Three methods of pickling passivation treatment of 304 stainless steel products Three methods of pickling passivation treatment of stainless steel products 1 General treatment (1) Pickling agent HNO36%～25%+HF0.5%～8% (volume fraction); Temperature 21 ° C ~ 60 ° C; time as needed; or pharmaceutical ammonium citrate 5% ~ 10% (mass fraction); temperature 49 ° C ~ 71 ° C; time 10 min ~ 60 min.
(2) passivation agent HNO 320% ~ 50% (volume fraction); temperature 49 ~ 71 ° C; time 10min ~ 30min; or temperature 2l ~ 38 ° C; time 30min ~ 60min; or pharmaceutical HNO320% ~ 50% + Na2Cr207H2O22% ~ 6% (mass fraction); temperature 49 ° C ~ 54 ° C; time 15 min ~ 30 min; or temperature 21 ° C ~ 38 ° C; time 30 min ~ 60 min.
(3) descaling pickling agent H2SO 48% ~ 11% (volume fraction);
Temperature 66 ° C ~ 82 ° C; 6 inches between 5 min ~ 45 min; and pharmaceutical HNO36% ~ 25% + HF 0.5% ~ 8% (volume fraction); temperature 21 ° C ~ 60 ° C; or HNO315% ~ 25% + HFl% ~ 8% (volume fraction).
2 Paste treatment (1) Take the internal surface weld of Guangzhou Petrochemical Urea Stainless Steel new equipment and the passivation of the base material passivation and maintenance surface grinding as an example of pickling paste: 25% HNO3~+4%HF+7l% Condensed water (volume fraction) and BaSO4 were adjusted to a paste. Passivation paste: 30% HNO3 or 25% HNO3 + 1% (mass fraction) K2Cr2O7 and BaSO4 are adjusted to a paste. The surface is coated for 5 to 30 minutes, rinsed with condensed water to pH = 7, and a single passivation method can also be used for spraying hydrogen peroxide.
(2) Take the patent of Shanghai Daming Iron Works as an example. Pickling passivation paste: HNO38%~14% (as passivating agent); HF10%~15% (as corrosive agent); hard moon S acid magnesium 2.2%~2.7% (as thickener) magnesium nitrate 60%～70 % (for filler, improve adhesion and permeability); sodium polyphosphate 2.3% ~ 2.8% (as a corrosion inhibitor); water (adjust viscosity).
3 Electrochemical treatment of the stainless steel workpiece to be treated as an anode, control the potentiostatic anode treatment, or the stainless steel workpiece as the cathode, control the constant potential for cathodic treatment, then the stainless steel workpiece as the anode, control the constant potential for the anode Treatment, and continue to change its constant potential for passivation treatment, the electrolyte solution uses HNO3. After this treatment, the properties of the stainless steel passivation film are improved, and the corrosion resistance is greatly improved. The pitting critical potential (Eb) is increased by about 1000 mV (in 3% NaCl) and the resistance to uniform corrosion is increased by three orders of magnitude (in 20% to 30% H2SO4 at 45 °C).
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