Integrated Assessment of Weldability of Steel with Increased Strength

Modern production of agricultural equipment and facilities, hulls of ships, stationary oil drilling platforms, wind energy installations and other metal structures makes extensive use of sheet steel of increased strength. The main manufacturing process is welding, the quality of which depends on multiple factors, including the ability of steel to resist welding. It is known that the properties of the thermal influence zone are highly dependent on phase transformations, the nature of which is determined by the intensity and development of diffusion processes of carbon redistribution and alloying elements under the impact of the welding thermal cycle. Therefore, it is necessary to evaluate the weldability of the steel of a certain chemical composition, in order to choose the optimal method and the technological parameters of the welding mode for the manufacture of a specific metal structure. In order to reduce material costs, you can use analytical calculation methods that were developed at the E.O. Paton Electric Welding Institute. They are based on the analysis of the literature and the study of about 150 diagrams of the thermokinetic decomposition of austenite. Mathematical models make it possible to predict with a sufficient degree of accuracy the phase composition and mechanical properties of the high-temperature thermal influence zone depending on the chemical composition and cooling time of the metal, heated to a maximum temperature of 1350ºC, in the temperature range 850-500ºC. However, such tests are quite expensive and do not allow optimization of weld properties when the welding mode, mode, welding materials and other underlying technological factors change. In this connection, the objective was to assess the reliability of the proposed methodology in the study of weldability of shipbuilding steel of the increased strength of the category E36, for the weakest T(transverse) – the orientation of the sheet of 50 mm thickness. A high performance of the steel category is achieved by a limited increase in the aluminium content or other grain-crushing elements (Nb, V, Ti), which ensures that the size of the austenitic grain is not greater than the fifth point. The research showed that analytical methods for calculating the mechanical characteristics of high temperature HAZ sites by chemical composition, taking into account the cooling rate after welding, provide a level of confidence sufficient for practical application and can be recommended for the primary evaluation of the properties of welded compounds of high-thickness steel plates of category E36 (T-orientation). The impact work (KV-40) of the high-temperature sections of the high-temperature thermal influence zone is not subject to an analytical evaluation with the degree of accuracy required for production practice