Sumitomo Metal Industries, Inc.

Hiroshi Okamoto

Kazuhiro Ogawa

Masanari Kimoto

Kunihiro Fukui

Takao Taka

Munekatsu Furugen

Atsushi Satoh

Jun-ichi Uchida

Clad pipe having an inner pipe and an outer pipe metallurgically bonded to each other is manufactured by a process comprising the steps of: (a) preparing an inner pipe and an outer pipe made of different metallic materials, the outer pipe having an inner diameter larger than the outer diameter of the inner pipe; (b) forming an Ni-B layer by electroplating or electroless plating on the surface of one of the pipes facing the other pipe when the two pipes are assembled, the Ni-B layer having a thickness of 2-100 .mu.m and consisting essentially, on a weight basis, of B: 0.5%-7%, Fe: 0%-30%, P: 0%-7%, and a balance of Ni and inevitable impurities; (c) assembling the two pipes by inserting the inner pipe into the outer pipe; (d) subjecting the assembled pipes to cold working for reduction in diameter to such a degree that the outer diameter of the inner pipe is reduced by from 0.5% to 10% to form raw clad pipe in which the inner and outer pipes are in contact; and (e) subjecting the raw clad pipe to heat treatment in the temperature range of 1050.degree.-1250.degree. C. for a time sufficient to metallurgically bond the inner and outer pipes by diffusion bonding.

Process for manufacturing clad pipe

A duplex stainless steel has a chemical composition consisting essentially, on a weight basis, of: C: 0.03% or less, Si: 1.0% or less, Mn: 1.5% or less, P: 0.040% or less, S: 0.008% or less, sol.Al: 0.040% or less, Ni: 5.0-9.0%, Cr: 23.0-27.0%, Mo: 2.0-4.0%, N: 0.24-0.32%, W: greater than 1.5% and at most 5.0%, optionally at least one element selected from the group consisting of Cu: 0.2-2.0% and V: 0.05-1.5% and/or the group consisting of Ca: 0.02% or less, Mg: 0.02% or less, B: 0.02% or less, and one or more rare earth metals: 0.2% or less in total, and a balance of Fe and incidental impurities. The chemical composition has a value of at least 40 for PREW defined by the following formula (a):

Duplex stainless steel having improved strength and corrosion resistance

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Minoo, Japan

Hiroshi Okamoto