This article is devoted to the following issues: calculating the values of temperatures obtained by simulating welding heating and the subsequent implementation of the welding process at the given mode parameters made it possible to obtain a welded joint of the rotor with an improved initial structure and increased mechanical properties, hydrogen resistance and durability by up to 10–15%; simulating welding heating in the areas of fusion, the overheating and normalization of the HAZ and the formation of austenite grains; specified welding heating creates the conditions for the formation of new products of austenite decomposition in the form of sorbitol in the area of the incomplete recrystallization of the HAZ. In air and gaseous hydrogen, the destruction of the combined joints took place on the weld metal, as well as on the fusion areas, the overheating and the incomplete recrystallization of the HAZ of 20H3NMFA steel as the base metal. Structural materials have a relatively low strength and high fracture toughness in air. This is manifested in a significant reduction in the elongation (δ), the area (ψ) and critical stress intensity factor (K_Ic) of welded joints and the endurance limit of cylindrical smooth rotor steel specimens, which were cut from transverse templates. Welded joints in the whole range of load amplitudes are sensitive to the action of hydrogen.

The effect of the metallurgical slags composition on their physical properties was studied employing the Directed Chemical Bonds Concept (DCBC). It provides an effective concentration and convolution of the ab-initio information on the type of bonds in multicomponent systems. The predictive models for viscosity (lnη) and electrical conductivity (lnχ) of CaF₂-Al₂O₃-CaO slag system have been built. Slag is a crucial part of various metallurgical processes. The electroslag remelting (ESR) is the best example because its efficiency and resulting ingot soundness strongly depend on slag properties. For the two slags (with 1.5 and 3% SiO₂), the condition of stable homogeneous structure (activation energies ratio Eη/Eχ ≤1) has been satisfied in the widest temperature range (1513–1773 K) with a suitable viscosity (0.02–0.09 Pa∙s) and electrical conductivity (100–270 1/Ohm∙m). The DCBC makes it possible to move from the empirical selection to the target-oriented design of a proper slag with specific physical properties.

The ironmaking and steelmaking industry is one of the heavy polluters responsible for nearly 7% of global carbon dioxide and greenhouse gas (GHG) emissions. Creating new technologies and equipment and renewing the assortment of metallurgy products is compulsory to achieve the goal of climate change prevention. Lightweight and advanced higher-strength steels (AHSS) to replace old mild grades and simultaneously decrease the mass of ready products is one of the efficient ways. Three generations of AHSS of different chemical compositions and properties have already been developed, including lightweight grades alloyed with a high aluminium content. A review of the Life Cycle Assessment (LCA) results proves the energy and environmental efficiency of Advanced High Strength Steels (AHSS) compared with aluminium and HSS for the same purpose structures in vehicles. Using aluminothermic ferroaluminium from secondary materials helps to reduce the cost of lightweight steels with high aluminium content due to the 2-3 times higher assimilation of aluminium by liquid steel at both deoxidation and alloying, which was experimentally proved for HSS grades. Due to less energy consumption at ferroaluminium than secondary aluminium ingots manufacturing, alloying of AHSS (10% wt of Al) by FeAl30 reduces GHG emission for more than 0.384 t CO2-eq per ton of steel.