Optimization of annealing cycle and Microstructural Characterization of cold rolled Titanium-stabilized Interstitial Free Steel

Abstract

Ultra Low carbon Interstitial free steels are extensively used in automotive segment for outer panel fabrication. These steels normally have low yield strength, low tensile strength, high r-bar  i.e plastic strain ratio, high strain rate sensitivity and excellent formability. Before in application, these thin strip coils are cold rolled & annealing after hot rolling. Cold rolled Ti-stabilized IF grade steel having Carbon around 30 ppm was given different annealing cycle. Mechanical properties i.e. YS, UTS & % El are evaluated at every step for understanding the change of material behaviour in terms of their strength and other formable parameters. Hardness in HRB scale evaluated and (plastic strain ratio) is calculated by using resonant frequency method in modul- drawability tester. Cold rolled and annealed at 650oC, 700oC & 725oC samples shows the elongation 40% & above. Similarly, for  is more than 2.0 for annealing temperature 650oc, 700oc & 725oC. The best combination of properties achieved when cold rolled sheet was annealing at 700oC i.e.  % elongation is 48% and r-bar is 2.25