Structure Of Weld Metal Research Articles

Experimental Studies of Corrosion Resistance of Welded Seams of Steel Structures with a High Sulfur Content in Surface Layers Using Modern Methods of Modeling

Analysis of literature sources and empirical data indicate a variety and a large volume of experimental material, which often characterizes the uncertainty and contradiction of information regarding the effect of sulphur and manganese on the corrosion behaviour of steels obtained using traditional methods. This leads to the need to search for new, alternative methods for its effective analysis. The task of assessing and predicting the corrosion properties of structural steels is a key one in the general problem of managing the operational reliability of welded metal structures and equipment for the chemical, metallurgical, oil and gas, mining and other industries. The possibilities of its solution consist of using new information technologies, a component of which is intelligent means of information processing, such as artificial neural networks (ANN). The use of ANN makes it possible to create qualitatively new hardware and software that significantly expand the classes of emerging problems and increase the efficiency of analysis and forecasting. In the process of long-term operation of metal structures in many industrial industries, the metal is in direct contact with sulfur-containing agents at high temperatures. This leads to the saturation of the surface layer of the metal with sulfur with a concentration of up to 0.6%, which further makes it impossible to carry out repair and welding operations due to the formation of hot cracks. It was found that adding metallic manganese into the electrode coating in an amount of 20-25% significantly increases (4-5 times) the resistance against the formation of hot cracks. Sulfur content in the deposited metal has the opposite effect on the appearance of hot cracks. So, with a sulfur content of 0.042% and more, the resistance of the metal against the formation of hot cracks decreases sharply. It is shown that an increase in the content of metallic manganese in the electrode coating significantly reduces the content of dissolved sulfur in the deposited metal. Moreover, this tendency is typical for steels with different sulfur content in the surface layers and with different service life. For example, for steel with a service life of 20 years, the initial sulfur content in the surface layer of the metal (up to 1 mm) was about 0.52%. Adding metallic manganese in the coating of electrodes in an amount of 20-25% made it possible to reduce the sulfur content in the deposited metal to 0.03-0.045%, i.e. 12.6-17.3 times. In addition, the corrosion rate decreases with an increase in the content of metallic manganese in the electrode coating. The lowest corrosion rate for all steels involved in the research was established at 20-25% manganese content in the coating.

Modern levels of structural strength assessment and the algorithm of implementation of the methodology of risk analysis of the operation of welded metal structures

Modern levels of structural strength assessment and the algorithm of implementation of the methodology of risk analysis of the operation of welded metal structures

Working conditions and health status in workers in boiler and welding production in power engineering

Introduction. Preserving the health of qualified workers of older age groups is especially important under conditions of exposure to occupational hazards. The purpose of the study was to assess the influence of occupational hazards on the development of occupational and somatic diseases among workers of various age groups in the main occupations of mechanical engineering. Materials and methods. The study tested the results of hygienic research at workplaces of an enterprise in the power engineering industry in the manufacture of welded metal structures. We assessed the health status in workers based on the results of an in-depth medical examination and ultrasound examination of the vessels of the upper extremities with assessment of blood flow indices. Using a survey method, data were obtained on assessing the influence of production factors on the health status in workers. Results. The working conditions in the main occupational workers groups were assessed as harmful grades 1–3, the priority occupational hazards were: increased noise, and at the workplaces of electric gas workers there were also fibrogenic aerosols, chemical substances, and heavy physical work. Electric and gas welders and boilermakers work in the most unfavourable conditions, about 30% of whom continue to work after reaching retirement age. We have established a significant gain in the incidence of arterial hypertension and sensorineural hearing loss among workers over 40 years of age and an increase in the prevalence of all chronic diseases in the age group over 60 years. Limitations. The study is limited by the number of workers examined and the lack of ability to assess the health status of the studied contingent of workers over time. Conclusion. In conditions of exposure to elevated noise and other occupational hazards, there is an enhancement in the prevalence of work-related and somatic diseases in workers over 40 years of age. With advancing age, the rise in the vascular resistance index is observed, however, the first signs of peripheral blood flow disturbance are often recorded at a young age. In this regard, it is necessary to introduce methods of early diagnosis and prevention of occupational and work-related pathology.

