Patent ID: 9103041
Filing Date: 2015-08-11
Classification: C23C,C23G,H01M,Y02E

Abstract:
1. A method for improving surface properties of stainless steel for bipolar plate of polymer electrolyte membrane fuel cell, the method comprising: press forming and hydro forming cold-rolled annealing stainless steel for bipolar plate; degreasing the press formed and hydro formed cold-rolled annealing stainless steel; pickling the degreased stainless steel with an aqueous sulfuric acid solution, the stainless steel comprising, by weight: C: 0.02% or less, N: 0.02% or less, Si: 0.4% or less, Mn: 0.2% or less, P: 0.04% or less, S: 0.02% or less, Cr: 25˜32%, Mo: 0.1 to 5%, Cu: 0.1 to 2%, Ti: 0.5% or less, Nb: 0.5% or less, and the balance of Fe and other inevitable elements; washing the pickled stainless steel with water; passivating the washed stainless steel by immersing the washed stainless steel in a mixture solution of nitric acid and hydrofluoric acid to form a passivation layer; and plasma-nitriding the passivated stainless steel to form a nitride layer on a surface of the stainless steel, wherein the nitride layer includes CrN and/or Cr