High-strength steels such as DOMEX 700 combine high mechanical strength and great ductility. However, when processed by welding their microstructure could present grain growth and deleterious phase formation. Nevertheless, using highpower GMAW-P the effects of electrode and shielding gas composition on the mechanical and microstructure properties of DOMEX 700 welded joints need to be understood. Thus, wire electrodes such as AWS ER 90S-D2 (A1) and AWS ER 120S-G (A2), and shielding gases such as Ar ? 15% CO 2 (G1) and Ar ? 8% CO 2 (G2) were used and the microstructure of welded joints was analyzed through optical and scanning electron microscope (SEM). Mechanical properties of joints was characterized through joint tensile test, impact test from 20 to-40°C, and microhardness in the joint cross-sectional. It is possible to highlight the increase in strength and elongation values with the use of electrode A2, and reduction in impact energy values for specimens welded by gas mixture G2.
Most of pipeline welding still applies manual procedures, which increase production time and is stressful to the welding operator. This happens mainly due to the accurate melt pool control that hand operation enables. It yields high flexibility between material addition and heat source and is therefore adaptable to the welding condition and situation of each moment. This feature is not fully found when mechanized welding with automatic feeding is performed, despite every benefit of welding automation. This renders an optimized parameterization of a complex task. Automatic orbital welding is already a reality, though only applied in large scale in developed countries and/or by few expert companies from developed countries, due to such controllability, repeatability, and robustness difficulties. In this paper, a concept for dynamic wire feeding and respective implementation and analysis are presented. It consists of a low-frequency wire speed oscillation, aiming to decouple wire speed and arc power to a larger extent, which approaches to manual procedure as it guarantees user flexibility, but still keeping the benefits of welding automation. ASTM 139 Grade D tubes were welded under stable processing conditions. The macrographs did not indicate discontinuities such as porosity or lack of fusion, resulting in complete joint penetration. The average welding speed reached was 27.8 cm/min (10.9 in/min), much higher than that found by other authors.
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