Practice of implementing the methodology of risk analysis of the operation of welded metal structures in Ukraine

Practice of implementing the methodology of risk analysis of the operation of welded metal structures in Ukraine

Influence of intense dynamic action on the structure and properties of austenitic weld metal with nitrogen

Influence of intense dynamic action on the structure and properties of austenitic weld metal with nitrogen

Interfacial microstructure characteristics and failure mechanism of the laser welding-brazing steel-Al joints with various welding parameters

The microstructure details of the interface, mechanical properties and failure mechanism of laser welding-brazing (LWB) steel-Al joints with various welding parameters were comparatively investigated. The emergence of ternary Fe–Al–Si intermetallic compounds (IMCs) was observed in the interfacial area of the joints prepared utilizing ER4047 filler. In contrast, only the binary Fe–Al IMCs were formed in the interfacial area of the joints prepared employing ER5356 filler. With the same laser tilt angle, the IMCs layer of the joints prepared with ER4047 was thinner than that of the joints prepared with ER5356, implying the rapid growth of the IMCs welded via the ER5356 filler. The tensile strength exhibited by the former surpassed that of the latter. Employing the same filler metal, the average thickness of the IMCs layer of the joints with laser tilt angle of 10° was smaller than that of the joints with laser tilt angle of 20°. The strength of the joints with smaller tilt angle was better than that of the ones with bigger tilt angle. The tensile test outcomes revealed that there existed failure competition among the Al alloy base metal (Al-BM), weld metal (WM) and interface structure. If the interface structure was Fe–Al IMC with high brittleness, the cracks propagated along the interface, and finally fractured at the interface. If the interface structure was Fe–Al–Si IMC with good toughness, the crack propagation in the interface region could be hampered. In this case, the joint was prone to occur via WM failure or even Al-BM failure modes.

Практика впровадження методології ризик-аналізу експлуатації зварних металоконструкцій в Україні

Практика впровадження методології ризик-аналізу експлуатації зварних металоконструкцій в Україні

Development of a method for computer processing of fractographic images to assess the cohesion of inclusions to the matrix in the weld metal after its operational degradation and hydrogenation

In this paper, the method for automated processing of digital fractographic SEM images based on the modified local Otsu approach was developed. The effectiveness of the developed method was demonstrated. The method is used to identify inclusions or their traces at the bottom of dimples in weld metal fractures with subsequent assessment of their quantity. It is assumed that a decrease in the cohesion of inclusions to the matrix is one of the signs of damage to the weld metal at the microstructural level. Consequently, the more inclusions were found at the bottom of ductile fracture dimples, the stronger their connection with the matrix and, accordingly, the less damage in the weld metal. The effect of operational degradation of the weld metal on a circumferential weld on thick pipes of thermal power plant steam pipelines is analyzed. For this purpose, the features of cohesion of inclusions with the matrix in the weld metal in the initial state and after operation on the main steam pipeline for 23 years were compared. The influence of hydrogen (absorbed by the weld metal during long-term operation, as well as during its additional electrolytic charging) on the cohesion of inclusions in its structure with the surrounding matrix is also considered. A decrease in cohesion between these two components of the weld metal structure under the influence of all analized factors is shown. Thus, a method for quantitative assessment of fractographic features caused by the decohesion of inclusions from the matrix developed on the basis of analysis and computer processing of scanning electron microscope images, can be used to assess the operational damage of the weld metal at the microscopic level.

The Role of the Weld Metal Structure Formation in Selecting Rational Cooling Rates When Welding K80 Strength Grade Steel

The Role of the Weld Metal Structure Formation in Selecting Rational Cooling Rates When Welding K80 Strength Grade Steel

The technology of arc welding of dissimilar steels

Arc narrow gap welding of the 35L carbon cast steel (cast carbon steel J03502, grade 1) and the 110G13L high-manganese steel (austenitic manganese steel, ASTM A128) is performed using chromium-nickel-manganese wires in a shielding gas mixture (GOST R ISO 14175–2010 – M21). The welded samples are examined by different methods including optical metallography, hardness measurement, and mechanical tests. The weld metal structure along the weld height in the welded samples proves to be fairly uniform, namely austenite with ferrite inclusions. The experiment results show that the mechanical properties of the weld metal correspond to the intermediate values for the joined steels. The developed technology has made it possible to produce a welded joint with high mechanical properties and a ductile structure.

