Stainless steel for separator of polymer fuel cell having excellent corrosion resistance
Disclosed is a stainless steel for a separator of a polymer fuel cell having excellent corrosion resistance. More particularly, disclosed is a stainless steel for a separator of a polymer fuel cell having excellent corrosion resistance in a sulfuric acid environment which is a fuel cell operating environment. According to an embodiment, the stainless steel for a separator of a polymer fuel cell includes, in percent by weight (wt %), 0.09% or less of C, 1.0% or more and less than 2.5% of Si, 1.0% or less (excluding 0) of Mn, 0.003% or less of S, 20 to 23% of Cr, 9 to 13% of Ni, 1.0% or less (excluding 0) of W, 0.10 to 0.25% of N, and the remainder of Fe and other inevitable impurities, wherein a corrosion resistance index represented by Formula (1) below is 7 or more. 3*W+1.5*Si+0.1*Cr+20*N−2*Mn (1) In Formula (1), W, Si, Cr, N, and Mn represent the content (wt %) of each element.
1 . An austenitic stainless steel for a separator of a polymer fuel cell comprising,
a matrix comprising, in percent by weight (wt %), 0.09% or less of C, 1.0% or more and less than 2.5% of Si, 1.0% or less (excluding 0) of Mn, 0.003% or less of S, 20 to 23% of Cr, 9 to 13% of Ni, 1.0% or less (excluding 0) of W, 0.10 to 0.25% of N, less than 0.6% of Mo and the remainder of Fe and other inevitable impurities; and
a passivated layer formed on a surface of the matrix in a form of oxide layer,
wherein a corrosion resistance index represented by Formula (1) below is 7 or more, and
wherein a value of Formula (2) below is 2.0 or more, and
wherein a value of Formula (3) below is from 1.4 to 2.0, and
wherein a thickness of the passivated layer is 6 nm or less:
3*W+1.5*Si+0.1*Cr+20*N−2*Mn Formula (1)
(wherein in Formula (1), W, Si, Cr, N, and Mn represent the content (wt %) of each element),
sum
of
contents
(
wt
%
)
of
Si
and
W
contained
in
passivated
layer
sum
of
contents
(
wt
%
)
of
Si
and
W
contained
in
matrix
,
Formula
(
2
)
(Cr+Mo+1.5Si+0.75 W)/(Ni+0.5Mn+20N+24.5 C) Formula (3)
(wherein in Formula (3), Cr, Mo, Si, W, Ni, Mn, N, and C represent the content (wt %) of each element).
2 . The austenitic stainless steel according to claim 1 , wherein an elongation is 40% or more.
3 . The austenitic stainless steel according to claim 1 , wherein a corrosion current density measured by applying a potential of 0.6 V relative to a calomel electrode for 24 hours in a mixed solution of sulfuric acid (H 2 SO 4 ) having a pH of 3 and hydrofluoric acid (HF) having a pH of 5.3 at 80° C. is 0.05 μA/cm 2 or less.
4 . The austenitic stainless steel according to claim 1 , wherein an amount of metal melted by applying a potential of 0.6 V relative to a calomel electrode for 24 hours in a mixed solution of sulfuric acid (H 2 SO 4 ) having a pH of 3 and hydrofluoric acid (HF) having a pH of 5.3 at 80° C. is 0.7 or less relative to that of the stainless steel 316L.