Microstructure and low temperature fracture of commercial low carbon pipe steel for modern gas pipelines Available to Purchase

Commercial low carbon steel of the X80 strength level was studied after controlled rolling and interrupted accelerated cooling. The steel microstructure and its fracture characteristics were evaluated in the test temperature range from +20 to –70°С. It was shown that the high values of mechanical properties (YS = 550 MPa, UTS = 680 MPa), the impact toughness (KCV = 310–400 J/cm²), and cold resistance (critical ductile-brittle transition temperature below— 70°С) are achieved due to the formation of a fine granular bainite structure (40%) in the ferrite matrix (53%). The fraction of brittle troostite (finely dispersed pearlite) after rolling and accelerated cooling is reduced to 6%. The granular bainite structure exhibited fine-grained regions of residual austenite (1–2%), carbides Fe₃C, Fe₂C, and Mn₇C₃, as well as FeAl intermetallic particles.