FBW) process suffering from poor plasticity, which will deteriorate the quality and lifecycle of finish products. Therefore, the FBW process of the 440CL high-strength-low-alloy (HSLA) steel was physically simulated and the influence of flash parameters on FBW joints was systematically evaluated in this study. The results showed that the width of heat affected zone increased with accumulated flash allowance (δf) while declined with accelerated flash speed (vf). The recrystallization level would be intensified with increased δf. Meanwhile, the acceleration in vf populated the WZ with a more homogeneous microstructure, higher recrystallization degree and lower dislocation density. The hardness in WZ slightly reduced (202 → 195 HV) as increased δf but obviously dropped (192 → 177 HV) as increased vf. All tensile samples were fractured at the BM location and the tensile properties of FBW joints exhibit a good match with those of BM, with a slight increase in strength (UTS: 468 ~ 493 MPa; YS: 370 ~ 403 MPa) but a mild decrease in plasticity (EL: 39 ~ 44%; RA: 74 ~ 79%). Furthermore, both the joint strength and ductility showed a downward tendency with the increment of δf. However, the strength slightly decreased while the ductility increased with the advancement of vf. These findings would be valuably referential to the real FBW of HSLA steels with optimized microstructure and mechanical performance. [ABSTRACT FROM AUTHOR]

The research investigates the structure of a welded joint of a railway rail after local heat treatment and without it. Macro- and microstructural analyses of rail samples were performed using optical microscopy methods. The hardness of the rail running surface in the heat-affected zone of butt welds was measured. It has been found that the formation of zones with reduced hardness is inevitable due to the temperature gradient created during the welding process. Moreover, using local induction heat treatment results in the formation of new, more extended zones with reduced hardness. It has been determined that the only solution to this problem is to reduce the extent of heat-affected zones to sizes that do not lead to increased wear and local crushing. [ABSTRACT FROM AUTHOR]

Flash butt weld failure due to oxide entrapment is one of the primary causes of wheel rim failures. The welding process parameter plays a critical role in eliminating the oxides from the bond line. Experimental investigations to understand the effect of initial jaw distance (IJD) and the number of preheating pulses (NP) on the upsetting length (UL) were studied. It was observed that IJD and NP played a critical role in altering the peak temperature achieved at the interface. Higher peak temperature at the interface helped achieve a larger upset length, forming a defect-free weld. Failure analysis of the flash butt welded fractured surface revealed the presence of penetrators/cold spots and oxide inclusion. The study suggested that a sufficient upset length was necessary to expel oxides/cold spots formed during welding for obtaining defect-free joints. Furthermore, increasing the preheating pulses smoothened the abutting edges and significantly reduced the defects. The presence of Goss, Rotated Goss, and Cube textures at the fusion zone of flash butt weld were found to be the enabler for crack propagation during post-weld forming operations once the crack has been initiated. [ABSTRACT FROM AUTHOR]

The objective of the study is to test the joints of waste reinforcing bar and steel wires for tension. The tests conducted within the conditions of construction enterprises of the Republic of Kazakhstan (RK) showed that, depending on the arrangement of production and the productivity of the production of reinforced concrete products, more than 2% of reinforcing steel is wasted. The authors are developing a technology for the efficient use of the waste reinforcing bar and steel wires in the production of reinforced concrete products. This article presents the results of a laboratory test of joining reinforcing bar waste and steel wires for tension. Experimental studies were carried out on the flash butt machine MSR-25 within the conditions of the laboratory base of the Kazakhstan Institute of Welding of the Karaganda Technical University (KTU). Samples were tested in the engineering laboratory of Karaganda Technical University. As a result of the test, it was found that the rods joined from several waste reinforcing bars and steel wires by the method of flash butt welding, having 2-3 joints each, withstand a load in the range of 25000 ÷ 40000 N. The test results showed sufficient strength of the welded joints. [ABSTRACT FROM AUTHOR]

