US 12,252,756 B2
High-strength seamless steel pipe and method for manufacturing same
Mitsuhiro Okatsu, Tokyo (JP); Masao Yuga, Tokyo (JP); and Toshiharu Hirama, Tokyo (JP)
Assigned to JFE Steel Corporation, Tokyo (JP)
Appl. No. 17/787,402
Filed by JFE Steel Corporation, Tokyo (JP)
PCT Filed Nov. 24, 2020, PCT No. PCT/JP2020/043651
§ 371(c)(1), (2) Date Jun. 20, 2022,
PCT Pub. No. WO2021/131461, PCT Pub. Date Jul. 1, 2021.
Claims priority of application No. 2019-235907 (JP), filed on Dec. 26, 2019.
Prior Publication US 2023/0023397 A1, Jan. 26, 2023
This patent is subject to a terminal disclaimer.
Int. Cl. C21D 9/08 (2006.01); C21D 8/10 (2006.01); C22C 38/00 (2006.01); C22C 38/02 (2006.01); C22C 38/04 (2006.01); C22C 38/06 (2006.01); C22C 38/16 (2006.01); C22C 38/22 (2006.01); C22C 38/24 (2006.01); C22C 38/26 (2006.01); C22C 38/32 (2006.01)
CPC C21D 9/08 (2013.01) [C21D 8/105 (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 38/16 (2013.01); C22C 38/22 (2013.01); C22C 38/24 (2013.01); C22C 38/26 (2013.01); C22C 38/32 (2013.01); C21D 2211/001 (2013.01)] 6 Claims
OG exemplary drawing
 
1. A high-strength seamless steel pipe having a steel microstructure with a prior austenite grain size of 11.0 or more in terms of a grain size number in compliance with ASTM E112, and having a yield strength of 862 MPa or more and 965 MPa or less,
wherein the high-strength seamless steel pipe has a KILIMIT value of 22.0 MPa√m or more as an evaluation index of sulfide stress corrosion cracking resistance,
where KILIMIT is a value determined from the intersection between (i) a linear regression line created by a stress intensity factor KISSC obtained in a DCB (Double Cantilever Beam) test conducted multiple times under different test conditions, and an applied stress intensity factor KIapplied at the tip of a notch in a test specimen before start of the DCB test, and (ii) a straight line on which KISSC and KIapplied are one-to-one.