PSI - Issue 71

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

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Fig. 3 XRD of 17-4 PH SS AR, ST+Aging 1h, ST+Aging 4h, ST+Aging 8h, ST+Aging 32h.

3.2 Microhardness The microhardness (measured in HV 0.3 ) of the 17-PH SS with respect to the aging duration at 480 °C is shown in Fig.4. The material in the as-received (AR) condition had a microhardness of 364 HV. Upon solution treatment (ST), the hardness decreased slightly to approximately 355HV, reflecting a more homogenized but slightly softened structure owing to the dissolution of the secondary phases. Compared to AR and ST, the microhardness increased after aging for 1h, from 364 to 421 HV. The hardness increased because of the precipitation of copper phases, which effectively restricted the movement of dislocations. Extending the aging time to 4 and 8 h did not lead to a significant change, with the hardness remaining at approximately 415 HV, indicating that the majority of precipitation and hardening occurred within the first hour of aging, with additional time having a marginal effect on the hardness. The increasing size of the Cu-rich precipitates caused the microhardness to drop to 392 HV when the aging time was extended to 32 h (Wang, Li et al. 2018). It is evident from Fig.4 that the microhardness values of 17-4 PH SS in the aged condition are higher than those in the AR and ST conditions, regardless of the aging duration.

Fig. 4 Microhardness of 17-4 PH SS under different material conditions.

3.3 Corrosion behaviour The evaluation of corrosion characteristics is vital to understand the degradation behavior of any material. In this study, both as-received and heat-treated 17-4 PH stainless steel sample coupons were exposed to 3.5 wt.% NaCl solution to measure the open circuit potential (OCP) for 1 hour followed by the potentio-dynamic polarization (PDP) testing. The variations in the OCP of 17-4 PH stainless steel in the as-received and heat-treated conditions were monitored as a function