Electron Microscopy Investigation of Inconel 625 Weld Overlay on Boiler Steel

Abstract

The investigation was focused on the microstructure characterization as well as changes in chemical composition and hardness of water wall tubing weld overlaid with Inconel 625. The analysis comprised studies in a light and electron microscopy scale that included the evaluation of weld overlays microstructure and microsegregation of alloying elements across the overlay and base metal interface. The particular attention was turned to the distribution of the main element content (Fe, Ni, Mo, Nb, Cr) in the base metal fusion zone as well as in the weld overlay itself. It was shown that the solidification process resulted in significant segregation in alloying elements giving rise to the substantial differences in chemical composition between dendrite cores and interdendritic spaces. It is believed that the microsegregation together with precipitation of secondary phases may contribute to the deterioration of corrosion resistance and overall mechanical properties of weld overlay including ductility and fracture toughness.

Performance of the INCONEL 625 alloy weld overlay obtained by FCAW process

“…Based on the results presented in Table 5, the values of the partition coefficient calculated for Nb (0.52), Mo (0.99), Cr (1.09) and Ni (1.12), indicate that Mo and Nb segregate during solidification into the liquid and, once solidification is finished, the interdendritic regions are considerably enriched with these elements, since values of k for Mo and Nb are lower than 1. These results are in accordance with other works [3,6,8,12,14,19,39,40]. According to CIESLAK et al [41], niobium free alloys solidify in a simple L → γ transformation without any eutectic-like reaction and exhibit a relatively narrow solidification temperature range.…”

High-Temperature Corrosion of Ni-Base Alloys by Waste Incineration Ashes

“…The microstructure and characteristics of weld overlays alloys Inconel 625 and 686 have been examined and discussed in publications [3,14,15]. The ashes used in this study were sampled from a fluidized bed waste incinerator.…”

Avaliação de Revestimentos de Liga de Níquel 625 Depositados pelo Processo Eletroescória

“…Neste aspecto, a Tabela 3, que mostra o valor do coeficiente de distribuição (k), contribui para o entendimento, já reportado pela literatura [4,14,[29][30][31][32] sobre a segregação de elementos como o Mo e Nb para a região interdendrítica, enriquecendo essa região e, consequentemente, empobrecendo o centro das dendritas desses elementos e os enriquecendo em elementos como o Ni. De fato, nota-se a tendência de uma leve segregação dos elementos Ni e Cr para o sólido (k>1) e de um potente efeito de segregação para as regiões interdendríticas do Mo e, principalmente do Nb, sendo este fato computado como responsável para a formação de fases secundárias em revestimentos com a liga de níquel 625 [4,32].…”

“…O revestimento por soldagem pode ser obtido por vários processos, tais como eletrodos revestidos, MIG/MAG, arame tubular, TIG, explosão e plasma [2,5,7,[9][10][11][12][13][14][15][16][17][18]. Em alguns casos, o tratamento térmico pós-soldagem (TTPS) é por vezes recomendado para aliviar tensões residuais, reduzir o teor de hidrogênio, ou homogeneizar a microestrutura [1,9,19].…”