| 摘要 |
PROBLEM TO BE SOLVED: To improve the corrosion resistance in an atmospheric environment and a water environment contg. chlorine ions by dipping stainless steel into a nonoxidizing aq. soln. in which ozone is dissolved and forming a passive film in which Cr is concentrated into the value equal to or above a specified one on the surface of the steel. SOLUTION: As an aq. soln. for dissolving ozone, general water such as clean water is used, but corrosive ions such as chlorine ions may be present therein. Moreover, an oxidizing soln. contg. a non-oxidizing acid such as hydrofluoric acid, sulfuric acid and hydrochloric acid is usable, but, preferably, the acid concn. of hydrofluoric acid is suppressed to <=5%, and that of hydrochloric acid to <=10%. In dipping treatment using the aq. soln. in which ozone has been dissolved, the concn. of ozone, temp. and dipping time in the aq. soln. are set in such a manner that the concn. of Cr in a passive film to be formed on the surface of stainless steel reaches >=50 atomic %. Preferably, the concn. of ozone is held to about 5 ppm, and the temp. to the range from ordinary temp. to 60 deg.C, and, as for the dipping time, the longer, the better.
|
