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Article

Effects of Passivation with Cu and W on the Corrosion Properties of Super Duplex Stainless Steel PRE 42

by
Dohyung Kim
1,2,
Seongjun Kim
3,
Jinyong Park
3,
Doo-In Kim
1,*,
Byung-Hyun Shin
3,* and
Jang-Hee Yoon
3,*
1
Innovative Graduate Education Program for Global High-Tech Materials and Parts, Pusan National University, Busan 46241, Republic of Korea
2
The Institute of Materials Technology, Pusan National University, Busan 46241, Republic of Korea
3
Busan Center, Korea Basic Science Institute, Busan 46241, Republic of Korea
*
Authors to whom correspondence should be addressed.
Metals 2024, 14(3), 284; https://doi.org/10.3390/met14030284
Submission received: 26 January 2024 / Revised: 24 February 2024 / Accepted: 26 February 2024 / Published: 28 February 2024
(This article belongs to the Special Issue Corrosion Behavior of Carbon Steels in Natural and Industrial Environments—2nd Edition)
Browse Figures
Versions Notes

Abstract

:
Carbon steel is subjected to several pretreatments to enable its use in highly corrosive environments, such as marine structures. However, its surface treatment is problematic owing to various processes, and these problems can be solved by replacing it with super duplex stainless steel (SDSS), which exhibits remarkable strength and corrosion resistance owing to its austenite and ferrite phases. EN 1.4410 and EN 1.4501 are the most extensively used SDSS grades in marine structures, as they exhibit exceptional strength and corrosion resistance in seawater. This study subjected EN 1.4410 and EN 1.4501 samples to specific heat treatment after casting and observed their structural alterations through field emission scanning electron microscopy. Their passivation states, with or without the Cu and W layers, were determined by examining their corrosion properties through open-circuit potential measurements, electrostatic polarisation tests, electrochemical impedance spectroscopy (EIS), and critical pitting temperature (CPT) analysis. The inclusion of Cu significantly improved the uniform corrosion resistance within the passivation layers, whereas the addition of W enhanced the pitting resistance (Epit, CPT). Additionally, the EIS analysis confirmed a double-layer structure in the passivation layer of EN 1.4501. Moreover, Cu did not act as a strengthening element of the passivation layer, whereas W significantly reinforced it.

