Welding of differentially heat-strengthened rails. Modeling of processes during welding and local thermal processing

Problem of generation of local hardened areas in weld metal d ing rails welding in production of continuous welded rails is solved by using local heat treatment of weld joint. As a result, appearance of quenching structures is excluded. However, new zones of thermal influence with reduced hardness may appear. During operation, such rails are characterized by increased wear of the rolling surface in these areas and collapse of the head at welded joint. It is the main reason for removing rails from the track earlier than time guaranteed. Application of new technology based on dependences of dispersion degree of the structural components (primarily perlite and carbide particles formed during obtaining welded butt joints of rails) on steel composition and rails cooling conditions is proposed. Cooling rate has a decisive influence on the degree of dispersion of ferritic-cementite structure formed during decomposition of austenite. When welding rails in a butt weld, generation of granular perlite is possible in the areas with temperature between Ac₁ and Ac_m points. To determine these critical temperatures, thermodynamic calculations were performed using Thermo-Calc^® software (TCFE database) taking into account chemical composition of the samples obtained by spectrometry. Fe – C state diagrams for 76KhSF rail steel were modeled with the minimum and maximum content of alloying elements according to the state standard GOST R 51685 – 2013. To obtain minimal volume of sections with reduced hardness, it is possible to conduct rails welding in hard conditions by electrocontact method using pulsating reflowing. To prevent formation of defective sections with quenching structure, it is possible to control cooling of welded joint using contact heating. Measurement of the temperature distribution during welding according to the given modes and controlled cooling confirms theoretical conclusions.

rails, contact welding, heat treatment, current, impulse, welding mode, hardness, heat affected zone

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