This research compares the mechanical behavior of two API steels (X60 and X70) used in the longest pipeline in the world for the conveyance of iron ore. Tensile tests, Charpy impact tests, CTOD tests and fatigue crack growth tests are performed at ambient temperature. Metallographic examination showed a banded microstructure consisting of polygonal ferrite and pearlite in both steels, with smaller grain size and the presence of a small quantity of bainite in the X70 steel. All the mechanical tests revealed a ductile behavior for the two steels. The X70 steel is preferable for the pipeline project, due its better mechanical resistance, with no significant loss of fracture toughness and fatigue resistance. Its performance could be even better, if an appropriate combination of thermomechanical processing parameters were able to produce a microstructure with minor amount of pearlite, where acicular ferrite/bainite are present.
Este é um artigo publicado em acesso aberto (Open Access) sob a licença Creative Commons Attribution Non-Commercial, que permite uso, distribuição e reprodução em qualquer meio, sem restrições desde que sem fins comerciais e que o trabalho original seja corretamente citado. Resumo: A soldagem de alto aporte térmico é uma alternativa que tem sido empregada na indústria naval e de petróleo para reduzir o número de passes de soldagem em estruturas espessas por meio do aumento da taxa de deposição. Isso tem levado desenvolvimento de aços e de consumíveis que permitem a obtenção de juntas com aceitável nível de tenacidade na zona termicamente afetada, mesmo com aportes térmicos muito elevados. Contudo, ainda não são muito claras as consequências do ponto de vista metalúrgico que este procedimento pode acarretar na zona fundida. O presente trabalho avalia a influência de aportes térmicos de até 17,1 kJ/mm na microestrutura e características mecânicas da zona fundida obtida na soldagem de um aço naval TMCP EH36 feita em único passe com o processo ao arco submerso multi-eletrodos e com adição de arame frio. A microestrutura foi comparada com a de soldas realizadas com energia menor e mapas de dureza foram produzidos e comparados, avaliando-se também a eficiência dos consumíveis geralmente aplicados para a soldagem e alto aporte. Foi observado que o teor de molibdênio na solda contribui de forma direta para a manutenção das propriedades mecânicas da zona fundida na soldagem de alto aporte térmico. Palavras-chave:Aço TMCP EH36; Arco submerso; Arame frio; Metalurgia da soldagem; Alto aporte térmico. Microstructure and Mechanical Characteristics of the Welding Zone of a Shipbuilding Steel Welded in Submerged Arc Welding with Very High Heat InputAbstract: High heat input welding is an alternative that has been employed to reduce the number of welding passes in thick structures with increasing deposition rate. This has led to the development of steels and consumables that allow to obtain joints with acceptable level of toughness in the Heat Affected Zone, even with very high heat inputs. However, the metallurgical consequences, which this procedure can cause in the welding zone, are not very clear yet. This research evaluates the heat input effect up to 17.1 kJ/mm on the microstructure and mechanical properties of the welding zone obtained in the welding of a TMCP EH36 shipbuilding steel in single pass with the submerged arc multi-electrodes with addition of cold wire. The microstructure was compared with that of welds performed with lower heat input and hardness maps were produced and compared, also evaluating the efficiency of consumables generally applied for welding and high input. It was observed that the molybdenum content in the weld acts directly to the maintenance of the mechanical properties of the welding zone in the high heat input welding.
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