Ferrite-based stainless steel for use in components of automobile exhaust system

1. A ferritic stainless steel for components of an automobile exhaust system, the ferritic stainless steel consisting of, in terms of percent by mass:

C: ≦0.015%;

Si: 0.01% to 0.50%;

Mn: 0.01% to 0.50%;

P: ≦0.050%;

S: ≦0.010%;

N: ≦0.015%;

Al: 0.010% to 0.100%;

Cr: 16.5% to 22.5%;

Ni: 0.51% to 2.0%;

Sn: 0.01% to 0.50%;

Mo: 0.01% to 0.2%;

either one or both of Ti: 0.03% to 0.30% and Nb: 0.03% to 0.30%; and

a remainder of Fe and inevitable impurities;

wherein:

a total elongation measured through a tensile test defined in JISZ2201 is 30.7% or more;

a ratio of a maximum corrosion depth of the ferritic stainless steel to a maximum corrosion depth of SUS436L is less than 1 in each of the following cases:

(a) where the maximum corrosion depth is measured by a method including:

(i) taking a test specimen from the ferritic stainless steel;

(ii) subjecting the test specimen to a heating treatment in air atmosphere at a temperature of 400° C. for 8 hours;

(iii) subjecting the heat-treated test specimen to a cycle corrosion test according to JASO-M609-91; and

(iv) measuring the maximum corrosion depth; and

(b) where the maximum corrosion depth is measured by a method including:

(i) the taking of the test specimen from the ferritic stainless steel;

(ii) the subjecting of the test specimen to the heating treatment in air atmosphere at the temperature of 400° C. for 8 hours;

(iii) subjecting the heat-treated test specimen to a condensed water corrosion test based on JASO-M611-92-A except that a concentration of Cl ions in a test liquid is set to 1000 ppm; and

(iv) the measuring of the maximum corrosion depth.

2. A ferritic stainless steel for components of an automobile exhaust system, the ferritic stainless steel consisting of, in terms of percent by mass:

C: ≦0.015%;

Si: 0.01% to 0.50%;

Mn: 0.01% to 0.50%;

P: ≦0.050%;

S: ≦0.010%;

N: ≦0.015%;

Al: 0.010% to 0.100%;

Cr: 16.5% to 22.5%;

Ni: 0.51% to 2.0%;

Sn: 0.01% to 0.50%;

Mo: 0.01% to 0.2%;

either one or both of Ti: 0.03% to 0.30% and Nb: 0.03% to 0.30%;

either one or both of B: 0.0002% to 0.0050% and Cu: 0.01% to 0.35%; and

a remainder of Fe and inevitable impurities;

wherein:

a total elongation measured through a tensile test defined in JISZ2201 is 30.7% or more;

a ratio of a maximum corrosion depth of the ferritic stainless steel to a maximum corrosion depth of SUS436L is less than 1 in each of the following cases:

(a) where the maximum corrosion depth is measured by a method including:

(i) taking a test specimen from the ferritic stainless steel;

(ii) subjecting the test specimen to a heating treatment in air atmosphere at a temperature of 400° C. for 8 hours;

(iii) subjecting the heat-treated test specimen to a cycle corrosion test according to JASO-M609-91; and

(iv) measuring the maximum corrosion depth; and

(b) where the maximum corrosion depth is measured by a method including:

(i) the taking of the test specimen from the ferritic stainless steel;

(ii) the subjecting of the test specimen to the heating treatment in air atmosphere at the temperature of 400° C. for 8 hours;

(iii) subjecting the heat-treated test specimen to a condensed water corrosion test based on JASO-M611-92-A except that a concentration of Cl ions in a test liquid is set to 1000 ppm; and

(iv) the measuring of the maximum corrosion depth.