Study of hardness distribution in a rail welded joint after welding with accelerated cooling

In order to improve parameters of rails and railroad wheels, it is necessary to examine new microstructures, new technologies for production and processing of rails. Pearlitic steels are widely used in the railroad industry worldwide, due to their good wear resistance and satisfactory impact strength, as well as due to their relatively low production cost. Mechanical properties of pearlitic steels are controlled by microstructure, which is created as a result of thermomechanical treatment, especially by such parameters as austenite grain size, interlamellar spacing in pearlite and dimension of a pearlite colony. Essential microstructural variations occur along the heat-affected area in the process of butt welding of rails. Significant variations of hardness and other mechanical properties in a metal welded joint are connected with cementite morphology. A soft area, which is observed in the heat-affected area of a welded joint and which is caused by cementite spheroidizing, leads to local hardness loss. The experimental results on evaluation of cooling rate influence in a rail welded joint on hardness in the heat-affected area are presented in this research. It was confirmed that variation of cooling rate influence in a rail welded joint finalizes in variation of spheroidizing tendency in the areas of lowered hardness.