Next Article in Journal
Application of Metal Shielding Materials to Protect Buildings Occupants from Exposure to the Electromagnetic Fields
Previous Article in Journal
Carbon-Fiber-Recycling Strategies: A Secondary Waste Stream Used for PA6,6 Thermoplastic Composite Applications
Previous Article in Special Issue
Experimental Measurement of Deposition Chloride Ions in the Vicinity of Road Cut
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Materials
Volume 16
Issue 15
10.3390/ma16155437
materials-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles thumb_up
...
Endorse textsms
...
Comment
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Microstructural Evolution and Micro-Corrosion Behaviour of Flash-Welded U71Mn Joints as a Function of Post-Weld Heat Treatment

by
Tingting Liao
1,*,
Xi Zhang
2,
He Yang
1,
Pan Zhou
1 and
Fei Chen
1
1
School of Materials and Environmental Engineering, Chengdu Technological University, No. 1, Section 2, Zhongxin Avenue, Pidu District, Chengdu 611730, China
2
School of Materials Science and Engineering, Southwest Jiaotong University, Chengdu 610031, China
*
Author to whom correspondence should be addressed.
Materials 2023, 16(15), 5437; https://doi.org/10.3390/ma16155437
Submission received: 6 July 2023 / Revised: 29 July 2023 / Accepted: 31 July 2023 / Published: 3 August 2023
(This article belongs to the Special Issue Corrosion Properties and Mechanism of Steels, Volume II)
Browse Figures
Versions Notes

Abstract

:
The microstructural evolution and corrosion behaviour of railroad flash-butt-welded U71Mn joints and the effect of heat treatment were investigated via scanning electron microscopy and electrochemical measurements. The joint structures were found to mainly comprise pearlite and a few ferrites. The grains became finer and more homogeneous after heat treatment. Additionally, there was a decrease in the corrosion current density (1.71 × 10−5 A cm−2) and increases in the absolute corrosion potential (0.86 mV) and corrosion resistance (1088.83 Ω−1cm2). This was primarily attributed to the fewer Cl− ions at the homogeneous grain boundaries and fewer oxidation reactions on the joints after heat treatment. The findings of this study explain corrosion failure and will guide the development of corrosion-resistant joints for improved railroad quality.

1. Introduction

Since the construction of the Qinghai–Tibet railway line in China to meet the increasing demand for economic and safe railway travel, there has been a need to develop higher-quality steel rail materials to reduce rail failure and maintenance costs [1,2]. U71Mn rail steel is one of the strongest rail materials, and is widely used for rail construction [3,4]. In rail tracks, the welded joint is considered the weakest section in the seamless line, which directly affects the service life of the welded rail [5,6,7]. Among the available welding technologies, flash-butt welding is considered the most reliable for achieving stability, as demonstrated by its high efficiency, heat concentration, and high performance [8,9].
During the operation of a high-speed rail track, crack defects usually occur on the rail surface owing to manufacturing defects or long-term operational loads [10,11]. These cracks progressively result in peeling or fracturing, which limits the life span of the railway. Corrosion, which occurs via several mechanisms, is one of the main modes of failure of rail tracks [12,13,14]. Thus, understanding the corrosion characteristics of rails is important to the service life of the rail joints [15,16,17], especially in different microzones exposed to aggressive environments [18,19]. Lanzutti et al. [20] investigated Gr. 91 steel welded joints after post-weld heat treatments and developed a correlation between their corrosion and microstructure. They reported that the heat-affected zone (HAZ) is the most active site after welding and that tempering decreased its corrosion resistance. Ding et al. [21] investigated the corrosion behaviour of 316L/52M/A508 welded joints with dissimilar metals. Through electrochemical experiments, they noted the formation of a duplex structure consisting of an oxide film with different element distributions. Xu et al. [22] investigated copper/316L stainless-steel dissimilar-metal welded joints using an electrolytic copper cathode plate. They reported the formation of corrosion pits when the γ phase was dissolved and eliminated from the surface. These results were confirmed by the transformation of the galvanic material based on the unstable microstructure of the γ and ε-Cu phases. Li et al. [23] discussed the corrosion behaviour of welded aluminium alloy A7N01P-T4 joints produced for high-speed trains. The Al cladding enhanced corrosion resistance by decreasing the corrosion currents and producing positive shifts in the potentials. Fattah-Alhosseini et al. [24] studied the relationship between the microstructure and corrosion behaviour of dissimilar friction stir-welded joints and investigated the formation of equiaxed recrystallised grains.
In the case of U71Mn rail steel, which is the alloy most frequently used for railway construction in China, researchers have focused on the mechanical properties of the welded joints [25,26] instead of the corrosion performance of the steel [27,28,29]. As U71Mn welded joints are subjected to the highest risk during service, and there is a need to investigate the variations in the weld grain size with the heterogeneous chemical compositions and microstructures [26]. Additionally, there is a need to examine the corrosion performance of flash-welded U71Mn welded joints to prolong their service lives. Their electrochemical behaviour and microstructural evolution should be analysed for this purpose.
In the present study, we fabricated U71Mn welded joints via flash welding and examined the effect of a post-weld heat treatment applied at approximately 910 °C on the relationship between the joints’ microstructural evolution and corrosion performance via electron microscopy and electrochemical measurements. Our findings regarding the corrosion response mechanisms of the flash-welded U71Mn joints are expected to contribute to improving the service life and quality of steel rails and developing corrosion-resistant joints.

