Einfluss der TM-Behandlung von Nb-mikroiegierten Fein-kornbaustaehlen auf die Eigenschaften von Kaltbaendern

Thermomechanical processing of hot-rolled HSLA steel strip has made it possible to increase the yield point and tensile strength levels to within the range of tempering steels. Similarly high mechanical properties of cold-rolled HSLA steels could be achieved previously only by applying high cold reductions, which resulted, however, in correspondingly lower elongation characteristics. A new process has made it possible to produce now cold-rolled strip featuring both high strength levels and substantially improved elongation characteristics. A major feature is thereby the possibility of retaining a sufficient amount of Nb in solution during cold rolling to ensure an approximately balanced recrystallization, i.e. softening, and precipitation hardening during subsequent annealing. A further objective of the investigation was to determine the extent to which the properties of cold-rolled strip could be optimized by varying the hot rolling parameters. It has been established that the hot rolling parameters which ensure the retention of a relatively high amount of niobium in solution have a positive effect on the properties of cold-rolled strip. Consequently, a relatively high rolling end temperature and a limited reduction in the last hot rolling pass as well as rapid cooling of the strip after hot rolling to a sufficiently low coiling temperature are advantageous in this respect.