Nippon Steel Sumitomo Metal Corporation

Masayuki Morimoto

Toru Takayama

Tomohiko Omura

Atsushi Soma

Mitsuhiro Numata

The present invention provides a steel which simultaneously satisfies a plurality of characteristics, specifically, a steel for tubes with excellent sulfide stress cracking resistance, including, C: 0.2 to 0.7%; Si: 0.01 to 0.8%; Mn: 0.1 to 1.5%; S: not more than 0.005%; P: not more than 0.03%; Al: 0.0005 to 0.1%; Ti: 0.005 to 0.05%; Ca: 0.0004 to 0.005%; N: not more than 0.007%; Cr: 0.1 to 1.5%; and Mo: 0.2 to 1.0%; the balance being Fe, Mg and impurities, being characterized in that: the content of Mg is not less than 1.0 ppm and not more than 5.0 ppm; and inclusions of not less than 50% of the total number of those in steel have such a morphology that Mg&#x2014;Al&#x2014;O-based oxides exist at the central part of the inclusion, Ca&#x2014;Al-based oxides enclose the Mg&#x2014;Al&#x2014;O-based oxides, and Ti-containing-carbonitrides further exist on a periphery of the Ca&#x2014;Al-based oxides.

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Kobe, Japan

Masayuki Morimoto