Kabushiki Kaisha Kobe Seiko Sho

Kohjiro Kitahata

Kazutoshi Shimogori

Toshio Fukuzuka

Yasushi Torii

Takuo Hosoda

Disclosed herein is a rolled steel having excellent resistance to sulfide stress corrosion cracking. It comprises 0.20-0.40 wt. % C, .ltoreq.0.50 wt. % Si, .ltoreq.1.90 wt. % Mn, .ltoreq.0.06 wt. % Al, 0.0030-0.0090 wt. % N, 0.005-0.10 wt. % Nb, 0.005-0.050 wt. % Ti, and the balance iron and inevitable impurities. The rolled steel contains at least 4.times.10.sup.8 ultrafine carbonitride particles or 0.1 .mu.m or smaller per mm.sup.3 as a result that a bloom or slab having the above components is soaked, subjected at 1200.degree.-950.degree. C. to rough rolling under conditions of a total reduction percentage of 75% or lower, cooled at a cooling rate of 1.5.degree. C./sec. or higher after completion of the rough rolling and until the initiation of finish rolling, and then completed with its final rolling above the A.sub.1 transformation temperature. A process for producing the above rolled steel is also disclosed.

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Akashi, Japan

Kohjiro Kitahata