Corrosion Studies of Austenitic and Ferritic Stainless Steels in Solution Containing Chloride Ions

The corrosion behavior of stainless steel AISI 304 and AISI 430 was investigated in NaCl 3.0% in the presence and absence of the pyridine and benzimidazole inhibitors. The electrochemical study was performed using the technique of polarization, the surface morphology of the electrodes was characterized by using the techniques of X-rays Diffraction, Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM) and the composition was investigated by EDX (Energy Dispersive X-rays). Figure 1 shows the X-ray diffraction pattern of stainless steels investigated in this paper. As can be seen in this Figure, the AISI 304 steel has diffraction peaks at the following 2θ angles: 44.59 °, 50.79 °, 74.71 ° and 90.62 ° that have been associated  of nickel-iron (FeNi) phase composed (PDF [3-1209]). Beyond this phase was also observed phase of chromium (Cr) peaks (at 44.56 ° and 84.84 °) associated with the X-ray diffraction pattern PDF-data [1-1261]. It is perceived that there is a separation between two different cubic phases, but the chromium phase has a space group Im3m while the iron-nickel phase has not been identify the spatial group. The results obtained by the potentiodynamic polarization curves showed that the AISI 304 steel is more resistant AISI 430. The efficiency of the inhibitor was tested at six different concentrations (2 ppm, 25 ppm, 50 ppm, 100 ppm, 500 ppm and 1000 ppm) for each, and all concentrations was observed an increase in potential, so raising corrosion resistance. All analyzes obtained show that higher corrosion resistance with 50 ppm of pyridine for steel AISI 304 and 50 ppm of benzimidazole to AISI 430.

Figure 1. XRD pattern of the AISI 304.

Table 1. Results obtained from Tafel studies for the alloys in different concentration of the pyridine inhibitor.

	AISI 304			AISI 430
Solution (NaCl 3%)	Ecorr (mV)	Rp (kΩ cm2)	I (%)	Ecorr (mV)	Rp (kΩ cm2)	I (%)
Absence of inhibitor	-283	31.05	-	-426	1.94	-
5 ppm	-200	79.00	61.0	-415	2.19	11.4
25 ppm	-193	94.65	67.9	-403	3.83	49.3
50 ppm	-186	105.80	70.7	-385	4.42	56.1
100 ppm	-203	83.48	62.8	-327	8.87	78.1
500 ppm	-213	62.54	50.4	-300	18.44	89.5
1000 ppm	-221	49.27	37.0	-314	5.09	61.9

This paper was supported by the funding agencies: FAPES, CAPES and CNPq.