US 12,338,942 B2
Seamless steel pipe and method of manufacture thereof
Shunsuke Sasaki, Tokyo (JP); Ryosuke Tachi, Tokyo (JP); Hiroyuki Yamasaki, Tokyo (JP); and Hiroyuki Fukuda, Tokyo (JP)
Assigned to JFE STEEL CORPORATION, Tokyo (JP)
Appl. No. 18/020,458
Filed by JFE STEEL CORPORATION, Tokyo (JP)
PCT Filed Jul. 21, 2021, PCT No. PCT/JP2021/027349
§ 371(c)(1), (2) Date Feb. 9, 2023,
PCT Pub. No. WO2022/038956, PCT Pub. Date Feb. 24, 2022.
Claims priority of application No. 2020-138500 (JP), filed on Aug. 19, 2020.
Prior Publication US 2023/0265947 A1, Aug. 24, 2023
Int. Cl. B21B 19/04 (2006.01); F16L 9/02 (2006.01)
CPC F16L 9/02 (2013.01) [B21B 19/04 (2013.01)] 9 Claims
OG exemplary drawing
 
1. A seamless steel pipe having:
a t/Dout of 0.05 to 0.40, where t is a wall thickness (mm) of the seamless steel pipe, and Dout is an outside diameter (mm) of the seamless steel pipe,
a maximum depth dmax (mm)≤0.350 for defects in an inner surface of the seamless steel pipe in a cross section of the seamless steel pipe perpendicular to a pipe axis,
an average defect depth dave (mm)≤0.200 for defects having a depth of 0.050 mm or more in the inner surface of the seamless steel pipe,
per millimeter of an inner circumferential length of the seamless steel pipe, at most 30 defects having a depth of 0.050 mm or more in the inner surface of the seamless steel pipe,
a chemical composition comprising, in mass %:
C: 0.05 to 0.45%,
Si: 0.05 to 0.45%,
Mn: 0.05 to 1.2%, and
Cr: less than 4.5%, and
a microstructure comprising ferrite grains having an average grain size of 15 μm or less.