1. Introduction

Carbon steel is the most widely used structural material in various industries. However, its low corrosion resistance renders it unsuitable for use in highly corrosive environments. Therefore, surface treatments are typically employed to enhance its corrosion resistance. Among the diverse industrial environments, settings such as offshore platforms are exposed to particularly harsh conditions of seawater and maritime winds, which cause considerable corrosion and abrasion. Although existing surface treatment technologies have significantly improved the abrasion and corrosion resistance of carbon steel, they are still insufficient for materials used on offshore platforms. Although studies on the addition of elements such as Cu to enhance the corrosion resistance of steel have been conducted, they have obtained insufficient results, and further research is required to develop materials with higher corrosion resistance.
Among the various types of steel, stainless steel is particularly interesting because of its remarkable corrosion resistance and strength [1,2,3,4,5], whereas duplex stainless steels (DSSs) exhibit excellent strength and corrosion resistance owing to their high Cr and Ni contents [6,7,8]. DSSs are graded based on their pitting resistance equivalents (PRE = wt.% Cr + 3.3 wt.% Mo + 16 wt.% N), with super grade DSSs (SDSSs) having PREs of 40–50 [9,10,11]. However, the high alloy content of SDSS makes controlling its microstructure and chemical composition challenging. Cu and W have demonstrated superior corrosion resistance compared with other austenitic stainless steels, and their effects on SDSSs are similar to those on austenitic stainless steels [12,13,14]. EN 1.4501 is prepared by adding Cu and W to EN 1.4410.
SDSSs (EN 1.4410 and EN 1.4501) are sensitive to heat treatment conditions, which necessitates their appropriate processing. Previous studies have extensively investigated various heat treatment conditions for SDSSs, and this study selected optimal solution annealing conditions accordingly [15,16,17,18]. Although the effect of chemical composition on corrosion resistance has been investigated in previous studies, insufficient attention has been paid to discern the relationship between the state of the passivation layer and corrosion properties [19,20,21]. Therefore, studying the state and alloying properties of the passivation layer in SDSSs is essential to facilitate material selection based on the usage environment. However, quantitative analyses of the effects of Cu and W are lacking. Therefore, it is imperative to analyse the impact of Cu and W on SDSS after solution annealing at various temperatures.
Variations in the microstructure and chemical composition of SDSSs depend on the solution annealing temperature, which directly affects their corrosion resistance [22,23,24]. Although previous research, notably Kim’s investigation into the impact of Cu and W content on strength, has offered some insights, the application of SDSSs in seawater necessitates a deeper exploration of their electrochemical properties [3,25,26]. Cu bolsters resistance to uniform corrosion, whereas W fortifies the material against pitting corrosion [27,28,29]. Thus, meticulous analyses of the influences of Cu and W additions on the formation and behaviour of the passivation layer, particularly its electrochemical properties, are imperative for SDSSs with these augmentations. Surprisingly, despite the widespread use of EN 1.4410 in marine settings, comprehensive studies on this critical aspect are scarce.
Various studies have comprehensively explored the microstructure and chemical composition of SDSSs during each phase to improve their corrosion resistance. Notably, Nillson investigated the intricacies of heat treatment conditions, whereas Tehovnik et al. focused on the phase and composition variation at different heat treatment temperatures [1,2,10]. In addition, Abdolvand provided valuable insights into the mechanical properties of the weld zones in SDSSs [30]. Despite the knowledge provided in these studies, the electrochemical properties of the passivation layer are not yet fully understood, particularly the influence of various Cu and W compositions on SDSS characteristics [14]. Therefore, it is critical to investigate the corrosion behaviour of SDSSs employed in practical applications, particularly in environments such as seawater, to obtain a more comprehensive understanding of their overall performance.
Some comprehensive investigations have been conducted to scrutinise the impact of Cu and W augmentations on the passivation layers of SDSSs [8,31,32]. The initial steps involved confirming the volume fractions using a Schaeffler diagram, followed by subjecting the material to various solution heat treatments at different temperatures. Microstructural analysis was performed using field emission scanning electron microscopy (FE-SEM), whereas energy-dispersive X-ray spectroscopy (EDS) was employed for composition analysis. Because of the limitations of EDS, the nitrogen composition was inferred from the fractions of austenite and ferrite. Subsequently, the electrochemical properties after heat treatment were thoroughly assessed. This entailed an array of analyses, including open-circuit potential (OCP) measurements, potentiodynamic polarisation tests, critical pitting temperature (CPT) determination, and electrochemical impedance spectroscopy (EIS). Further characterisation involved subjecting the surface to X-ray photoelectron spectroscopy (XPS), a technique instrumental in elucidating the influence of chemical composition on the formation of the passivation layer. This multifaceted approach aimed to comprehensively understand the interplay between material composition, processing, and the resultant electrochemical behaviour in SDSSs, particularly in terms of their passivation layer dynamics with Cu and W additions.

2. Materials and Methods

2.1. Materials and Heat Treatment

Table 1 lists the chemical compositions of the SDSS samples, obtained through inductively coupled plasma mass spectrometry (ICP-MS), which was used to assess the impact of Cu and W on the passivation layer of SDSS (POSCO SS, SDSS, PRE above 40 to 50) with a PRE of 42 (PRE = wt.% Cr + 3.3 wt.% Mo + 16 wt.% N) [1,6,33,34]. The Schaeffler diagram shown in Figure 1 was used to determine the appropriate heat treatment conditions [2]. Heat treatments were conducted at 1100 and 1080 °C for EN 1.4410 and EN 1.4501, respectively, followed by a rapid quenching process. The sequence of the heat treatment procedures is shown in Figure 2. After casting, the initially heterogeneous microstructures underwent a one-hour treatment at each designated temperature [11,24]. This duration aimed to stabilise the microstructure via solution heat treatment, ensuring its readiness for the subsequent analysis of the effects of Cu and W on the passivation layers of the SDSSs. The samples used in the heat treatments and analysis were round SDSS bars with a diameter of 5 cm and a height of 1 cm, fabricated by casting.

