| 摘要 |
<p>The present invention relates to a high strength steel having a tensile strength (TS) of 900 MPa or more, a yield point (YP) of 700 MPa or more, and a Brinell hardness (HB) of 360 or more by forming a structure of mastensite and tempered martensite by direct quenching; and to a manufacturing method thereof. According to the present invention, the method to manufacture the high strength steel includes: (a) a step of reheating a slab at a temperature of 1100-1200°C, wherein the slab includes 0.1-0.8 wt% of carbon (C), 0.1-0.5 wt% of silicon (Si), 3.0-8.0 wt% of manganese (Mn), 0.03 wt% or less of phosphorous (P), 0.01 wt% or less of sulfur (S), 0.2-0.8 wt% of aluminum (Al), 0.1-1.0 wt% of molybdenum (Mo), 0.01-0.05 wt% of niobium (Nb), 0.01-0.04 wt% of titanium (Ti), 0.002 wt% or less of boron (B), 0.1-0.3 wt% of nickel (Ni), and remainder consisting of iron (Fe) and impurities; (b) a step of hot-rolling the reheated steel at a finishing rolling temperature (FRT) of 900-1000°C; and (c) a step of cooling the hot-rolled steel.</p> |
