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Article

Effect of Nitrogen on Precipitate Characteristics and Pitting Resistance of Martensitic Stainless Steel

by
Hui Xu
1,
Jinbin Wang
2,
Yugui Li
3,*,
Bin Wang
1,4,
Huaying Li
1 and
Guangming Liu
1
1
School of Materials Science and Engineering, Taiyuan University of Science and Technology, Taiyuan 030024, China
2
State Key Laboratory of Rolling and Automation, Northeastern University, Shenyang 110819, China
3
School of Mechanical Engineering, Taiyuan University of Science and Technology, Taiyuan 030024, China
4
State Key Laboratory of Advanced Stainless Steel Taiyuan Iron and Steel (Group) Co., Ltd., Taiyuan 030003, China
*
Author to whom correspondence should be addressed.
Materials 2024, 17(15), 3817; https://doi.org/10.3390/ma17153817
Submission received: 4 July 2024 / Revised: 22 July 2024 / Accepted: 31 July 2024 / Published: 2 August 2024
(This article belongs to the Special Issue Advances in Mechanical Properties and Structure of Metal and Metal Composites)
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Versions Notes

Abstract

:
High-carbon–chromium martensitic stainless steel (MSS) is widely used in many fields due to its excellent mechanical properties, while the coarse eutectic carbide in MSS deteriorates corrosion resistance. In this work, nitrogen was added to the MSS to improve corrosion resistance. The effects of nitrogen on the microstructure and corrosion resistance of MSS were systematically studied. The results showed that the addition of nitrogen promoted the development of Cr2N and reversed austenite, effectively inhibiting the formation of δ-ferrite. Therefore, the durability of the passivation film was improved, the passivation zone was expanded, and the susceptibility to metastable pitting was decreased. As a consequence, nearly two orders of magnitude have been achieved in the pitting potential (Epit) of MSS containing nitrogen, and the polarization resistance value (Rp) has gone up from 4.05 kΩ·cm2 to 1.24 × 102 kΩ·cm2. This means that in a corrosive environment, nitrogen-treated MSS stainless steel is less likely to form pitting pits, which further extends the service life of the material.

1. Introduction

High-carbon–chromium martensitic stainless steel (MSS), as an important bearing material, finds widespread application in fields like marine vessels, aerospace, petrochemicals, and the nuclear industry, due to its high hardness and corrosion resistance [1,2]. However, the precipitation of coarse eutectic carbides reduces fatigue life and corrosion resistance [3,4]. As science, technology, and industry advance, there is a growing demand for materials with specific properties, especially in harsh conditions such as highly corrosive environments. This presents significant challenges for the microstructure and corrosion resistance of martensitic stainless steel. Therefore, research into new alloying methods to enhance the microstructure and properties of martensitic stainless steel has become a key focus in materials science.
Nitrogen (N), as a strong austenitic-forming element, is widely used in the steel alloying process [5,6,7]. Adding nitrogen to steel significantly impacts the microstructure of retained austenite, martensite shape, grain size, and precipitates [8,9,10]. It has been discovered that in 9Cr18Mo steel, substituting some of the C with N can decrease the quantity and size of eutectic carbides. As a result, the mesh eutectic carbides gradually vanish [11]. In a study by Li et al. [12], it was observed that increasing the nitrogen content in 4Cr13 steel reduced the precipitation of primary carbides and contributed to the refinement of dendrites.
Recently, researchers have revealed that adding nitrogen to steel enhances the interaction between N and Cr, resulting in the formation of fine nitrides and carbonitrides that disperse throughout the matrix [13]. This reduces the Cr that combines with C to form carbides, the carbon–chromium element segregation is reduced, the chance of large-grained carbide formation is reduced, and the carbide size is significantly refined [14,15].
In addition, although the thin (nanoscale) oxide layers naturally formed on the surface of stainless steel are effective in slowing corrosion, they are prone to localized breakdown, which accelerates the dissolution process of the underlying metal [16]. The presence of nitrogen can minimize defect density, increase the thickness of the passivation film, promote the enrichment of Cr in the passivation film, reduce metastable pitting sensitivity, and improve the ability of repassivation [17,18,19].
Leda et al. [20] reported that in 0.7C-13Cr martensitic stainless steel, the partial replacement of carbon with nitrogen (0.2 wt.%) can decrease pits. Shimada et al. [21] pointed out that when the performance of 0.65C-16Cr martensitic stainless steel is optimized, its nitrogen content should be controlled at 0.25 wt.%. Moreover, Qi et al. [22] showed that the corrosion resistance of nitrogenous MSS was excellent, but it did not show a monotonous trend with the increase in nitrogen content. Therefore, the action mechanism of nitrogen on MSS is complicated, and limited reports have been made to explain the effect of N on the microstructure evolution and the corrosion resistance of MSS. Thus, the effect of nitrogen on the corrosion resistance and microstructure evolution of MSSs is worthy to be systematically studied, which would provide valuable insights for the design and optimization of MSSs to adapt to industrial applications.
The work thoroughly investigates the nitrogen form in MSS and discusses its detailed impact on microstructure and electrochemical behavior. It also uncovers the specific mechanism through which nitrogen influences the microstructure and pitting resistance of MSS. The systematic analysis and experimental verification presented in this study provide an essential theoretical basis and practical guidance for understanding the role of nitrogen in MSS.

2. Materials and Methods

2.1. Materials Preparation

In this study, the N-free and 0.16 wt.% N MSS used was customized by a commercial company. The supply state is forged. Chemical analysis was performed using an optical emission spectrometer (ARL 4460, Thermo Scientific, Waltham, MA, USA), and to more accurately determine the nitrogen content, a special oxygen and nitrogen analyzer (ON736, LECO, Saint Joseph, MI, USA) was introduced for secondary detection. The chemical compositions are shown in Table 1. To make the description more concise, these two materials are designated as 0 N and 0.16 N in subsequent discussions. Spheroidal annealing treatment was carried out first during the material preparation process. The purpose was to uniform the structure, eliminate internal stress, and prepare the structure for subsequent quenching. The specific procedure was to place the sample in the furnace at 200 °C, then increase it to 875 °C and hold it for 5 h, then furnace cooled to 700 °C and kept for another 3 h, followed by cooling to 600 °C in furnace, finally air-cooled to room temperature [23]. After annealing, the samples were subjected to austenitization at 1030 °C for an hour. After austenitizing, the samples were quickly quenched in oil until cooled to ambient temperature. The quenched specimens underwent a low-temperature treatment at −80 °C for 2 h, followed by tempering at 300 °C for 2 h, illustrated in Figure 1a. The variation in phase fractions and precipitation with austenitizing temperature in the range of 500–1200 °C in the equilibrium conditions was calculated by the Thermo-Calc software 2023a equipped with the TCFE9 database.

