The aim of the present work is to verify the microstructural behavior of a B 521 tantalum alloy UNS Grade R05200 after welding, in relation to the welding thermal cycle. The joint design was a 1.5 mm thickness circumferential butt welding, on a 32 mm outside diameter pipe, welded in 1 G position (horizontal, flat, and rotating). The chosen welding process was gas tungsten arc welding (GTAW). The microstructural analysis showed the presence of coarse, dendritic-columnar structures, as well as a hexagonal cell, with no cracks noted. Hardness tests showed an increase in hardness, from 120 HV to 425 HV, in the heat-affected zone. Through finite element methods, the behavior of the temperature field was estimated and compared.

Trabajo recibido el día 07 de diciembre de 2010 y aceptado en su forma final el día 17 de enero de 2012.

Nickel-chromium-molybdenum alloys are especially used in manufacturing components for the aeronautical and the petrochemical industries. This article focused on determining the microstructural performance of this kind of alloy, welded with E NiCrFe-3 of 3,25 mm diameter electrode. The butt welding was obtained by preparing the edges at 60°. The microstructural variations were evaluated by optical microscopy, and the hardness analysis was carried out in the affected areas by the thermal welding cycle. To determine chromium and nickel equivalent, the Schaeffler diagram was used, which allowed obtaining the chemical composition resulting from the deposit. The structure of this alloy in the joint is austenitic, and it was determined by structural transformations consisting of skeleton type ferrite morphology, aligned the heating source of the electric arc. It was also proved the formation phases of primary austenite, austenite Widmanstátten, and the precipitation of secondary austenite to the interior of the ferrite, where structure of austenite Widmanstátten is the most fragile.