COMPARATIVE STUDIES OF WELDED JOINTS OF RAILS AFTER VARIOUS HARDENING METHODS

Abstract

The paper studies changes in temperature and pressure during hardening using the factory and upgraded sprayer of the UIN cooling system. The hardness distribution was studied for one- and two-sided cooling. The analysis of the obtained results shows that the greatest decrease in hardness is observed at a distance of 50 mm from the weld center. These points are the heat-affected zone from the action of the inductor of the induction unit. According to the regulatory documentation, a decrease in hardness of up to 15% is allowed during heat treatment of a welded joint compared to the hardness of the base metal. The results were obtained after upgrading the induction unit cooling sprayer in terms of expanding the hole zone and increasing the diameter of the holes in the lower shelf of the sprayer. The hardness measurement results indicated the shortcomings of induction heating during local heat treatment with a one-sided air distribution system on an induction unit of the UIN-001-100/RT-S(P) type. It was necessary to modify the cooling sprayer design to increase the intensity of the compressed air flow and to ensure uniform distribution of the air flow velocity onto the rail head. Also, to achieve an air flow rate of at least 200 m/s in the upper hardening unit, it is necessary to change the compressor unit control system. The sprayer modification allowed to increase the intensity of the hardening device operation in the central area of the rail head and the heat-affected zone from the inductors. The modification of the upper hardening unit ensures uniform distribution of the air on the rolling surface of the head during hardening and uniform distribution of hardness in the central area of the head, in the areas of the rail fillets, in the transition zones. This will eliminate the defect of chipping and crushing of the rail head metal during the operation of welded joints.