2.2. Microstructure Characterization

Before the experiments, 10 × 10 × 3 mm samples were cut from heat-treated MSSs, grounded by 400–1500 grit abrasive paper in sequence, polished with 1.5 µm diamond spray, rinsed with deionized water and alcohol, and dried with hot air.
The microstructure was observed by scanning electron microscope (SEM, Zeiss Ultra-55, Jena, Germany) equipped with electron backscatter diffraction (EBSD, Oxford Instruments, Abingdon-on-Thames, UK) and transmission electron microscopy (TEM, FEI-Tecnai G2-F20, Thermo Fisher Scientific, Waltham, MA, USA).
SEM specimens etched using Vilella’s reagent (consisting of 1 g of picric acid, 10 mL of hydrochloric acid, and 100 mL of ethanol) [23], EBSD specimens were prepared by electro-polishing with 8 vol% perchloric acid and 92% ethanol at 30 V for 20 s. The EBSD tests, conducted at 20 KV with a step size of 0.16 μm, subsequently had their data analyzed using AztecCrystal 2.1. The TEM foils were ground to a thickness of 50 μm with a diameter of 3 mm and electro-polished via a twin-jet machine in a solution containing 8 vol% perchloric acid.
The element distribution of specimens was analyzed by the energy dispersive spectrometer (EDS) attached to SEM and an electron probe micro-analyzer (EPMA, JXA-8530 F, JEOL Co., Ltd., Kyoto, Japan). Phase characterizations were performed by X-ray diffraction (XRD, SmartLab 9 kW, Rigaku, Tokyo, Japan) with Cu Kα radiation, at a scanning rate of 2°/min from 20° to 90°.

2.3. Electrochemical Measurement

The specimens intended for electrochemical examination were first sliced into a shape measuring 10 × 10 × 3 mm. Subsequently, they were embedded in epoxy resin, thereby exposing approximately 0.38 cm2. Before the electrochemical testing, each specimen underwent the same grinding and polishing procedures as outlined in the sample preparation detailed in Section 2.2.
The electrochemical tests were performed using the Electrochemical workstation (CS235OH, Corrtest Instrument, Wuhan, China), which was equipped with a standard three-electrode cell (illustrated in Figure 1b). The tests included open-circuit potential (OCP) determination, electrochemical impedance spectroscopy (EIS) analysis, and potentiodynamic polarization (PDP) testing. In this system, the saturated calomel electrode (SCE) served as the reference electrode, a thin platinum sheet was used as the counter electrode (CE), and the sample to be measured was employed as the working electrode (WE). The electrolyte utilized in the experiment was 3.5 wt.% NaCl solution, prepared by dissolving analytically pure NaCl in deionized water and allowing it to stand until fully dissolved. At room temperature, OCP measurements were conducted for 2400 s for each sample. After a stable OCP value was reached, EIS tests were performed using an amplitude of ±10 mV, with a frequency sweep range from 10−2 Hz to 105 Hz. The collected EIS data were thoroughly analyzed and fitted using ZSimpwin 3.60. The PDP tests were conducted at a scan rate of 0.3 mV/s, with a scanning potential range from −0.45V (vs. OCP) to 0.45V (vs. OCP). To ensure the reliability of the experimental data, all tests were conducted in triplicate.

3. Results and Discussion

3.1. Microstructural Characteristics

Figure 2 shows the microstructure of 0N and 0.16N specimens. In 0 N steel, reticulate δ-ferrite, martensite, and a large amount of coarse Cr-rich carbides were observed (Figure 2(a1,a3)). Moreover, needle-like precipitates were also found (Figure 2(a2)). However, the microstructure of the 0.16 N specimen consisted only of martensite without δ-ferrite, and fine Cr-rich carbides (Figure 2(b1,b3)). Compared to the 0 N specimen, the precipitates in the 0.16 N specimen were significantly refined, and the amount of precipitation was also decreased. Research has shown that the formation of the δ-ferrite in 0 N steel is mainly due to the high chromium equivalent and relatively low nickel equivalent. Nitrogen has a strong stabilizing effect on austenite. Adding nitrogen to martensitic stainless steel can effectively inhibit δ-ferrite [24]. It was observed that the precipitates were enriched with a significant amount of the Cr element as depicted in Figure 2(a3,b3). However, the 0.16 N specimen shows a more even distribution of Cr. Some researchers reported that in martensitic stainless steel, the addition of nitrogen can increase the state density of Fermi level, resulting in a short-range ordered arrangement, so that the distribution of Cr atoms is more uniform, which can inhibit the aggregation of Cr atoms, delaying the generation of Cr-rich precipitated phase, and reducing the size of precipitation [25].
According to the calculation result of Thermo-Calc software based on the TCFE9 database, adding nitrogen significantly diminished the δ phase region, expanded the regions of M2N and γ phase, and reduced the dissolution temperature of M23C6 from 1080 °C to 1030 °C (Figure 3). The phase variation in SEM analysis agrees with this. The reason is that nitrogen in steel could impede the formation of M23C6 carbides and slow down the growth kinetics by diminishing the diffusion rate of Cr within the matrix [26,27,28], reducing the lattice parameter while increasing the interfacial mismatch [22,29,30,31].
The distribution of elements in experimental steels is shown in Figure 4. The enrichment of chromium in the precipitates was clearly observed, which is in agreement with the EDS analysis results (Figure 2(a3,b3)). However, the distribution of nitrogen in the 0.16 N specimen was uniform. Wang et al. [32] reported in their study that replacing part of the carbon in an Fe-12.8%Cr-1.3%Ni-0.5%Mo-0.19%C welding wire with nitrogen effectively inhibited the formation of grain boundary precipitates and improved the distribution uniformity of elements in the material. Our observations are consistent with this finding.
To investigate the microstructure characteristics of experimental steels in greater depth, an EBSD analysis was conducted. The color orientation diagrams of the inverse pole figure (IPF) of the experimental steels are shown in Figure 5(a1,b1), respectively. In the 0 N specimen, lath-shaped martensite and δ-ferrite, featuring blocky and bamboo-like morphologies, were observed, as indicated by the red arrows, and the average width of δ-ferrite was determined to be 5.75 ± 0.8 μm. To identify δ-ferrite more accurately, a Kernel Average Misorientation (KAM) analysis was carried out (as shown in Figure 5(a3,b3)). It is reported that the dislocation density of martensitic grains is proportional to its KAM value [33,34], that is, the larger the dislocation density, the higher the KAM value. On the contrary, δ-ferrite grains exhibit lower KAM values due to fewer dislocations.
As shown in Figure 5(a2), there is a small amount of austenite in the 0 N specimen. This is attributed to the reverse transformation of martensite to austenite during the tempering process, while the partitioning of C and Mn atoms into austenite improves its stability; therefore, austenite is retained at room temperature; Raabe et al. [35,36] reached this conclusion in a previous study. Compared with the 0 N sample, the austenite content in the 0.16 N sample (Figure 5(b2)) was significantly increased. This is because N significantly improves the stability of austenite, increasing the proportion of this phase in the sample of 0.16 N at room temperature [37]. Studies have shown that reversed austenite has a good promotion on pitting resistance because its presence enhances the stability of the passive film [38,39].
In the phase maps, the blue line represents high-angle grain boundaries (HABs, misorientation angle ≥ 15°) and the yellow one represents low-angle grain boundaries (LABs, 2° < misorientation angle < 15°). It is worth noting that with the addition of nitrogen, the density of martensitic lath increased significantly (Figure 5(b2)). In lath martensite, the lath boundaries are low-angle boundaries (LABs), while the packet and block boundaries generally appeared as high-angle boundaries (HABs), which was confirmed in a previous study [40,41].
An XRD analysis was performed to thoroughly investigate the types and the existing forms of precipitates. As shown in Figure 6a, the XRD spectra indicate that M23C6 carbides are the major precipitate. After adding nitrogen to the steel, there is a decrease in the amount of M23C6 carbides based on peak intensities. To further clarify the existence form of nitrogen in nitrogen-containing martensitic stainless bearing steel, Figure 6b shows the XRD pattern of electrolytically extracted precipitates. A peak representing M2N nitride appears.
Figure 7 shows the TEM micrographs and selected area electron diffraction (SAED) patterns of the precipitates in experimental steels. In N-free steel, granular, rod-like, and needle-like precipitates can be observed in Figure 7a–c, identified as M23C6 (~500 nm) and M3C carbides, respectively. Granular Cr-rich M23C6 (~300 nm), needle-like precipitates, and M2N (~120 nm) were observed in 0.16 N steel (Figure 7d–f). Therefore, combined with the above analysis results, it can be stated that nitrogen exists in 0.16N steel in solid solution and as Cr-rich nitrides. Furthermore, the width of martensitic laths also fluctuated simultaneously. More specifically, the average lath width decreased from 1.32 μm (Figure 7c) to 0.2 μm (Figure 7e). The width of the lath is closely related to the grain size of the prior austenite, and the width of the lath is narrowed after adding nitrogen, indicating that the grain is refined. The reason is that nitrogen, as an interstitial atom, migrates to the grain boundaries, and there is a strong interaction between Cr and N atoms, forming a Cr-N complex, which inhibits austenite grain boundary migration. At the same time, nitrogen and other elements form nitrogen-rich precipitates, which can pin the grain boundaries and inhibit the grain boundary migration, thus refining the prior austenite grains [20,42].

