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

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 AC3, 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 AC3, 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.

Numerical Investigation of Residual Stress Formation Mechanisms in Flash-Butt Welded Rail

“…According to the AREMA recommendation [18], flash-butt welding is controlled to minimize the amount of martensite in any rail region. Also, the findings of both Skyttebol et al [10] and Pereira et al [16] reveal no major change in the hardness and microstruc-ture of the heat-affected zone (HAZ). Thus, phase transformation is not considered in the present numerical investigation.…”

“…They found that the rapid quenching before the complete austenitepearlite transformation can increase the tensile residual stress. Pereira et al [16] performed a metallographic examination of a flash-butt weld joint. They found that there was no formation of acicular microstructures (i.e., martensite/bainite) in the web region and the rail foot, which were the regions with a higher cooling rate.…”

“…Although there are various works [6,[10][11][12][13][14][15][16] devoted to the numerical investigation of residual stress in flash-butt welded rails, the mechanism of residual stress formation in flash-butt welded rails at various stages of heating and cooling has not been clearly discussed, and the process of residual stress formation in a welded joint is far from completely understood. It is therefore the objective of the present work to investigate the mechanisms of residual stress formation in a flash-butt welded rail.…”

Influência da microestrutura antes e depois da soldagem de topo por centelhamento de trilhos ferroviários: uma abordagem de fadiga de contato de rolamento, transformações de fases e simulação por elementos finitos.

“…Esta menor tendência de formar ferrita pró-eutetoide também é observada nos perfis de dureza dos trilhos usados, nos quais não há diminuição evidente da dureza na área central das soldas. A formação de ferrita pró-eutetoide é comum para aços com carbono equivalente mais próximo do equilíbrio eutetoide e tem sido observada por vários autores [31,33,116].…”

“…Uma diferença entre as simulações presentes e as simulações realizadas por Pereira et al [116] é a consideração no presente estudo da simetria de reações na face "aquecida" pelo processo de soldagem de topo por centelhamento (Flash-Butt). O presente modelo considerou simetria de reação entre os eixos x e y (que são os sentidos transversal e vertical do trilho respectivamente), porém deixou-se o eixo z (sentido horizontal ao trilho) livre de restrição ao deslocamento.…”