2.2. Microstructure and Volume Fraction

The preparation of SDSS involved a meticulous process. Initially, the material was polished with diamond paste, followed by electrical etching in a 20 wt.% NaOH solution at 5 V for 10 s [6,23,24]. This electro-etching was aimed at ensuring the grain boundaries of the austenite and ferrite. Microstructural examinations were conducted using high-resolution FE-SEM (SUPRA 40VP system, Zeiss, Land Baden-Württemberg, Germany). The volume fraction was measured from the FE-SEM images at a magnification of 200×, and the chemical composition was analysed without etching. EDS was used to confirm the chemical composition, excluding nitrogen, which was calculated based on the volume fraction [21,35,36]. This thorough methodology enabled a comprehensive understanding of the microstructure of the material, which is crucial for evaluating the effects of Cu and W on the passivation layer of an SDSS, and was observed five times at 200× [11,33]. The chemical composition was analysed without etching. The chemical composition was confirmed using EDS; however, the chemical composition of N was calculated based on the volume fraction [1,2].
Nr = chemical composition of NTotal wt.% − FerriteVF × 0.05 wt.%

2.3. Corrosion Properties

The corrosion properties were assessed using a three-electrode cell configuration with a potentiometer (Versa State 3.0, AMETEK, Inc., Berwyn, PA, USA) [1,6,22]. This setup consisted of a working electrode (the specimen under observation, an analysis area of 1 cm2), a reference electrode (RE, saturated calomel electrode (SCE, KCl electrolyte solution)), and a counter electrode (CE, Pt mesh) [25]. The evaluation involved various electrochemical tests conducted in different electrolytes: 3.5 wt.% NaCl for OCP, potentiodynamic polarisation tests, and EIS [8,31,32]. In addition, CPT analysis was performed using a 5.85 wt.% NaCl electrolyte. OCP measurements tracked the voltage changes over 3600 s, providing insights into the reactivity and potential alterations post passivation. Potentiodynamic polarisation tests were used to determine the electrochemical behaviour by varying the current density (A/cm²) across a potential range of −0.6–1.2 V. EIS was conducted at a frequency range of 10−1–107 Hz in the 3.5 wt.% NaCl electrolyte (maintaining a potential of 230 mV and a current density of 300 μA/cm2) [3,27,37]. CPT was instrumental in assessing the efficacy of the passivation layer when the current density surpassed 100 μA/cm2 [26,38,39]. The temperature was increased at a rate of 1 °C/min to identify the point at which the pits exhibited stable growth. This multifaceted approach allowed for a comprehensive evaluation of the corrosion behaviour of the material under different conditions, elucidating the influence of Cu and W on the passivation layer of the SDSS. The electrochemical analysis was conducted seven times.

2.4. Passivation Layer

To verify the effects of Cu and W on the passivation layer of SDSS, the binding energy of the passivation layer was assessed through angle-resolved X-ray photoelectron spectrometry (AR-XPS) [40,41,42]. XPS analysis was performed on a cubic sample having dimensions of 0.5 × 0.5 × 0.5 cm3. A combined analysis of the EIS and XPS results confirmed the respective effects of Cu and W on the passivation layer, providing a more comprehensive understanding of their effects on the electrochemical behaviour of SDSS.

3. Results and Discussion

3.1. Microstructure

SDSS requires heat treatment because the volume fraction of austenite and ferrite changes depending on the heat treatment temperature. Solid-solution heat treatment was performed to optimise the corrosion resistance of the material [1,2,4,16,17]. The microstructure was confirmed through solution heat treatment after casting, as illustrated in Figure 3, wherein austenite is indicated in light grey, whereas the base microstructure (ferrite) is indicated in dark grey. Notably, the corrosion resistance of SDSS was optimal under an austenite (γ)–ferrite (δ) ratio of 5:5, where the PREs of austenite and ferrite were equal. The difference in the PREs of austenite and ferrite decreases the corrosion resistance, leading to galvanic corrosion. Figure 4 shows that the volume fractions aligned with the proportions achieved during solution annealing, as noted by Nilson and Tan. This indicates that the aforementioned heat treatment and materials are optimal for enhancing corrosion resistance.
After solution annealing, the chemical composition was analysed before determining the electrochemical properties. Table 2 lists the chemical compositions, and Figure 5 illustrates the PRE values derived from these compositions. The calculated PRE was 42, with an error margin of less than 0.4. A low PRE gap of austenite and ferrite indicates corrosion sites along the grain boundaries [1,6,22].
Solution annealing equalised the volume fractions and chemical compositions of austenite and ferrite. Given that the SDSS treated with solution annealing exhibited the most favourable electrochemical properties, analysing the effects of Cu and W on these properties is imperative.

