Mechanical properties, microstructure and toughness assessment of a X70 pipeline steel

Abstract This study was performed to fully characterize the microstructure, texture and mechanical properties of API X70 steel in terms of tensile and compressive responses and toughness. The toughness was studied using a compact-tension specimen that was machined in three directions. The variations in the toughness values along three orientations were studied and revealed almost similar high values of 124 ± 4 MPa√m. Compression experiments were performed over a wide range of strain-rates. A compression split Hopkinson pressure bar (SPHB) was used for performing dynamic experiments. API X70 exhibited positive strain-rate sensitivity of 0.01. Electron back scattered diffraction and optical microscopy revealed a grain size of 2.4 µm with an average misorientation angle of 30°. Texture study revealed high orientation density values around the γ-fiber. The results suggest that the present steel exhibits high strength, elongation and toughness.