Effect of Ti-enriched Carbonitride on Microstructure and Mechanical Properties of X80 Pipeline Steel

In this study, two API X80 pipeline steels were fabricated by varying Ti additions, and their microstructures and fracture characteristics were analyzed to investigate the effects of Ti-enriched carbonitride on the tensile properties and Charpy impact properties. Lathy bainite, a mass of matensite/austenite (M/A), coarse cubic Ti-enriched inclusions, chain-typed Ti-enriched precipitations, weak toughness and high tensile strength were found as consequences of higher amount of Ti content. Those large scale and chain-typed Ti-enriched car-bonitrides are one kind of crack sources during fracture. The negative effect of higher amount of Ti on the impact properties is increased with decreased temperature.