3.2. Effect of Nitrogen on Electrochemical Behavior

3.2.1. OCP and Potentiodynamic Polarization Measurement

Figure 8a features the OCP measurements. With the increase in experimental time, the OCP of 0.16 N steel remained stable (around −160 mV). In contrast, nitrogen-free steel exhibited potential transient fluctuations, which may have resulted from the metastable pitting nucleation and subsequent recovery [43], as well as a consistent decrease, reaching a much lower value.
Figure 8b shows the PDP curves of the experimental MSSs, and the pitting potential (Epit) of the test steels was determined when the current density at the specimen surface exceeded 0.1 mA/cm2 (listed in Table 2). From the curves, the 0.16 N specimen exhibits a clear passive region before the applied potentials reach Epit. However, in the 0 N steel, in the passive region, severe current fluctuations can be seen, due to the existence of massive Cr-rich precipitates, signifying the extensive initiation and subsequent repassivation of metastable pits [44]. These observations indicate that the inclusion of 0.16 wt.% N can notably suppress the occurrence of metastable pitting and substantially elevate the Epit value.
Table 2 gives the electrochemical parameters obtained from the potentiodynamic polarization curves. The corrosion potential (Ecorr) and corrosion current density (icorr) were obtained via the extrapolation method. It is noted that the OCP values of the samples (Figure 8a) are larger than their Ecorr values (Figure 8b). This may be due to the formation of a passivation film on the surface of the specimen during their long-term immersion in the solution during the OCP measurement, and the obtained potential value should be the potential of the oxide film [45]. Thus, the Ecorr measured for the sample in this work should correspond to the potential of the bare metal surface in its active condition, which should be lower than the potential of the passivation film [46]. According to the PDP test methodology, ipass is measured when the polarization potential reaches the passive region. The passivation current density (ipass) of the 0.16 N sample is 1.26 μA/cm2, lower than that of the 0 N sample (8.32 μA/cm2), which demonstrates that the passive film of the nitrogen-containing MSS is more protective when exposed to a chloride environment.

