The present invention relates to an energy-efficient quenching and non isothermal partitioning process applied on a medium carbon (0.25-0.55 wt.% C) hot-rolled steel  to achieve advanced high strength combined with good ductility and toughness. The invention comprises design of suitable alloy composition, casting, forging, hot  rolling and the use of quenching and non isothermal partitioning process. The developed steel shows multiphase microstructure containing martensite, retained austenite,  carbides, and bainite. The developed steel is hard and exhibit ultrahigh strength (Hardness: 350-650 HBW, Yield Strength (YS): 800-1300 MPa; Ultimate Tensile  Strength (UTS): 1100-2000 MPa), and excellent ductility and toughness (Total Elongation (TE): 8-35 %, Charpy V-Notch (CVN) impact toughness: 10-45 J at room  temperature and 5-30 J at -40oC, and Fracture toughness (KIC): 40-90 MPam1/2).