Influence of deformation degree of austenitic steels welded joints on structural state and internal stresses felds in weld line zone

Nowadays initial assessment of welding quality is performed by testing equipment with increased loads (high pressure) at technical devices of hazardous production facilities. Test requirements are regulated by standardized documents of the Federal Service for Environmental, Technological and Nuclear Oversight of Russia (Rostekhnadzor). Recently, along with traditional tests, a “stress test” was used – the essence of which is to load pipeline section to the yield point, followed by leak test. However, in scientifc publications there is practically no information about physical processes occurring in the base metal and in welded joints during such tests. In addition, effect of preload (deformation) on the parameters of substructure and internal stresses feld in welded joints of austenitic steels and, consequently, on the further trouble­free operation of the tested equipment was not evaluated. The paper analyzes changes in structural state and values of internal stresses in the samples of austenitic steel under the action of high loads. It substantiates the use of modulated current welding with automatic control of heat input process in molten weld pool. The admissible limits values of plastic deformation are argued when testing technical devices with high pressure for this type of steel. In order to reduce the risk of damage to austenitic steels welded joints of technical devices of hazardous industrial facilities, performed by pulsed welding with small­drop transfer, and to exclude formation of microdefects in them, high pressure tests (stress test) can be performed under loads that create deformations in metal, not exceeding 5 %. For joints welded by manual arc welding, deformations should be less than 5 %. Welded joints made by pulsed welding with large­drop transfer (with and without defects) are not recommended to be tested with high pressure.

INVESTIGATION OF THE INFLUENCE OF TEMPERATURE INCREASE ON THE STRUCTURAL STATE OF LOW-CARBON LOW-ALLOY STEEL

Problem statement. The development and implementation of low-carbon low-alloy steels of high strength in the structural elements of blast furnaces, which will operate in conditions of heating to high temperatures is an urgent problem and can give a significant effect during the operation of buildings and structures.. Purpose of the article. establishing changes in the structural state of low-carbon low-alloy steels depending on the temperature rise. Conclusion. Conventionally, the temperatures at which the studied steels can be operated can be divided into two levels: the temperature below which no significant structural changes are detected; temperature at which significant structural changes are observed, which lead to a decrease in the reliability of structures. The presence of two levels associated with both the development of diffusion processes and the ability of the structural state to resist the effects of temperature stresses (structural stability). The structural stability of steel with increasing temperature is due to the processes that bring the system closer to the position of thermodynamic equilibrium compared to low temperature (structural state at room temperature), which is usually optimal in terms of performance. Such changes include the processes of recrystallization, coagulation of secretions and other phase transformations that lead to changes in the macro- and microstructure that impair the performance properties of the material. At relatively high temperatures, these processes occur at a significant rate, as a result of which they are crucial in limiting the possibility of using this material.