Abstract
Strain aging behavior of microalloyed low carbon seamless pipeline steel with normalized (ferritic-pearlitic) and quenched-and-tempered (ferritic-cementitic) microstructures has been investigated in different pre-strains at 250°C. The yield ratios of steels with ferritic-pearlitic microstructure at different pre-strains are significantly higher than that with ferritic-cementitic microstructure. It is attributed that an interaction between particles and dislocation is stronger for quenched-and-tempered steel in comparison with that for normalized steel. Therefore, strain aging resistance of normalized steel is, to a great extent, better than that of quenched-and-tempered steel. Unlike welded pipe, few carbon atoms in supersaturated solid solution diffuse to the mobile dislocations, forming Cottrell atmospheres and producing strain aging phenomenon in seamless pipe. This different is attributed to the different pipe making technique: TMCP (Thermo-Mechanical Control Process) for welded pipe and traditional heat-treatment for seamless pipe.
