Development of High Strength Hot Rolled Coils with Enhanced Formability Property

Abstract High strength low alloy steels are used now-a-days commercially with increased strength, toughness, formability and weldability for a variety of critical applications such as long and cross members of auto chassis, pre-engineered building (PEB) structures, high mast lighting poles, wind poles, welded pipes etc. To meet these requirements, special quality hot rolled formable grades such as HSFQ (High Strength Formab le Quality) 350/ 450, IS 10748 Gr. V & IS 5986 Fe 510 have been developed at Rourkela Steel Plant (RSP) that co mbine micro-alloying with controlled processing considering customer's requirement and plant's capability for producing these grades. The newly developed HSFQ hot rolled steel possess an attractive combination of strength and formability property which is typically quantified as high elongation (25 % min ) and hole expansion ratio (145 % min) coupled with lo wer YS/ UTS ratio (0.80-0.85). Th is has been possible as a result of innovative alloy design and synergistic effect o f Nb & Si during controlled processing. In case of IS 10748 Gr. V & IS 5986 Fe 510 grades, the unique feature was the comb ination of very h igh strength (UTS: 500-600 MPa and YS: 310-400 MPa) along with reasonable % EL (20-30) for its forming properties. Micro-alloying with Nb helps to achieve the desired properties by obtaining the required microstructures in the hot rolled coils. The applicat ion of these steel demands good internal soundness and cleanliness to arrest the cracking susceptibility o f the fin ished products during forming / welding operations