High strength low-alloy (HSLA) steels have been employed in the automotive industries to produce chassis, part of suspensions, and truck wheels, among others. They present good strength and mechanical toughness, in addition to good formability and weldability. However, good weldability depends on the welding process and parameters. For mechanical components with occurrence of cracks, fatigue life can be quantified by the fatigue crack growth stage. This paper aims to evaluate the fatigue crack growth in HSLA steel plates welded by flash butt welding and laser beam welding. The different welding processes and welding parameters used resulted in their distinct microstructures. The different microstructures showed significant differences in hardness; however, they showed no significant differences in fatigue crack growth. Moreover, the weld beads showed higher resistance to fatigue crack growth when compared to the base metal. For cracks propagating across the weld beads obtained by laser beam welding, with crack initiating at the base metal and growing toward the heat-affected zone and weld bead, a drop in the fatigue crack growth rate was observed as the crack tip approached the microstructure gradient found between these regions. [ABSTRACT FROM AUTHOR]

In this study, the microstructure and performance of newly designed dual-phase steel (DP590) after joining by flash butt welding (FBW) for vehicle wheel rims was analysed and compared by two simulations, i.e., physical simulation and numerical simulation, due to the high acceptance of these two methodologies. Physical simulation is regarded as a thermal–mechanical solution conducted by the Gleeble 3500 simulator and which can distribute the heat-affected zone (HAZ) of the obtained weld joint into four typical HAZs. These are coarse-grained HAZ, fine-grained HAZ, inter-critical HAZ and sub-critical HAZ. A combination of ferrite and tempered martensite leads to the softening behaviour at the sub-critical HAZ of DP590, which is verified to be the weakest area, and influences the final performance due to ~9% reduction of hardness and tensile strength. The numerical simulation, relying on finite element method (FEM) analysis, can distinguish the temperature distribution, which helps us to understand the relationship between the temperature distribution and real microstructure/performance. Based on this study, the combination of physical and numerical simulations can be used to optimise the flash butt welding parameters (flash and butt processes) from the points of temperature distribution (varied areas), microstructure and performance, which are guidelines for the investigation of flash butt welding for innovative materials.

Microcontroller regulator of flash butt welding with compensation of disturbances by the mains voltage on welding current is described. In the algorithm of the regulator operation, nonlinear control characteristics are presented in a tabular form. The algorithm for determining the required angle of thyristor opening during oscillations of mains voltage is described. The choice of parameters was substantiated, influencing the creation of the controller using widely used microcontrollers. 9 Ref., 3 Tabl., 2 Fig. [ABSTRACT FROM AUTHOR]

U75V rail steel is widely used in railways in China, including train tunnels in mountain and subsea projects, where it suffers from selective corrosion near welded joints. To ensure adequate railway service life, this study examines the effect of the normalisation process on the electrochemical behaviour of U75V rail-welded joints (URWJs) manufactured by flash butt welding (FBW) using potentiodynamic polarisation and electrochemical impedance spectroscopy (EIS). Corrosion morphology and elemental distribution analyses were performed to investigate the corrosion behaviour. The results show that the grains within the joints became finer and more homogeneous after normalisation, with a lower corrosion rate and higher corrosion resistance. It is demonstrated that fewer corrosion products were formed on the surface of the normalised joints after electrochemical test, and the corrosion resistance of the URWJs improved, owing to the formation of denser passivation films caused by normalisation. These mechanisms of corrosion response help explain corrosion failure in railway lines, as well as also help optimise the welding process and normalising processes to obtain a corrosion-resistant microstructure and ensure the quality of welded joints.

