Posco Co., Ltd

Dong-Wan Kim

Sung-Il Kim

Hyun-Taek Na

Sung-Ii Kim

The present invention provides a steel sheet comprising by weight: C: 0.10-0.30%; Si: 0.001-1.0%; Mn: 0.5-2.5%; Cr: 0.001-1.5%; Mo: 0.001-0.5%; Al: 0.001-0.5%; P: 0.001-0.01%; S: 0.001-0.01%; N: 0.001-0.01%; B: 0.0001-0.004%; Ti: 0.001-0.1%; Nb: 0.001 to 0.1%; and the balance consisting of Fe and inevitable impurities, and satisfying relational expression (1), and a microstructure includes comprising: a martensite phase; a bainite phase, wherein the fraction of the martensite phase is 50-90%, the fraction of the bainite phase is 5-50%, the sum of the fractions of the martensite phase and the bainite phase is 90% or more; and the balance consisting of a ferrite phase.CL<1,  [Relationship Expression (1)]CL=−0.692−0.158×[Mn]+0.121×[Mn]+0.061×[Cr]−0.319×[Mo]+0.035×[Hardness_HRC] (where CL is an effective cracking index, [Mn], [Cr] and [Mo] are the percentages by weight of respective corresponding alloy elements, and [Hardness_HRC] is a Rockwell hardness (HRC).)

High-strength hot-rolled steel sheet having excellent blanking properties and uniformity, and manufacturing method thereof

Provided is a method for manufacturing a steel sheet, the method including: reheating a steel slab at a temperature of 1200° C. to 1350° C., the steel slab including, by weight %, carbon (C): 0.05% to 0.14%, silicon (Si): 0.01% to 1.0%, manganese (Mn): 1.5% to 2.5%, aluminum (Al): 0.01% to 0.1%, chromium (Cr): 0.005% to 1.0%, phosphorus (P): 0.001% to 0.05%, sulfur (S): 0.001% to 0.01%, nitrogen (N): 0.001% to 0.01%, niobium (Nb): 0.005% to 0.06%, titanium (Ti): 0.005% to 0.11%, and a balance of iron (Fe) and inevitable impurities; finish hot rolling the reheated steel slab under predetermined conditions to obtain a hot-rolled steel sheet; cooling the hot-rolled steel sheet at a cooling rate of 10° C./s to 100° C./s to a temperature of 400° C. to 500° C. after the finish hot rolling; and coiling the steel sheet at a temperature of 400° C. to 500° C. after the cooling.

High-strength steel sheet having excellent impact resistant property and method for manufacturing thereof

Provided is a high-strength steel sheet having high impact resistance. The steel sheet includes: by weight %, carbon (C): 0.05% to 0.14%, silicon (Si): 0.01% to 1.0%, manganese (Mn): 1.5% to 2.5%, aluminum (Al): 0.01% to 0.1%, chromium (Cr): 0.005% to 1.0%, phosphorus (P): 0.001% to 0.05%, sulfur (S): 0.001% to 0.01%, nitrogen (N): 0.001% to 0.01%, niobium (Nb): 0.005% to 0.06%, titanium (Ti): 0.005% to 0.11%, and the balance of iron (Fe) and inevitable impurities. The steel sheet has a microstructure comprising ferrite and bainite in a total area fraction of 90% or more. The steel sheet has a value of 0.05 to 1.0 as a shear texture ({110}&#x3c;112&#x3e;, {112}&#x3c;111&#x3e;) area ratio of a center region (ranging deeper than 1/10t to &#xbd;t in a thickness direction, t refers to thickness (mm)) and a surface region (ranging from a surface to 1/10t in the thickness direction).

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Gwangyang-si, South Korea

Dong-Wan Kim