13th International Conference on Fracture June 16–21, 2013, Beijing, China -1- Evaluation of delamination mechanisms from Charpy impact test in API-X70 steel Hudison Haskel1,, Ederson Pauletti1, Juliana P. Martins2, André L.M.Carvalho1* 1 Department of Materials Engineering, States University of Ponta Grossa-UEPG 2 Department of Chemical Engineering, Federal Technological University of Paraná-UTFPR * Corresponding author: andrelmc@uepg.br Abstract In this article was investigated the mechanisms of delamination phenomena occurs in the X70 steel during fracture process from the Charpy impact testing. Microtexture and Taylor factor map analysis were performed by electron backscatter diffraction (EBSD) technique in two fractured surface regions, namely, in the perpendicular and parallel regions to the propagation fracture direction where delamination occurred. As result, was observed two types of delaminations during fracture process, the crack arrester-type delamination and crack divider-type delamination. The main microtexture components obtained in the perpendicular and parallel regions to the direction of fracture propagation from orientation distribution function (ODF) were (221) [1-10] (223) [1-10] (112) [1-3 -2] (332) [023] and (223) [0-32] and (332) [1-10] orientations, respectively. It was also observed the presence of the (100) planes and Taylor factor value close to 2.7 in the respective regions investigated, consequently, a smaller stored energy was observed. Keywords Delamination, Charpy impact test, crystallography orientation 1. Introduction The transport of oil and gas through pipelines requires steels that are characterized by a combination of high strength and toughness, these steels are specified by the API 5L standard. However, during the fracture process by Charpy impact test, these steels exhibit the phenomenon known as delamination. This delamination can be attributed to crystallographic texture, intergranular fracture along grain boundaries of retained austenite, segregation of elements such as phosphorus and sulfur, microstructural anisotropy, banding, inclusions and aligned particles [1]. In this context many studies have been conducted to determine the relationship between microstructure and mechanical properties, where the technique by electron backscatter diffraction (EBSD) has been gained the ability to relate the spatial distribution of plastic deformation with the microstructural characteristics. Besides it allows a better understanding of the mechanisms responsible for the nucleation and propagation of cracks from delamination, which is a major problem in HSLA steels [2,3].The aim of present work is to investigate the mechanisms of delamination phenomena takes place in the API 5L X70 steel during fracture process from the Charpy impact testing in specimens with L-T and T-L orientations. Evaluation of microtexture and Taylor factor mapping were performed from the EBSD technique in two regions, namely, in the perpendicular and parallel regions to the propagation fracture direction where delamination occurred.
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