| Popis: |
The process of operation of vehicles is determined by the interaction of the wheel and rail. The result is the effect arising from the friction of rolling and especially from the friction of the wheel sliding on the rail during braking, in relation to these changes there is a significant increase in the intensity of wear of the wheels of rolling stock. Based on research in recent years, it is known that the strength of pearlitic rail steels has reached its limit. Based on the literature analysis, steels used in world practice for the production of railway rails from bainite were identified and compared with the chemical compositions of steels used in various fields in Ukraine. In order to determine the influence of basic chemical elements through known isothermal (TTT) diagrams and the actual chemical composition on the formation of the structure with the subsequent construction of thermokinetic (ССТ) diagrams. A promising approach is to increase resistance through the manufacture of railway rails with bainitic structure. The regularities of the decay kinetics of austenite grade 30HGS with 0.28% C, 1.49% Si, 0.92% Mn, 0.99% Cr were studied by the method of mathematical modeling. The intervals of cooling rates, within which the change of the mechanism of structure formation at austenite decay is observed, are determined. It is shown that at the cooling rate up to ~ 3°С/s the decay of austenite occurs with the formation of pre-eutectoid ferrite and perlite; at 3°C/s... 10°C/s the steel structure consists of pre-eutectoid ferrite, perlite and bainite; at 10°C/s ... 20°C/s - from pre-eutectoid ferrite, perlite, bainite and martensite; at 20°C/s ... 30°C/s - from bainite and martensite; at a cooling rate of 50°C/s the decay of austenite occurs with the formation of martensite. The critical cooling rate for the investigated steel is in the range of 30… 50ºС/s. The chemical composition of experimental steels for railway rails was developed and ingots smelting up to 10 kg were smelted in the laboratory. |
