Microstructure, mechanical properties and hydrogen induced cracking susceptibility of X80 pipeline steel with reduced Mn content

A low carbon X80 pipeline steel with reduced Mn content has been thermomechanically processed. The microstructure, mechanical properties and susceptibility of the steel to hydrogen induced cracking (HIC) were studied. Yield strength levels up to 595 MPa, tensile strength levels up to 721 MPa and toughness levels up to 100% of shear area at −15 °C for drop wear tear test (DWTT) were achieved while no HIC crack was observed. The microstructure predominantly consisted of acicular ferrite (AF) together with small amount of granular bainite (GB) and martensite/austenite (M/A) constituent. The microstructure also contained high dislocation density and dislocation substructure. Precipitates of different morphologies and size ranges were observed and include cuboidal (70-100 nm), irregular (80-120 nm), spherical (30-70 nm) and fine precipitates (5-10 nm). The results indicate that the X80 steel with reduced Mn content is suitable for sour service application.