PSI - Issue 71

G. Narasinga Rao et al. / Procedia Structural Integrity 71 (2025) 317–324

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of time, and their values are listed in Table 3. In general, the OCP is the equilibrium potential of a sample that is isolated in a given environment when no external current flows (open circuit). The OCP value is often used to understand the tendency of a material to corrode (more negative value indicates a strong anodic nature of a metal). Fig.5 illustrates the OCP vs. time curves of the as-received and solution-treated + aged (different aging periods) samples. It is evident from Fig.5 that the heat-treated (ST + Aging) samples exhibited better (less negative) potential than the as-received sample. After exposure to 3.5 wt.% NaCl solution for one hour, all samples have almost reached a steady state. This steady-state condition is essential for initiating PDP testing without any electrochemical noise. It is to be noted that, compared to heat treated samples, the as-received sample OCP has the lowest value of -0.1959 V (Vs SCE), indicating a higher tendency towards corrosion. Among the heat-treated conditions, the ST+Aging 4h sample exhibited the highest OCP values for the entire one hour exposure to the NaCl medium, indicating that an aging period of after solution treatment is optimum to have less tendency towards corrosion.

Fig. 5 Open-circuit potential (OCP) as a function of time.

Fig. 6 Cyclic Potentiodynamic polarization curves of as-received (AR), ST+Aging 1h, ST+Aging 4h, ST+Aging 8h, ST+Aging 32h of 17–4 PH SS.

The potentio-dynamic polarization behaviour of 17-4 PH stainless steel under different material conditions has been studied in 3.5 wt.% NaCl immediately after OCP evaluation. To determine the corrosion current density (i corr ) and corrosion potential (E corr ), the Tafel extrapolation technique was utilized in the linear polarization region, as shown in Fig. 6. During the Tafel extrapolation, two tangents (anodic and cathodic) were drawn to identify the intersection point, which eventually provides the i corr and E corr values. The obtained i corr values of 17-4 PH stainless steel under different material