Methodology for the Study of Residual Temperature Stresses in the Butt Contour of a Welded Joint Made of Carbon and High-Alloy Structural Steels during Multi-Pass Welding

The method of investigation of residual temperature stresses in the butt contour of the welded joint "shell – plate" made of carbon and high-alloy structural steels during multi-pass welding is described. The temperature problem was solved on the basis of the obtained experimental data of temperature measurement at the reference points of the structure during the application of the rollers. A solution is proposed that takes into account several stages, each of which corresponds to a specific intermediate temperature field due to the peculiarities of welding technology. The evaluation of residual stresses was carried out on the basis of the energy theory of plasticity, taking into account the dependences of the yield strength and elastic modulus of welded metals on temperature.

Microstructure and Mechanical Properties of Welded Joints of 1.4462 Duplex Steel Made by the K-TIG Method

K-TIG (Keyhole Tungsten Inert Gas) method is a new, emerging welding technology that offers a significant acceleration of the joining process, even for very thick plates. However, its potential for welding of certain materials is still unknown. Particularly challenging are duplex steels as this technology does not allow the use of a filler material, which is crucial for these steels and for weld joint microstructure adjustment. In order to demonstrate the suitability of this technology for single-pass welding of 1.4462 duplex steel detailed studies of the microstructure of the weld joints obtained for different linear energies were carried out and discussed with respect to their mechanical properties. According to the results obtained, the heat-affected zone (HAZ) shows a microstructure similar to the HAZ of duplex steel welded with the traditional TIG multi-pass methods. However, the weld, due to the lack of filler material, had a microstructure different to that typical for duplex steel welded joints and was also characterized by an increased content of ferrite. However, all joints, both in terms of microstructure and mechanical properties, met the requirements of the relevant standards. Moreover, the K-TIG process can be carried out in the linear energy range typical of duplex steel welding, although further optimization is needed.

Prerequisites for developing an advanced welding technology for repair of worn elements of steam-conducting systems

The main disadvantage of standard technologies of welding steam pipelines of thermal power plants is that they can allow the presence of defective structures close to the defective ones in the metal of the seam and in the sections of the HAZ. In this regard, the question arises about the development of a new technology that will provide the appropriate structure and properties that will increase the service life of steam pipelines and get a significant economic effect. Goal. The goal is improvement of the technology of welding pipelines of thermal power plants based on the study of the features of the formation of welded joints operating in Creep conditions. Methodology. The level of wear of the elements of the Steam-conducting path was estimated taking into account the provisions of the regulatory documentation of metallographic analysis, determination of chemical composition and properties, as well as the degree of their deformation. Results. It is revealed that welded joints are characterized by initial structural heterogeneity, which is closely related to long-term strength, ductility and impact strength. For example, at different sections of a welded joint, there is a different intensity of transition of alloying elements and, accordingly, a different type of structural component can be formed. The proposed technology of welding repair of damaged elements of steam pipelines using mechanized welding in CO2+Ar provides for the production of welded joints with a higher level of uniformity of structure, chemical composition and properties. Scientific novelty and practical significance. The welding technology has been improved, which includes developing the modes for performing repair work by mechanized welding in an Ar + CO2 environment of steam pipeline samples with a depth of ≥ 20 mm and a width of ≥ 30 mm, and differs from the known ones by using linear energy welding of 1.2–1.5 MJ/m.

Acoustic methods in real-time welding process monitoring: Application and future potential advancement

The rapid advancement of the welding technology has simultaneously increased the demand for the online monitoring system in order to control the process. Among the methods that could be possibly used to assess the weld condition, an air-borne acoustic method grasps the attention from scholars due to its ability to provide a simple, non-contact, and low-cost measurement system. However, it is still lack of resources involving this subject in an attempt to deeply understand the emitted sound behaviour during welding especially when dealing with a complete deviation of a process parameter, welding types, workpiece material as well as the noise from the surrounding. This paper reviews the application of the acoustic method in monitoring the welding process. Specifically, this review emphasized the source of both structure-borne and air-borne acoustic during the welding process and the significance of applying the acoustic method in more detail. By focusing on the liquid state welding process, the scope of discussion converged on the arc and laser welding process. In the last part of this review, the potential future advancement of this method is pointed out before the overall conclusion is made.

Characteristics of six layered Al/Si3N4 functionally graded materials prepared through two-step pressureless sintering process

The rapid advancement of the welding technology has simultaneously increased the demand for the online monitoring system in order to control the process. Among the methods that could be possibly used to assess the weld condition, an air-borne acoustic method grasps the attention from scholars due to its ability to provide a simple, non-contact, and low-cost measurement system. However, it is still lack of resources involving this subject in an attempt to deeply understand the emitted sound behaviour during welding especially when dealing with a complete deviation of a process parameter, welding types, workpiece material as well as the noise from the surrounding. This paper reviews the application of the acoustic method in monitoring the welding process. Specifically, this review emphasized the source of both structure-borne and air-borne acoustic during the welding process and the significance of applying the acoustic method in more detail. By focusing on the liquid state welding process, the scope of discussion converged on the arc and laser welding process. In the last part of this review, the potential future advancement of this method is pointed out before the overall conclusion is made.