EFFECTS OF COLD-ROLLING AND ANNEALING CONDITIONS ON THE PROPERTIES OF BAKE HARDENABLE ULC STEELS

摘要

The influences of annealing conditions on bake hardening (BH) property in the continuous annealing route were studied in this paper with Ti+Nb bearing ultra-low carbon bake hardening (ULC-BH) steels. The effects of the cold rolling reduction rate, soaking temperatures, slow cooling conditions and rapid cooling conditions were evaluated to clarify the complex metallurgical interactions. The soaking temperature has a significant effect in increasing the dissolution of solute carbon content and enhances the BH property. Slow cooling was found to slightly promote the BH values with higher cooling rates as the re-precipitation was prevented and the supersaturated solute carbon could remain in the solid solution. The effects of rapid cooling starting temperatures were also investigated in this paper but no obvious tendency was observed. The corresponding grain sizes were calculated and analyzed to help evaluate the influence of cold-rolled reduction and grain boundaries. It was concluded that greater BH was achieved by larger grain sizes with less cold-rolled reduction.