Effect of Micro-Texture on Fracture Separation in X80 Line Pipe Steel

During tests on pipe and steel for the 2^nd west-east gas pipeline project (WEPP) in china, fracture separation was found in X80 line pipe steel plates in tensile tests, charpy impact tests and DWTT tests. In this paper, fracture separation is investigated by using EBSD technique to analyze microstructure and compare it with microstructure transformation of the material after annealing. Results show that there are obvious texture of {111} <110> and {110} <001> in hot rolling plate, but a reduction of this two textures and a new texture of {110} <111> are found after annealing at 700°C for 2 hours. It is found in charpy impact tests that {111} <110> micro-texture as a main factor leading to fracture separation was eliminated in annealed specimens. The average grain size of specimen changes from 2.2687μm to 2.8362μm comparing with hot rolling plate because of the decomposition of Bainite. Results of Orientation Imaging display that the proportion of substructure and the distribution of misorientation of grain boundary of annealed specimens do not changed remarkably in contrast to the original ones. It is concluded that, X80 steel has well heat stability.