Kobe Steel, Ltd.

Nippon Kokan Kabushiki Kaisha

Bunshiro Sakai

Makoto Yamada

Itaru Watanabe

Tomokazu Godai

Koshiro Tsukada

Isao Aida

Masatoshi Nakagaki

Mutsuro Araki

A method of manufacturing a thick, high-strength steel pipe for low temperature service comprising the steps of forming into tubular shape a steel plate having a thickness of over 12 mm and a specific composition, of which the C.sub.eq value is adjusted to less than 0.50, when the Mn content is less than 1.0 % whereas the C.sub.eq value is adjusted to less than 0.45 when the Mn content is over 1.0 % and less than 2.0 %, and nextly of welding said tube form at high speeds and high efficiency by the process of single electrode or multiple electrode large-current gas-shielded arc welding with one pass per electrode on each side of the seam at a specific condition, each electrode preferably consisting of a solid wire essentially containing less than 0.3 % Ti with or without the addition of less than 0.01 % B, and said steel pipe having, in its as-welded condition, mechanical properties such that the yield point of the base metal portion is over 60,000 psi and the weld zone has a maximum hardness of less than Hv10-280 and a Charpy test absorbed energy of over 7 Kg.m at -10.degree. F. Even when the C.sub.eq value of said steel plate is less than 0.65, a thick, high-strength steel pipe for low temperature service having equal mechanical properties to the above mentioned pipe may be manufactured, after welding, by subjecting the welded pipe to a post heat treatment in which the welded pipe is held at a temperature between 500.degree. and 700.degree. C for less than 1 hour.

Method of manufacturing thick, high-strength steel pipe for low

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Yokohama, Japan

Bunshiro Sakai