	US 12,221,663 B2
	Martensitic stainless steel seamless pipe for oil country tubular goods, and method for manufacturing same
Mami Endo, Tokyo (JP); Yuichi Kamo, Tokyo (JP); and Masao Yuga, Tokyo (JP)
Assigned to JFE STEEL CORPORATION, Tokyo (JP)
Appl. No. 17/058,781
Filed by JFE STEEL CORPORATION, Tokyo (JP)
PCT Filed Apr. 25, 2019, PCT No. PCT/JP2019/017539 § 371(c)(1), (2) Date Nov. 25, 2020, PCT Pub. No. WO2019/225281, PCT Pub. Date Nov. 28, 2019.
Claims priority of application No. 2018-100107 (JP), filed on May 25, 2018.
Prior Publication US 2021/0198764 A1, Jul. 1, 2021
Int. Cl. C21D 9/08 (2006.01); C21D 1/18 (2006.01); C21D 6/00 (2006.01); C22C 38/00 (2006.01); C22C 38/02 (2006.01); C22C 38/04 (2006.01); C22C 38/06 (2006.01); C22C 38/42 (2006.01); C22C 38/44 (2006.01); C22C 38/46 (2006.01); C22C 38/48 (2006.01); C22C 38/50 (2006.01); C22C 38/52 (2006.01); C22C 38/54 (2006.01)

CPC C21D 9/08 (2013.01) [C21D 1/18 (2013.01); C21D 6/004 (2013.01); C21D 6/005 (2013.01); C21D 6/007 (2013.01); C21D 6/008 (2013.01); C22C 38/001 (2013.01); C22C 38/002 (2013.01); C22C 38/005 (2013.01); C22C 38/02 (2013.01); C22C 38/04 (2013.01); C22C 38/06 (2013.01); C22C 38/42 (2013.01); C22C 38/44 (2013.01); C22C 38/46 (2013.01); C22C 38/48 (2013.01); C22C 38/50 (2013.01); C22C 38/52 (2013.01); C22C 38/54 (2013.01); C21D 2211/008 (2013.01)]

10 Claims

1. A martensitic stainless steel seamless pipe for oil country tubular goods having a chemical composition comprising, by mass %:

C: 0.010% or more;

Si: 0.5% or less;

Mn: 0.05 to 0.50%;

P: 0.030% or less;

S: 0.005% or less;

Ni: 4.6 to 8.0%;

Cr: 10.0 to 14.0%;

Mo: 1.0 to 2.7%;

Al: 0.1% or less;

V: 0.005 to 0.2%;

N: 0.1% or less;

Ti: 0.010 to 0.054%;

Cu: 0.01 to 1.0%;

Co: 0.01 to 1.0%; and

the balance being Fe and incidental impurities,

wherein the following formulae (1) and (2) satisfy formula (3) below:

−0.0278Mn+0.0892Cr+0.00567Ni+0.153Mo−0.0219W−1.984N+0.208Ti−1.83 (1)

−1.324C+0.0533Mn+0.0268Cr+0.0893Cu+0.00526Ni+0.0222Mo−0.0132W−0.473N−0.5Ti−0.514 (2)

where C, Mn, Cr, Cu, Ni, Mo, W, N, and Ti represent the content of each element by mass %, and the content is 0% for elements that are not contained,

−0.600≤formula (1)≤−0.412, and −0.400≤formula (2)≤0.100 (3),

the martensitic stainless steel seamless pipe has a yield stress of 758 MPa or more, and

no crack is observed in a sample piece of the martensitic stainless steel seamless pipe subjected to a test environment created by adjusting a pH of a 20 wt % NaCl aqueous test solution having a liquid temperature of 25° C. 0.1 bar H₂S, and a balance of CO₂, to 4.0 with addition of 0.82 g/L of sodium acetate and acetic acid, and a stress 90% of the yield stress being applied for 720 hours in the test solution.