Reduced spheroidization in rail flash-butt welding by selective alloying

Abstract

Thermal cycle (welding simulations) at the inter-critical region were performed on an Si and V micro-alloyed (not heat-treated) rail steel. The beginning of austenitization temperature (Ac1) in the micro-alloyed rail steel occurred significantly above that observed in an alternative heat-treated rail steel. Very little pearlite alteration was observed until austenitization at a temperatures above 750°C, where there was a reduction in hardness and onset of spheroidization. The maximum spheroidization together with the lowest observed hardness occurred at 760°C. It was also observed that there is a linear correlation between hardness and volume fraction of spheroidization of cementite. By the dilatometric variation, contraction due to austenitization was observed only from 760°C onwards in the 60 s isothermal period at the austenitization temperature. These results may lead to a new approach to weldability and reduction of the softened region concerning rail welding.