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Steel pipe and steel sheet

A technology for steel plates and steel pipes, applied in furnace types, furnaces, heat treatment furnaces, etc., can solve the problems of reduced SSC resistance, accelerated cooling, and surface hardening of steel plates, and achieve excellent DWTT characteristics, sulfide stress crack resistance and hydrogen induced resistance. Excellent effect of crack resistance

Active Publication Date: 2021-02-02
NIPPON STEEL CORP
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

However, in the production methods of Patent Documents 1 to 4, the steel sheet is subjected to accelerated cooling, and there is a problem that the surface layer of the steel sheet is hardened.
As a result of investigation by the inventors of the present invention, it has been revealed that the SSC resistance of such a steel sheet may be lowered in a case-hardened steel sheet.
[0006] In addition, in the past, when the thickness of the plate is thin, as shown in Non-Patent Document 1, accelerated cooling may not be applied, but air cooling after rolling may be used to manufacture
However, in the case of air-cooled manufacturing, ferrite (polygonal ferrite) will be formed, reducing SSC resistance

Method used

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  • Steel pipe and steel sheet
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Examples

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Embodiment 1

[0201] Next, examples of the present invention will be described. The conditions in the examples are examples of conditions employed to confirm the practicability and effects of the present invention, and the present invention is not limited to such examples of conditions. The present invention can adopt various conditions as long as the object of the present invention is achieved without departing from the gist of the present invention.

[0202] Steel sheets having the chemical composition (the balance being Fe and impurities) and Ceq shown in Table 1 were hot-rolled, cooled, and reheated under the conditions shown in Table 2A and Table 2B to manufacture steel sheets.

[0203]

[0204]

[0205]

[0206] A test piece was prepared from the manufactured steel plate, and the structure at a position (t / 4) of 1 / 4 of the plate thickness from the surface of the steel plate was observed with a scanning electron microscope at a magnification of 1000 times to determine the inte...

Embodiment 2

[0223] The steel plates shown in Tables 1 to 3 are formed into tubular shapes by C-type forming machine, U-type forming machine, and O-type forming machine, and the end faces are tack welded, formally welded from the inner and outer surfaces, and then expanded to produce Steel pipes for pipelines. Furthermore, submerged arc welding was used for formal welding.

[0224] In the table, the steel plate No.S-x (x=1 to 54) was formed to be steel pipe No.P-x (x=1 to 54).

[0225]A test piece was prepared from the base material portion of the produced steel pipe, and the fraction (area ratio) of each structure of the surface layer metal structure and the internal metal structure was calculated. Specifically, the microstructure at the 1 / 4 position (t / 4) of the plate thickness from the steel plate surface was observed with a scanning electron microscope at a magnification of 1000 times, and the internal metal structure was determined. The rest of the structure not described in the tab...

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Abstract

A steel pipe comprises a base material part which is composed of a tubular steel sheet having a specified chemical composition and a weld part which is arranged at a butt joint part of the steel sheetand extends in the direction of the length of the steel sheet, wherein the internal metallic structure contains both or one of granular bainite and bainite at a total areal ratio of 85% or more and also contains MA at an areal ratio of 1.0% or less, the maximum hardness and the average hardness in the internal metallic structure are 248 Hv or less and 170 to 220 Hv, respectively, the base material part has a texture having a {100}<110> integration degree of 1.5 or more on a plane that is parallel with a sheet surface positioned at a depth of 1 / 4 from the aforementioned surface as observed inthe sheet thickness direction, the metallic structure in a surface layer part contains both or one of granular bainite and tempered bainite at a total areal ratio of 95% or more, the metallic structure in the surface layer part has maximum hardness of 250 Hv or less, and the thickness of the steel sheet is 15 mm or less.

Description

technical field [0001] The present invention relates to a steel pipe and a steel plate suitable as a raw material of the steel pipe. Background technique [0002] In recent years, diversification of energy supply sources has been promoted due to increasing demand for oil and natural gas, etc. As a result, crude oil and natural gas are being actively exploited in severe corrosive environments where development has been abandoned in the past, for example, in corrosive environments containing hydrogen sulfide, carbon dioxide, chloride ions, and the like. Along with this, steel pipes used in pipelines for transporting crude oil and natural gas are required to have excellent hydrogen-induced cracking resistance (HIC resistance). Additionally, steel pipes in pipelines used to transport oil and gas are exposed to corrosive gases produced from oil wells. Therefore, steel pipes (line pipes) used in pipelines are required to be resistant to sulfide stress cracking (SSC resistance) i...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): C22C38/00C22C38/58
CPCC22C38/58C22C38/02C22C38/04C22C38/14C22C38/12C22C38/002C22C38/001C22C38/08C22C38/16C22C38/005C22C38/18C22C38/20C22C38/24C22C38/22C22C38/46C22C38/44C22C38/42C22C38/28C22C38/50C21D8/0226C21D8/0263C21D2211/002C21D2201/05C21D1/02C21D1/78C21D6/005C21D6/008C21D8/105C21D9/08C21D8/10C21D9/085C22C38/06C22C38/26C22C38/48C21D1/19C21D9/46
Inventor 筿原康浩原卓也海老原洁筒井一辉服部丰阿部望桥本晃
Owner NIPPON STEEL CORP
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