Controlled Rolling of X80 Pipeline Steel in the Austenite Recrystallization Temperature Region and Its Effect on the Microstructure and Mechanical properties

In recent years, the improvement in the strength and toughness of X80 pipeline steel by only controlled rolling in the nonrecrystallization temperature region has been limited, it is difficult to meet higher application demands. Therefore, to further improve the effect of controlled rolling on the strength and toughness, the controlled rolling of X80 pipeline steel in the austenite recrystallization temperature region and its effect on the microstructure and mechanical properties after final rolling in the nonrecrystalization temperature region are investigated by thermal simulation experiments and hot-rolling experiments. An increase in the last-pass rough-rolling deformation in the austenite recrystallization temperature region refines the austenite grain size after rough rolling and finish rolling, making the austenite grain size smaller and more uniform and improving the strength and low-temperature impact toughness. The mechanism of austenite evolution based on the last-pass deformation in the austenite recrystallization temperature region is revealed. The finer and more uniform austenite grain size accelerates the refinement of the granular bainite microstructure at room temperature. The main strengthening mechanisms are dislocation strengthening and grain refinement strengthening. The increase in toughness is due to the presence of a high percentage of high-angle grain boundaries, which significantly impede crack propagation.