Welded Joints Of Structural Steels Research Articles

Thermal cycles, structure and properties of welded joints in structural steels during welding in extreme cold conditions

The article summarizes research on the thermal cycles, structure, and properties of welded joints made from low-alloy and low-carbon steels during arc welding in sub-zero temperatures. This review aims to analyze previous research to create solid recommendations for welding steel bridge structures during winter conditions. The results of a comparison of experimental measurements of thermal cycles of welding samples with different sizes made at room and subzero ambient air temperatures (down to minus 50 °C) are considered. It is shown that in small plates with dimensions of 200 × 250 × 10 mm, due to more intense heat reflection from the edges of the specimen, the thermal cycles of welding at different temperatures do not differ significantly. In more massive samples (sized 450 × 250 × 10 mm), an increase in the cooling rate of the overheated welded joint area is observed compared to room temperature welding. The impact of hydrogen on the development of cold cracks in low-alloy steels during welding at temperatures below freezing is examined. Metallographic analysis has revealed that the structural changes that occur during the welding of various steel grades are notably different and are influenced by the steel’s chemical composition as well as the thermal cycle parameters of the welding process. Dilatometric studies indicate that variations in the levels of alloying elements within different grades significantly influence the kinetics of austenite transformation. Therefore, to identify the best welding techniques for subzero temperatures, it is essential to consider not just how heat disperses in these conditions, but also the kinetics of phase changes and their effects on the structure and properties of the products resulting from austenite decomposition.

Application of local approaches to the assessment of fatigue test results obtained for welded joints at sub-zero temperatures

Several studies have found significant increase in the fatigue strength of welded joints of structural steels at sub-zero temperatures. This study addresses the research by investigating the applicability of local fatigue assessment methods to welded joints exposed to sub-zero temperatures. For this purpose, fatigue test results of two fillet weld details with weld toe and weld root failure are evaluated at a range of temperatures using a variety of structural hot-spot and notch stress approaches, then are compared to the nominal stress approach. Large differences in prediction accuracy are found for the analysed assessment methods and both failure locations.

Influence of low temperature on structure and impact strength of structural steels welded joints

The article is devoted to the study of the relationship between climatic conditions of construction, installation and repair during the operation of industrial technical systems and the structure and properties of welded joints of structural steels. It has been established that the main technological factor affecting the crystallization of the weld metal from the melt is the heat input transmitted by the heating source - an electric arc, during welding at all intervals of the formation of one-piece joints. The research results made it possible to justify the conditions under which the formation of one-piece compounds occurs. The frequency ranges of controlled heat input, that maintain a specified set of welded joints mechanical properties are determined.

Investigation of the structure of welded joints performed at negative ambient air temperatures

During welding, the ambient air temperature can significantly affect the obtained structures and mechanical properties of the welded joint. The given paper presents the results of the analysis of the structural and phase composition of welded joints obtained by the method of pulse-arc welding at a sub-zero ambient temperature. The effect of ambient temperature on the structure of the weld metal and the heat-affected zone during welding is investigated. The issue concerns structural low-carbon and low alloy steels. The microstructure is examined by scanning electron microscopy. The specifics of the effect of the modulation frequency of the welding current and the welding temperature on the microstructure of welded joints of structural steels of 09Mn2Si and St3sp grades are revealed. The present work allows conducting further research on the areas of the heat-affected zone, which will make it possible to evaluate their effect on the mechanical properties of the welded joint as a whole

Enhancement of the service life of welded metal structures by high-frequency mechanical peening

We generalize the results of investigations into the high-frequency mechanical peening of welded joints of structural steels of different strength grades and aluminum alloys. As a result, we show the high efficiency of using high-frequency mechanical peening for enhancing the fatigue resistance of welded joints of metal structures at the stages of their manufacture and operation.