3.2.2. Electrochemical Impedance Spectroscopy Measurements

To delve deeper into understanding how nitrogen addition affects the corrosion process, we conducted EIS tests. As illustrated in the Nyquist plot (Figure 9a), the radius (R) of the capacitive arc for nitrogen-containing MSS is significantly larger than that of nitrogen-free MSS. The corrosion resistance of steel is intimately correlated with the radius (R) of the capacitive arc [47]. The larger radius indicates that the more difficult the charge transfer, the greater the polarized resistance and the better the corrosion resistance [48,49].
Figure 9b shows the Bode plots of the experimental MSSs. In the amplitude plot, |Z|0.01Hz is the impedance mode value at a fixed frequency of 0.01 Hz, which corresponds to the polarization resistance. It is commonly used to evaluate the barrier characteristics of the corrosion layer on the material surface, reflecting the corrosion resistance of the material in the solution [50]. The impedance modulus at low frequency (|Z|0.01Hz) of 0 N steel is nearly 104 Ω·cm2, almost one order of magnitude lower than |Z|0.01Hz of 0.16 N steel (105 Ω·cm2).
In the phase angle diagram, the characteristics of the phase angle change curve can provide important information about the corrosion tendency of the material. The width of the phase angle curve and the height of the phase angle peak are the key indices to evaluate the corrosion resistance of materials. From the phase angle diagram (Figure 9b), the maximum phase angle value of the 0.16 N sample is close to 82°, while the 0 N sample is approximately 76°. Meanwhile, the 0.16 N steel has a wider frequency range of phase angles, which indicates that a more stable passivation film is formed on the surface of the 0.16 N specimen in 3.5% NaCl solution. The reason is that the high phase angle peak usually leads to the formation of a more stable and dense passivation film or protective layer on the material’s surface, which can effectively isolate the contact between the corrosive medium and the material matrix. The higher the peak phase angle, the more stable the sample surface is and the stronger the corrosion resistance. Secondly, a wider frequency range of phase angles usually means that the material can maintain its stability over a wider frequency range, which means it can resist corrosion under different environments and conditions [51,52,53].
The equivalent circuits for analyzing the impedance data from the experiment are illustrated in Figure 10. The EIS data were fitted and analyzed using the Z-SimpWin3.60 software. From the Bode plots (Figure 9b), the 0 N sample exhibits one time constant, whereas the diagrams for the 0.16 N sample display two time constants, namely the double layer and the passive film [54]. The equivalent circuits with one time constant (Figure 10a) and two time constants (Figure 10b) were applied to fit the obtained EIS data.
As shown in Figure 10, the critical electrochemical parameters, including solution resistance (Rs), passive film resistance (Rf), constant phase element of passive film (CPEf), charge transfer resistance (Rct), and constant phase element for double layer (CPEdl) were estimated (summarized in Table 3).
The impedance of the CPE (Z(CPE)) can be described by the following equation [55]:
Z ( C P E ) = Q − 1 ( j ω ) − α
where Q is the admittance value of CPE, j is an imaginary number (j2 = 1), ω is the angular frequency, and αf is the dispersion coefficient [56], where αf ranges from −1 to 1. When αf = 1, the CPE becomes a pure capacitor. However, due to the dispersion effect, it usually deviates from the pure capacitance, so αf decreases [57].
Table 3 lists the best fitting parameters for EIS. The goodness of fit between experimental data and simulation results was quantitatively evaluated using the chi-square (χ2) method [57]. The calculated χ2 values of the 0 N and 0.16 N samples were 9.3 × 10−4 and 1.5 × 10−4, respectively, implying a good quality of fitting. The dispersion coefficient of the αf values for all the samples is smaller than 1, suggesting that the impedance behavior deviates from that of a pure capacitor and is attributed to the inhomogeneities of the passive film [58,59]. The αf value of 0.16 N is closer to 1, indicating a more uniform distribution of the passive film formed on the martensitic stainless steel with added nitrogen. In addition, it is generally acknowledged that the rate of the interfacial reactions can be determined by the polarization resistance (Rp), defined as Rp = (ZF)ω=0 (ZF represents the faradic impedance and “ω” is the angular frequency, respectively), which is directly related to the corrosion resistance of metal [60]. Therefore, the Rp of equivalent circuits in Figure 10a,b can be calculated as Rp = Rf and Rp = Rf + Rct, respectively [61]. As is shown in Table 3, the 0.16 N sample exhibits the highest Rp value of 1.24 × 102 kΩ·cm2. This means that after adding nitrogen to MSS, the performance and ability of the passive film have been enhanced.

3.2.3. Corrosion Mechanism Analysis

For 0 N and 0.16 N martensitic stainless steels, precipitates have a significant impact on their corrosion performance. It is believed that Cr-rich M23C6 carbides give rise to Cr-depleted zones in their vicinity, which subsequently hinder the development of protective passivation films and elevate the vulnerability to pitting [60,62]. The addition of N to martensitic stainless steel inhibits the precipitation of M23C6, alleviates the consumption of Cr, reduces the Cr depletion to a certain extent, and ultimately improves the pitting resistance of the steel.
To further illustrate the pitting mechanism, a schematic diagram was inferred based on existing theories, as shown in Figure 11. The surface of stainless steel forms a passivation film, providing protection against electrolyte corrosion. The passive layer in the vicinity of the carbides displays microscopic chemical discontinuities [61], resulting in areas depleted of Cr, as illustrated in Figure 11a. This leads to the formation of a weakly passivated film that allows chloride ions to permeate easily and become a preferred site for pit nucleation in chlorine solutions. Research has revealed that chloride ions can react with the metal substrate at the interface between the metal and the film, forming metal chlorides. In solutions containing chloride ions, the failure (or breakdown) of the passivation layer is rooted in the gradual accumulation of chloride ions at the metal/film interface after they penetrate through the protective film layer [18]. In the initial stage of pitting, due to the destruction of the passivation film, Cl− accelerates the erosion of the matrix, and the metal cation (M+) in the matrix dissolves and diffuses, forming a rust layer around the pits [63,64] (Figure 11b). During the pitting process, the cationic hydration product H+ dissolved in the pit is formed. When the metal dissolution rate is accelerated, the hydration process is also significantly accelerated, resulting in a gradual decrease in the surface pH value of the pit. When the pH value in the pit is below a certain critical value, it will hinder the repassivation process of the passivation film, which will promote the deterioration of the pit and eventually form a stable pitting (Figure 11c).
However, according to the adsorption mechanism, the adsorption of Cl− on the passivation film leads to the formation of MClx (M stands for Fe, Cr, etc.) and the rupture of the passivation film [65,66]. With the thinning of the passivation film, the presence of nitride in it can induce the repulsion and desorption of Cl−, thus inhibiting the corrosion caused by chloride ions [65,67]. In addition, nitrogen is enriched at the metal/oxide film interface and reacts with H+ to form NH4+ or NH3, which plays a key role in buffering the pH value in the metastable pit, facilitates the early repassivation process, inhibits the development of the growth pit, and, thus, enhances the pitting resistance (Figure 11d).

4. Conclusions

The present study delves into the profound influence of nitrogen on the precipitates, phase evolution, and corrosion properties, especially pitting corrosion resistance in martensitic stainless steel. The following primary conclusions are drawn from this study:
(1) In this study, the nitrogen in martensitic stainless steel mainly exists in Cr-rich nitride and solid solutions. Nitrogen addition effectively inhibits the production of δ-ferrite. The precipitates are all rich in Cr, and the Cr distribution in 0.16 N steel is more uniform, which can reduce the adverse effect of Cr depletion on corrosion resistance.
(2) Nitrogen addition significantly reduces the current fluctuations during polarization tests, that is, reduces the sensitivity of metastable pitting, enlarges the passivation zone, and makes the passivation film more uniform and stable. At the same time, the pitting potential (Epit) increased significantly (241.69 mV), which is two orders of magnitude higher than the 0 N specimen, and the passive current density (ipass) decreased, but the change is not significant.
(3) The electrochemical impedance spectroscopy (EIS) results confirm that the 0.16 N steel impedance modulus at low frequency (|Z|0.01 Hz) and capacitive loop radius are larger, and the frequency range of phase angle curve is wider, i.e., the passive film of the nitrogen-containing MSS is more protective when exposed to a Cl--containing environment.

