| 摘要 |
PROBLEM TO BE SOLVED: To provide a stainless steel-made water circulation system comprising pipes, tanks, etc., wherein water circulating and flowing in its inside is not stained by eluted metal ions. SOLUTION: The stainless steel-made water circulation system comprising pipes, tanks, etc., is made by using stainless steel containing 0.6 mass% or lower Ni, 1.2 mass% or lower Mn, 0.01 mass% or lower S, and 0.003 mass% or lower Ca as a base material and by covering the surface of the base material with a passive film with a Fe concentration of 75 atom% or lower and a Cr concentration of 25 atom% or higher. The passive film with a high Cr concentration is formed by immersing the stainless steel in an ozone- or organic acid-containing solution, or by the nitric acid electrolysis, nitric acid immersion, or nitric-hydrofluoric acid immersion of annealed stainless steel, or by annealing the stainless steel in a reducing atmosphere. The stainless steel used as the base material may further contain at least one element selected from among 3.0 mass% or lower Mo, 1.0 mass% or lower Nb, 1.0 mass% or lower Ti, and 1.0 mass% or lower Al. COPYRIGHT: (C)2004,JPO
|
