PSI - Issue 71

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

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To evaluate the microstructures of the as-rolled, solution-treated, and aged samples, they were examined under a microscope (RMM 08; Radical ProCAM metal analyzer). X-ray diffraction (XRD, Rigaku, Japan) was used to identify the different phases present in the material, and Cu Kα radiation was used with a step size of 0.02° and 2θ range of 40 100°.

Table 2: Heat treatment of 17-4PH SS for 1h, 4h, 8h, and 32h aging durations and sample designations.

Label

Heat treatment

ST

Solution heat treatment at 1040 o C for (1h) followed by water quenching

ST+Aging 1h ST+Aging 4h ST+Aging 8h ST+Aging 32h

ST+Aging at 480 °C for 1h followed by air cooling ST+Aging at 480 °C for 4h followed by air cooling ST+Aging at 480 °C for 8h followed by air cooling ST+Aging at 480 °C for 32h followed by air cooling

Microhardness measurements (VH1-MDX Economet Chennai Metco, India) were performed on metallographically polished specimens. A 300 g load (HV 0.3 ) was applied for 15 s for each measurement, with ten indentations made on each sample. The average hardness value was calculated, and all tests were conducted at ambient temperature.

Fig.1 Heat treatment profiles of the experiments.

The electrochemical corrosion characteristics of the as-received and heat-treated 17-4 PH SS samples were evaluated using potentiodynamic polarization techniques. The tests were performed using a three-electrode setup linked to a CH instrument potentiostat (USA). Polished 17-4 PH stainless steel working electrodes (0.7854 cm² exposed area) were immersed in distilled water containing 3.5 wt.% NaCl solution. A graphite rod was used as the counter electrode, and an electrode made of saturated calomel (SCE) was used as the reference electrode. Prior to polarization, the samples underwent a one-hour open-circuit potential (OCP) stabilization. Potentiodynamic scans were performed from -700 mV to 700mV at a sweep rate of 1 mV/s. Using the Tafel extrapolation, the corrosion current density (i Corr ), corrosion potential (E corr ), and rate of corrosion (mm/year) were calculated using the following equations (Chaudhary, Baral et al. 2023). Both OCP and PDP measurements were carried out on three samples under each material condition, and the average values were considered to summarize the results. ( ) = 0.00327 Where W E represents the equivalent weight, A is the exposed area of the working electrode in square centimeters, D is the density of the material in grams per cubic centimeter, and i corr is the corrosion current in microamperes. The density of the 17-4PH SS samples was 7.75 g/cc. The material had an equivalent weight of 25.15.