Ferrite-based stainless steel with high resistance to corrosiveness caused by exhaust gas and condensation and high brazing properties and method for manufacturing same

1. A ferritic stainless steel, comprising, by mass %:

C: 0.001% to 0.030%;

Si: 0.01% to 1.00%;

Mn: 0.01% to 2.00%;

P: 0.050% or less;

S: 0.0100% or less;

Cr: 11.0% to 30.0%;

Mo: 0.75% to 3.00%;

Ti: 0.001% to 0.026%;

Al: 0.001% to 0.030%;

Nb: 0.010% to 1.000%; and

N: 0.050% or less,

with a remainder being Fe and inevitable impurities,

wherein an amount of Al, an amount of Ti, and an amount of Si (mass %) satisfy Al/Ti≥8.4Si-0.78,

a rolling direction is represented by an L direction, a direction perpendicular to the rolling direction is represented by a C direction, a direction inclined at 45° with respect to the rolling direction is represented by a V direction, and arithmetic average roughness values of a steel surface in the respective directions are respectively represented by R aL , R aC , and R aV (unit: μm), then (R aL +R aC +2R aV )/4≤0.50 and |(R aL +R aC −2R aV )/2|≤0.10 are satisfied.

2. The ferritic stainless steel according to claim 1 , further comprising, by mass %, any one or more of:

Ni: 0.01% to 3.00%;

Cu: 0.050% to 1.500%;

W: 0.010% to 1.000%;

V: 0.010% to 0.300%;

Sn: 0.005% to 0.500%,

Sb: 0.0050% to 0.5000%,

Mg: 0.0001% to 0.0030%,

B: 0.0002% to 0.0030%;

Ca: 0.0002% to 0.0100%;

Zr: 0.010% to 0.300%;

Co: 0.010% to 0.300%,

Ga: 0.0001% to 0.0100%,

Ta: 0.0001% to 0.0100%, and

REM: 0.001% to 0.200%.

3. The ferritic stainless steel according to claim 2 ,

wherein an amount of change in grain size number (GSN) before and after a thermal treatment at 1,150° C. for 10 minutes in a vacuum atmosphere of 50 Pa or lower is 5.0 or less.

4. The ferritic stainless steel according to claim 3 which is used in automobile mufflers, exhaust heat recovery devices, and EGR coolers that are automobile parts exposed to exhaust gas-condensate environments.

5. The ferritic stainless steel according to claim 2 which is used in automobile mufflers, exhaust heat recovery devices, and EGR coolers that are automobile parts exposed to exhaust gas-condensate environments.

6. The ferritic stainless steel according to claim 1 ,

wherein an amount of change in grain size number (GSN) before and after a thermal treatment at 1,150° C. for 10 minutes in a vacuum atmosphere of 50 Pa or lower is 5.0 or less.

7. The ferritic stainless steel according to claim 6 which is used in automobile mufflers, exhaust heat recovery devices, and EGR coolers that are automobile parts exposed to exhaust gas-condensate environments.

8. The ferritic stainless steel according to claim 1 which is used in automobile mufflers, exhaust heat recovery devices, and EGR coolers that are automobile parts exposed to exhaust gas-condensate environments.