| 摘要 |
<p>PURPOSE: A high-strength API(American Petroleum Institute) hot rolled steel sheet and a manufacturing method thereof are provided to secure a high-strength API hot rolled steel sheet with a low yield ratio of 0.8 or less by maintaining a lo content of manganese and adding a proper amount of chrome. CONSTITUTION: A method for manufacturing a high-strength API hot rolled steel sheet comprises a step of finish-rolling a slab, which is rough-rolled to an RDT(Roughing Delivery Temperature) of 950-850°C, to an FDT(Finishing Delivery Temperature) of 800°C-Ar3(S110) and a step of cooling and coiling the hot rolled sheet at a CT(Coiling Temperature) of 600-550°C(S120). The slab comprises C(Carbon) of 0.05-0.09wt.%, Si(Silicon) of 0.1-0.3wt.%, Mn(Manganese) of 1.3-1.6wt.%, P(Phosphorus) of 0.018wt.% or less, S(Sulfur) of 0.003wt.% or less, Cr(Chromium) of 0.1-0.2wt.%, Ni(Nickel) of 0.1-0.2wt.%, Mo(Molybdenum) of 0.1-0.3wt.%, Ti(Titanium) of 0.01-0.05wt.%, Nb(Niobium) of 0.05-0.1wt.%, V(Vanadium) of 0.01-0.05wt.%, and Fe(Iron) and inevitable impurities of the remaining amount.</p> |
