Corrosion behavior of nitride layer obtained on AISI 316L stainless steel via simple direct nitridation route at low temperature

• Published in: Materials chemistry and physics 2011-04, Vol.126 (3), p.507-514
• Main Authors: Hamdy, Abdel Salam, Marx, Brian, Butt, Darryl
• Format: Article
• Language: English
• Subjects: 316L stainless steels; Austenitic stainless steels; Corrosion; Corrosion resistance; Electrochemical impedance spectroscopy; Electrochemical techniques; Heat resistant steels; Nitride layer; Nitrides; Polarization; Potassium nitrates; Protective coatings; Stainless steels; Synthesis; Thermochemical treatment
• ISSN: 0254-0584; 1879-3312
• DOI: 10.1016/j.matchemphys.2011.01.037

► New thermochemical low-temperature nitride synthesis route in potassium nitrate salt in nitrogen atmosphere at 450 °C was proposed. ► The corrosion protection performance offered by this route was very promising for stainless steel. ► The paper provided an attempt towards determining the optimum conditions for synthesis of nitride coatings of superior corrosion resistance for stainless steel substrate. Newly developed low-temperature nitride synthesis route was used to introduce interstitial nitrogen into the passive layer of as-received and as-polished 316L stainless steel. The new thermochemical route is based on treating the stainless steel samples in potassium nitrate melt in an ultra pure nitrogen atmosphere at 450 °C. Electrochemical impedance spectroscopy (EIS) and dc polarization measurements have been used to evaluate the nitride layer performance in 3.5% NaCl solution. Results showed a marked increase in the corrosion resistance of nitrided stainless steel even after maintaining two weeks in NaCl solution. The effect of the treatment temperature was also studied. Data showed that the as-polished samples nitrided at 450 °C have the highest corrosion resistance. The polarization resistance ( R p) for the as-polished and as-received blank stainless steel samples was estimated by EIS were approximately 4.0 × 10 4 Ω cm 2 and 2.0 × 10 4 Ω cm 2, respectively. The R p increased by a factor of 2.5–5 for the nitrided samples. Increasing the nitriding temperature from 450 to 600 °C affects negatively the corrosion resistance of stainless steel in NaCl solution. The R p of the samples nitrided at 600 °C decreased sharply being almost 1/30 of the R p of the samples nitrided at 450 °C. Linear polarization measurements showed that the lowest corrosion rates and highest polarization resistances obtained from the as-polished nitrided samples at 450 °C. It has been found from the potentiodynamic measurements that the E corr of the as-polished nitrided samples at 450 °C is nobler than that measured from the other groups. The surface morphology was analysed by optical microscope and SEM-EDS under different nitriding conditions.