Stainless steel for polymer fuel cell separator and method of manufacturing the stainless steel
Provided are stainless steel for a polymer fuel cell separator and a method of manufacturing the stainless steel, in which a surface modification technique based on wet processing is applied to a surface of stainless steel used for parts such as an anode and a cathode, etc., of a stack that generates electricity, thereby improving corrosion resistance and electric conductivity, and preventing moisture from being formed.
1 . A method of manufacturing stainless steel for a polymer fuel cell separator, the method comprising:
providing a stainless base material comprising, by weight %, C: 0.01 to 0.08%, Si: 0.3 to 1.0%, Mn: 0.3 to 2.0%, Cr: 15 to 35%, Cu: 1.0% or less, N: 0.01 to 0.05%, Ti: 0.3% or less, Nb: 0.3% or less, and as the rest, Fe and inevitable impurities, the stainless base material having a passivation film formed on a surface thereof;
performing degreasing processing by immersing the surface of the stainless base material in a degreasing solution, wherein the degreasing solution contains 0.1 to 3 mol/L of sodium hydroxide, 0.01 to 2 mol/L of silicate, 0.005 to 0.8 mol/L of phosphate, and 0.02 to 3 mol/L of carbonate, along with a surfactant and an emulsifier;
after etching the degreasing-processed stainless base material with an etching solution, performing desmut processing with a desmut solution; and
performing surface stabilization on the etched and desmut-processed stainless base material with a surface stabilization solution,
wherein the degreasing processing includes performing immersion processing in the degreasing solution at 30 to 70° C. for 0.5 to 5 minutes, and
wherein after the degreasing processing, the etching, and the surface stabilization, the stainless steel comprises a surface modification layer having an interfacial contact resistance of 10 to 35 mΩ·cm 2 , and containing 15% less oxygen and 15% more chromium than a comparable layer produced without undergoing the degreasing processing, the etching, and the surface stabilization.
2 . The method of claim 1 , wherein the stainless base material further comprises one or more kinds of P: 0.14 weight % or less, S: 0.03 weight % or less, H: 0.004 weight % or less, and O: 0.007 weight % or less.
3 . The method of claim 1 , wherein the etching processing comprises performing immersion for 0.2 to 2 minutes in an etching solution, heated to 40 to 80° C., comprising at least two or more of 2.5 to 6.2 mol/L of sulfate ions, 0.1 to 2.0 mol/L of nitrate ions, and 1.0 to 5.0 mol/L of fluoride, and
the desmut processing comprises performing immersion for 0.5 to 2 minutes in a desmut solution, heated to 40 to 80° C., comprising 1.5 to 6.0 mol/L of hydrogen peroxide, 1.0 to 4.0 mol/L of fluoride, and 0.001 to 0.01 mol/L of a corrosion inhibitor.
4 . The method of claim 1 , further comprising, after performing the surface stabilization, performing stabilization thermal processing for stabilization of the surface-stabilized stainless base material.
5 . The method of claim 4 , wherein the stabilization thermal processing is performed at 150 to 250° C. for 1 to 10 minutes.
6 . A method of manufacturing stainless steel for a polymer fuel cell separator, the method comprising:
providing a stainless base material comprising, by weight %, C: 0.01 to 0.08%, Si: 0.3 to 1.0%, Mn: 0.3 to 2.0%, Cr: 15 to 35%, Cu: 1.0% or less, N: 0.01 to 0.05%, Ti: 0.3% or less, Nb: 0.3% or less, and as the rest, Fe and inevitable impurities, the stainless base material having a passivation film formed on a surface thereof;
performing degreasing processing by immersing the surface of the stainless base material in a degreasing solution to remove an organic matter from the surface, wherein the degreasing solution contains 0.1 to 3 mol/L of potassium hydroxide, 0.01 to 2 mol/L of silicate, 0.005 to 0.8 mol/L of phosphate, and 0.02 to 3 mol/L of carbonate, along with a surfactant and an emulsifier;
after etching the degreasing-processed stainless base material with an etching solution, performing desmut processing with a desmut solution; and
performing surface stabilization on the etched and desmut-processed stainless base material with a surface stabilization solution that includes nitrate of 2.7 to 13.8 mol/L, sulfate of 0.05 to 0.5 mol/L, and surfactant,
wherein the degreasing processing includes performing immersion processing in the degreasing solution at 30 to 70° C. for 0.5 to 5 minutes, and
wherein after the degreasing processing, the etching, and the surface stabilization, the stainless steel comprises a surface modification layer having an interfacial contact resistance of 10 to 35 mΩ·cm 2 , and containing 15% less oxygen and 15% more chromium than a comparable layer produced without undergoing the degreasing processing, the etching, and the surface stabilization.