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 further heat treatment of large-sized products. In the work the formation of joints of thermo mechanically strengthened 2219-T87 alloy during flash butt welding was investigated. It was found that a low-temperature resistance heating in combination with a short-term heating by flashing provide the formation of defect-free welded joints. Metallographic examinations showed that the 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 Tabl., 7 Fig. [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 article presents a study of the accuracy of reproduction of parameters of operational control of flash butt welding of railway rails in order to increase the reliability of evaluating the compliance of the process to the Technical Specifications (TS) and improve the quality of welded joints. For the statistical analysis of protocols of welding rails at rail-welding enterprises the review of existing indices of accuracy and stability of technological processes was made. For the analysis, the coefficient of variation Cv was chosen, which is not related to the tolerance of the deviation of the process parameter. Evaluations of Cv coefficients according to the welding protocols of more than 10 thous. joints and more than 100 specimens of a technological test for the stationary machine K1000 showed that the mode parameters set directly by the control system, are reproduced with an error of not more than 1.5%. The Cv coefficients increase sharply for the rate of flashing, transition from flashing to deposition and particularly deposition, which are included in the TS for welding rails and an active electric power, that occurred during flashing at the input of the welding transformer. The studies of Cv coefficients with grouping of welding data by six months showed that the variation of process parameters had no trends and the process was stable over time with a sufficient accuracy. The mean values and the standard deviation of the parameters of the process of welding rails and specimens of a technological sample differ within the statistical error, which indicates the possibility of approximating the results of test studies on the rail joints. Evaluation of effect of parameters of the process of rate, allowance and energy of flashing on the heat-affected-zone (HAZ) with the use of linear regression dependence showed an essential dependence of HAZ on variation of electric energy during flashing. For control of active energy, the measuring converter of average active electric power with a pulse output was developed, which is adapted to the control systems of K1000 and K922 machines with input signals of current to 1000 A and voltage to 440 V, a frequency band of these signals to 1 kHz and the resulted error of measurement to 1%. It is recommended to include active power energy released during melting at the input of the welding transformer in the list of control parameters to the TS, and to improve the quality of joints not only to control the parameters within tolerance, but to create the conditions of the smallest variation of parameters from obtained data. 7 Ref., 1 Tabl., 4 Fig. [ABSTRACT FROM AUTHOR]

The article presents a study of the accuracy of reproduction of parameters of operational control of flash butt welding of railway rails in order to increase the reliability of evaluating the compliance of the process to the Technical Specifications (TS) and improve the quality of welded joints. For the statistical analysis of protocols of welding rails at rail-welding enterprises the review of existing indices of accuracy and stability of technological processes was made. For the analysis, the coefficient of variation Kv was chosen, which is not related to the tolerance of the deviation of the process parameter. Evaluations of Kv coefficients according to the welding protocols of more than 10 thou joints and more than 100 specimens of a technological test for the stationary machine K1000 showed that the mode parameters set directly by the control system, are reproduced with an error of not more than 1.5 %. The Kv coefficients increase sharply for the rate of flashing, transition from flashing to upsetting and particularly upsetting, which are included in the TS for welding rails and an active electric power, that occurred during flashing at the input of the welding transformer. The studies of Kv coefficients with grouping of welding data by six months showed that the variation of process parameters had no trends and the process was stable over time with a sufficient accuracy. The mean values and the standard deviation of the parameters of the process of welding rails and specimens of a technological test differ within the statistical error, which indicates the possibility of approximating the results of test studies on the rail joints. Evaluation of effect of parameters of the process of rate, tolerance and energy of flashing on the heat-affected zone (HAZ) with the use of linear regression dependence showed an essential dependence of HAZ on variation of electric energy during flashing. For control of active energy, the measuring converter of average active electric power with a pulse output was developed, which is adapted to the control systems of K1000 and K922 machines with input signals of current to 1000 A and voltage to 440 V, a frequency band of these signals to 1 kHz and the resulted error of measurement to 1 %. It is recommended to include active electric power released during flashing at the input of the welding transformer in the list of control parameters to the TS, and to improve the quality of joints not only to control the parameters within tolerance, but to create the conditions of the smallest variation of parameters from obtained data. [ABSTRACT FROM AUTHOR]

Flash butt welding is a high-efficiency welding technology that is widely used in industrial development. However, the inclusions and defects generated during the process are unacceptable. The presence of inclusions is one of the main factors affecting the quality of flash butt welding. Suitable flash butt welding parameters such as the preheating temperature and upset distance are essential to eliminate inclusions. In this study, because the number of inclusions on the end face is greatly affected by the flash welding time and upset distance, the impact of different upset distances on the number of inclusions was studied by fixing the flash welding time. Further observations were conducted using a scanning electron microscope. Image analysis software was used on the obtained photos to quantitatively analyze the inclusions on the welding surface. A statistical analysis of the experimental data showed that the upset distance was related to the number of inclusions, and the total number of inclusions on the welding surface had a negative impact on the strength of the product.

