PURPOSE: To obtain the steel excellent in corrosion resistance under a corrosive environment containing sulfurous acid ions even after heating and having superior workability ad high frequency tube making property by regulating components among respective alloying elements and forming a passivating film having A1 concentrated layer.
CONSTITUTION: A ferritic stainless steel having a composition which contains, by weight, 0.015% or less C, 0.1-0.5% Si, 0.4% or less Mn, 0.04% or less P, 0.01% or less S, 0.6% or less Ni, 18-23% Cr, 1.3-2.5% Mo, 0.1-0.3% Cu, 0.1-0.6% Nb, 0.05-0.3% Ti, 0.01-0.3% A1, and 0.02% or less N and satisfies C+N≤0.03 and Nb+Ti≥7(C+ N)+0.15 and where the value of P defined by P=5Ti+20(A1-0.01) is regulated to 1.0 or higher, is used. A base material made of this steel is annealed and subjescted to acid pickling including electrolytic treatment in nitric acid and immersion in a mixed acid solution of nitric acid and hydrofluoric acid, thereby, a passivating film which has Al concentrated layer and where the Al content in the part of the highest Al concentration is regulated to a value two or more times the Al content in the base material is formed on the surface of the base material. By this method, the desired steel can be obtained.
FURUKI TOSHIYUKI
ADACHI TOSHIRO
SUGIMOTO YASUHIRO
