*2.4. Potentiodynamic Polarization*

Potentiodynamic polarization was performed at a scan rate of 1 mV/s using a potentiostat (PC/750; Gamry Instruments, Warminster, PA, USA). Samples were degreased with acetone and ethanol solution after polishing, and a standard three-electrode system was used to measure the icorr and Ecorr of the samples. The reference electrode was a saturated calomel electrode, with graphite used as the counter electrode (the sample was used as the working electrode). NaCl solution (3.5 wt%) and1MH2SO4 solution were used as the electrolytes at room temperature. The corrosive mediums of 3.5% NaCl and 1.0 M sulfuric acid solution were prepared from analytical-reagent-grade sodium chloride, sulfuric acid, and double-distilled water. Both the NaCl solution and H2SO4 solution were kept in open-air condition. All the experiments were carried out at room temperature in the open atmosphere, under unstirred conditions. The surface area of samples exposed to the solution differed from sample to sample; however, during plotting, this was standardized according to the same sample area. Tables 2 and 3 present the icorr and Ecorr values obtained by the Tafel extrapolation.


**Table 2.** Ecorr and icorr values of maraging steel in 3.5% NaCl solution.

**Table 3.** Ecorr and icorr values of maraging steel in1MH2SO4 solution.


#### *2.5. Electrochemical Impedance Spectroscopy (EIS)*

EIS was performed using the potentiostat (Gamry Instruments) in a three-electrode system and at an amplitude range of 10 mV rms and a frequency interval of 0.1–30 kHz. These experiments were also done in the same solutions, i.e., 3.5% NaCl solution and 1.0 M H2SO4 solution. Here also all experiments were done at room temperature where solutions were kept in open air and unstirred condition. At each frequency, the absolute impedance and a Nyquist plot were obtained. The obtained impedance data were fit to an appropriate equivalent electrical circuit, with the fitting performed using a simplex fit mode and using both the real and imaginary components of the data. The impedance data were interpreted based on an equivalent electric circuit, and Nyquist plots were obtained at the open-circuit potential for all samples at different solutions.