3.2. Electrochemical Properties

The electromotive force series denotes the initiation potential of the pure materials rather than that of the alloys. The OCP was used for electrochemical potential measurements of the materials, and the results are shown in Figure 6 [20,21,26]. Notably, EN 1.4501 exhibited a higher potential than EN 1.4410.
The potentiodynamic polarisation test results, shown in Figure 7 and summarised in Table 3, illustrate the electrochemical behaviour of the materials. Under active polarisation, the potentials are equivalent; however, the current densities differ. The passivation potentials range from −0.1 to 1.0 V, whereas the pitting potential of EN 1.4501 is higher than that of EN 1.4410. EN 1.4501 exhibits a lower corrosion rate during passivation because of the presence of Cu. The advanced pitting potential (Epit) indicates the effect of W.
Electrochemical analysis confirmed that the Cu and W added to the SDSS acted as reinforcing elements for the passivation layer. Figure 8 shows the CPT curves, and Figure 9 shows the pitting morphology after CPT. Both Cu and W acted as strengthening agents for the passivation layer, and despite exhibiting equivalent PRE values, a difference exceeding 1 °C from 75.2 to 76.4 °C was observed in the CPT (Blue line: CPT measurement starting time) values [39,43,44]. Considerable research has been conducted on enhancing the corrosion resistance of stainless steels. This study substantiates the effects of adding Cu and W alloys to bolster the passivation layer and improve corrosion resistance. Additionally, EN 1.5401 experienced metastable pitting during the CPT, which initially disappeared. This phenomenon was observed in the passivation layer strengthened with Cu and W that underwent re-passivation.
The surface resistance evaluations through EIS revealed differences between EN 1.4410 and EN 1.4501. Figure 10 shows the Bode and Nyquist plots, and Table 4 lists the major values of the EIS results. EN 1.4501 exhibited a two-step passivation layer, indicating potential improvements in corrosion resistance [27,31,45]. The Bode plots show the differences in lZl and Z phases with respect to frequency, whereas the Nyquist plot shows the effects of Cu and W. Typically, the curve and Rp of EN 1.4410 reflect the passivation results of the SDSS. However, in this study, the curve and Pp of EN 1.5401 do not reflect the passivation results of the SDSS because the curve exhibits two steps and the value is high. The passivation resistances of EN 1.4410 and EN 1.5401 were 260 and 403 kΩ, respectively. This difference indicates an advanced corrosion resistance.
Electrochemical analysis confirmed that both Cu and W added to the SDSS functioned as reinforcing elements for the passivation layer, and despite having the same PRE values, their CPT values differed by more than 1 °C. Considerable research has been conducted to enhance the corrosion resistance of stainless steels. This study substantiates the effects of adding Cu and W alloys to bolster the passivation layer and improve corrosion resistance.

4. Discussion

SDSS, renowned for its exceptional strength and corrosion resistance, is more suitable than surface-treated carbon steel for harsh environments containing chloride ions, such as offshore platforms. However, current research is focused on strengthening its passive layer. This study specifically investigated the influence of Cu and W on the passive layers of SDSS alloys to enhance our understanding of their properties and performance under demanding conditions.
The introduction of Cu and W into the chemical composition of SDSS alloys led to variations in the solution annealing temperature, which was tailored to achieve equivalent PREs [1,2,6,23]. After solution annealing at 1100 and 1080 °C, the addition of Cu and W induced discrepancies in the electrochemical properties of SDSS specimens, even in those with comparable PRE values. Consequently, an increase in the corrosion potential (Ecorr) and a decrease in the corrosion rate (Icorr) were observed during active polarisation in the potentiodynamic polarisation curve. Furthermore, the pitting potential (Epit) increased from 1.10 to 1.16 V [16,20,46]. The potentiodynamic polarisation curve clearly illustrates the impact of Cu and W on corrosion behaviour. In particular, the CPT analysis showed enhanced resistance to pitting only in EN 1.4501 owing to Cu and W, whereas EIS delineated their influence on passivation. The passivation layer, characterised by a double layer, improved with the addition of Cu and W. The resistance to pitting was enhanced because the breach point in the passivation layer was delayed by the reinforcement configuration.
XPS analysis revealed the factors influencing the passivation layer, and the results presented in Figure 11 and Table 5 reveal that the W4+ reactant played a pivotal role [40]. In EN 1.4410, the passivation layer primarily comprises Cr2+, whereas that of EN 1.4501 is reinforced with a double layer attributed to W4+ [13,19]. The relatively slower reactivity of W4+ compared to the galvanic corrosion within the passivation layer enhanced its strengthening effect. These outcomes were evident in the OCP, potentiodynamic polarisation curves, and CPT analyses. By contrast, no Cu is observed in the surface composition analysis, which contrasts with the EDS findings. Therefore, based on the XPS results, Cu does not appear to reinforce the passivation layer of SDSS.
Various factors augment the pitting corrosion resistance of SDSS, with the reinforcement of the passivation layer by W demonstrating efficacy despite the reduction in Mo content [21,26,46]. Nonetheless, a deeper investigation into the influence of W on the grain morphology and size of SDSS is imperative for the development of advanced, highly corrosion-resistant materials.
The addition of W to SDSS enhanced its resistance to pitting corrosion (local corrosion) by reinforcing the passivation layer. However, owing to its body-centred cubic lattice structure, W acts as a ferrite-stabilising element and experiences higher stresses than other atoms, given its atomic number of 74 (a larger atomic size than Fe, Cr, and Ni). Consequently, excessive W content can decrease the corrosion resistance as the solution annealing temperature is increased. By contrast, Cu incorporated into SDSS comprises a face-centred cubic lattice structure, serving as an austenite-stabilising element and thereby reducing the uniform corrosion rate. Although increasing the Cu-alloy content decreased the uniform corrosion rate, it did not enhance the resistance in pitting environments. Additionally, Cu-induced austenite stabilisation lowers the solution annealing temperature. However, the solution annealing temperature must be reduced cautiously as it approaches the precipitation temperature of the secondary phases (Sigma and Chi).

