Mechanical Properties and Microstructure of X120 Grade High Strength Pipeline Steel

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. The steel exhibited outstanding mechanical properties with yield strength levels of up to 951 MPa and tensile strength levels up to 1023 MPa. The sharp notch toughness with absorbed energy values of 227 J/cm2 at —30 °C and shear area of up to 95% in drop weight tear test (DWTT) at temperature of —20 °C 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 with the range of precipitation size from a few to tens nanometers.