Influence of delamination on microtexture and J-R curve in API X60 steel

摘要

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.