A new ultrahigh strength pipeline steel with high yield strength and high impact toughness was fabricated in this work, and mechanical properties and microstructure of the steel were investigated in this paper. The steel exhibited outstanding mechanical properties with yield strength levels of up to 951MPa and Tensile strength levels up to 1023MPa. The sharp notch-toughness with absorbed energy values of 227J/cm2 at Temperatures of -30℃ and %shear of up to 95% in drop weight tear test (DWTT) at temperatures of -20℃ were achieved. It was found that microstructure of the steel comprises a majority of low carbon lath bainite with different sublaths and sub-sublaths, meanwhile there is a high density of dislocation between laths and the dispersed film-like martensite-austenite (M-A) constituents. Most of the precipitates in this steel are duplex type containing Nb and Ti with characterized morphology of cap. The precipitation size is a few to a few tens nanometers.
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