Comparison of corrosion behavior among I/M, P/M and MIM SUS304 stainless steels by electrochemical method

Materials used for this experiment were three kinds of Type 304 stainless steels: the first one was made by the conventional wrought process (I/M), the second one was made by conventional powder metallurgy process (P/M) and the third one was made by Metal Injection Molding process (MIM). Using these three stainless steel specimens the corrosion behavior of them were investigated in the aqueous solution (2.5kmol/m ³H ₂SO ₄+0.2kmol/ m ³NaCl) through potentiodynamic polarization curve measurement and electrochemical impedance spectroscopy (EIS). In EIS measurement, a natural electrode potential with perturbation AC potential, amplitude of which was 10mV was applied to the specimen, and analyzing frequency range was from 100 kHz to 1 mHz. Both the potentiodynamic polarization curve and the Nyquist plot curve of MIM specimen were similar to I/M specimen. These curves of P/M specimens were differed greatly from those of MIM and I/M specimens. Therefore it might be suggested that MIM process is quite suitable to improve the corrosion resistance. On the other hand, time constants of P/M and MIM specimens are similar, but they differed remarkably from that of I/M specimen, which is considered to be due to the remained pores in P/M and MIM specimens.