Effect of deformation amount distribution in the austenite recrystallization temperature region on the microstructure and mechanical properties of the X70 pipeline steel

In this study, the effect of deformation amount distribution of X70 pipeline steel on the microstructure and mechanical properties in the austenite recrystallization temperature region are investigated. The results reveal that the austenite grain size is smaller and more uniform by increasing the last-pass rough rolling deformation amount in the austenite recrystallization region. An increase in the last-pass rough-rolling deformation amount can also improve the strength and low-temperature toughness. The deformation mechanism and microstructural evolution based on the last-pass in the austenite recrystallization temperature region are clarified. The final microstructure refinement effect of granular bainite and acicular ferrite attribute to the finer and more uniform original austenite grain size. The main strengthening mechanisms are grain boundary strengthening and dislocation strengthening. The high proportion of the high-angle grain boundary is significantly greater for improving the strength and toughness, which impedes dislocations to slip across grain boundaries.