Author Contributions

Data Curation, H.X. and J.W.; Funding Acquisition, Y.L.; Writing—Original Draft Preparation, H.X.; Writing—Review and Editing H.X., J.W., B.W., and G.L.; Resources, H.L., B.W., Y.L. and G.L. All authors have read and agreed to the published version of the manuscript. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the “Central Guiding Local Science and Technology Development Fund Project, grant number YDZJSX2021A036”, “Graduate Education Innovation Project of Taiyuan University of Science and Technology, grant number SY20220003”, “National Natural Science Foundation of China, grant number 52375364”, “Basic Research Program of Shanxi Province, grant number TZLH20230818001”, and “Shanxi Province’s Key Core Technology and Common Technology Research and Development Project, grant number 20201102017”.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The datasets used and/or analyzed during the current study will be made available from the corresponding author upon reasonable request.

Conflicts of Interest

Author Bin Wang was employed by the company State Key Laboratory of Advanced Stainless Steel Taiyuan Iron and Steel (Group) Co., Ltd. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

References

  1. Krishna, S.C.; Karthick, N.K.; Jha, A.K.; Pant, B.; Venkitakrishnan, P.V. Microstructure and Properties of Nitrogen-Alloyed Martensitic Stainless Steel. Metall. Microstruct. Anal. 2017, 6, 425–432. [Google Scholar] [CrossRef]
  2. Ebert, F.-J. An Overview of Performance Characteristics, Experiences and Trends of Aerospace Engine Bearings Technologies. Chin. J. Aeronaut. 2007, 20, 378–384. [Google Scholar] [CrossRef]
  3. Xu, H.-F.; Wu, G.-L.; Wang, C.; Li, J.; Cao, W.-Q. Microstructure, hardness and contact fatigue properties of X30N high nitrogen stainless bearing steel. J. Iron Steel Res. Int. 2018, 25, 954–967. [Google Scholar] [CrossRef]
  4. Xu, H.-F.; Yu, F.; Wang, C.; Zhang, W.-L.; Li, J.; Cao, W.-Q. Comparison of microstructure and property of high chromium bearing steel with and without nitrogen addition. J. Iron Steel Res. Int. 2017, 24, 206–213. [Google Scholar] [CrossRef]
  5. Wang, Z.; Li, R.; Chen, M.; Yang, K.; Sun, Z.; Zhang, X.; Tang, S.; Sun, G. Enhanced wear and corrosion resistance of the laser direct metal deposited AISI 316L stainless steel by in-situ interstitial N alloying. Opt. Laser Technol. 2024, 171, 110381. [Google Scholar] [CrossRef]
  6. Wang, Y.; Wang, Z.; Wang, W.; Ma, B. Effect of nitrogen content on mechanical properties of 316L (N) austenitic stainless steel. Mater. Sci. Eng. A 2023, 884, 145549. [Google Scholar] [CrossRef]
  7. Hao, X.; Sun, X.; Zhao, T.; Zhang, M.; Wang, Y.; Zhang, F.; Zhao, J.; Wang, T. Effect of N on microstructure evolution and strain hardening of high-Mn austenitic steel during tensile deformation. Mater. Sci. Eng. A 2024, 896, 146291. [Google Scholar] [CrossRef]
  8. Feng, H.; Li, H.-B.; Jiang, Z.-H.; Zhang, T.; Dong, N.; Zhang, S.-C.; Han, P.-D.; Zhao, S.; Chen, Z.-G. Designing for high corrosion-resistant high nitrogen martensitic stainless steel based on DFT calculation and pressurized metallurgy method. Corros. Sci. 2019, 158, 108081. [Google Scholar] [CrossRef]
  9. Chang, R.; Li, J.; Gu, J. Effect of nitrogen on microstructure and corrosion resistance of Cr15 super martensitic stainless steel. Corros. Eng. Sci. Technol. 2019, 54, 225–232. [Google Scholar] [CrossRef]
  10. Jiao, W.-C.; Li, H.-B.; Dai, J.; Feng, H.; Jiang, Z.-H.; Zhang, T.; Xu, D.-K.; Zhu, H.-C.; Zhang, S.-C. Effect of partial replacement of carbon by nitrogen on intergranular corrosion behavior of high nitrogen martensitic stainless steels. J. Mater. Sci. Technol. 2019, 35, 2357–2364. [Google Scholar] [CrossRef]
  11. Wang, R.; Li, F.; Yu, Z.; Kang, Y.; Li, M.; Hu, Y.; An, H.; Fan, J.; Miao, F.; Zhao, Y.; et al. Influences of partial substitution of C by N on the microstructure and mechanical properties of 9Cr18Mo martensitic stainless steel. Mater. Des. 2023, 236, 112497. [Google Scholar] [CrossRef]
  12. Li, S.-h.; Li, J.; Zhang, J.; Shi, C. Effect of nitrogen on microstructure and microsegregation of martensitic stainless steel 4Cr13 produced by electroslag remelting. J. Iron Steel Res. Int. 2022, 30, 1854–1861. [Google Scholar] [CrossRef]
  13. Bénéteau, A.; Weisbecker, P.; Geandier, G.; Aeby-Gautier, E.; Appolaire, B. Austenitization and precipitate dissolution in high nitrogen steels: An in situ high temperature X-ray synchrotron diffraction analysis using the Rietveld method. Mater. Sci. Eng. A 2005, 393, 63–70. [Google Scholar] [CrossRef]
  14. Lee, J.-B.; Yoon, S.-I. Effect of nitrogen alloying on the semiconducting properties of passive films and metastable pitting susceptibility of 316L and 316LN stainless steels. Mater. Chem. Phys. 2010, 122, 194–199. [Google Scholar] [CrossRef]
  15. Ha, H.; Jang, H.; Kwon, H.; Kim, S. Effects of nitrogen on the passivity of Fe–20Cr alloy. Corros. Sci. 2009, 51, 48–53. [Google Scholar] [CrossRef]
  16. Pistorius, P.C.; Burstein, G.T. Aspects of the effects of electrolyte composition on the occurrence of metastable pitting on stainless steel. Corros. Sci. 1994, 36, 525–538. [Google Scholar] [CrossRef]
  17. Olefjord, I.; Wegrelius, L. The influence of nitrogen on the passivation of stainless steels. Corros. Sci. 1996, 38, 1203–1220. [Google Scholar] [CrossRef]
  18. Saadi, S.A.; Yi, Y.; Cho, P.; Jang, C.; Beeley, P. Passivity breakdown of 316L stainless steel during potentiodynamic polarization in NaCl solution. Corros. Sci. 2016, 111, 720–727. [Google Scholar] [CrossRef]