Fatigue life prediction using two stage model for AISI 304L cruciform joints, with different fillet geometry, failing at toe

Reports in the literature indicate that the fillet geometry affects the fatigue properties of cruciform welded joints in structural steels. In an attempt to study the above effect with respect to stainless steel sheet metal welded joints, load carrying transverse fillet welded cruciform joints having a two fillet geometry were fabricated from AISI 304L stainless steel using gas tungsten arc welding and gas metal arc welding with 308L electrodes. The objective of the present work is to predict the fatigue life of AISI 304L cruciform joints failing at the weld toe using a two stage model. The local stress life method was applied to calculate the fatigue crack initiation life, whereas the fatigue crack propagation life was estimated using fracture mechanics concepts. Constant amplitude fatigue tests with stress ratio R ~ 0 were carried out using a 100 kN servohydraulic Dartec universal testing machine at a frequency of 30 Hz. An automatic crack monitoring system based on crack propagation gauges was used to obtain the propagation data during the fatigue process. The predicted lives were compared with the experimental values.

Cold cracks in welded joints of structural steels

The present survey is devoted to the investigation of a dangerous phenomenon (quite often observed in the process of arc welding) of the formation of hydrogen-induced cold cracks in welded joints of structural steels. We briefly analyze the existing models of the mechanism of hydrogen embrittlement. It is shown that difficulties in understanding the processes of initiation and growth of cold cracks are explained not only by the necessity of determination of the principal factors which govern the embrittling action of hydrogen but also by the absence of reliable knowledge of the microscopic mechanisms of fracture processes in metals. We suggest a new model of hydrogen embrittlement of metals with bcc lattice developed at the Paton Institute of Electric Welding. According to this model, atomic hydrogen adsorbed on the metal surface in the form of anions affects the surface energy of submicrocracks appearing in dislocation clusters in the process of deformation whose initial period of propagation obeys the classical Griffith scheme. The proposed model enables one to explain all known distinctive features of the cold cracking of welded joints and forms a groundwork for the physical simulation based the use of mathematical methods and aimed at the quantitative evaluation of the contribution of each factor to the indicated processes.

Characteristics of static and fatigue strength and of crack resistance of welded joints in structural steels at low temperatures. Communication 1

The article presents the results of experimental investigations of the effect of low temperatures (down to 77°K) on the resistance to static and low cycle deformation and rupture of steels 09G2S, 10KhSND, 06G2AF, 20KhGSA, 07Kh3GNMYuA, and ON6. It also presents the dependences of the theoretical characteristic of low cycle fatigue mTe of steels at low temperature under rigid loading on the index of ductility {ie022-01} under static loading and test temperatures down to 77°K.

Characteristics of static and fatigue strength and of crack resistance of welded joints in structural steels at low temperatures. Communication 2

Characteristics of static and fatigue strength and of crack resistance of welded joints in structural steels at low temperatures. Communication 2

Diagnostics of threshold characteristics of welded joints in structural steels

Diagnostics of threshold characteristics of welded joints in structural steels

Structural and mechanical heterogeneity of heat affected zone and impact toughness of welded joints in structural steels

Structural and mechanical heterogeneity of heat affected zone and impact toughness of welded joints in structural steels

Effect of high tempering on the structure and properties of the metal of the heat-affected zone of welded joints of structural steels

1. High tempering at 620–650°C with the object of reducing residual welding stresses leads to poorer strength characteristics of the base metal and of the metal of the HAZ of welded joints of steels VSt3sp, 09G2S, and 10KhSND and to increased plasticity; in steel with nitride strengthening 15G2AF the strength characteristics of the base metal and of the metal of the HAZ are somewhat improved, and plasticity is impaired. 2. The application of high tempering at 620–650°C does not increase the toughness of the metal of the HAZ of welded joints made with large heat input to steels VSt3sp, 09G2S, and 10KhSND. 3. In specifying high tempering for the purpose of reducing residual welding stresses, it is necessary not to be guided solely by the degree of reduction of the stress level but also to take into account the possible changes of the mechanical properties and of the toughness of the metal of the separate sections of the welded joints, and this also depends on the system of alloying the steel.

Low-cycle fatigue of welded joints of structural steels during the formation and propagation of cracks during biaxial bending

Low-cycle fatigue of welded joints of structural steels during the formation and propagation of cracks during biaxial bending

Low-cycle strength of welded joints in structural steels in a pulsating load cycle

Low-cycle strength of welded joints in structural steels in a pulsating load cycle