A study and development of technology for surface induction hardening of railroad rails from low-alloy steel

Abstract

A technology of heat treatment of railroad rails using induction heating has been developed and installed in the Azovstal' metallurgical works. It provides the requisite combination of properties in the metal of rail heads. However, the metal of the web and the bottom of the mils remains in the initial (unhardened) state. Under severe operational conditions (small-radius curves, high axial loads, and composite configuration of the road) the wear resistance of the head and the structural strength of the web and the bottom not hardened in the plant have to be increased. The properties of the rail steel can be improved by alloying it using the most effective and available elements. Currently, in Ukraine this is manganese. The present paper is devoted to the effect of manganese additives on the phase transformations in induction hardening and the specific features of the formed structure and properties of the rail steel. Optimum parameters for heat treatment of rails are recommended.The international standards VIC 860 and ISO 5003 envisage up to 1.7% manganese in the composition railroad steels, but under the condition of special welding of rail sections and use in an unhardened state.The Azovstal' plant has decided to organize production of railroad rails from carbon steel of a standard composition having an elevated content of manganese (0.95 -1.3%) and microadditives of vanadium (0.03-0.07%) and titanium (0.007-0.025%) with hardening the surface from induction heating.In order to provide head properties corresponding to the specifications, special treatment regimes had to be developed for each change in the chemical composition of the steel.We studied two rail steels, the chemical composition of which is presented in Table 1.Azovstal" Metallurgical Works, Mariupol, Ukraine; Kharkov State Engineering University of Agriculture, Kharkov, Ukraine.Based on the results of a dilatometric study we determined the critical points in rapid heating (Vh = 8 K/sec) to 900~ and in cooling at a rate v c = 3 K/sec (Table 1).In order to develop an optimum regime for induction heating of heads from steel I we studied the pearlite-austenite transformation in rapid heating (v h ___-8 K/sec) determining the temperature of full homogenizing of austenite and the depth of induction heating of the head at which the pearliteto-austenite transformation completed fully.The degree of the saturation of the y-solid solution by carbon and the alloying elements in heating of the steel agrees sufficiently well with the variation of the coercive force H c and the hardness (Fig. 1).Analyzing the data of Fig. 1 we see that after quenching from 760~ Hc grows jumpwise from the initial value (H~ = 20 mA/m) to a maximum (Hc m~x = 78 mA/m). In the temperature range of760-870~ H~ diminishes insubstantially and then stabilizes at a level of 70 mA. The variation of the hardness occurs more smoothly than H~ (Fig. 1). The maxi-

Optimisation Design of a Low-Frequency Eddy Current Rail Heater

“…Eddy current rail heaters have been widely used for preheating railroad tracks to prevent them from cracking due to thermal stresses [17,18]. The principle behind these heaters is based on the induction of eddy currents in the rail tracks, which generate heat due to the resistance of the metal [19][20][21][22]. This heat helps to reduce the temperature differential between the rail and the surrounding environment, thereby reducing the thermal stresses.…”