| 摘要 |
<p>Disclosed are a hot-rolled steel sheet for oil country tubular goods, which satisfies standard K55 (a yield strength of 379-552 MPa and a tensile strength of equal to or more than 655 MPa) and has excellent impact toughness by increasing the space of perlite lamellar by controlling alloying constituent and a hot-rolled process condition, and a manufacturing method thereof. According to the present invention, the method for manufacturing the hot-rolled steel sheet includes: (a) a step of reheating a slab sheet at a slab reheating temperature (SRT) of 1150-1250 deg.C, wherein the slab sheet includes 0.33-0.37 wt% of carbon (C), 0.25 wt% or less of silicon (Si), 1.4-1.6 wt% of manganese (Mn), 0.01 wt% or less of phosphorous (P), 0.001 wt% or less of sulfur (S), 0.02-0.04 wt% of aluminum (Al), 0.01-0.02 wt% of titanium (Ti), 0.1-0.3wt% of nickel (Ni), 0.001-0.003 wt% of calcium (Ca), 0.006 wt% or less of nitrogen (N), the remainder consisting of iron (Fe) and inevitable impurities; (b) a step of hot-rolling the reheated slab sheet at a finish delivery temperature (FDT) of 780-820 deg.C; and (c) a step of cooling and coiling the hot-rolled sheet at a coiling temperature (CT) of 600-700 deg.C.</p> |
