Development and Modeling of Welding Differentially Heat-Strengthened Railway Rails. Laboratory Studies

In this paper, we study the effect of welding modes with subsequent isothermal exposure on the quality parameters of the welded joint under laboratory conditions using rail steel samples. Welding of the samples was performed by passing pulses of alternating electric current after welding. Welding was carried out using an MS-2008M resistance butt welding machine with several changes in the control actions. Chromel–alumel thermocouples were used to measure the metal temperature in the heat-affected zone (HAZ). The collection and processing of data from thermocouples was performed using the “Tempol” measuring complex. The temperature of the metal of the welded seam (where it is not possible to install a thermocouple) was measured using a HotFind-D thermal imager. Experimental results and physical and mechanical properties of samples: hardness HB, HAZ length, yield strength, ultimate strength, relative elongation, relative narrowing, and presence of non-metallic inclusions in weld metal are presented. The calculation of hardness deviations (decrease–increase, total deviation) on the surface of the welded joint of the samples was carried out in relation to the requirements established by GOST R 51685–2013. A resistance butt welding method that allows obtaining a welded joint of products from rail steel with a uniform distribution of hardness and a small HAZ is proposed. The dependence of microhardness on the volume fraction of structural components was determined. The effect of the parameters of pulse contact post-weld heating on the decrease in the hardness of the welded joint metal relative to the hardness of the base metal and on the length of the HAZ are modeled. The proposed method allows regulating the metal structure of the welded joint of the rails without resorting to additional local heat treatment.