Stainless steel substrate for solar cell having superior insulating properties and low thermal expansion coefficient and method of producing the same
Provided is a stainless steel substrate for a solar cell, the stainless steel substrate including, by mass %, Cr: 9% to 25%, C: 0.03% or less, Mn: 2% or less, P: 0.05% or less, S: 0.01% or less, N: 0.03% or less, Al: 0.005% to 5.0%, Si: 0.05% to 4.0%, and a remainder including Fe and unavoidable impurities, in which an oxide film containing (i) Al 2 O 3 in an amount of 50% or more or containing (i) Al 2 O 3 and (ii) SiO 2 in a total amount of 50% or more is formed on a surface of stainless steel having a composition which contains Al: 0.5% or more and/or Si: 0.4% or more and satisfies the following expression (1). Cr+10Si+Mn+Al>24.5 (1)
1. A stainless steel substrate for a solar cell having superior insulating properties and a low thermal expansion coefficient, the stainless steel substrate comprising:
stainless steel which contains, by mass %,
Cr: 9% to 25%,
C: 0.03% or less,
Mn: 2% or less,
P: 0.05% or less,
S: 0.01% or less,
N: 0.03% or less,
Al: 0.005% to 5.0%,
Si: 0.05% to 4.0%, and
a remainder including Fe and unavoidable impurities, satisfies one or both of Al content is 0.5% or more and Si content is 0.4% or more, and satisfies the following expression (1); and
an oxide film formed on a surface of the stainless steel, the oxide film containing (i) Al 2 O 3 in an amount of 50% or more or containing (i) Al 2 O 3 and (ii) SiO 2 in a total amount of 50% or more,
Cr+10Si+Mn+Al>24.5 (1)
where a symbol of each element in the expression (1) represents the amount (mass %) of the element in the steel, wherein the oxide film contains (iii) Mg Al 2 O 4 .
2. The stainless steel substrate for a solar cell having superior insulating properties and a low thermal expansion coefficient according to claim 1 ,
wherein the stainless steel contains Al: 2.0 to 5.0% and Si: 0.3 to 4.0%.
3. The stainless steel substrate for a solar cell having superior insulating properties and a low thermal expansion coefficient according to claim 1 ,
wherein the stainless steel further contains one element or two or more elements selected from the group consisting of, by mass %,
Sn: 1% or less,
Zr: 0.5% or less,
Mg: 0.0001 to 0.005%,
Ni: 1% or less,
Cu: 1% or less,
Co: 0.5% or less,
Mo: 2% or less,
V: 0.5% or less,
B: 0.005% or less,
Ca: 0.005% or less,
La: 0.1% or less,
Y: 0.1% or less,
Hf: 0.1% or less,
REM: 0.1% or less,
Nb: 1% or less, and
Ti: 1% or less.
4. The stainless steel substrate for a solar cell having superior insulating properties and a low thermal expansion coefficient according to claim 3 ,
wherein an amount of (iii) MgAl 2 O 4 in the oxide film is 5% or more.
5. A method of producing a stainless steel substrate for a solar cell having superior insulating properties and a low thermal expansion coefficient, the method comprising:
a film forming step of subjecting the stainless steel having the composition according to claim 1 to a heat treatment in an atmosphere containing water vapor in a temperature range of 300° C. to 1000° C. to form an oxide film on a surface of the stainless steel.
6. The method of producing a stainless steel substrate for a solar cell having superior insulating properties and a low thermal expansion coefficient according to claim 5 ,
wherein in the film forming step, the heat treatment is performed in an atmosphere containing water vapor having a dew point of 40° C. or higher.
7. The stainless steel substrate for a solar cell having superior insulating properties and a low thermal expansion coefficient according to claim 2 ,
wherein the stainless steel further contains one element or two or more elements selected from the group consisting of, by mass %,
Sn: 1% or less,
Zr: 0.5% or less,
Mg: 0.005% or less,
Ni: 1% or less,
Cu: 1% or less,
Co: 0.5% or less,
Mo: 2% or less,
V: 0.5% or less,
B: 0.005% or less,
Ca: 0.005% or less,
La: 0.1% or less,
Y: 0.1% or less,
Hf: 0.1% or less,
REM: 0.1% or less,
Nb: 1% or less, and
Ti: 1% or less.
8. The stainless steel substrate for a solar cell having superior insulating properties and a low thermal expansion coefficient according to claim 7 ,
wherein the oxide film contains (iii) MgAl 2 O 4 .
9. The stainless steel substrate for a solar cell having superior insulating properties and a low thermal expansion coefficient according to claim 8 ,
wherein an amount of (iii) MgAl 2 O 4 in the oxide film is 5% or more.
10. A method of producing a stainless steel substrate for a solar cell having superior insulating properties and a low thermal expansion coefficient, the method comprising:
a film forming step of subjecting the stainless steel having the composition according to claim 2 to a heat treatment in an atmosphere containing water vapor in a temperature range of 300° C. to 1000° C. to form an oxide film on a surface of the stainless steel.
11. A method of producing a stainless steel substrate for a solar cell having superior insulating properties and a low thermal expansion coefficient, the method comprising:
a film forming step of subjecting the stainless steel having the composition according to claim 3 to a heat treatment in an atmosphere containing water vapor in a temperature range of 300° C. to 1000° C. to form an oxide film on a surface of the stainless steel.