2. Materials and Methods

2.1. Preparation of U71Mn Welded Joints

Hot-rolled U71Mn rail sections (60 kg m−1) were purchased from Pan Zhihua Iron and Steel (China). Table 1 lists the chemical composition of the U71Mn rail obtained from the vacuum direct reading spectrometer (QSN750, OBLF, Dortmund, Germany) and Chinese standards [30,31] to ensure the quality of the rail before the welding technology. Welded joints were prepared using a welding machine (UN5-150ZB, Aige Technology Co., Ltd., Chengdu, China; 9350 kg, with an upsetting force of 800 kN and a rated frequency of 50 Hz). The as-produced joints are referred to as W1. Some of the welded joints were normalised in two stages using a dual-frequency induction heating machine (ZH650, Aige Technology Co., Ltd., Chengdu, China). The final temperature was set to 910 °C, and the final air blast temperature to 600 °C. The post-weld heat-treated joints are referred to as W2.
The areas of the welded joints prepared via flash-butt welding can be divided into three sections according to their typical microstructures: the base metal (BM), HAZ, and weld metal (WM). A schematic of the sampling points of rail steel is shown in Figure 1. The working surface is the approximate size and shape of the material used for testing in each zone.

2.2. Electrochemical Test

To determine the electrochemical properties of each microzone of a U71Mn flash-welded joint, sample dimensions of 10 mm × 10 mm × 10 mm were obtained from the WM, HAZ, and BM, respectively. The working electrodes were connected to a copper wire and embedded into epoxy resin. Before obtaining the electrochemical measurements, the exposed areas of the working electrodes were ground using 2000-grit paper and ultrasonically cleaned with absolute ethyl alcohol. The electrochemical experiments were carried out on a CS310 electrochemical workstation, using a traditional three-electrode cell with a platinum mesh counter electrode and Ag/AgCl (saturated KCl) as the reference electrode. Before the test, the sample was immersed in a 3.5% NaCl solution for 30 min to equilibrate. The cell was then stabilised in an open circuit state by immersing it in a 3.5% NaCl solution for 30 min. To maintain a stable system, the potentio-dynamic polarisation (PDP) curve was checked at a scanning rate of 0.5 mV s−1 and a potential range of −500–500 mV relative to the open-circuit potential (OCP).
The corrosion potential and current density were obtained from the PDP curves using the Tafel linear extrapolation method [32]. Electrochemical impedance spectroscopy (EIS) measurements were conducted by applying an excitation voltage of 10 mV within a frequency range of 10−2–105 Hz under the OCP condition. The EIS data were fitted using ZView software (version 3.1). To ensure repeatability, all the measurements were performed at least three times under the same conditions, including the immersion in a 3.5% NaCl solution at a temperature of 25 °C.

2.3. Surface Morphology

The metallographic morphologies of the U71Mn rail joints were observed using an optical microscope (AxioLab.A1, ZEISS, Jena, Germany). The morphologies of the corrosion products were investigated via scanning electron microscopy (SEM, Gemini, ZEISS, Germany). Elemental distributions were detected via energy-dispersive spectroscopy (EDS), along with SEM.

3. Results and Discussion

3.1. Metallographic Microstructural Characterisation

The metallographic microstructures of the BM and welded joints are depicted in Figure 2. As shown in Figure 2a, the BM microstructure primarily consists of lamellate pearlite and a minor presence of ferrite. The BM remained unmelted during the welding process and also serves as one of the microzones of the welded joint. Figure 2b–e show the representative microstructures of different zones in the welded joints, including BM, HAZ, and WM. At low magnifications, weld seams are clearly visible in the weld zones of W1 (Figure 2c) and W2 (Figure 2e) at 100× magnification. The fusion zone is a narrow transition area (about 300 μm) between the weld metal and the base metal in the welded joint. At high magnifications (500×), reticulated ferrite encloses the pearlite in the welding line. By contrast, the size of the reticulated ferrite is about 40 μm in W1 and 20 μm in W2. Furthermore, Figure 2b,c show the coarse grain and uneven grain distributions typical of W1’s microstructure, while Figure 2d,e exhibit uniformly distributed fine grains in W2’s weld zones due to re-austenitisation after the post-weld heat treatment.