The effects of operational conditions on dissimilar Al-Cu flash welded joint quality have been studied using a series of industrial welding experiments. Macro- and microstructural analyses of dissimilar aluminum-copper joints produced by flash butt welding are performed in the present work. Various process conditions including standard and non-standard operational conditions were assessed during the welding experiments. Optical and scanning electron microscopy and electron dispersive x-ray spectroscopy are used to investigate and assess the metallurgical joints created through this process. For suboptimal process conditions, voids (5 mm wide, 1 mm deep) were observed at the joint interface. Some of the voids contained remnants of molten metal while some were empty. Al-Cu intermetallic compounds at the joint area were investigated, and their chemical compositions are determined. The profile of the joint interface was observed to be wavy which is attributed to the voids on the copper side and insufficient material flow of the copper during the upset. The effects of welding parameters on the waviness of the interfaces are investigated. The results show that the waviness of the interface increases with increasing the heat intensity (heat/joint area). No correlation was observed between the flashing speed and the waviness of the interfaces. [ABSTRACT FROM AUTHOR]

Flash butt welding (FBW) is extensively used for joining front end of incoming hot rolled coil to the tail end of the previous coil in pickling and tandem cold rolling mill (PLTCM). Improper welding causes failure in the cold rolling strands in the later stages. Hence, it is of paramount importance to establish a sound weld line by selecting the right welding process parameters. Optimizing the process parameters largely depends on the thickness and chemistry of the steels because slight variations in steel chemistry can cause weld failures. Recently, during flash butt welding of hot rolled Interstitial Free (IF) steel from TSK (Steel A) in the cold rolling mill (CRM) of TSJ (Steel B), adjustments had to be made in the welding parameters to enable smooth cold rolling. The flash butt welded TSK coils showed oxides of Fe, Mn, Al and Ti on fractured surfaces with the standard TSJ welding parameters. Back up study suggested that higher Mn, Al and Ti levels in the TSK coils were possibly responsible for greater volume fraction of oxides at the weld zone. Since, flash butt welding is done without the use of shielding gas, oxidation of the molten pool happens at the abutting edges. Improper process parameters can lead to the entrapment of oxides at the fusion line causing failure initiation. Therefore, this called for a change in welding parameter from the set value. Increasing the flashing length and upset length enabled in removing the excessive oxides formed during the flashing stage and prevented failure of the welds. The downstream end has hence been stabilized. [ABSTRACT FROM AUTHOR]

• A database comprising 155 fatigue test results of flash-welded steel rebars were established. • The trained ML models offer highly accurate predictions of the fatigue life of flash-welded steel rebars. • The factors influencing the fatigue life of flash-welded connections can be elucidated using SHAP analysis. • The fatigue life of various flash-welded steel rebars can be generalized by the data-driven ANN model. The fatigue failure of steel rebars joined by flash butt welding is a contributing factor to structural damage in reinforced concrete structures. In this work, a series of fatigue tests based on steel rebars joined by flash butt welding were carried out, and a fatigue life database consisting of 155 specimens were obtained. Three distinct machine learning models are utilized to analyze and predict the fatigue life of the steel rebars joined by flash butt welding. Additionally, The SHapley Additive exPlanations (SHAP) method is employed to assess the significance and impact of each input parameter on the model predictions. The results demonstrate the superior performance of the ANN model, with an R2 of 0.865, MSE of 0.134, MRE of 0.872, and MAE of 0.171. The factors influencing the fatigue life of steel rebars joined by flash butt welding, ranked in descending order of significance, are stress amplitude, rebar diameter, stress ratio, loading frequency, and material strength. The experimental and predicted values for the 2 million fatigue stress amplitude differ by 4.64 MPa (approximately 2.99 %), demonstrating the robust generalization capabilities of the ANN model, enabling accurate predictions of the fatigue life of steel rebars joined by flash butt welding throughout the entire cycle. The proposed model can be used to assess the fatigue life and design fatigue stress amplitude of steel rebars joined by flash butt welding, offering a promising alternative to fatigue testing. [ABSTRACT FROM AUTHOR]

