Development of High Strength Hot Rolled Coils for Automotive Sector in Underpowered Mill at Rourkela Steel Plant 2014-28-0012

Development of economical, as rolled, high strength low alloy steels is the requirement of the day due to its unique features such as increased strength, toughness, formability and weldability property. These materials are required for a variety of critical applications such as long and cross members of auto chassis, pre-engineered building (PEB) structures etc. In line with the developmental trend and market requirement, special quality hot rolled formable grades such as HSFQ 350/ 450 (High Strength Formable Quality) have been selected for development at Rourkela Steel Plant (RSP). 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 lower YS/UTS ratio (0.80-0.85). This has been possible as a result of innovative alloy design and synergistic effect of Nb & Si during controlled processing.

Similarly medium carbon steels are being used for wide range of automotive applications. Selected difficult-to-cast medium carbon grades e.g. MC 40 & MC 55 have been successfully developed and subsequently commercialized at integrated steel plant. The metallurgical factors contribute for development of these grades are control of Al (< 0.04 %) & N content (∼60 ppm) along with control of excessive segregation of carbon in the steel and presence of inclusions like aluminium oxide and MnS which are mainly responsible for inadequate cold reducibility.