Ferritic stainless steel and method for manufacturing same, ferritic stainless steel sheet and method for manufacturing same, and fuel cell member

1. Ferritic stainless steel, comprising, by mass %:

Cr: 12.0% to 16.0%;

C: 0.020% or less;

Si: 1.10% or more and 2.50% or less;

Mn: 1.00% or less;

P: 0.050% or less;

S: 0.0030% or less;

Al: 1% or more and 2.50% or less;

N: 0.030% or less;

Nb: 0.001% to 1.00%;

Ni: 0% to 1.0%;

Cu: 0% to 1.0%;

Mo: 0% to 1.0%;

Sb: 0% to 0.5%;

W: 0% to 1.0%;

Co: 0% to 0.5%;

V: 0% to 0.5%;

Ti: 0% to 0.5%;

Zr: 0% to 0.5%;

La: 0% to 0.1%;

Y: 0% to 0.1%;

Hf: 0% to 0.1%;

REM: 0 to 0.1%;

one or more of B: 0.0200% or less, Sn: 0.20% or less, Ga: 0.0200% or less, Mg: 0.0200% or less, and Ca: 0.0100% or less; and a balance being Fe and impurities,

wherein Expression (1) is satisfied,

10(B+Ga)+Sn+Mg+Ca>0.020  (1)

where each of the element symbols in Expression (1) indicates the content, in mass %, each of the elements in the steel, and

wherein a concentration of Nb at a crystal grain boundary is within a range of 3.0% to 10% by mass %.

2. The ferritic stainless steel according to claim 1 , comprising B: 0.0002% or more and 0.0200% or less by mass %.

3. The ferritic stainless steel according to claim 1 , comprising:

0.005% or more and 0.20% or less by mass % of Sn,

wherein a concentration of Sn at a crystal grain boundary is 1.0% to 5.0% by mass %.

4. The ferritic stainless steel according to claim 1 , comprising, by mass %:

Nb: 0.15% or more and 1.00% or less.

5. The ferritic stainless steel according to claim 1 , comprising, by mass %, one or more of Ni: 0.10% to 1.0%, Cu: 0.10% to 1.0%, Mo: 0.10% to 1.0%, Sb: 0.01% to 0.5%, W: 0.10% to 1.0%, Co: 0.10% to 0.5%, V: 0.10% to 0.5%, Ti: 0.01% to 0.5%, Zr: 0.01% To 0.5%, La: 0.001% to 0.1% or less, Y: 0.001% to 0.1%, Hf: 0.001% to 0.1%, and REM: 0.001% to 0.1%.

6. The ferritic stainless steel according to claim 1 , which is applied to a fuel reformer, a heat exchanger, or a fuel cell member.

7. The ferritic stainless steel according to claim 1 , which is applied to a combustor or a burner member.

8. A fuel cell member formed of the ferritic stainless steel according claim 1 .

9. A method for manufacturing the ferritic stainless steel according to claim 1 , the method comprising:

performing hot working on a ferritic stainless steel having the composition according to claim 1 ;

performing a heat treatment at a temperature higher than 700° C. thereafter;

performing cold working thereafter;

performing final annealing at a temperature higher than 700° C. thereafter; and

performing one of the following steps selected from (i) and (ii):

(i) performing a heat treatment to retain a temperature within a temperature range of 600° C. to 700° C. for longer than 1 minute and 3 hours or shorter after the final annealing;

(ii) performing a cooling in the final annealing with a passage time in the temperature range of 600° C. to 700° C. set to longer than 1 minute;

thereby resulting in the ferritic stainless steel according to claim 1 .