PROCESSING OF NB-MICROALLOYED HIGH STRENGTH STEEL ON A THIN SLAB PLANT

A 0.05% carbon, 0.04% niobium microalloyed line pipe steel has been produced by thin slab casting and direct rolling. 52 mm thick slabs have been cast and direct rolled on a 6 stand hot rolling mill to 6 and 10 mm thick hot strip after a 20-minute tunnel furnace transit between 1070 and 1100°C. At each stand, production parameters as temperature and rolling force have been registered. Even at elevated rolling reductions, rolling force and torque did not exceed the specified maximum load. Both, the 6mm as well as the 10 mm thick hot strip have a microstructure and the mechanical properties largely meet those of the targeted fine-grained steel grade (API X52) coming even close to X60 grade that is a future challenge. The yield point is above 460 MPa, the ultimate tensile strength above 520 MPa and the elongation is more than 25% while the Charpy impact value exceeds 180 Joule at -20°C.