Posco Co., Ltd

Eul-Yong Choi

Yeon-Sang Ahn

Chang-Hyo Seo

Kang-Hyun Choi

Min-Seo Koo

Jae-Hoon Lee

Man-Young Park

Jong-Chan Park

Jong-Kweon Kim

Provided are a high-strength steel sheet and a method for manufacturing same, the high-strength steel sheet including: an alloy system having C, Si, Mn, Cr, Al, Nb, Ti, B, P, S, N, and the remainder of Fe and other inevitable impurities. The contents of C, Si, and Al satisfy equation (1) below. The microstructure includes, by an area fraction, greater than 50% to 70% or less of tempered martensite, and the remainder of residual austenite, fresh martensite, ferrite, and bainite, in which a cementite phase as a second phase is precipitated and distributed in an area fraction of 1-3% between bainite laths, or at a lath on the tempered martensite or grain boundaries. [Equation (1)][C]+([Si]+[Al])/5; 0.35 wt. % (wherein [C], [Si], and [Al] denote wt % of C, Si, and Al, respectively.)

High-strength steel sheet and manufacturing method thereof

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

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Gwangyang-si, South Korea

Eul-Yong Choi