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The main objective of this research is to better understand the correlation between the constituent phases presented in the super-duplex steel SAF 2507 when it is under welding process by arc shielding gas MIG-MAG (Metal Inert Gas-Metal Active Gas). Conventional short circuit transfer and derivative STT (Surface Tension Transfer) using the 2594 welding wire as a filler metal and the effects on welding power in hardness, toughness and pitting corrosion are considered here. The results showed that the welding energy (Ew) changed the α/γ-phase's balance and occasionally formed σ-phase in ferrite grain boundaries which led to changes in hardness, toughness and pitting corrosion resistance in molten zone (MZ), heat activated zone (HAZ) and metal base regions (MB). Furthermore, the increased amount of γ-phase improved the pitting corrosion resistance index (PRENγ) mainly in the MZ. This is due to decrease of α-phase fraction and formation of coarser grains, for higher welding energy. The toughness in the MZ decreased with less formation of γ-phase, coalescence of ferritic grains and localized formation of σ-phase, raising the hardness in the HAZ when the welding energy was lower.
ResumoO objetivo deste estudo foi avaliar a soldabilidade do aço da classe API 5L X80 de fabricação nacional quanto ao trincamento pelo hidrogênio. Para isto, o aço foi soldado pelo processo arame tubular usando como metal de adição o arame AWS E110-MC com 1,6 mm de diâmetro e como gás de proteção a mistura 75% Argônio+25%CO2. Foram adotados quatro níveis de energia de soldagem, 0,7 kJ/mm, 1,10kJ/mm, 1,60 kJ/mm e 2,00 kJ/mm e o ensaio de soldabilidade utilizado foi o WIC. Para as quatro energia de soldagem foi constatada a presença de trincas que iniciavam na região de grãos grosseiros da ZTA (RGGZTA) e se pronunciavam para a zona fundida (ZF). A ZTA apresentou um comportamento microestrutural com presença de bainita e a ZF com predominância de ferrita acicular. A microdureza na ZF foi superior em relação às demais regiões. Palavras-chave: Aço API X80; Processo de soldagem com arame tubular; Trinca induzidas pelo hidrogênio; Ensaio WIC.
EVALUATION OF WELDABILITY API 5L X80 STEEL SOLDIER BY CASE USING TUBULAR WIRE TEST WELDABILITY WIC AbstractThe aim of this study was to evaluate the weldability of steel grade API 5L X80 as the cracking by hydrogen. For this, the steel was welded by FCAW process using as filler metal wire AWS E110-MC with 1.6 mm in diameter and as a protective gas mixture Argon plus 25% CO2. Four levels of welding energy, 0.7 kJ / mm, 1.10 kJ / mm, 1.60 kJ / mm and 2.00 kJ / mm were used and weldability test adopted was WIC. For the four welding heat input showed the presence of cracks that initiated in the region of the HAZ coarse grains (HAZCG) and were pronounced to weld metal (WM).The HAZ presented a microstructural behavior in presence of bainite and WM predominantly acicular ferrite. The microhardness in WM was higher compared to other regions.
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