The structural changes resulting from the Flash Butt Welding (FBW) of pearlitic rails have been associated with wear/premature failures, despite this, there are no studies applying dilatometry to correlate the welding thermal cycles with the microstructural development of such material. The microstructural evolution of the heat affected zone is clarified with the aid of dilatometry. The increase in the steel hardenability associated with a larger austenitic grain size promotes the austenite-pearlite transformation at lower temperatures in the grain growth region. This explains why this region has larger pearlite colony size but smaller interlamellar pearlite spacing and higher hardness than the grain refined region. Partial cementite spheroidization in the heat affected zone is responsible for significant decrease in hardness and tensile strength and is correlated to localized dipping, rolling contact fatigue and failures. A dilatometry based methodology is proposed to define a process window and control the post-weld cooling rate at the rail head in order to improve the weld performance due to a better hardness profile, without increasing costs or welding time. For the steel evaluated, a 20% increase in the hardness of the softened area at the HAZ was obtained by dilatometric simulation of a safe accelerated cooling (5 °C/s). [ABSTRACT FROM AUTHOR]

Highlights • Flash butt weld fusion line showed least toughness compared to CGHAZ, FGHAZ and parent material. • Goss texture and LABs were maximum at region close to the fusion line and decreased towards the parent material. • Drop in toughness is due to the presence of Goss texture and higher fractions of low angle grain boundaries. Abstract Flash butt welds show variation in impact toughness from the fusion line (FL) to the parent material (PM). A direct correlation of the variation in toughness, (1 1 0)[0 0 1] Goss texture and grain boundary misorientation fractions were observed. PM texture transformed to Goss, rotated Goss and rotated cube components in the thermo-mechanically affected zone (TMAZ) due to the shear deformation experienced during the upsetting stage. Whereas in the heat affected zone (HAZ) adjacent to TMAZ only microstructural changes were observed. Formation of (1 1 0)[0 0 1] texture component, higher fraction of Low Angle Grain Boundaries (LABs) as a result of deformation close to FL resulted in deterioration of toughness. [ABSTRACT FROM AUTHOR]

Following fast upsetting deformation, the welding seam (WS) is formed at the surface of flash butt welded Inconel718 joint due to dynamic recrystallisation. The dissolution of γ″ and γ′ phases during temporary flashing is mainly responsible for the ∼30% hardness decrease in the heat-affected zone (HAZ). A wider zone with lowered hardness indicates a broader HAZ created with a gentler temperature gradient. The increased temperature in the whole HAZ leads to more serious formation of carbides and liquation at the grain boundaries. Such unsuitable microstructure accounts for a 50–70% loss of ductility, while only ∼10% of ductility is lost in another welding joint with suitable temperature gradient. [ABSTRACT FROM AUTHOR]

Flash butt welding is a resistance type metal joining process designed to produce butt welds between two materials of similar cross section. The primary objective of this study was to develop numerical simulation technique for prediction of temperature histories in flash butt welded bars. Welding process variables that affect temperature which were examined include; pre-heat, boundary convection severity, flash duration and material properties. Temperature profile plots were along the longitudinal and radial directions of the bar. The effect of nodal densities on temperature values at a point was examined. Finite element software ANSYS 16.0 was used to solve the quasi-linear thermal transient equation. Non-uniform plane77 mesh size was used in order to allow for higher concentration of nodes around the heat affected zone (HAZ). Applying a bar diameter of 25 mm, length 250 mm and flash duration of 4 seconds, indicated peak temperature values were 1400, 1238.9, 910.18 and 650.68 °C at distance 0, 1, 3 and 5 mm from the weld flash line. Peak temperatures generally increased with increased pre-heat condition and flash duration. Simulated peak temperatures were compared with weld temperature results of other related works and close correlations were observed. [ABSTRACT FROM AUTHOR]

The effects of process variables on weld quality are being studied for the Flash Butt Welding of SPFH 590 steel. The resulting welded metal and heat affected zones were characterized by tensile testing, bending testing, Rockwell hardness testing and microstructural analyzed by optical microscopy, and scanning electron microscopy. The results indicated a transformation of the metal joint from ferrite laminar to acicular ferrite. During the welding process, the long-shaped grains grew and became rounded-shaped, and through the cooling process, some side plate Widmanstatten ferrite structure is formed. The significance of process factor levels on microstructure, weld zone strength, and fracture characteristics were analyzed. The welding process parameters, 5V (voltage), 2.3 mm (upset), and 2 s (flashing time), displayed the best properties combination (strength and ductility) of all the test performed. [ABSTRACT FROM AUTHOR]

