Posco

Posco Co., Ltd

Yeon-Sang Ahn

Jin-Keun Oh

Il-Ryoung Sohn

Sang-Ho Han

Kwang-Geun Chin

Chang-Hyo Seo

Kang-Hyun Choi

Seong-Ju Kim

Eul-Yong Choi

Ki-Hyun Park

Provided are a cold-rolled steel sheet and a method for manufacturing same, the steel sheet containing, by weight %, 0.03 to 0.07% of C, 0.3% or less of Si, 2.0 to 3.0% of Mn, 0.01 to 0.10% of Sol·Al, 0.3 to 1.2% of Cr, 0.03 to 0.08% of Ti, 0.01 to 0.05 of Nb, 0.0010 to 0.0050% of B, 0.001-0.10% of P, 0.010% or less of S, 0.010% or less of N, the balance being Fe and other impurities, and having a microstructure comprising 75% or more to less than 87% by area of a transformed structure and 13 to 25% by area of ferrite, wherein the transformed structure includes martensite and bainite, the martensite has an average particle diameter of 2 μm or less, the bainite has an average particle diameter of 3 μm or less, the bainite fraction of 3 μm or more is 5% or less.

Cold-rolled steel sheet having excellent bendability and hole expandability and method for manufacturing same

Provided is a method of manufacturing a high strength steel sheet having excellent workability, including: reheating a steel slab; hot-rolling the reheated steel slab at an Ar3 transformation point or higher; coiling in a temperature range of 400 to 700&#xb0; C.; primary cooling at a cooling rate of 0.1&#xb0; C./s or less to room temperature; producing a cold rolled steel sheet at a cold reduction ratio of 40 to 70%; continuously annealing the cold rolled steel sheet in a temperature range of Ac1+30&#xb0; C. to Ac3&#x2212;20&#xb0; C.; secondary cooling at a cooling rate of 10&#xb0; C./s or less to 630 to 670&#xb0; C.; third cooling to 400 to 500&#xb0; C. at a cooling rate of 5&#xb0; C./s or more in a hydrogen; maintaining for 70 seconds or more; hot-dip galvanizing; and performing a final cooling to Ms or less at a cooling rate of 1&#xb0; C./s or more.

Method of manufacturing high-strength steel sheet having excellent processability

Provided is a high-strength steel sheet having a tensile strength of 780 MPa or higher. The high-strength steel sheet has a low yield ratio and excellent ductility (El) and strain hardening exponent (n) and thus has enhanced processability.

High-strength steel sheet having excellent processability and method for manufacturing same

Provided is a high-strength steel sheet including, in % weight, carbon (C): 0.04 to 0.15%, silicon (Si): 0.01 to 1.0%, manganese (Mn): 1.8 to 2.5%, molybdenum (Mo): 0.15% or less (excluding 0%), chromium (Cr): 1.0% or less (excluding 0%), phosphorus (P): 0.1% or less, sulfur (S): 0.01% or less, aluminum (Al): 0.01 to 0.5%, nitrogen (N): 0.01% or less, boron (B): 0.01% or less (excluding 0%), antimony (Sb): 0.05% or less (excluding 0%), one or more of titanium (Ti): 0.003 to 0.06% and niobium (Nb): 0.003 to 0.06%, a balance of Fe and other unavoidable impurities, and contents of the C, the Si, the Al, the Mo and the Cr satisfy the following Expression 1: Expression 1: {(2&#xd7;(Si+Al))+Mo+Cr}/C&#x2265;20. The high-strength steel sheet comprises: a ferrite phase, a bainite phase, a martensite phase, and a residual austenite phase, the ferrite phase being less than 40% of area fraction in the microstructure.

High-strength steel sheet with excellent crashworthiness characteristics and formability and method of manufacturing the same

Provided is a high-strength steel sheet including, in % weight, carbon (C): 0.04 to 0.15%, silicon (Si): 0.01 to 1.0%, manganese (Mn): 1.8 to 2.5%, molybdenum (Mo): 0.15% or less (excluding 0%), chromium (Cr): 1.0% or less (excluding 0%), phosphorus (P): 0.1% or less, sulfur (S): 0.01% or less, aluminum (Al): 0.01 to 0.5%, nitrogen (N): 0.01% or less, boron (B): 0.01% or less (excluding 0%), antimony (Sb): 0.05% or less (excluding 0%), one or more of titanium (Ti): 0.003 to 0.06% and niobium (Nb): 0.003 to 0.06%, a balance of Fe and other unavoidable impurities, and contents of the C, the Si, the Al, the Mo and the Cr satisfy the following Expression 1: Expression 1: {(2&#xd7;(Si+Al))+Mo+Cr}/C&#x2265;15. The high-strength steel sheet comprises: a ferrite phase, a bainite phase, a martensite phase, and a residual austenite phase, the ferrite phase being less than 40% of area fraction in the microstructure.

Provided is a high tensile strength steel having a tensile strength of 780 MPa grade or higher which is used for structural members of automobiles, and more specifically relates to high tensile strength steel having excellent bendability and stretch-flangeability while still satisfying characteristics of DP steels of low yield ratio and high ductility, and to a manufacturing method thereof.

High tensile strength steel having excellent bendability and stretch-flangeability and manufacturing method thereof

The present invention relates to a high-strength steel sheet and, more specifically, to a dual-phase steel sheet having excellent formability, so as to be appropriately applied to vehicle panels and the like, and a manufacturing method therefor.

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Gwangyang-si, South Korea

Yeon-Sang Ahn