Static recrystallization behavior and technological improvement of X80 pipeline steel with heavy thickness produced by hot continuous rolling

The static recrystallization behavior of deformed austenite in X80 pipeline steel with heavy thickness manufactured by the 2160 Hot Continuous Rolling Production Line in Shougang Qiangang was investigated by double hit compression experiment.According to the results,the production technology was improved and optimized.The mechanical properties of X80 pipeline steel obtained by the optimized production technology were tested using tensile,impacting and drop weight tearing tests(DWTT).The microstructure was observed and analyzed using optical microscope(OM),scanning electron microscope(SEM) and transmission electron microscope(TEM).It is shown that deformation temperature is the main factor that influences the static recrystallization behavior.Carbonitride precipitation inhibits recrystallization and causes a plateau in the softening ratio curve.The static recrystallization activation energy of X80 pipeline steel was regressed and calculated to be 380 kJ·mol^-1,and its rationality was also discussed according to previous references and investigations.After the technology optimization,the microstructure of X80 pipeline steel is uniform and refined,and represents typical acicular characteristics.Precipitates in the steel mainly include the complex(Ti,Nb)(C,N) and single NbC particles.The tensile properties of X80 steel(tested with bar specimens) exceed relevant standards a lot;especially the toughness at low temperature such as impacting and DWTT properties is excellent.