Fractal evaluation of grain boundaries branching in the structure of weld metal of low-alloy steels

Fractal evaluation of grain boundaries branching in the structure of weld metal of low-alloy steels

Methods to reduce residual welding stresses in mining excavator metal structures

Residual stresses in metal structures of mining machinery caused by welding occur due to simultaneous uneven heating and cooling of local sections of structures, variable cooling rates in the different areas of the weld and deformations caused by metallurgical phase transformations. Residual stress in the welded joint can significantly increase the external load that can lead to structural failure. Research on the calculation, measurement and relief of residual stresses under welding is an important issue when predicting the service life of metal structure units of mining machinery and equipment. An accurate quantitative estimation of residual stresses in welded products, repair welds included, as well as the search for the fundamental principles of the elimination methods of residual deformations are of considerable practical interest, which is relevant for the authors of this paper. The study involved a general review of the latest researches in the field of estimation and measurement of residual stresses caused by electrogas welding. It has been proposed to use various techniques and analytical methods for quantitative estimation of welded joint residual stresses on the basis of fracture mechanics, which enabled to take preventative measures at early stages to reduce the cost of repair and maintenance of welded metal structures of mining excavators. The conducted study resulted in formulating the proposals on relief of residual welding stresses in the metal structures of mining excavators.

Improving the Safety of Operation of Overhead Cranes with Welded Modular Construction Based on the Analysis of Their Accidents

Introduction. The article presents an analysis of the destruction of welds that occurred during the operation of modular overhead cranes. Measures are proposed to prevent the occurrence of such defects in the future, reduce the likelihood of accidents and improve the safety of operation of overhead cranes with a welded modular construction. The relevance of the work is due to the fact that in the Russian Federation approximately 65% of the lifting cranes registered with Rostechnadzor have fulfilled the standard service life.The work objective is to improve the safety of operation of modular overhead cranes and the reliability of their welded metal structures. Achieving the objectives of the work, based on the analysis of the destruction of metal structures of overhead cranes, a diagnostic map of welded joints of metal structures of end beams with modules of travelling wheels of overhead cranes was compiled. The use of the proposed diagnostic card in a production environment will significantly improve the quality of diagnostics of welded joints.Materials and Methods. Investigations of accidents of load-bearing metal structures of cranes by methods of technical diagnostics of destruction of welds that occurred during the operation of overhead cranes of modular design have been carried out. This made it possible to develop a number of measures to prevent accidents of overhead cranes initiated by the destruction of their welded modular structures.Results. Based on the analysis of accidents, a diagnostic map of destructing welded joints of metal structures of end beams with modules of travelling wheels of an overhead crane has been compiled. The use of the proposed diagnostic card will increase the reliability of welded metal structures and improve the quality of diagnostics of welded joints in production conditions.Discussion and Conclusions. As a result of the analysis of structural failures of modular overhead cranes, a number of measures are proposed to prevent the formation of such defects, the occurrence of accidents due to them, and to improve the safety of operation of overhead cranes.

Влияние технологических параметров на структуру металла изделий, полученных методом прямого лазерного выращивания из титанового порошка ВТ6

Direct laser deposition is an efficient approach to manufacturing or repairing a range of metal goods. The process involves creating a three-dimensional solid object layer by layer. The weld metal structure primarily affects mechanical properties of the deposited parts, making it important to establish the specifics of microstructure formation. We analysed the microstructure of VT6 alloy samples deposited on a substrate forged from the same VT6 titanium alloy. Different modes of deposition and subsequent heat treatment resulted in samples with differing structures. We established characteristic features of microstructure formation for all modes. We investigated the effect of heat treatment on the sample structure after laser welding in the initial state and after heat treatment. The results obtained may help reduce the cost of repairing and manufacturing titanium alloy parts for gas turbine engines.

