Abstract: Conventional annealing process (long time at low temperature) and rapid annealing process (instantaneous at high temperature) were compared and analyzed from four aspects of microstructure, grain size distribution, grain orientations and mechanical properties of cold rolled ultra-low carbon steel by means of OM, SEM, EBSD and uniaxial tensile test. The results show that after rapid annealing at 650 ℃ for 15 s, the yield strength and tensile strength of the tested steel are 445.38 MPa and 494.07 MPa, respectively, which are obviously increased from that of conventional annealed (i.e., the yield strength and tensile strength being 274.35 MPa and 388.99 MPa, respectively), while the elongation is still guaranteed up to 24.7%. The grain refinement and the typical γ orientation are the main reasons for the difference of properties between the conventional and rapid annealed specimens, where the grain refinement is the dominant. The rapid annealing has a higher grain refinement strengthening effect, but it deteriorates the work hardening ability and leads to a decrease in elongation. In addition, the rapid annealing inhibits the precipitation of the second phase particles while refines them. By comparison, the rapid annealed specimens show a typical γ orientation, which is more conducive to improving the rolling performance, but that by conventional annealing show a near γ orientation which has less such effect.

Key words: rapid annealing, recrystallization, grain refinement, texture, mechanical properties