US 12,134,809 B2
High strength steel sheet having excellent high-temperature elongation characteristic, warm-pressed member, and manufacturing methods for the same
Je-Woong Lee, Gwangyang-si (KR); and Sang-Ho Han, Gwangyang-si (KR)
Assigned to POSCO CO., LTD, Pohang-si (KR)
Filed by POSCO Co., Ltd, Pohang-si (KR)
Filed on May 8, 2023, as Appl. No. 18/144,394.
Application 18/144,394 is a division of application No. 16/470,401, granted, now 11,680,305, previously published as PCT/KR2017/014582, filed on Dec. 12, 2017.
Claims priority of application No. 10-2016-0174960 (KR), filed on Dec. 20, 2016.
Prior Publication US 2023/0287545 A1, Sep. 14, 2023
Int. Cl. C22C 38/04 (2006.01); C21D 8/02 (2006.01); C22C 38/02 (2006.01); C22C 38/18 (2006.01)
CPC C22C 38/04 (2013.01) [C21D 8/0226 (2013.01); C21D 8/0236 (2013.01); C22C 38/02 (2013.01); C22C 38/18 (2013.01); C21D 2211/005 (2013.01); C21D 2211/009 (2013.01); C22C 2204/00 (2013.01)] 4 Claims
OG exemplary drawing
 
1. A high strength steel sheet having excellent high-temperature elongation characteristics, comprising, by weight %:
carbon (C): 0.4 to 0.9%,
chromium (Cr): 0.01 to 1.5%,
phosphorus (P): 0.03% or less (excluding 0%),
sulfur (S): 0.01% or less (excluding 0%),
nitrogen (N): 0.01% or less (excluding 0%),
alkali-soluble aluminum (sol·Al): 0.10% or less (excluding 0%),
a balance of iron (Fe) and inevitable impurities, and
comprising at least one among manganese (Mn): 2.1% or less (excluding 0%), and silicon (Si): 1.6% or less (excluding 0%),
wherein a microstructure comprises 80% or more of pearlite and 20% or less of ferrite by area fraction,
wherein the pearlite comprises cementite having a major axis length of 200 nm or shorter, and
wherein the cementite of the pearlite has an N value of 60% or more according to the following Relational Expression 2,
N (%)=Nx/(Nx+Ny)*100  Relational Expression 2
in the above Relational Expression 2, Nx is the number of cementite whose major axis length is 200 nm or less, and Ny is the number of cementite whose major axis length exceeds 200 nm.