Fissuração pelo hidrogênio em um aço API 5L X70 soldado com eletrodos celulósicos de diferentes níveis de resistência

• Ano de defesa: 2018
• Autor(a) principal: Camila Goes Mattioli
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de Minas Gerais; UFMG
• Palavras-chave em Português: ARBL; Hidrogênio difusível; Fissuração por hidrogênio; Eletrodo celulósico; Ensaio de implante; API 5L X70; Soldagem; Engenharia metalúrgica; Aço de alta resistencia; Metalurgia de transformação
• Link de acesso: http://hdl.handle.net/1843/BUOS-B3DJ93

The search for materials with high mechanical strength without the loss of their tenacity led to the development of high strength and low alloy steels (HSLA). This type of steel has commonly low carbon content and small additions of alloying elements. Within this classification are the steels used in pipelines for the transportation of ores, gases and oils, which follow the American Petroleum Institute (API) standard. These steels face a major problem arising from welding, which is cold cracking, which is the subject of many studies around the world and this work. In the case of this study, the implant test was used to study the effect of the heat input and the mechanical resistance of the weld metal on the susceptibility of an API 5L X70 steel to the cracking by hydrogen. With this test it was possible to vary the application of the load stressing the test specimen (implant pin) and verify the presence of cracks in the material. The welds were made with the gravity welding device, through which it was possible to vary the heat input of the process. Two cellulosic electrodes with different levels of mechanical resistance were used, being AWS E6010 the one with lower mechanical resistance than steel (undermatching) and AWS E8010, with similar strength. The diffusible hydrogen levels of the electrodes were determined by gas chromatography. As a result of the implant test, it was observed that even welds that didnt fail showed a big amount of cracks. However, these cracks did not reach a critical size for the final break of the specimen test being tested. The presence of cracks may be due to the cooling condition of the weld bead, which led to the appearance of brittle and susceptible cracking microstructures. It was also observed a greater cracking tendency when the AWS E6010 electrode was used. This can be related to the lower mechanical resistance presented by its weld metal and also to the fact that the electrode is less chemically bonded. Thus, the weld metal may have been transformed in higher temperatures, which led to a greater migration of the hydrogen to the HAZ