Evaluation of the Effect of Heat Input and Cooling Rate of Rail Flash-Butt Welding using Finite Element Method Simulation

Avaliação do Efeito do Aporte Térmico e da Taxa de Resfriamento da Soldagem de Topo de Trilho por Meio de Simulação pelo Método dos Elementos Finitos

Abstract

Simulations using the finite element method (FEM) were done to understand the effects of heating/cooling rates on the distribution of residual stresses. Two material parameters from rails were used while the boundary conditions remained constant: heat-affected zone size, maximum temperature and heating extraction rate. To complement the analysis, a flash-butt weld of a Premium rail was done with welding parameters adjusted to obtain a narrow HAZ, without forced cooling, to examine the microstructure formed in the critical regions in the web and the edge of the rail foot. The results showed that there was a concentration of vertical residual stresses in the web region, while the presence of horizontal compression residual stresses was mostly superficial in the rail head region. The main result from the simulation sets was that when using two simulation parameters with similar materials (rails) substantially different results were obtained. Metallographic examinations showed that there was no presence of acicular microconstituents (martensite/bainite). In the rail web, proeutectoid ferrite was observed in the central region, cementite in a previous austenitic grain boundary, in the region that reached temperatures close to A_C3, and almost complete spheroidization in the region of maximum spheroidization. In contrast, in the rail foot edge region, there was a completely pearlitic microstructure, in the central region and in the zone that reached temperatures close to A_C3, and a lower volume of spheroidization in the region where maximum spheroidization is typically observed, probably due to the higher cooling rate in this region.

Keywords:
Rail; Welding; Flash-butt; FEM; Simulation; Residual stresses