Automobile manufacturers have started using ultra high strength steel (UHSS) in lower thicknness to reduce the weight of their car and improved passenger safety. As a result steel manufacturers are facing continuous challenges to develop Ultra high strength steels (UHSS) in lower thicknesses with suitable formability.
In line with this, Indian steel manufacturers has also started developing different UHSS which includes hot rolled DP540/DP590/DP780/SPF590 etc. for automotive wheel rim applcation and S500MC/S650MC for automotive log and cross member application. ALM650 is one such UHSS grade recently developed whose yield strength (YS) requirement is >650 MPa, tensile strength (UTS) requirement is >700 MPa and total elongation >14%.
This newly developed UHSS, conforms to the specification of S650MC as per EN-10149-2. Chemistry and rolling parameters were designed taking into consideration of mechanical properties requirement including fatigue strength, suitable microstructure to achieve this combination of properties as well as the CSP process characteristics.
Yield strength was achieved up to 680 MPa with total elongation of 20% in transverse direction, impact transition temperature at −40 Deg C and hole expansion ratio (HER) 110%. With the use of this steel weight savings can be achieved up to 30%. Without any pilot plant facility, developing such grade through in house R&D and industrial trials was a great challenge to the team. This was possible due to excellent teamwork and support from management and customer.
This paper describes the experience of developing this ultra-high-strength steel in thin slab caster.