US 11,959,159 B2
Austenitic stainless steel having excellent pipe-expandability and age cracking resistance
Sang Seok Kim, Pohang-si (KR); Deok Chan Ahn, Seoul (KR); Mi-Nam Park, Pohang-si (KR); Hyun Woong Min, Yongin-si (KR); and Yung Min Kim, Pohang-si (KR)
Assigned to POSCO CO., LTD, Pohang-si (KR)
Appl. No. 17/275,408
Filed by POSCO, Pohang-si (KR)
PCT Filed Aug. 22, 2019, PCT No. PCT/KR2019/010718
§ 371(c)(1), (2) Date Mar. 11, 2021,
PCT Pub. No. WO2020/054999, PCT Pub. Date Mar. 19, 2020.
Claims priority of application No. 10-2018-0109790 (KR), filed on Sep. 13, 2018.
Prior Publication US 2022/0049333 A1, Feb. 17, 2022
Int. Cl. C22C 38/58 (2006.01); C21D 6/00 (2006.01); C21D 8/10 (2006.01); C21D 9/08 (2006.01); C22C 38/00 (2006.01); C22C 38/02 (2006.01); C22C 38/04 (2006.01); C22C 38/42 (2006.01); C22C 38/44 (2006.01)
CPC C22C 38/58 (2013.01) [C21D 6/004 (2013.01); C21D 8/105 (2013.01); C21D 9/08 (2013.01); C22C 38/001 (2013.01); C22C 38/02 (2013.01); C22C 38/04 (2013.01); C22C 38/42 (2013.01); C22C 38/44 (2013.01); C21D 2211/001 (2013.01)] 1 Claim
OG exemplary drawing
 
1. An austenitic stainless steel comprising, in percent (%) by weight of the entire composition,
C: 0.01 to 0.04%,
Si: 0.1 to 1.0%,
Mn: 0.1 to 2.0%,
Cr: 16 to 20%,
Ni: 6 to 10%,
Cu: 0.1 to 2.0%,
Mo: 0.2% or less,
N: 0.035 to 0.07%, and
the remainder of iron (Fe) and other inevitable impurities,
wherein the C+N satisfies 0.06 to 0.1%,
wherein an Md30 value in equation (1) is −10° C. or less, and an average grain size is 45 μm or more,
Md30=551−462*(C+N)−9.2*Si−8.1*Mn−13.7*Cr−29*(Ni+Cu)−18.5*Mo  (1)
where, C, N, Si, Mn, Cr, Ni, Cu, and Mo represent the content, % by weight, of each element,
wherein a product of the Md30 (° C.) value represented by the equation (1) and the average grain size (μm) satisfies less than −500,
wherein a work-hardening exponent n value in a range of true strain 0.3 to 0.4 satisfies the range of 0.45 to 0.5,
wherein an aging crack limited drawing ratio of the stainless steel is 2.97 or more, and
wherein a hole expansion rate (HER) represented by equation (2) is 72% or more
HER=(Dh−D0)/D0×100  (2)
where Dh is an inner diameter after fracture and D0 is an initial inner diameter.