Microstructural characterization and mechanical properties of high-strength steel weld metals obtained by GMAW process with rotating electrode (GMAW-RE)

Abstract

The GMAW process with rotating electrode (GMAW-RE) is a variation of the conventional GMAW process, where the electrode is submitted to a rotating movement, with pre-established rotation diameter and frequency. The method improves the lateral fusion along the sidewalls and contributes to the improvement of narrow gap welding, with significant gains in costs and productivity due to the reduced volume of the deposited weld metal. Although there are some studies about operational characteristics of the process, the literature involving mechanical properties of welded joints remains limited, requiring more experimental evidence to confirm the potential of this process for replacement of conventional GMAW process in industry. This work shows comparative analysis of mechanical and microstructural properties of high-strength steel weld metals obtained by the conventional GMAW and GMAW-RE processes. The weld metals obtained by multipass welding performed in steel plates with dimensions of 500 × 300 × 10 mm were submitted to Charpy-V notch, microhardness tests and metallographic examination from samples removed transversally to the weld bead. The residual stresses were analyzed using X-ray diffraction method at the top surface of the welded joints in the longitudinal and transverse directions of the weld bead. The results showed that the GMAW-RE welding procedure attained the approved standard according to the ASME IX Code, despite using materials with different mechanical strengths once the rupture of the test specimen after tension test has occurred on the base metal 7.4 mm far from fusion line. The joints did not show evidence of lack of fusion along the sidewalls, as verified by the bend tests and metallographic examination. In addition, the GMAW-RE process provided a weld metal with slightly superior mechanical properties compared to the GMAW process due to the more refined microstructure observed with higher amount of acicular ferrite, which favors the impact behavior. The association of higher productivity, reduced costs, lower residual stresses and adequate mechanical properties indicates that GMAW-RE process has a potential alternative for replacement of the GMAW in industrial applications.