Texture, microstructure and mechanical properties of laser beam welded AISI 2507 super duplex stainless steel

This study investigates weldability of AISI 2507 super duplex stainless steel (SDSS) sheets with laser welding. The impact of heat inputs and post-weld heat treatment (PWHT) on the mechanical properties, texture, microstructure and the surface of joints were analyzed. The microhardness and tensile strength values of the samples welded with the lowest weld heat input was detected to be greater than samples welded with the high heat input. The highest values for tensile strength, bending force and impact toughness in welded samples have been identified as 891 MPa, 1092 N and 58.4 J respectively. The effect of PWHT caused a decrease in the hardness and tensile strength of all samples, and improved the toughness and ductility properties. While dislocations and stacking faults were observed in the base material microstructure, twinning formation was also detected in the weld metal. Secondary austenite (γ2) and Cr23C6 carbides were also found after heat treatment. Variations in the coincidence site lattice (CSL) boundary proportions and the Schmid factors (SFs) directly affected the mechanical properties. In the 2D- and 3D-orientation distribution function (ODF) base material and weld metal maps, the δ-ferrite and γ-austenite textures performed high-density γ-fiber and α-fiber orientations and a low-density (110) <110> rotated cube component, and showed high-density γ-fiber and low-density α-fiber RD//<110> orientations after heat treatment. When the orientation relationships of the heat-treated sample were examined, Kurdjumov–Sachs (K–S) and Nishiyama–Wassermann (N–W) relationships were determined between the γ/α phases in the base material and weld metal, in addition to these orientation relationships, a occasionally seen (100)γ//(100)α Bain orientation relationship was also found in the non-heat-treated sample. The atomic concentrations of the non-heat-treated and heat-treated weld metals exhibited an increase in the O1s spectrum and decreases in the Ni 2p, Fe 2p, Mo 3d and Cr 2p spectra with increasing sputtering time. Diffusion of H− ion with low density to ferrite and austenite grains on weld metal structure was observed.

Structure, defect substructure and fracture surface of low-carbon alloy steel welds

By the methods of scanning and transmission electron microscopy a structural phase state, defect substructure and fracture surface of low carbon alloy steel welds produced with use of carbon-containing addition and without it are investigated. The study of etched metallographic section structure of welds revealed a presence of a large amount of second phase particles (carbides, sulfides, oxides, etc.). It is shown that in weld with a carbon-containing addition the particles locate chaotically, and in weld without addition they decorate boundaries of ferrite grains. Dimensions of second phase particles vary in the limits from 0.8 &mu;m to 5 &mu;m and are identical for both types of welds. Analysis of fracture surface structure of welds is carried out. A presence of nonmetallic inclusions is detected. They are typical of mainly weld produced without a carbon-containing addition which may indicate its increased brittleness. Amount of micropores in fracture of weld with carbon-containing addition is many times greater than that in weld without addition, which is indicative of gas removal in use of carbon-containing addition. The quantitative analysis of structure and dislocation substructure parameters of weld metal is carried out, the estimates of contributions of scalar and excess dislocation density to strength of welds are performed. It is shown that higher values of scalar and excess dislocation density in the weld formed without carbon-containing addition in flux may be responsible for material embrittlement. A large quantity of stress concentrators in the weld without carbon-containing addition may result in material embrittlement.

PERFORMANCE CHARACTERISTICS OF NICKEL-CONTAINING STEEL STRUCTURES DURING MECHANIZED WELDING-SURFACING WITH MODIFIED (DOSED) ELECTRODE WIRE FEEDING

