13th International Conference on Fracture June 16–21, 2013, Beijing, China -1- Influence of delamination on microtexture and J-R curve in API X60 steel Ederson Pauletti1, , Hudison L. Haskel1, 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: Large–diameter, high-pressure gas transmission pipelines have been used more and more widely all over the world. With the development of the pipeline network, safety and maintenance become an important task. Controlled thermo-mechanical processing is considered as the primary route for the development of API grade linepipe steels because it provides desirable and fine grained microstructure. It is known that crystallographic orientation can generate anisotropy of mechanical properties. Furthermore, studies on pipeline steels, such as X60, X70 and X80, suggest that delamination phenomenon the fracture surface in fracture toughness test specimens affects the measured fracture toughness and therefore safety evaluation of pipeline steels. Microtexture analysis by electron backscattering diffractions (EBSD) was carried out to obtain crystallographic orientation from the fracture process in which occurs the delamination phenomenon. Experimental results obtained by EBSD technique have shown that delamination phenomenon occurs in the {100}<011>crystallographic orientation. The α fiber texture such as :{113}<110>, {112}<110> and {223}<110>, have produced anisotropic mechanical properties that during fracture process act to reduce the plastic constraint and contributing to increase the stress plane Keywords Delamination, fracture toughness test , crystallographic orientation, API X70 steel 1. Introduction One of the most widely used classes of steel pipes is based on the standard API (American Petroleum Institute), which are classified according to chemical composition and mechanical properties [1]. These steels generally undergo thermomechanical processing, associated with addition of alloying elements such as Nb and Ti to obtain a material with high toughness and ductility, as well as good weldability, well known as HSLA steels (high strength low alloy) [2]. The thermomechanical processing imposed on HSLA leads to generation of preferential orientation (texture), resulting in anisotropy mechanical properties [3-6]. The occurrence of texture is most evident during the controlled rolling process which can produce recrystallization, transformation and deformation texture [3]. Special attention should be given the {100} <110> texture component which is parallel to the rolling plate direction. During the monotonic and dynamic test this component contributes to the occurrence of cleavage planes [3, 7 ,8 ,9, 10]. This cleavage planes also contribute to appearance of the delamination (split), as can be seen in Fig. 1. Other factors leading to the occurrence of delaminations are the formation of precipitates at grain boundaries [11, 12], inclusions [13, 14], elongated grains [11, 15], decohesion of grain boundaries [13, 14]. The aim of present work was to investigate the microtexture from the delamination region takes
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