ELECTRIC RESISTANCE WELDED STEEL PIPE

WIPO Patent Application WO/2022/044271

A1

This electric resistance welded steel pipe comprises a base material part having a predetermined chemical composition and a welded part. If tB is the wall thickness of the base material part and tS is the wall thickness of the welded part, the microstructure of the base material part at a position where the depth from the outer surface is (1/4)tB is composed of, in area%, from 10% to 50% of bainite, from 50% to 90% of polygonal ferrite, and 1% or less of residual structures, while having an average crystal grain size of 20 μm or less; the microstructure of the welded part at a position where the depth from the outer surface is (1/4)tS is composed of, in area%, from 70% to 90% of bainite, polygonal ferrite, and 1% or less of residual structures, while having an average crystal grain size of 15 μm or less. The degree of integration of (001) at the butted surface of the welded part is 1.5 or less; the hardness of the welded part is 250 Hv or less; and at -20°C, the base material part and the welded part have a Charpy impact absorbed energy of 150 J or more, a yield stress of from 360 MPa to 600 MPa, and a tensile strength of from 465 MPa to 760 MPa.

NAGAI KENSUKE (JP)
YOKOI TATSUO (JP)
KAWANO HIDETO (JP)
KOBAYASHI SHUNICHI (JP)
IWAMOTO SHUJI (JP)

PCT/JP2020/032636

March 03, 2022

August 28, 2020

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NIPPON STEEL CORP (JP)

C22C38/00; C22C38/58; C21D8/10; C21D9/08; C21D9/50

WO2013027779A1	2013-02-28
WO2018008194A1	2018-01-11

JP6693610B1	2020-05-13
JP2020066747A	2020-04-30
JP6587041B1	2019-10-09
JP2013139051A	2013-07-18
KR20160078600A	2016-07-05
JP2007138289A	2007-06-07
JP2007138290A	2007-06-07
JP6213703B1	2017-10-18

TANAI Sumio et al. (JP)

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