CORROSION ENGINEERING SECTION 357 CORROSION—Vol. 62, No. 4 Submitted for publication June 2005; in revised form, November 2005. ‡ Corresponding author. E-mail icosta@ipen.br. * IPEN/CNEN-SP, CCTM, Av. Lineu Prestes, 2242–Cidade Universi- tária, CEP 05508-000, São Paulo–SP, Brazil. ** LEC, Departamento de Química–CFM, Campus Trindade, CEP 88040-900–UFSC, Florianópolis–SC, Brazil. Corrosion Resistance of Injection-Molded 17-4PH Steel in Sodium Chloride Solution I. Costa, ‡, * C.V. Franco,** C.T. Kunioshi,* and J.L. Rossi* ABSTRACT The corrosion resistance of 17-4PH powder injection-molded (PIM) martensitic stainless steel (SS) was evaluated in natu- rally aerated sodium chloride (NaCl) solution (3 wt%) at 25°C. This resistance was investigated by analyzing the curves of the evolution of open-circuit potential with time (E ocp vs. time), electrochemical impedance spectroscopy (EIS), and surface observation by scanning electron microscopy (SEM) at increas- ing times of immersion. The susceptibility to pitting was inves- tigated using cyclic potentiodynamic polarization curves and SEM observation after polarization. Additionally, the suscepti- bility to intergranular corrosion was evaluated by a modified procedure described in ASTM A 262 Practice A. The results of the 17-4PH PIM steel were compared to that of a 17-4PH steel produced by conventional metallurgy. The results showed that under steady-state conditions the PIM steel presented a behavior typical of passive metals during the whole test pe- riod (60 days of immersion). This was indicated by the E ocp vs. time curves, EIS results, and SEM observation of the surface at increasing periods of immersion. The steel showed a bright metallic surface and no signs of corrosion during the whole period of the test. Cyclic potentiodynamic polarization curves indicated that both 17-4PH steels, conventional and PIM, are susceptible to pitting but the PIM steel showed a slightly increased susceptibility to pitting, which was supported by posttest observation by SEM. In the PIM steel, pits seemed to be related to the porosity that had inner oxide inclusions. The 17-4PH steel, produced by both PIM technology and conven- tional metallurgy, did not show a susceptibility to intergranu- lar corrosion by ASTM A 262 Practice A. KEY WORDS: electrochemical impedance spectroscopy, martensitic stainless steel, passive films, pitting corrosion, polarization INTRODUCTION Precipitation-hardenable (PH) steels are stainless steels (SS) that can be hardened by aging heat treat- ments. They are classified as austenitic, semiausten- itic, or martensitic steels. The 17-4PH (17Cr-4Ni) SS type belongs to the precipitation-hardened martensitic group. 1 It has a martensitic structure with low carbon content. After aging treatments its microstructure comprises tempered martensite and extremely fine, copper-rich intermetallic precipitates, whose prop- erties depend on the aging temperature used. Heat treatment is straightforward and, with the exception of the solution treatment, is usually carried out at rel- atively low temperatures. The alloy is ferromagnetic, in both the solution-treated and aged states. The 17-4PH steel is one of the most widely employed pre- cipitation-hardened SS, being commonly used in nu- clear power plants, aircraft and gas turbines, oil and gas wells, and chemical process components owing to a combination of good mechanical properties and cor- rosion resistance at temperatures up to approximately 700°C. It also has a moderate corrosion resistance to salt spray atmosphere. Some of its properties, such as electrical resistivity, thermal expansion, and ther- mal conductivity are similar to those of austenitic and duplex steels, while its mechanical strength, after the 0010-9312/06/000067/$5.00+$0.50/0 © 2006, NACE International