Investigations were carried out into the special features of resistance flash butt welding of ring-shaped components of frames of 1545KM alloy, the welding conditions were determined, and the structure, mechanical properties, and service properties of the welded joints were examined in the composition of the fuel tank of a rocket carrier. [ABSTRACT FROM PUBLISHER]

The analysis of basic parameters of flash butt welding was carried out according to the data of current technological reports formed by the computer control system during welding of rails. The opportunity to develop the model for predicting the output quality index of welded butt of a rail, i.e. fracture load of specimen and deflection, was shown based on the parameters of welding process applying different methods of statistical analysis, in particular, correlation and regression analysis and neural networks. The calculations were carried out according to the experimental data obtained at the Kiev rail welding enterprise during welding of rails in the welding machine K1000. 6 Ref., 2 Tables, 5 Figures. [ABSTRACT FROM AUTHOR]

The object of the present investigations was to evaluate the effect of flash butt welding parameters on microstructures and mechanical properties of HSLA 590CL welded joints in wheel rims by adjusting welding parameters separately. The amount of Widmanstatten ferrites and bainite in the weld metal, and grain size were observed with the adjustment of welding parameters. The tensile strength of welded joints met the strength requirement of wheel rims steels, but the tensile strength and tensile fracture were different in different welding parameters. Micro-hardness distributions of welded joints in different welding parameters were similar, that is the maximum micro-hardness occurred in the weld and micro-hardness decreased from the weld to base metal. A certain degree of softening phenomenon was found in the heat affected zone (HAZ), which should result from the heat input in the flash butt welding. Two failure mechanisms of wheel rims in the expanding process were investigated. The first type fractured at the HAZ and showed ductile fracture characteristics, the crack initiation located at the thinning location. The second type fractured at the weld and showed brittle fracture characteristics. [ABSTRACT FROM AUTHOR]

The flash allowance and upset allowance have significant effects on characteristics of flash butt welded RS590CL steel joints. The overheated zone (OZ) widths increased with flash allowance (δf) increase, and decreased as the upset allowance (δu) increased. The coarsened upper bainite was formed in interface zone (IZ) and OZ as δf increased. With increasing δu, the large plastic deformation occurred and the interface formability improved. The hardness in IZ was a little lower than that in its vicinity OZ due to some ferrite existence and dislocation amount decreased in IZ. The tensile strengths of flash butt welding (FBW) joints were in good match with base metal and the ductilities were lower. The maximum bending crack length was 0.68 mm which indicated that the bending properties of FBW joints were good. Under this experiment, relatively large δf (10–12 mm) and δu (5.5–6.5 mm) were recommended for the benefit of high quality FBW joints. [ABSTRACT FROM AUTHOR]

Weld thermal cycles, microstructures and mechanical properties of flash butt welded RS590CL steel joints have been investigated. The results indicated that the weld thermal cycles are characterized by high peak temperatures and rapid heating and cooling rates, and the joints included the weld interface zone (WZ), coarse grain zone (CZ), fine grain zone (FZ) and partially recrystallized zone (PZ). The WZ and CZ consist mainly of coarsened upper bainite while the FZ has a fine equiaxed grain structure containing ferrite and pearlite with NbC precipitates. The WZ and CZ have higher hardness compared with the FZ, PZ and base metal. The joint strength (584-611 MPa) can match the base metal strength (575–595 MPa). The impact toughness of weld interface zone in the joints depends on welding parameters. The excessive flash allowance results in reducing the joint toughness. The reasons for the reduced joint toughness are related to the coarsened upper bainite, retained oxides and joining defects in the weld interface zone. The suitable combination of flash allowance (8–9 mm), upset allowance (5.5–7.0 mm) and upset pressure (123–160 MPa) is beneficial for the improvement of joint toughness. [ABSTRACT FROM AUTHOR]

