Guilherme Vieira Braga Lemos

Progress in friction stir welding of Ni alloys

ABSTRACT In recent years, interest has been increasing in application of Nickel alloys in the oil industry. For subsea engineering, the possibility to weld high-strength materials in an effective manner is essential. Friction Stir Welding (FSW) is alternative to join several materials retaining their properties or even improving them. This fact is relevant for Corrosion-Resistant Alloys (CRA) used in deep-water exploitation of hydrocarbons. Publications up to now have focused on FSW of Inconel® series as alloy 600, 625, and 718. To provide a solid basis for development, this review discusses the crucial points for FSW. The tool materials are described, as well as the joint microstructure and properties achieved. Furthermore, the basics of the corrosion resistance and the early corrosion studies of FSW joints are presented. It is concluded that FSW is a promising process for Ni alloys, but depends on upcoming research regarding tool technology and corrosion investigations.

Residual stress analysis of drive shafts after induction hardening

Typically, for automotive shafts, shape distortion manifests itself in most cases after the induction hardening by an effect known as bending. The distortion results in a boost of costs, especially due to machining parts in the hardened state to fabricate its final tolerances. In the present study, residual stress measurements were carried out on automotive drive shafts made of DIN 38B3 steel. The samples were selected in consequence of their different distortion properties by an industrial manufacturing line. One tested shaft was straightened, because of the considerable dimensional variation and the other one not. Firstly, the residual stress measurements were carried out by using a portable difractometer, in order to avoid cutting the shafts and evaluate the original state of the stresses, and afterwards a more detailed analysis was realized by a conventional stationary diffractometer. The obtained results presented an overview of the surface residual stress profiles after induction hardening and displayed the influence of the straightening process on the redistribution of residual stresses. They also indicated that the effects of the straightening in the residual stresses cannot be neglected.

Residual stress and microstructural features of friction-stir-welded GL E36 shipbuilding steel

ABSTRACT The purpose of the present study was to fulfil the knowledge gap concerning residual stresses evaluation of friction stir welded GL E36 shipbuilding steel. Plates of 6 mm thickness were welded using two different welding speeds (1 and 3 mm s−1) at a constant rotational speed of 500 rev min−1. This led to different thermal cycles and the objective is to analyse the resulting microstructures and residual stress states. Therefore, in this work, residual stresses were evaluated by X-ray diffraction; metallography and microhardness testing were performed to support these measurements. Results showed that welds produced with different heat inputs have distinguishable residual stress distributions. Increases in the welding speed led to higher residual stress and microhardness in the stir zone.

CARACTERIZAÇÃO DE UMA JUNTA SOLDADA DE INCONEL 625 OBTIDA PELO PROCESSO FRICTION STIR WELDING

A Nickel superalloy, Inconel 625, was studied in the current work. Friction Stir Welding was carried out with tool rotational speeds ranging from 1200 to 200 rpm and welding speed between of 1 mm/s. In addition, metallographic and microhardness analyzes were performed in the joints. The solid state process was effective and resulted in increased microhardness in the welded joints. Finally, it is suggested that a lower heat input leads to sound welds. Increasing the tool rotational speed (1200 rpm) achieved a higher heat input and porosity formation.