Stainless steel for separation plate of polymer electrolyte membrane fuel cell having improved hydrophilic property and corrosion resistance, and manufacturing method therefor

A method of manufacturing stainless steel for a separator of a polymer electrolyte membrane fuel cell, the method comprising:

• manufacturing a stainless steel sheet by performing cold rolling on stainless steel;
• a heat treatment process of forming a first passivation film on a surface of the stainless steel sheet by performing bright annealing on the stainless steel sheet;
• and
• a film reforming process of forming a second passivation film on the surface of the stainless steel sheet by reforming the first passivation film,
• wherein a ratio of Cr hydroxide/Cr oxide included in the second passivation film ranges from 0.75 to 1.6, and the second passivation film has a contact angle (θ) of 70° or less,
• wherein the film reforming process comprises:
• a first film reforming process of performing electrolytic treatment in a sulfuric acid solution at a first current density;
• a second film reforming process of performing electrolytic treatment in the sulfuric acid solution at a second current density, the second current density being equal to or less than the first current density;
• and
• a third film reforming process performed by immersion in a mixed acid solution comprising nitric acid and hydrofluoric acid, and
• wherein in the first film reforming process, a potential of the stainless steel sheet, corresponding to the first current density, satisfies Equations 1 and 2 below:
• E
• cathode
• ≥
• 1.
• (
• 1
• )
• ❘
• "\[LeftBracketingBar]"
• E
• cathode
• ❘
• "\[RightBracketingBar]"
• +
• ❘
• "\[LeftBracketingBar]"
• E
• anode
• ❘
• "\[RightBracketingBar]"
• ≥
• 2.
• 0
• (
• 2
• )
• Wherein the unit of the potential of the stainless steel sheet is volt (V).