Abstract:The aim of this research is to present a comparative analysis between theoretical and experimental thermal fields as well as a microstructural behaviour and residual stresses applying multiple weld beads in the joint of two API 5L X52 pipe sections. The thermal field, microstructural and residual stresses were numerically modelled through the finite element method (FEM) and compared to experimentally. The simulation conditions used in the FEM analysis were similar considerations to the underwater welding conditions. The finite element analysis was carried out, first by a non-linear transient thermal analysis for obtaining the global temperature history generated during the underwater welding process. Subsequently, a microstructural behaviour was determined using the temperatures distribution obtained in the pipe material by calculating the structural transformations of the material during the welding process, and finally a stress analysis was developed using the temperatures obtained from the thermal analysis. It was found that this simulation method can be used efficiently to determinate with accuracy the optimum welding parameters of this kind of weld applications.Key-words: API 5L X52; Finite element analysis; Residual stresses; Temperature field; Underwater welding. Análise Termo-mecânica e Microestrutural da União Soldada Durante Soldagem SubaquáticaResumo: O objetivo deste trabalho é apresentar uma análise comparativa entre os campos térmicos teóricos e experimentais, bem como um comportamento microestrutural e as tensões residuais aplicando cordões em solda multipasses na união de duas seções de tubo API 5L X52. O campo térmico, as microestruturas e as tensões residuais foram numericamente modelados através do método por elementos finitos e comparados com o experimental. As condições de simulação utilizadas na análise por elementos finitos foram consideradas semelhantes às condições de soldagem subaquáticas. A análise por elementos finitos foi efetuada, primeiramente uma análise térmica transiente não linear para obter a evolução da temperatura global gerada durante a soldagem subaquática. Depois, um comportamento microestrutural foi determinado usando a distribuição de temperaturas obtida no material do tubo calculando as transformações estruturais do material no processo, e, finalmente, uma análise de tensões foi desenvolvida utilizando as temperaturas obtidas a partir da análise térmica. Foi encontrado que este método pode ser utilizado eficientemente para determinar com precisão os parâmetros de soldagem ótimos neste tipo de soldagem por simulação.Palavras-chave: API 5L X52; Análise de elementos finitos; Tensões residuais; Campo de temperatura; Soldagem subaquática.

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Two metal fillers with TiC nanoparticles (TiC NPs) of less than 100 nm for the overlay process is an alternative to hardfacing for treating surfaces subjected to severe wear. In this work, the effect of tribological behavior for TiC NPs addition on two Co-based filler materials, as well as the dilutions, was studied. Mixtures of Co-based filler metals without and with 0.5% and 2% TiC NPs were deposited onto D2 steel plates using PTA (Plasma Transferred Arc). The BET surface area was 0.17 m2 g-1 and 0.31 m2 g-1, respectively, for Stellite 6 and 12. The distribution of ca 23% macroporous for Stellite 6 was sufficient to get inside the TiC NPs, as well as in the case of Stellite 12, with a pore distribution of ca 13%. Stellite 12 has an increase in the dilutions (70%) and enthalpies showed endothermic reactions. Stellite 6 with NPs was determined to be most effective in increasing the wear resistance.

This study describes the phase evolution during solidification under continuous cooling conditions of a hypo-peritectic multicomponent steel. Additionally, the mechanical behavior and dimensional variation of the solid-liquid skin were evaluated by using mathematical expressions reported in the literature as a function of the proportion of phases and solute distribution respectively. The crack susceptibility of the solid-liquid skin depended on the proportion of phases and it occurred in two solid fraction regions, independently of the cooling rate. For the region exhibiting the lowest solid fraction values this susceptibility was associated to g phase, while at the highest solid fraction values it was related to d phase. At the end of the peritectic transformation the highest contraction observed can be considered as an additional contribution to the crack susceptibility in the solid fraction range of 0.92-0.98. The significant microsegregation of Mn observed for high cooling rates promotes a change in the solidification mode, from a hypo-peritectic mode into a hyper-peritectic mode and the expansion of solid formed from the remaining liquid.

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