Nippon Steel Corporation

Nippon Steel Sumitomo Metal Corporation

Hidenori Shitamoto

Masayuki Sagara

Daisuke Motoya

A duplex stainless steel with good low-temperature toughness is provided. The duplex stainless steel has a chemical composition of, in mass %: up to 0.03% C; 0.1 to 0.8% Si; up to 2.3% Mn; up to 0.040% P; up to 0.010% S; up to 0.040% sol. Al; 3 to 7% Ni; 20 to 28% Cr; 0.5 to 2.0% Mo; more than 2.0% and not more than 4.0% Cu; 0.02 to 0.5% Co; 0.1 to 0.35% N; up to 0.010% O; and other elements, the steel having a microstructure including an austenite phase and a ferrite phase, the ferrite phase having an area percentage of 30 to 60%, the steel satisfying the following Formula, (1);0.70&#xd7;Ni&#x2264;Ni&#x2003;&#x2003;(1),where Niand Niare obtained by using an electron-beam microanalyzer to measure Ni content and, in a distribution of Ni content, determining two maximum frequencies, and treating the one with a higher Ni content as Niand treating the one with a lower Ni content as Ni.

Duplex stainless steel and method of manufacturing duplex stainless steel

Provided is a method for producing a welded steel pipe having excellent buckling resistance. The method for producing a welded steel pipe according to the present embodiment includes steps of: preparing a welded pipe, and expanding the welded pipe over the entire length thereof by using a pipe expanding head such that an undulation wavelength ratio D defined by Formula (1) is not more than 0.8, or not less than 1.8:&#x2003;&#x2003;(1),where p is an undulation wavelength in the axial direction of the welded steel pipe, and &#x3bb; is a Timoshenko's buckling wavelength as defined by Formula (2):&#x3bb;=3.44&#xd7;()&#x2003;&#x2003;(2),where r is an inner radius of the welded steel pipe and t is a wall thickness of the welded steel pipe.

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Tokyo, Japan

Hidenori Shitamoto