The article describes the study of welding processes with the subsequent control of cooling of full-profile rail joints, produced by passing alternating electric current pulses after welding. The influence of welding modes on the quality of welded joint was investigated. Welding was carried out on a resistance butt welding machine MCP-6301 in conditions of the rail welding company LLC "RSP-M" (RSP-29). For research, the samples of P65 type full-profile rails of DT350 category 600 mm long were

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... t out. The isothermal holding conditions after welding were controlled using a personal computer with a change in the program of the SIMATIC S7-300 industrial controller and the software SIMATIC STEP 7, which allows modes of controlled cooling to be set. The control program was written in the LAD graphic language. To search for optimal modes of controlled cooling, a complete factor experiment N = 2k was carried out. Non-heat-treated joints were tested for three-point static bending according to the state standard STO RZD 1.08.002 – 2009 "Railway rails, welded by electric contact method". Static bending tests were carried out on the press of PMS-320 type. Values of the force arising during bending Pbend and the bend deflection fpr at which the control sample is destroyed, were determined, as well as maximum values of these indicators if the sample was not destroyed during the tests. During the experiments, regression models were obtained for output parameters of the bending force and bend deflection. Macrostructure of the samples and distribution of the metal hardness on rolling surface of the rails welded joint were studied. A new method of resistance butt welding was developed, which makes it possible to obtain a welded connection of P65 type rails of DT350 category with properties that exceed the technical requirements of the mentioned state standard.