Recent Developments of High Strength Linepipe Steels on Coil

The present paper deals with the recent steel development for linepipe applications at ArcelorMittal. With the recent upgrade of the downcoiler capabilities in three European steel plants it is now possible to supply hot rolled coils in width up to 2150mm for the economical production of X70 large diameter, spiral welded transmission trunk lines with 25.4mm wall thickness. In view of the increased dimensional feasibility range a couple of new product development projects had been launched. Two of these products with very demanding application properties are already being industrialized. It concerns respectively X70 in 22mm thickness with improved low temperature BDWTT properties (85% shear area at −10°C) and X80 in 16mm, likewise with low temperature BDWTT properties and, additionally, with low Y/T ratio. The first pre-series deliveries have been successfully transformed to pipes in one of our client’s spiral welded pipe mill. Another product development project which is still in the conception phase concerns the development of X100 in thickness up to 12.7mm. The actual progress of the mentioned projects will be documented here. Key for the realization of such demanding products is a precise control of the final microstructure. This is in particular true for high strength steels with improved toughness. Therefore, a lot of research efforts were spent in order to understand the link between microstructures and properties. Our current understanding will be detailed in this paper.