Research on the Strengthening and Toughening Mechanism of Nb Bearing X60 Pipeline Steel by CSP Process

摘要

Compared with conventional process, the cast slab grain of CSP is coarse, as a result of the absence of the two times phase transformations; and the incomplete dynamic recrystallization (DRX) during the rolling easily causes the mixed grain structure in the product. Nb bearing X60 pipeline steel is successfully developed on CSP line in Baotou Iron & Steel (Group) Co. Ltd. With the mixed grain structure, the strengthening and toughening mechanism of X60 pipeline steel is investigated, which is controlled by the uniform microstructure and the precipitation of the second-phase particles. It is shown that DRX is incomplete during 1st and 2nd passes, and mixed grain structure occurs. By means of the adjustment of deformation parameters in passes and the control of second-phase particles, the deformations of 3rd ～ 6th passes are controlled in the non-recrystallization zone, non-uniform grains are broken up, and the mixed grain structure is eliminated.