Welding of differentially heat-strengthened rails. Laboratory studies

In laboratory conditions, influence of modes of welding with subsequent isothermal holding on quality parameters of welded joint was studied on rail steel samples. Samples were welded with pulses of alternating electric current after welding. Welding was carried out on MS-2008M resistance butt welding machine with a number of alterations of control actions. To measure temperature of the metal in heat affected zone (HAZ), chromel-alumel thermocouples were used. Collection and processing of data from thermocouples was carried out using TEMPOL measuring complex. Temperature of the weld (where it is not possible to install a thermocouple) was measured using HotFind-D thermal imager. Experimental results and physicomechanical properties of the samples are presented: HB hardness, HAZ length, yield strength, tensile strength, ultimate elongation, contraction ratio, and presence of non-metallic inclusions in weld metal. Deviations of hardness were calculated in comparison with the requirements established by GOST R 51685 – 2013 state standard on the surface of samples’ welded joints: decrease-increase and total deviation of hardness. Method of resistant butt welding is proposed, which makes it possible to obtain welded joint of items produced of rail steel with a uniform distribution of hardness and small zone of thermal influence. Dependence of microhardness on volume fraction of structural components was determined. Models of impact of pulsed contact post-welding heating parameters on lowering hardness of weld metal compared to the base metal and on the extent of heat-affected zone were constructed. The proposed method allows us to adjust structure of metal welded joints of rails without additional local heat treatment.

рельсы, контактная сварка, термическая обработка, ток, импульс, режим сварки, твердость, зона термического влияния

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