Effect of Molybdenum Addition and Specimen Orientation on Microstructure and Mechanical Properties of API X70 Linepipe Steels

This study aims to examine the correlation between microstructures and mechanical properties of two high-strength API X70 linepipe steels with different specimen directions Moaddition. The microstructure Mo-added steel has an irregularly shaped AF, GB matrix pearlite because relatively large deformation in non-recrystallization temperature region, while that Mo-free shows a PF bainitic microstructure. In steel, M/A (martensite-austenite) granular bainite (GB) act as crack initiation sites decreased upper shelf energy increased ductile brittle transition (DBTT). Regardless Mo addition, all demonstrate higher strength lower elongation T direction than L short dislocation glide path ease pile-up at grain boundaries. impact test specimens T-L had absorbed DBTT those L-T former exhibit shorter unit compared latter.