Justification of obtaining fine-grained structure of welded joints at high-intensity impulse effect on welding circuit

Abstract

An effective method of improving the reliability of operation of thermal and nuclear power facilities is to improve the quality of manufacture, installation and repair of their thermal and generating power equipment. One of the ways to improve the quality, technological and service properties of welded joints in the process of their implementation is to influence the structure of the crystallizing metal by thermal, electric high-intensity impulse effect for its grinding. This work proposes the results of an experimental study to substantiate the production of a fine-grained structure of welded joints obtained using manual arc welding with coated electrodes at a high-intensity impulse effect (QPS) with a fi.g.= 40×103 Gts frequency, voltage Ui.g.= 80.0 V, on the welding circuit. The energy characteristics of the process can be used to assess the effect of high-intensity impulse action on the welding circuit, including the arc plasma and the structure of the resulting weld. As the energy characteristics of the welding process, the welding current Iwd, the voltage on the arc discharge Ud, the power Rp. Oscillograms of the specified characteristics were obtained, as well as the values of the maximum (peak) and average power released in the welding circuit when QPS is exposed to it and without its use were determined. Energy evaluation of input of additional high-intensity pulse effect on welding circuit as ultrasonic energy for cavitations of surface layer of welding bath at QPS was performed. Direct current arc discharge at application of high-intensity pulse effect with frequency of fi.g.= 40×103Gts (QPS) is source of cavitations of liquid phase of metal of welding bath in limited surface layer of preset thickness. It can be assumed that the crystallization of the bath takes place in layers when the welding circuit is subjected to high-intensity pulse exposure with a frequency of fi.g.= 40×103 Gts (QPS). In this case, the growing crystals break when the liquid phase oscillates due to friction forces arising between the moving liquid phase and the growing crystal. At the site of crystal fracture, zones of dynamically super cooled metal are formed, which leads to the appearance of new crystallization centers, and a fine-grained structure of the weld appears.