Steel and oil well steel pipe

Abstract

Provided are a steel and an oil well steel pipe which have excellent SSC resistance, even in a high pressure H2S environment. This steel contains 0.15-0.45% of C, 0.10-1.0% of Si, 0.10-0.8% of Mn, atmost 0.050 of P, at most 0.010% of S, 0.01-0.1% of Al, at most 0.010% of N, 0.1-2.5% of Cr, 0.35-3.0% of Mo, 0.05-2.0% of Co, 0.003-0.040% of Ti, 0.003-0.050% of Nb, 0.01-0.50% of Cu, and 0.01-0.50% of Ni, and satisfies the equation below. In the microstructure, the grain size of prior-austenite is less than 5 microns, and the block size is less than 2 microns. The steel contains at least 90 vol%total of tempered martensite and tempered bainite. C+Mn / 6+(Cr+Mo+V) / 5+(Cu+Ni) / 15-Co / 6+ alpha>=0.70 (1), (3C+Mo+3Co) / (3Mn+Cr)>=1.0 (2).

Description

technical field [0001] The present invention relates to steel materials and steel pipes for oil wells, and more specifically, to steel materials and steel pipes for oil wells suitable for use in acidic environments. Background technique [0002] Oil wells and gas wells (hereinafter, both oil wells and gas wells are collectively referred to simply as "oil wells") have become deeper and higher strength steel pipes for oil wells are required. Specifically, steel pipes for oil wells of 80ksi grade (yield stress of 80 to 95ksi, or 551 to 655MPa) and 95ksi grade (yield stress of 95 to 110ksi, or 655 to 758MPa) are widely used, and more recently, 110ksi grade (yield stress of 655 to 758MPa) has been further pursued. Steel pipes for oil wells with a stress of 110-125ksi, that is, 758-862MPa) and 125ksi grade (yield strength of 125-140ksi, that is, 862-965MPa). [0003] Deep wells are mostly acid environments containing corrosive hydrogen sulfide. Steel pipes for oil wells used in ...

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Problems solved by technology

[0012] However, in Patent Document 1 to Patent Document 3, the fracture toughness value in the DCB test is not studied.

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