5. Conclusions

To confirm the effects of Cu and W on the passivation layer of SDSS, the microstructure and electrochemical properties of EN 1.4410 and EN 1.4501 were analysed, and the following conclusions were drawn:
  • Even with the addition of less than 1 wt.% of Cu and W, the solution annealing temperature of the SDSS alloys varied. Equivalent phase fractions and PRE values were achieved for EN 1.4410 and EN 1.4501 after solution heat treatments at 1100 and 1080 °C, respectively, indicating differences in their electrochemical properties. Therefore, as Cu and W are key alloy elements that affect the corrosion resistance of SDSS, precise investigations of their alloy characteristics are imperative.
  • The pitting corrosion resistance of SDSS alloys in Cl ion electrolyte solutions depended on the PRE; however, the addition of Cu and W changed their corrosion behaviours and resistances. The addition of Cu decreased the corrosion rate (from 1 × 10−7 to 2 × 10−7), and the addition of W increased the pitting corrosion resistance (from 1.10 to 1.16 V in the potentiodynamic polarisation results and from 75.2 to 76.7 °C on the CPT curve). The addition of Cu and W increased the corrosion resistance owing to the formation of an advanced passivation layer.
  • The electrochemical characteristics of SDSS are influenced by the chemical composition of its passivation layer, with W playing a significant role in its enhancement, as corroborated by the EIS and XPS analyses. The EIS results revealed that the passivation layer of SDSS containing Cu and W comprised two distinct layers. W contributed to the reinforcement of this passivation layer (from 260 to 403 kΩ Ohms on the Nyquist plot of EIS) by facilitating the formation of reactive species, leading to the development of an advanced passivation layer characterised by a double layer, as evidenced by XPS findings. Thus, the corrosion resistance of SDSS can be strengthened by the chemical composition of the passivation layer, particularly by the addition of W.
  • The solution annealing temperature of EN 1.4501 was reduced to 1080 °C by adding Cu and W. However, the passivation layer strengthened by W improved its pitting resistance. EN 1.4501 exhibited a stronger passivation layer than EN 1.4410; therefore, it has an improved seawater lifespan. In this study, the influence of alloy materials on the passivation layer of SDSS was investigated to develop highly corrosion-resistant materials. This study is expected to facilitate the future development of SDSS for use in various environments.