  19. Cheng, X.Y.; Zhang, H.X.; Li, H.; Shen, H.P. Effect of tempering temperature on the microstructure and mechanical properties in mooring chain steel. Mater. Sci. Eng. A 2015, 636, 164–171. [Google Scholar] [CrossRef]
  20. Leda, H. Nitrogen in martensitic stainless steels. J. Mater. Process. Technol. 1995, 53, 263–272. [Google Scholar] [CrossRef]
  21. Shimada, T.; Yamamoto, A.; Abe, S. The effect of nitrogen content on material properties of high carbon stainless steel SUS440A. Tetsu Hagane 1996, 82, 309–314. [Google Scholar] [CrossRef] [PubMed]
  22. Qi, X.; Mao, H.; Yang, Y. Corrosion behavior of nitrogen alloyed martensitic stainless steel in chloride containing solutions. Corros. Sci. 2017, 120, 90–98. [Google Scholar] [CrossRef]
  23. Jiang, Z.H.; Feng, H.; Li, H.B.; Zhu, H.C.; Zhang, S.C.; Zhang, B.B.; Han, Y.; Zhang, T.; Xu, D.K. Relationship between Microstructure and Corrosion Behavior of Martensitic High Nitrogen Stainless Steel 30Cr15Mo1N at Different Austenitizing Temperatures. Materials 2017, 10, 861. [Google Scholar] [CrossRef] [PubMed]
  24. Ma, X.P.; Wang, L.J.; Qin, B.; Liu, C.M.; Subramanian, S.V. Effect of N on microstructure and mechanical properties of 16Cr5Ni1Mo martensitic stainless steel. Mater. Des. 2012, 34, 74–81. [Google Scholar] [CrossRef]
  25. Gavriljuk VG, B.H. Precipitates in Tempered Stainless Martensitic Steels Alloyed with Nitrogen, Carbon or Both. Mater. Sci. Forum 1999, 318–320, 71–80. [Google Scholar] [CrossRef]
  26. Danielsen, H.K.; Villa, M.; Gutiérrez Guzmán, F.; Fæster, S.; Dahl, K.V.; Vegter, R.H.; Jensen, O.L.; Hummelshøj, T.S.; Lehmann, B.; Jacobs, G.; et al. New White Etch Cracking resistant martensitic stainless steel for bearing applications by high temperature solution nitriding. Wear 2023, 534–535, 205134. [Google Scholar] [CrossRef]
  27. Perdew, J.P.; Zunger, A. Self-interaction correction to density-functional approximations for many-electron systems. Phys. Rev. B 1981, 23, 5048–5079. [Google Scholar] [CrossRef]
  28. Wang, C.; Wang, C.-Y. Ni/Ni3Al interface: A density functional theory study. Appl. Surf. Sci. 2009, 255, 3669–3675. [Google Scholar] [CrossRef]
  29. Feng, H.; Jiang, Z.; Li, H.; Lu, P.; Zhang, S.; Zhu, H.; Zhang, B.; Zhang, T.; Xu, D.; Chen, Z. Influence of nitrogen on corrosion behaviour of high nitrogen martensitic stainless steels manufactured by pressurized metallurgy. Corros. Sci. 2018, 144, 288–300. [Google Scholar] [CrossRef]
  30. Reed, R.P. Nitrogen in austenitic stainless steels. JOM 1989, 41, 16–21. [Google Scholar] [CrossRef]
  31. Lewis, M.H.; Hattersley, B. Precipitation of M23C6 in austenitic steels. Acta Metall. 1965, 13, 1159–1168. [Google Scholar] [CrossRef]
  32. Wang, J.B.; Zhou, Y.F.; Xing, X.L.; Liu, S.; Zhao, C.C.; Yang, Y.L.; Yang, Q.X. The effect of nitrogen alloying to the microstructure and mechanical properties of martensitic stainless steel hardfacing. Surf. Coat. Technol. 2016, 294, 115–121. [Google Scholar] [CrossRef]
  33. Li, K.; Zhan, J.; Yang, T.; To, A.C.; Tan, S.; Tang, Q.; Cao, H.; Murr, L.E. Homogenization timing effect on microstructure and precipitation strengthening of 17–4PH stainless steel fabricated by laser powder bed fusion. Addit. Manuf. 2022, 52, 102672. [Google Scholar] [CrossRef]
  34. Caballero, A.; Ding, J.; Ganguly, S.; Williams, S. Wire+ Arc Additive Manufacture of 17-4 PH stainless steel: Effect of different processing conditions on microstructure, hardness, and tensile strength. J. Mater. Process. Technol. 2019, 268, 54–62. [Google Scholar] [CrossRef]
  35. Kuzmina, M.; Ponge, D.; Raabe, D. Grain boundary segregation engineering and austenite reversion turn embrittlement into toughness: Example of a 9wt.% medium Mn steel. Acta Mater. 2015, 86, 182–192. [Google Scholar] [CrossRef]
  36. Raabe, D.; Sandlöbes, S.; Millán, J.; Ponge, D.; Assadi, H.; Herbig, M.; Choi, P.P. Segregation engineering enables nanoscale martensite to austenite phase transformation at grain boundaries: A pathway to ductile martensite. Acta Mater. 2013, 61, 6132–6152. [Google Scholar] [CrossRef]
  37. Wang, Y.; Zhang, X.; Jiang, L.; Yuan, C.; Zhang, J.; Yan, Q. Advancement of strength and toughness in ultra-low carbon martensitic stainless steel by reversed austenite. Nucl. Mater. Energy 2024, 38, 101601. [Google Scholar] [CrossRef]
  38. Wang, P.; Zheng, W.; Dai, X.; Zhang, P.; Wang, Y. Prominent role of reversed austenite on corrosion property of super 13Cr martensitic stainless steel. J. Mater. Res. Technol. 2023, 22, 1753–1767. [Google Scholar] [CrossRef]
  39. Song, Y.; Li, X.; Rong, L.; Li, Y. The influence of tempering temperature on the reversed austenite formation and tensile properties in Fe–13%Cr–4%Ni–Mo low carbon martensite stainless steels. Mater. Sci. Eng. A 2011, 528, 4075–4079. [Google Scholar] [CrossRef]
  40. Morito, S.; Tanaka, H.; Konishi, R.; Furuhara, T.; Maki, T. The morphology and crystallography of lath martensite in Fe-C alloys. Acta Mater. 2003, 51, 1789–1799. [Google Scholar] [CrossRef]
  41. Morito, S.; Huang, X.; Furuhara, T.; Maki, T.; Hansen, N. The morphology and crystallography of lath martensite in alloy steels. Acta Mater. 2006, 54, 5323–5331. [Google Scholar] [CrossRef]
  42. Fan, R.; Gao, M.; Ma, Y.; Zha, X.; Hao, X.; Liu, K. Effects of Heat Treatment and Nitrogen on Microstructure and Mechanical Properties of 1Cr12NiMo Martensitic Stainless Steel. J. Mater. Sci. Technol. 2012, 28, 1059–1066. [Google Scholar] [CrossRef]
