US 11,708,623 B2
High-strength steel sheet having excellent impact resistance, and method for manufacturing same
Sung-Il Kim, Gwangyang-si (KR); and Seok-Jong Seo, Gwangyang-si (KR)
Assigned to POSCO CO., LTD, Pohang-si (KR)
Appl. No. 16/955,648
Filed by POSCO, Pohang-si (KR)
PCT Filed Nov. 20, 2018, PCT No. PCT/KR2018/014267
§ 371(c)(1), (2) Date Jun. 18, 2020,
PCT Pub. No. WO2019/124765, PCT Pub. Date Jun. 27, 2019.
Claims priority of application No. 10-2017-0178856 (KR), filed on Dec. 22, 2017.
Prior Publication US 2020/0385840 A1, Dec. 10, 2020
Int. Cl. C21D 9/46 (2006.01); C22C 38/00 (2006.01); C21D 8/02 (2006.01); C22C 38/02 (2006.01); C22C 38/04 (2006.01); C22C 38/06 (2006.01); C22C 38/12 (2006.01); C22C 38/14 (2006.01); C22C 38/32 (2006.01)
CPC C21D 9/46 (2013.01) [C21D 8/0205 (2013.01); C21D 8/0226 (2013.01); C21D 8/0263 (2013.01); C22C 38/001 (2013.01); C22C 38/002 (2013.01); C22C 38/02 (2013.01); C22C 38/04 (2013.01); C22C 38/06 (2013.01); C22C 38/12 (2013.01); C22C 38/14 (2013.01); C22C 38/32 (2013.01); C21D 2211/001 (2013.01); C21D 2211/002 (2013.01); C21D 2211/005 (2013.01); C21D 2211/008 (2013.01)] 3 Claims
OG exemplary drawing
 
1. A steel sheet having impact resistance, comprising, in wt %:
0.05 to 0.12% of C, 0.01 to 0.5% of Si, 0.8 to 2.0% of Mn, 0.01 to 0.1% of Al, 0.005 to 1.2% of Cr, 0.005 to 0.5% of Mo, 0.001 to 0.01% of P, 0.001 to 0.01% of S, 0.001 to 0.01% of N, 0.001 to 0.03% of Nb, 0.005 to 0.03% of Ti, 0.001 to 0.2% of V, 0.0003 to 0.003% of B, and a remainder of Fe and unavoidable impurities,
a microstructure comprises tempered martensite as a main structure, and a remainder of tempered bainite,
the number of one or more of carbides and nitrides having a diameter of 0.1 μm or more per circle observed in a 1 cm2 unit area is 1×103 or less,
the number of precipitates having a diameter of 50 nm or more including one or more of Ti, Nb, V, and Mo observed in a 1 cm2 unit area is 1×107 or less,
the steel has a difference in hardness between a t/2 position and a t/4 position to 30 Hv or less, based on the thickness (t),
the steel sheet has a yield strength of 900 MPa or more, and a Charpy V-Notched energy at −40° C. of 30 J or more, and
the contents of Mn, Cr and Mo satisfy the following Relational expression 1:
T=Mn/(Cr+Mo), 1.0≤T≤3.0  [Relational expression 1].