Expandable high-strength steel material and expanded high-strength steel pipe having superior expandability and collapse resistance, and methods for manufacturing thereof

Abstract

There are provided an expandable high-strength steel material and an expanded high-strength steel pipe having excellent expandability and collapse resistance, and methods for manufacturing the expandable high-strength steel material and the expanded high-strength steel pipe. The expandable high-strength steel material including, by weight, manganese (Mn): 12% to 18%, carbon (C): 0.3% to 0.6%, and a balance of iron (Fe) and inevitable impurities, wherein the carbon (C) and the manganese (Mn) satisfy the following condition: 23 <= 35.5C + Mn <= 38. Before being expanded, the expandable high-strength steel material has an austenite single phase microstructure, and after being expanded, the expandable high-strength steel material has a microstructure including 5 area% to 50 area% martensite and 50 area% to 95 area% austenite.

Description

technical field [0001] The present invention relates to an expandable high-strength steel material and an expanded high-strength steel pipe having excellent expansibility and crush resistance, and a manufacturing method of the expandable high-strength steel material and the expanded high-strength steel pipe. Background technique [0002] Generally, when installing steel pipes below the earth's surface in an oil field (underground), a hole is first drilled to a predetermined depth in the ground, and a steel pipe portion called a "casing" is installed therein to prevent the hole from collapsing. Thereafter, further holes are drilled from the lower end of the casing to form a deeper well, and a new casing is installed through the previously installed casing. This work is repeated to finally connect the well tubing (pipe) to the oil formation. If drilling very deep wells, various casings with different diameters are used. Since the diameter of the oil well pipe through which o...

AI Technical Summary

Problems solved by technology

However, the application of the carbon steel disclosed in Patent Document 1 as an expandable steel material is limited because the disclosed carbon steel has low expansibility below the level of about 20%.

In addition, it is difficult to obtain the desired strength after the expansion of carbon steel, and due to the Bauschinger effect, the crush strength of carbon steel is low

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