Microstructure and Deformation Characteristics of X80 High Deformability Pipeline Steel
Two kinds of X80 high deformability pipeline steels have been processed by applying two-stage cooling process (TSC) and heat treatment on-line process (HOP). The microstructure of TSC steel and HOP steel are polygonal ferrite (PF) + quasi-polygonal ferrite (QF) + granular bainite (GB) multiphase and QF + GB+ martensite-austenite (M/A) multiphase respectively. In HOP steel, the volume of M/A is much more and the size is much larger than that in TSC steel. Some degenerated M/A constituents are also observed in HOP steel. The HOP steel has shown higher tensile strength, lower yield ratio and lower uniform elongation than TSC steel. The strain-nI (instantaneous n-value) curve of HOP steel could be divided into two stages and the TSC’s could be separated to three stages.
Jianzhong Wang and Jingang Qi
D. L. Meng et al., "Microstructure and Deformation Characteristics of X80 High Deformability Pipeline Steel", Advanced Materials Research, Vols. 299-300, pp. 323-327, 2011