Purpose. To study and analyze in a comparative order the influence of factors of the controlled pulse process of electrode wire supply on some basic mechanical characteristics of seams and welded rollers in the processes of welding and surfacing of nickel-containing steels.&#x0D; Methods of research. The study the mechanical characteristics of seams and welded rollers was carried out using modern laboratory equipment and appropriate techniques. This made it possible to determine how the pulse feed parameters affect the strength characteristics of the weld and near the weld zone over the entire cross-sectional area of the weld or weld layer. Detailed characteristics of feed pulses were determined using a welding process analyzer to obtain oscillograms of power parameters of arc combustion with their analysis, including determining the stability of the arc process for different types of pulses. Important for the improvement of welding results is the controlled nature of the electrode metal transfer synchronous with the pulsed movement of the electrode. It is noted that the energy consumption of the arc process during the pulse supply of the electrode wire with an indication of its reduction compared to traditional welding.&#x0D; Experimental work was performed using a special electrode wire, which is usually used for welding and surfacing of nickel-containing steels. These processes were carried out in a protective environment of CO2 in automatic mode.&#x0D; Results. Due to the fact that the strength characteristics of the weld are among the most important, attention is paid to their definition and analysis. The strength characteristics depend on many parameters, in particular the thermal characteristics of the process, the structure of the weld metal, the presence of non-metallic inclusions and so on. All these factors were studied with the help of appropriate instruments, and on the basis of numerous comparative photos of microstructures on sections of the cross section. The analysis of the sections revealed the types of microstructures obtained, the presence of inclusions and more. It is determined, in particular, that the structure of weld metal in pulsed electrode wire welding differs significantly from the structure of traditional welding in reducing inclusions, finer grains, etc., which improves the mechanical properties of the weld and seam area.&#x0D; Scientific novelty. Based on a series of experimental studies, the use of pulse algorithms for the movement of the electrode wire with certain parameters in automatic mode for welding and surfacing of nickel-containing steels to improve the mechanical properties of seams and welded rollers.&#x0D; Practical value. It is determined that the method of pulse welding of electrode wire to the controlled variant, including nickel-containing steels is effective and can be widely used in industry using specially designed equipment that provides a suitable process with stronger characteristics.

Investigation of processes in spark gap during contact butt welding of railway rails

Modern equipment for contact butt welding of railway rails has a huge number of technological parameters (input factors) that affect the quality of the resulting welded joint. These parameters do not allow the optimal welding modes to be fully selected. The study of the processes occurring in the spark gap (formation of microcontacts, increase or decrease in their cross-sectional area, explosion of the resulting microcontacts) will make it possible to determine the amount and uniformity of the invested heat during rail welding. The acquired knowledge will reduce the number of influencing factors on quality of the welded joint. Using a large amount of statistical data, the authors have investigated the processes occurring in the spark gap during contact butt welding of railway rails of R65 type of DT350 category on K1000 rail welding machine. When studying the influence of movable plate movement of the welding machine during reflow on the strength of welding current, it was determined that there is no dependence between these values. The random nature of distribution of the welding current values is assumed, changing as a result of the processes of formation, existence and explosion of a large number of tiny electrical contacts. Based on the analysis of frequency distribution, it is certain that distribution of the spark gap resistance does not correspond to the normal distribution law. As the sample increases, the deviation from it increases; visually the histogram describes the gamma distribution. With the help of the gamma distribution law, the welding current forces during contact butt welding were modeled by reflow. The research results are planned to be used to simulate thermal processes and formation of the structure of weld metal and the zones of thermal influence of railway rails welded joint.

Influence of Welding Regimes on Structure and Properties of Steel 12KH18N10T Weld Metal in Different Spatial Positions

Influence of Welding Regimes on Structure and Properties of Steel 12KH18N10T Weld Metal in Different Spatial Positions

An experimental investigation on the effect of gas tungsten arc welding current modes upon the microstructure, mechanical, and fractography properties of welded joints of two grades of AISI 316L and AISI310S alloy metal sheets

In this investigation, dissimilar welded joints of AISI 316 L and AISI 310S stainless steels were produced using continuous and pulsed modes current of the gas tungsten arc welding process. A filler metal type ER309L was used to strengthen the welded joints. The fracture mode of the tensile and Charpy impact test samples was studied using a field emission scanning electron microscope (FE-SEM). Results showed that the welded joints were broken in the 316 L steel side during the tensile test due to the presence of lower alloying elements in this steel compared with the AISI 310S stainless steel. As well, microhardness and Charpy impact tests results showed that changing the welding current from continuous to the pulsed one increased the values of these two mentioned attributes. Fractography analysis, performed on the fracture surfaces of both joints, showed a completely ductile fracture under both tensile and Charpy impact tests. Moreover, microstructural observations showed that the weld metal (WM) structure was austenitic-ferritic (AF) and contained columnar and equiaxed dendrites. Changing the welding current from the continuous to the pulsed one led to the transformation of the columnar dendrites to the very fine equiaxed dendrites. This welding current variation reduced the dendrite size of the WM and decreased the area of the unmixed zone (UMZ). Finally, XRD results indicated that austenite was the predominant phase in the welded joints.