Improvement in steel weldability for large diameter thick-walled gas pipelines by optimizing chemical composition

The problem is considered of improving impact strength and brittle failure resistance of heat-affected zone (HAZ) metal during welding of thick-walled (30–40 mm) gas pipelines. It is shown that the best HAZ properties are obtained in the case of forming low-carbon bainite in this zone with slow post-welding cooling rates. The carbon content is reduced in pipe steel for this purpose; solid solution elements are added, which increase austenite stability, and microalloying with niobium and titanium is carried out in order to retard grain growth by carbonitride particles.