  43. Lu, S.-Y.; Yao, K.-F.; Chen, Y.-B.; Wang, M.-H.; Ge, X.-Y. Influence of Heat Treatment on the Microstructure and Corrosion Resistance of 13 Wt Pct Cr-Type Martensitic Stainless Steel. Metall. Mater. Trans. A 2015, 46, 6090–6102. [Google Scholar] [CrossRef]
  44. Ilevbare, G.O.; Burstein, G.T. The role of alloyed molybdenum in the inhibition of pitting corrosion in stainless steels. Corros. Sci. 2001, 43, 485–513. [Google Scholar] [CrossRef]
  45. Yuan, F.; Wei, G.; Gao, S.; Lu, S.; Liu, H.; Li, S.; Fang, X.; Chen, Y. Tuning the pitting performance of a Cr-13 type martensitic stainless steel by tempering time. Corros. Sci. 2022, 203, 110346. [Google Scholar] [CrossRef]
  46. Cui, Z.; Wang, L.; Ni, H.; Hao, W.; Man, C.; Chen, S.; Wang, X.; Liu, Z.; Li, X. Influence of temperature on the electrochemical and passivation behavior of 2507 super duplex stainless steel in simulated desulfurized flue gas condensates. Corros. Sci. 2017, 118, 31–48. [Google Scholar] [CrossRef]
  47. Gao, B.; Xu, T.; Wang, L.; Liu, Y.; Liu, J.; Zhang, Y.; Sui, Y.; Sun, W.; Chen, X.; Li, X.; et al. Achieving a superior combination of tensile properties and corrosion resistance in AISI420 martensitic stainless steel by low-temperature tempering. Corros. Sci. 2023, 225, 111551. [Google Scholar] [CrossRef]
  48. Fan, Y.; Liu, W.; Li, S.; Chowwanonthapunya, T.; Wongpat, B.; Zhao, Y.; Dong, B.; Zhang, T.; Li, X. Evolution of rust layers on carbon steel and weathering steel in high humidity and heat marine atmospheric corrosion. J. Mater. Sci. Technol. 2020, 39, 190–199. [Google Scholar] [CrossRef]
  49. Ma, H.; Liu, Z.; Du, C.; Wang, H.; Li, C.; Li, X. Effect of cathodic potentials on the SCC behavior of E690 steel in simulated seawater. Mater. Sci. Eng. A 2015, 642, 22–31. [Google Scholar] [CrossRef]
  50. Zhao, T.; Liu, Z.; Du, C.; Sun, M.; Li, X. Effects of cathodic polarization on corrosion fatigue life of E690 steel in simulated seawater. Int. J. Fatigue 2018, 110, 105–114. [Google Scholar] [CrossRef]
  51. Yang, Y.; Zhang, T.; Shao, Y.; Meng, G.; Wang, F. Effect of hydrostatic pressure on the corrosion behaviour of Ni–Cr–Mo–V high strength steel. Corros. Sci. 2010, 52, 2697–2706. [Google Scholar] [CrossRef]
  52. Duan, Z.; Man, C.; Dong, C.; Cui, Z.; Kong, D.; Wang, L.; Wang, X. Pitting behavior of SLM 316L stainless steel exposed to chloride environments with different aggressiveness: Pitting mechanism induced by gas pores. Corros. Sci. 2020, 167, 108520. [Google Scholar] [CrossRef]
  53. Li, X.; Wang, L.; Fan, L.; Zhong, M.; Cheng, L.; Cui, Z. Understanding the effect of fluoride on corrosion behavior of pure titanium in different acids. Corros. Sci. 2021, 192, 109812. [Google Scholar] [CrossRef]
  54. Pan, L.; Kwok, C.T.; Niu, B.; Huang, X.; Cao, Y.; Zou, X.; Yi, J. Enhancement in hardness and corrosion resistance of directed energy deposited 17-4 PH martensitic stainless steel via heat treatment. J. Mater. Res. Technol. 2023, 23, 1296–1311. [Google Scholar] [CrossRef]
  55. Shahriari, A.; Khaksar, L.; Nasiri, A.; Hadadzadeh, A.; Amirkhiz, B.S.; Mohammadi, M. Microstructure and corrosion behavior of a novel additively manufactured maraging stainless steel. Electrochim. Acta 2020, 339, 135925. [Google Scholar] [CrossRef]
  56. Blanc, C.; Orazem, M.E.; Pébère, N.; Tribollet, B.; Vivier, V.; Wu, S. The origin of the complex character of the Ohmic impedance. Electrochim. Acta 2010, 55, 6313–6321. [Google Scholar] [CrossRef]
  57. Liu, G.; Zhang, Y.; Wu, M.; Huang, R. Study of depassivation of carbon steel in simulated concrete pore solution using different equivalent circuits. Constr. Build. Mater. 2017, 157, 357–362. [Google Scholar] [CrossRef]
  58. Jorcin, J.-B.; Orazem, M.E.; Pébère, N.; Tribollet, B. CPE analysis by local electrochemical impedance spectroscopy. Electrochim. Acta 2006, 51, 1473–1479. [Google Scholar] [CrossRef]
  59. Chen, W.-C.; Wen, T.-C.; Teng, H. Polyaniline-deposited porous carbon electrode for supercapacitor. Electrochim. Acta 2003, 48, 641–649. [Google Scholar] [CrossRef]
  60. Lu, G.; Liu, Y.; Beiersmann, C.; Feng, Y.; Cao, J.; Müller, O. Challenges in and lessons learned during the implementation of the 1-3-7 malaria surveillance and response strategy in China: A qualitative study. Infect. Dis. Poverty 2016, 5, 94. [Google Scholar] [CrossRef]
  61. Lei, X.; Feng, Y.; Zhang, J.; Fu, A.; Yin, C.; Macdonald, D.D. Impact of Reversed Austenite on the Pitting Corrosion Behavior of Super 13Cr Martensitic Stainless Steel. Electrochim. Acta 2016, 191, 640–650. [Google Scholar] [CrossRef]
  62. Lu, S.-Y.; Yao, K.-F.; Chen, Y.-B.; Wang, M.-H.; Liu, X.; Ge, X. The effect of tempering temperature on the microstructure and electrochemical properties of a 13wt.% Cr-type martensitic stainless steel. Electrochim. Acta 2015, 165, 45–55. [Google Scholar] [CrossRef]
  63. Burstein, G.T.; Liu, C.; Souto, R.M.; Vines, S.P. Origins of pitting corrosion. Corros. Eng. Sci. Technol. 2004, 39, 25–30. [Google Scholar] [CrossRef]
  64. Gong, K.; Wu, M.; Xie, F.; Liu, G.; Sun, D. Effect of Cl− and rust layer on stress corrosion cracking behavior of X100 steel base metal and heat-affected zone in marine alternating wet/dry environment. Mater. Chem. Phys. 2021, 270, 124826. [Google Scholar] [CrossRef]
  65. Lothongkum, G.; Wongpanya, P.; Morito, S.; Furuhara, T.; Maki, T. Effect of nitrogen on corrosion behavior of 28Cr–7Ni duplex and microduplex stainless steels in air-saturated 3.5 wt% NaCl solution. Corros. Sci. 2006, 48, 137–153. [Google Scholar] [CrossRef]
