Pipeline Steel Hot-rolled Texture Plate Anisotropy

Pipeline used for oil and nature gas transportation, where the using environment is relatively poor, its special performance are specially required. Not only horizontal intensity is required, but also the strength of longitudinal and the strength uniformity in other directions are all high demanded in many working conditions. Therefore, the anisotropic behavior law of X80 pipeline steel was summarized in this article by the analysis of the results of the anisotropy in tensile strength and impact toughness. This article also investigated that how to reduce the anisotropic of tensile strength in pipeline steel by reasonable improvement of rolling process.From the results of mechanical properties tests for a high Nb X80 pipeline steel production we found that the horizontal have the highest value in yield strength and tensile strength; the lower value was found in longitudinal strength; the minimum value was found in the 30dec angle of Rolled direction. The contrary law was found in extensibility and contraction of cross sectional area. Anomaly was not found in chemical composition.microstructure is composed basically by polygonal ferrite and acicular ferrite.Tendency not discoved that crystal arranging in a direction towards.therefore, the possibility of the anisotropy caused by the microstructure factor was excluded and the possibility caused by texture was analyzed.Taylor model was applied in this paper to calculate the relation between texture and the tensile strength of a pipeline steel. It was found that the anisotropy of tensile strength was mainly controlled by the{112}<110> texture component.In order to reduce the{112}<110> texture component and decreasing the tensile strength anisotropy of the pipeline steel, the study on the hot rolling technology is necessary, which determines the texture evolution, In this article, different hot rolling processes, such as rolling temperature and rolling strain, were applied to change the final textures, by means of the analysis on the texture dependence on the hot rolled technologies and corresponding mechanism, it was found that the amount of {112}<110> texture could be reduced by means of increasing initial rolling temperature and decreasing the amount of rolling strain(about 5%)on the basis of reduction rate for industrial production(up to 50%), which results in a reduced tensile stress anisotropy.The anisotropies of impact energy are correlated to the presence of various texture components, as detected by the value analysis of Charpy impact test.the vertical impact energy is higher than other directions.as the impact energy decrease as the increase of the angle between vertical and other directions.The anisotropies of impact energy chang at different modes of fracture (brittle or cleavage(-100℃), mixed brittle-ductile (-60℃), and ductile (room temperature (RT). The anisotropies of impact energy obvious at ductile fracture, not obvirous at brittle or cleavage fracture.It was find that the anisotropies of impact energy in high temperature (up to the Ductile-brittle transition point) is made by the {110} texture.Increase the volume fraction of{110} texture is good to reduce the anisotropies of imgact energy.