| 摘要 |
Disclosed are a non-heat treated hot-rolled steel sheet which satisfies American Petroleum Institute (API) 5CT C90 standard by controlling alloy elements and process conditions without a quenching and tempering (QT) process, and a manufacturing method thereof. The non-heat treated hot-rolled steel sheet according to the present invention is composed of 0.08-0.12 wt% of carbon (C), 0.1-0.2 wt% of silicon (Si), 1.2-1.5 wt% of manganese (Mn), 0.05-0.10 wt% of niobium (Nb), 0.03-0.06 wt.% of vanadium (V), 0.01-0.03 wt% of titanium (Ti), 0.15-0.35 wt% of nickel (Ni), 0.4-0.8 wt% of chromium (Cr), 0.2-0.3 wt% of molybdenum (Mo), 0.001-0.004 wt% of calcium (Ca), and the rest of iron (Fe) and inevitable impurities. A microstructure is formed of a bainite structure as a main phase. The tensile strength (TS) is over 689 MPa and the yield strength (YS) is 621-724 MPa. |
