Application of Nb in TMCP structural steel plates with thickness up to 120 mm

During recent years the Thermo-Mechanical Controlled Process (TMCP) was developed for structural steel plates with thickness up to 120 mm. Niobium as a micro-alloy in the steel enables to achieve a substantial grain refinement if the plate is rolled with a skilled combination of rolling steps at specific temperatures. As the very fine grained microstructure improves toughness and increases the yield strength, this TMCP process enables the required tensile properties with a leaner chemical composition. The consequence of a leaner chemical composition, especially of lower carbon content and lower carbon equivalents, is an improved weldability. Such steels permit a wide range of welding conditions producing sound welds and acceptable HAZ properties, a benefit for the fabricator which often turns out in substantial savings when replacing conventional structural steel by TMCP steel. Thanks to the improved properties in parent metal and HAZ many impressive projects like offshore platforms, bridges, high rise buildings, foundations for offshore wind towers, were built from heavy TMCP rolled plates. This paper will explain the essentials of the production process, address some welding aspects and focus on reference projects which were recently realized with TMCP plates of Dillinger Hütte. (AU)