Abstract: The influence of accelerated cooling in (a+g) critical zone on the microstructure characterization and properties of an X100 pipeline steel is investigated by means of thermal simulation technique, microscopic analysis method and mechanical property testing. The results show that dual-phase microstructure of bainitic+ferrit (B+F) can be obtained by using accelerated cooling method in (a+g) critical zone, and (B+F) dual-phase microstructure has a continued yield capacity, high tendency of initial strain hardening and large uniform deformability. When accelerated cooling temperature is of 830~850 ℃ in critical zone, X100 pipeline steel can get excellent mechanical properties such as high strength-toughness, good ductility, high strain hardening exponent and low yield/tensile ratio because of the formation of fine bainite and ferrite with high density dislocation. When accelerated cooling temperature decreases, the strength of X100 pipeline steel decreases and its strain hardening exponent increases because of increasing of ferrite volume fraction.

Key words: Accelerated cooling in critical zone, Dual-phase microstructure, Properties, X100 pipeline steels