Effect of Alloying Elements on Recrystallization Kinetic During Continuous Annealing of ASTM A653 Grade 80 Strip

M.A. VICENTE ALVAREZ; TERESA PEREZ; FERNANDO ACTIS; PABLO CANTARELLI; RUBÉN HERRERA

Chicago IL, EE.UU.

Congreso; 6th International Conference on Zinc-Coated Steel Sheet (Galvatech '04); 2004

AIST

During the continuous annealing of cold rolled steel plates, hardness shows an abrupt fall when the cycle maximum temperature is increased. In this work, the effect of different alloys on the hardness curves for continuously annealed samples was studied. For plain carbon steels, the limiting temperature above which hardness plunges, coincides with the recrystallization temperature of the material, being around 580-600 deg.C (depending on the Mn and B contents). The addition of Nb produces a marked increase of this limiting temperature to ~630 deg.C. For 0.007% of Nb, hardness plunges due to the beginning of recrystallization at 630 deg.C, when the amount of Nb is increased to 0.011%, recrystallization is delayed and the material starts to soften due to recovery. For the higher Nb content (0.023 %), extended recovery takes place and softening is mainly due to recovery. As a consequence of these two effects, although the starting recrystallization temperature shifts up to 690 deg.C for 0.023 of Nb, the occurrence of recovery makes hardness to start falling at 630 deg.C, independently of Nb content. Finally, the optimum conditions to get G80 steel were determined for the different materials studied. To do so, the overheating effect at the edges of the strips was considered. From the industrial point of view, Nb addition probed to be the best alternative, because it produces the higher increase of the limiting temperature above which hardness starts falling.