Author Contributions

Conceptualisation, D.K.; methodology, B.-H.S.; validation, D.K., J.P. and B.-H.S.; formal analysis, D.K., J.-H.Y. and B.-H.S.; investigation, D.-I.K.; resources, S.K. and B.-H.S.; data curation, D.K.; writing—original draft preparation, D.-I.K.; writing—review and editing, D.K., J.-H.Y. and B.-H.S.; visualisation, J.P.; supervision, D.K., J.-H.Y. and B.-H.S.; project administration, D.K. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Korea Basic Science 1 Institute, grant number C330320; the Korean Institute for Advancement of Technology (KIAT) grant funded by the Korean Government (MOTIE), grant number P0023676 (HRD Programme for Industrial Innovation); and the BK21 FOUR programme, grant number 4120200513801, funded by the Ministry of Education (MOE, Korea) and the National Research Foundation of Korea (NRF).

Data Availability Statement

The original contributions presented in the study are included in the article, further inquiries can be directed to the corresponding authors.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Schaeffler diagram and volume fractions at 1050 °C of EN 1.4410 and EN 1.4501.
Figure 1. Schaeffler diagram and volume fractions at 1050 °C of EN 1.4410 and EN 1.4501.
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Metals 14 00284 g002
Figure 2. Schematic of the solution annealing process used to optimise the superior electrochemical properties of EN 1.4410 and EN 1.4501.
Figure 2. Schematic of the solution annealing process used to optimise the superior electrochemical properties of EN 1.4410 and EN 1.4501.
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Figure 3. FE-SEM images of solution-annealed super DSSs: EN 1.4410 (a) before and (b) after solution annealing at 1100 °C; EN 1.4501 (c) before and (d) after solution annealing at 1080 °C.
Figure 3. FE-SEM images of solution-annealed super DSSs: EN 1.4410 (a) before and (b) after solution annealing at 1100 °C; EN 1.4501 (c) before and (d) after solution annealing at 1080 °C.
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Figure 4. Volume fractions of solution-annealed EN 1.4410 at 1100 °C and EN 1.4501 at 1080 °C.
Figure 4. Volume fractions of solution-annealed EN 1.4410 at 1100 °C and EN 1.4501 at 1080 °C.
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Metals 14 00284 g005
Figure 5. PRE = wt.% Cr + 3.3 wt.% M o + 16 wt.% N of EN 1.4410 solution-annealed at 1100 °C and EN 1.4501 at 1080 °C.
Figure 5. PRE = wt.% Cr + 3.3 wt.% M o + 16 wt.% N of EN 1.4410 solution-annealed at 1100 °C and EN 1.4501 at 1080 °C.
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Figure 6. Potential (V) vs. time (s) curves. OCP curves of EN 1.4410 solution-annealed at 1100 °C and EN 1.4501 at 1080 °C in 3.5 wt.% NaCl electrolyte solution.
Figure 6. Potential (V) vs. time (s) curves. OCP curves of EN 1.4410 solution-annealed at 1100 °C and EN 1.4501 at 1080 °C in 3.5 wt.% NaCl electrolyte solution.
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Figure 7. Current density (µA/cm2) vs. potential (V) curves. Potentiodynamic polarisation curves of EN 1.4410 and EN 1.4501 solution-annealed in 3.5 wt.% NaCl electrolyte solution.
Figure 7. Current density (µA/cm2) vs. potential (V) curves. Potentiodynamic polarisation curves of EN 1.4410 and EN 1.4501 solution-annealed in 3.5 wt.% NaCl electrolyte solution.
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Figure 8. Current density (µA/cm2) vs. time (s) curves. CPT curves of solution-annealed super DSSs in 5.85 wt.% NaCl electrolyte solution.
Figure 8. Current density (µA/cm2) vs. time (s) curves. CPT curves of solution-annealed super DSSs in 5.85 wt.% NaCl electrolyte solution.
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Figure 9. Pitting morphologies after CPT tests of solution-annealed (a) EN 1.4410 and (b) EN 1.4501 in 5.85 wt.% NaCl electrolyte solution.