  66. Meng, G.; Li, Y.; Shao, Y.; Zhang, T.; Wang, Y.; Wang, F. Effect of Cl− on the Properties of the Passive Films Formed on 316L Stainless Steel in Acidic Solution. J. Mater. Sci. Technol. 2014, 30, 253–258. [Google Scholar] [CrossRef]
  67. Grabke, H.J. The Role of Nitrogen in the Corrosion of Iron and Steels. ISIJ Int. 1996, 36, 777–786. [Google Scholar] [CrossRef]
Materials 17 03817 g001
Figure 1. Schematic diagram of (a) heat treatment process, (b) electrochemical device of the experimental steels.
Figure 1. Schematic diagram of (a) heat treatment process, (b) electrochemical device of the experimental steels.
Materials 17 03817 g001
Materials 17 03817 g002
Figure 2. SEM micrographs and the EDS-mapping: (a1–a3) 0N and (b1–b3) 0.16 N specimens.
Figure 2. SEM micrographs and the EDS-mapping: (a1–a3) 0N and (b1–b3) 0.16 N specimens.
Materials 17 03817 g002
Materials 17 03817 g003
Figure 3. Variation of phase fractions in the temperature range calculated by Thermo-Calc software.
Figure 3. Variation of phase fractions in the temperature range calculated by Thermo-Calc software.
Materials 17 03817 g003
Materials 17 03817 g004
Figure 4. EPMA results of (a) 0 N and (b) 0.16 N MSSs. The red arrow is the N-rich area, and the white box is the magnification image of the N-rich area.
Figure 4. EPMA results of (a) 0 N and (b) 0.16 N MSSs. The red arrow is the N-rich area, and the white box is the magnification image of the N-rich area.
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Materials 17 03817 g005
Figure 5. EBSD-inverse pole figure (IPF), phase, and KAM maps of (a1–a3) 0 N and (b1–b3) 0.16 N steels.
Figure 5. EBSD-inverse pole figure (IPF), phase, and KAM maps of (a1–a3) 0 N and (b1–b3) 0.16 N steels.
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Materials 17 03817 g006
Figure 6. XRD patterns of (a) 0 N and 0.16 N MSSs, (b) electrolytically extracted precipitates in 0.16 N MSS.
Figure 6. XRD patterns of (a) 0 N and 0.16 N MSSs, (b) electrolytically extracted precipitates in 0.16 N MSS.
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Materials 17 03817 g007
Figure 7. TEM images and SAED patterns of 0 N (a–c) and 0.16 N (d–f) MSSs.
Figure 7. TEM images and SAED patterns of 0 N (a–c) and 0.16 N (d–f) MSSs.
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Materials 17 03817 g008
Figure 8. Results of electrochemical tests: (a) OCP, (b) PDP curves of the tested steels.
Figure 8. Results of electrochemical tests: (a) OCP, (b) PDP curves of the tested steels.
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Materials 17 03817 g009
Figure 9. EIS results of 0 N and 0.16 N MSSs: (a) Nyquist plots and (b) Bode plots.
Figure 9. EIS results of 0 N and 0.16 N MSSs: (a) Nyquist plots and (b) Bode plots.
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Materials 17 03817 g010
Figure 10. Equivalent circuit used to fit EIS data: (a) 0 N model, (b) 0.16 N model.
Figure 10. Equivalent circuit used to fit EIS data: (a) 0 N model, (b) 0.16 N model.
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Materials 17 03817 g011
Figure 11. Schematic illustration of the effect of nitrogen and Cr-rich M23C6 carbides on the pitting behavior of the experimental MSSs. (a) formation of passive film on the surface, (b,c) pitting mechanism of the 0N steel, (d) pitting mechanism of the 0.16N steel.
Figure 11. Schematic illustration of the effect of nitrogen and Cr-rich M23C6 carbides on the pitting behavior of the experimental MSSs. (a) formation of passive film on the surface, (b,c) pitting mechanism of the 0N steel, (d) pitting mechanism of the 0.16N steel.
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Table 1. Chemical compositions of the experimental MSSs (wt.%).
Table 1. Chemical compositions of the experimental MSSs (wt.%).
SteelsCCrMoNMnSiFe
0N0.3015.171.02/0.450.55Bal.
0.16N0.3115.160.970.160.420.51Bal.
Table 2. The electrochemical parameters of experimental MSSs derived from OCP and PDP measurements.
Table 2. The electrochemical parameters of experimental MSSs derived from OCP and PDP measurements.
SamplesOCP/mVipass/(μA/cm2)Epit/mVicorr/(μA/cm2)Ecorr/mV
0 N−250.28.3−6.80.9−339.5
0.16 N−124.71.2241.60.1−281.0
Table 3. The optimal fitting results of EIS parameters obtained through Z-SimpWin.
Table 3. The optimal fitting results of EIS parameters obtained through Z-SimpWin.
SamplesRs
(Ω·cm2)		CPEfRf (kΩ·cm2)CPEdlRct
(kΩ·cm2)		Χ2
Qf
(MΩ−1/cm−2sα)		αfQdl
(MΩ−1/cm−2sα)		αdl
0 N4.864.77 × 10−40.804.05///9.31 × 10−4
0.16 N4.058.39 × 10−50.957.27 × 10−31.19 × 10−40.821.24 × 1021.53 × 10−4
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Xu, H.; Wang, J.; Li, Y.; Wang, B.; Li, H.; Liu, G. Effect of Nitrogen on Precipitate Characteristics and Pitting Resistance of Martensitic Stainless Steel. Materials 2024, 17, 3817. https://doi.org/10.3390/ma17153817

AMA Style

Xu H, Wang J, Li Y, Wang B, Li H, Liu G. Effect of Nitrogen on Precipitate Characteristics and Pitting Resistance of Martensitic Stainless Steel. Materials. 2024; 17(15):3817. https://doi.org/10.3390/ma17153817

Chicago/Turabian Style

Xu, Hui, Jinbin Wang, Yugui Li, Bin Wang, Huaying Li, and Guangming Liu. 2024. "Effect of Nitrogen on Precipitate Characteristics and Pitting Resistance of Martensitic Stainless Steel" Materials 17, no. 15: 3817. https://doi.org/10.3390/ma17153817

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