Boil for 1 hour in a treatment bath containing 5ml/L monoethanolamine and 5g/L sodium chloride; after cleaning, bleach for 30 minutes in a treatment bath containing 5ml/L sodium hypochlorite (150g/L effective chlorine), 5g/L sodium nitrate (corrosion inhibitor), and pH 4-4.5; finally, treat with sodium sulfite (3g/L) at 60℃ for 15min or treat with 1-1.5g/L insurance powder at 85℃ for 20-30min, and clean.