NaCl Solution Electrochemical Behavior Of Precipitation Hardening Stainless Steel

0Cr17Ni4Cu4Nb martensite precipitation-hardening stainless steel and0Cr17Ni7Al semi-austenitic precipitation-hardening stainless steel are the most widely used precipitation-hardening stainless steel nowadays. Because of their good corrosion consistence and comprehensive mechanical properties, they are widely used in shipbuilding industry. Pitting corrosion happens easily when ship devices service in seawater for long time, which shortens their life span. So the study of critical condition and mechanism of pitting corrosion at different temperature and different pH in Cl" medium has very important practical value to protect precipitation-hardening stainless steel from pitting corrosion.The electrochemical behavior of0Cr17Ni4Cu4Nb and0Cr17Ni7A1precipitation-hardening stainless steel in NaCl solution has been studied by electrochemical technology, and the following results:1. With temperature falling\NaCl concenteation decreasing\pH increasing, the critical pitting potential Eb of the two kinds of precipitation-hardening stainless steel decrease, which improves pitting corrosion resistance.2. The cyclic anodic curve shows that with temperature increasing\NaCl concentration increasing\pH decreasing, the value of Eb-Ep and relative annular area value increased, which promotes self-catalytic acidification in pitting hole and leads to dissolution of stainless steel anode active.3. The AC impedance spectroscopy results show that with temperature falling\NaCl concentration decreasing\pH increasing, the double-layer capacitance of stainless steel(C1) and the equivalent capacitance of passive film(C2) decrease, the charge transfer resistance (Rt) and the equivalent resistance of passive film increase, the low frequency impedance magnitude increase and the phase angle decrease, the frequency domain of phase angle peak move to high frequency zone. All these above form a barrier layer of high resistance-low capacitance which can inhibit and slow down the corrosion reaction.4. The M-S curve results show that the passivation film is a N-type semiconductor structure, and Mott-Schottky curve is a straight line and it’s slope is positive in the potential range of-0.4～0.4V. With temperature falling\pH increasing, the donor-density decrease as well as the passivation film structure become stable improving pitting corrosion resistance. 5. The XRD results show that the surface of0Cr17Ni4Cu4Nb stainless steel after corrosion is constituted by Fe, Fe2O3, Fe3O4, Cr2O3and FeCl3; The corrosion surface of0Cr17Ni7Al stainless steel is constituted by Fe, AlCrFe2, Fe2O3, Fe3O4, Cr2O3, AICl3and FeOCl. All these suggests that Cl-is involved in the corrosion process of stainless steel.