High strength low alloy (HSLA) steels have been widely used in the manufacture of wheel rim on account of the higher strength and larger elongation compared to the traditional low carbon steels. This experimental investigation was aimed to evaluate the microstructure and fracture mechanism of a flash butt welded 380CL steel by comparing the failed wheel rim and the survived wheel rim. The results showed that the continuous banded structure in the HAZ and the serious Widmanstatten ferrite in the weld were the major reasons for the failure of the wheel rim. The micro-hardness of two joints was similar in the overall profile. For the joint of the failed rim, the micro-hardness at the weld was the highest at 254 HV and the lowest micro-hardness value was in the HAZ. The high yield ratio of the failed wheel rim resulted in poor formability in the flaring process. The fracture mechanism of the failed rim was the mixture of ductile and brittle fracture modes. The crack initiation was the fusion zone of the weld having highest micro-hardness, then the cracking propagated along the weld metal to the middle of the wheel rim, a limited deviation was found in the terminal of the crack. The large ferrite grain in the HAZ was the main reason for the brittle–ductile transition. [ABSTRACT FROM AUTHOR]

Transmission electron microscopy is used to study the welds between high-carbon pearlitic and chromium-nickel austenitic steel workpieces performed by flash butt welding. It has been established that lamellar pearlite colonies alloyed with chromium and nickel are formed in the weld zones between dissimilar steels. Thin austenite interlayers have been detected in the center of ferrite plates. The structure formed presents the C-F-A-F-C-F-A-F (and so on) sequence of three plate-shaped phases. The ferrite-cementite structure in alloyed-pearlite colonies is finer than that in unalloyed pearlite. [ABSTRACT FROM AUTHOR]

Medium carbon steel rails are commonly jointed by flash butt welding procedures. To ensure an adequate service life for the structural component, commonly subjected to fatigue loading, a rigorous quality control should be performed, both in welding parameters and in the surface quality of the welded joint. This work investigated the causes of recurrent failures in railroads, with cracking always initiated in the rail in the region of the welded joint. Two case studies are presented. Aiming to execute the failure analysis, all standard procedures were applied, with a careful assessment of the material characteristics and the fractured surface. It was concluded that, for both cases, fatigue cracks initiated near the weld bead and spread in a brittle mode, leading to premature fracture of the material. An in-depth analysis of the rails showed that the surface finishing of the weld bead was not appropriate, generating undesirable stress concentration. Some undesirable microstructural characteristics were also found in the weld region. A recommendation to control welding parameters and to change the procedure of surface finishing of welded joints was held, aiming to decrease the number of accidents on the railroads. [ABSTRACT FROM AUTHOR]

To provide serviceability of joints of pipelines produced using flash butt welding (FBW) alongside with the condition of strength the requirement to impact toughness KCV is set forth. Its level is established according to the requirements to the joints produced using arc welding methods, for which the probability of appearance of crack-like defects in them is peculiar. Absence of even preconditions to formation of cracks in the FB-welded joints allows initiating the review of requirements to impact toughness. As the standard level the KCV value is offered, which is reliably provided at optimum mode of FBW performance. The sufficiency of such KCV level is proved by reliable many-years practice in operation of different-purpose pipelines without fractures, including main pipelines of large diameter (up to 1420 mm). For the given KCV value at the working circumferential stresses in the pipeline and axial ones equal to half of their value, the critical sizes of hypothetic through longitudinal and circumferential cracks are calculated. Their sufficient sizes prove in appropriateness of such approach. [ABSTRACT FROM AUTHOR]

Flash butt welding is a high-efficiency welding technology that is widely used in industrial development. However, the inclusions and defects generated during the process are unacceptable. The presence of inclusions is one of the main factors affecting the quality of flash butt welding. Suitable flash butt welding parameters such as the preheating temperature and upset distance are essential to eliminate inclusions. In this study, because the number of inclusions on the end face is greatly affected by the flash welding time and upset distance, the impact of different upset distances on the number of inclusions was studied by fixing the flash welding time. Further observations were conducted using a scanning electron microscope. Image analysis software was used on the obtained photos to quantitatively analyze the inclusions on the welding surface. A statistical analysis of the experimental data showed that the upset distance was related to the number of inclusions, and the total number of inclusions on the welding surface had a negative impact on the strength of the product. [ABSTRACT FROM AUTHOR]