CCT Diagram of Ferrite/Martensite Dual-phase Steel with Part Austenitizing and Complete Austenitizing

The complete and part austenitizing continuous cooling transform(CCT) diagrams of cold rolled hot dip galvanized dual-phase steel of Fe-C-Mn-Cr-Nb-Ti series were measured respectively by using Formaster thermal dilatometer.The phase transformation law of the dual phase steel during continuous cooling process was studied,and the difference of complete and part austenitizing CCT diagrams of the experimental steel was also analyzed from the prospective of dynamics.The results show that,when the cooling rates was 1,3 ℃·s-1 and 5 ℃·s-1,the ferrite starting transformation temperatures of the experimental steel with part austenitizing were higher than the ones of with complete austenitizing as 36,25 ℃ and 44 ℃,respectively.The cooling rates range of bainite transformation of the experimental steel with part austenitizing was 1-40 ℃·s-1.The cooling rates range not only moved to the low cooling rates area,but also moved to the high cooling rates area,which became wider than the one of the experimental steel with complete austenitizing.When the cooling rate range was 1-10 ℃·s-1,the bainite transformation starting temperature of the experimental steel with part austenitizing was lower than the one of the experimental steel with complete austenitizing.While the case was the opposite when the cooling rate range was 15-20 ℃·s-1.For the cold rolled hot dip galvanized dual-phase steel,the cooling rate should be more than 40 ℃·s-1 in order to obtain the final dual-phase microstructure with ferrite and martensite.