Hot rolled steel product with ultra-high strength minimum 1100mpa and good elongation 21%

Abstract

Present invention discloses a high strength hot rolled steel product with tensile strength at least 1100 MPa and elongation not less than 21%. The steel further has uniform elongation not less than 10% and yield and tensile ratio 0.6-0.7. The steel further has tensile toughness in the range 19-23.5 GPa %. The developed steel is primarily aimed for automotive structural applications and also for many other such as defence where good combination of strength and ductility required is very high. The developed steel product has following composition C: 0.15-0.23, Mn: 0.8-2.1, Si: 0.3-1.1, Cr: 0.8-1.3, Mo: 0.08-0.25, Nb: 0.018-0.035, Ti—0.01-0.1 S—0.008 max, P—0.025 max, Al—0.05 to 0.3, N—0.005 max. The liquid metal was continuous cast into slab casting. The cast slab was soaked above 1150° C. for few hours and subsequently the cast structure was broken by deformation prior to hot rolling. The slab was then hot rolled into strip with thickness not less than 10 mm with finish rolling temperature in austenite region and subsequently cooled to above Ms (martensite temperature) but below Bs (Below Bainite start temperature) to avoid polygonal ferrite. The steel with above mentioned properties was developed using existing hot rolling.