Microstructural analysis and mechanical behavior of the HAZ in an API 5L X70 steel welded by GMAW process

• Published in: Welding in the world 2021-06, Vol.65 (6), p.1051-1060
• Main Authors: Dagostini, Vinícius dos Santos, Moura, Ariane Neves de, Luz, Temístocles de Sousa, Castro, Nicolau Apoena, Orlando, Marcos Tadeu D’Azeredo, Vieira, Estéfano Aparecido
• Format: Article
• Language: English
• Subjects: Allotropic transformation; Bainite; Base metal; Charpy impact test; Chemistry and Materials Science; Electron backscatter diffraction; Ferrite; Fracture toughness; Gas metal arc welding; Grain boundaries; Heat affected zone; Heat treating; High strength low alloy steels; Martensite; Materials Science; Mechanical properties; Metallic Materials; Microstructural analysis; Microstructure; Misalignment; Retained austenite; Review Article; Robot arms; Solid Mechanics; Theoretical and Applied Mechanics
• ISSN: 0043-2288; 1878-6669
• DOI: 10.1007/s40194-021-01102-6

This study aimed to investigate the heat-affected zone (HAZ) behavior in an API 5L X70 steel welded by the gas metal arc welding process (GMAW). In the steel welding processes, this region is very critical due to microstructural and allotropic transformations that affect the mechanical properties. Three samples were welded using a robotic arm with different welding speeds, thus obtaining three different heat inputs, which were 2.0 kJ/mm, 2.5 kJ/mm, and 3.0 kJ/mm. For all heat inputs, the microstructures of the HAZ showed the Widmanstätten ferrite, Acicular ferrite, bainite, and martensite and retained austenite, which influenced the mechanical properties of this region. The electron backscattering diffraction analysis showed that the presence of low-angle grain boundaries (2–15°) increases the fracture toughness. The kernel average misorientation map and the results of the Charpy impact test showed that the heat input of 3.0 kJ/mm lead to characteristics of the HAZ that are remarkably similar to the base metal (BM).