Figure 9. Pitting morphologies after CPT tests of solution-annealed (a) EN 1.4410 and (b) EN 1.4501 in 5.85 wt.% NaCl electrolyte solution.
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Figure 10. EIS results of solution-annealed super DSSs in 3.5 wt.% NaCl electrolyte solution. Bode plots of (a) IZI (Ω) and (b) phase of Z (Ω) as functions of frequency. (c) Nyquist plot and EIS circuit under the passivation condition.
Figure 10. EIS results of solution-annealed super DSSs in 3.5 wt.% NaCl electrolyte solution. Bode plots of (a) IZI (Ω) and (b) phase of Z (Ω) as functions of frequency. (c) Nyquist plot and EIS circuit under the passivation condition.
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Figure 11. Binding energy (eV) vs. count (s) curves (XPS diagram) of EN 1.4410 and EN 1.4501 at 1100 and 1080 ℃, respectively. Binding energy curves of (a) Cr from 564 to 590 eV, (b) Mo from 224 to 240 eV, and (c) W from 24 to 38 eV.
Figure 11. Binding energy (eV) vs. count (s) curves (XPS diagram) of EN 1.4410 and EN 1.4501 at 1100 and 1080 ℃, respectively. Binding energy curves of (a) Cr from 564 to 590 eV, (b) Mo from 224 to 240 eV, and (c) W from 24 to 38 eV.
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Table 1. Chemical compositions of the SDSS samples EN 1.4410 and 1.4501, obtained through ICP-MS.
Table 1. Chemical compositions of the SDSS samples EN 1.4410 and 1.4501, obtained through ICP-MS.
MaterialCNMnNiCrMoCuWFe
EN 1.44100.010.270.86.825.03.80.20.02Bal
EN 1.45010.010.240.66.725.23.70.70.60Bal
Table 2. Chemical compositions of major alloys, obtained through EDS, after solution annealing of EN1.4401 at 1100 °C and EN 1.4501 at 1080 °C.
Table 2. Chemical compositions of major alloys, obtained through EDS, after solution annealing of EN1.4401 at 1100 °C and EN 1.4501 at 1080 °C.
Material (wt.%)PhaseCrNiMoCuWNFe
EN 1.4410Austenite23.3 ± 0.57.9 ± 0.23.2 ± 0.10.2 ± 0.10.00.51Bal
Ferrite26.6 ± 0.65.5 ± 0.24.4 ± 0.20.2 ± 0.10.00.05Bal
EN 1.4501Austenite23.8 ± 0.68.2 ± 0.23.0 ± 0.10.9 ±0.10.5 ± 0.10.49Bal
Ferrite26.6 ± 0.65.2 ± 0.24.4 ± 0.10.5 ± 0.10.7 ± 0.10.05Bal
Table 3. Predominant values in the potentiodynamic polarisation curve after solution annealing of EN 1.4410 and EN 1.4501 in 3.5 wt.% NaCl electrolyte solution.
Table 3. Predominant values in the potentiodynamic polarisation curve after solution annealing of EN 1.4410 and EN 1.4501 in 3.5 wt.% NaCl electrolyte solution.
MaterialEcorrIcorrEpit
EN 1.4410−0.12 V1 × 10−7 A/cm21.10 V
EN 1.4501−0.12 V2 × 10−7 A/cm21.16 V
Table 4. Predominant values from the EIS of solution-annealed super DSSs, EN 1.4410 and EN 1.4501.
Table 4. Predominant values from the EIS of solution-annealed super DSSs, EN 1.4410 and EN 1.4501.
MaterialCPERp (1+2) (kOhms)
C1C2n
EN 1.44106.22.9 × 105 260
EN 1.45016.22.9 × 1051.7 × 105403
Table 5. Surface chemical compositions of EN 1.4410 and EN 1.4501 obtained through XPS.
Table 5. Surface chemical compositions of EN 1.4410 and EN 1.4501 obtained through XPS.
Material (at.%)Mo3dNi2p3O1sCr2p3Fe2p3W4f
EN 1.44104.284.514.8225.2651.130.00
EN 1.45013.954.5414.8625.8650.400.39
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Kim, D.; Kim, S.; Park, J.; Kim, D.-I.; Shin, B.-H.; Yoon, J.-H. Effects of Passivation with Cu and W on the Corrosion Properties of Super Duplex Stainless Steel PRE 42. Metals 2024, 14, 284. https://doi.org/10.3390/met14030284

AMA Style

Kim D, Kim S, Park J, Kim D-I, Shin B-H, Yoon J-H. Effects of Passivation with Cu and W on the Corrosion Properties of Super Duplex Stainless Steel PRE 42. Metals. 2024; 14(3):284. https://doi.org/10.3390/met14030284

Chicago/Turabian Style

Kim, Dohyung, Seongjun Kim, Jinyong Park, Doo-In Kim, Byung-Hyun Shin, and Jang-Hee Yoon. 2024. "Effects of Passivation with Cu and W on the Corrosion Properties of Super Duplex Stainless Steel PRE 42" Metals 14, no. 3: 284. https://doi.org/10.3390/met14030284

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