3.2. Polarisation Curve

Figure 3 shows the results of the potentio-dynamic polarisation tests of the BM and welded joints in a 3.5 wt.% NaCl aqueous solution. The corrosion currents and potentials obtained are summarised in Figure 4. The polarisation curves of the microzones of the welded joints are similar for both W1 and W2. Compared with the BM, the WM and HAZ exhibit more negative corrosion potentials and higher corrosion current densities, indicating higher corrosion rates. The corrosion current densities of the BM, HAZ, and WM in W2 are 1.21 × 10−5, 1.89 × 10−4, and 1.71 × 10−4 A cm−2, respectively (Figure 4). The corrosion potentials of the BM, HAZ, and WM in W2 are −0.808, −0.826, and −0.857 mV, respectively. Similar results were obtained for W1. A larger corrosion current density and larger absolute value of the corrosion potential indicate a higher corrosion rate and weaker corrosion resistance [33]. Thus, the two different microzones, WM and HAZ, exhibit higher corrosion rates and lower levels of corrosion resistance than the BM. This is attributed to the high reactivity and preferential corrosion of the WM and HAZ microzones when exposed to severe environments.
Comparing the microzones of W1 and W2, both welded joints exhibit similar corrosion potentials and current densities. The corrosion current densities of the WM of W1 and W2 were 2.17 × 10−5 and 1.71 × 10−5 A cm−2, respectively, and their corrosion potentials were −0.892 and −0.857 mV, respectively. Compared with W1, W2 has a lower corrosion current density and lower negative corrosion potential, indicating a lower corrosion rate and higher corrosion resistance.
Passivation was observed in all the samples. With increasing potential, rapid anodic dissolution occurred, with the resulting passivation coating protecting the underlying metal from further corrosion. The passivation areas for the WM of W2 were larger than those of W1, indicating the higher density of the corrosion products formed on the surfaces of the welded joints of W2. This suggests that the welded joints inhibit the diffusion of the electrolyte. The potential passivation range of W2 is slightly larger than that of W1, implying a greater positive potential on the W2 surface when the passivation layer is broken. Thus, the protective ability of the passivation layer of W2 is better than that of W1.

3.3. Resistance

To further investigate the EIS results, the measured data were fitted using the equivalent circuit shown in Figure 5. The Nyquist plots of the BM, W1, and W2 have capacitive loops in which the radius of the quasicircle is positively related to the resistance. The BM has the highest total resistance (R1 + R2, 1437 Ω−1cm2). In contrast, the total resistance of W2 (1056.16 Ω−1cm2) is larger than that of W1 (829.89 Ω−1cm2), suggesting a higher corrosion resistance of W2 after the post-weld heat treatment.
Figure 6 shows Bode plots of the U71Mn rail joints. In Figure 6a, each curve has two time-constant features within the frequency range. The maximum phase angle of the BM (~63.3°) is larger than that of the welded joints, and that of W2 (~48.8°) is slightly larger than that of W1 (~48.3°), indicating an improvement in the maximum phase angle of the welded joints after the post-weld heat treatment.
Furthermore, the value of |Z| at a fixed frequency of 0.1 Hz corresponds to the polarisation resistance, reflecting the corrosion resistance of the materials in the solution. As shown in Figure 6b, the |Z| value at 0.1 Hz for the W2 samples (2.91 Ω cm−2) is higher than that of W1 (2.73 Ω cm−2), indicating the higher corrosion resistance of W2 in a 3.5% NaCl solution.
Representative data from the Nyquist and corresponding Bode plots are shown in Table 2. Because the microstructures of the welded joints included finer and more homogeneous grains after the post-weld heat treatment, W2 exhibits a lower corrosion current density and higher corrosion resistance than W1.

3.4. Morphological Analysis of the Corrosion Products

The corrosion morphologies of the BM and welded joints after electrochemical testing are shown in Figure 7. The BM and W2 are lightly etched and exhibit few micrometre-sized pits. Extensive localised corrosion sites are distributed in W1. Thus, mild corrosion occurred in BM and W2, whereas severe corrosion occurred in W1. These results agree well with the polarisation curve and corrosion resistance results. Irregular surfaces with cracks in the corrosion products can be observed in the BM and welded joint, suggesting the clustering of the widely dispersed corrosion pits on the surface. Compared with W2, the rust layers of W1 are more heterogeneous, with smaller spacing and more defects, indicating a lower ability of the former to protect the rail joint surfaces. This is confirmed by the occurrence of evident corrosion pits on the W1 surface.
The smaller and more uniform grains of W2 promote the formation and stabilisation of a compact and thick corrosion product layer. Ion diffusion across the grain boundaries is impeded by the thick and compact products, which suppress cathodic corrosion reactions [34]. In contrast, the focal corrosion products [35] in W1 contribute little to protecting the material owing to the large amount of internal defects and loosened structures.
The elemental compositions were analysed via EDS, as shown in Figure 8 and Table 3. Compared with the corrosion-product-free sites, the corrosion products have lower Fe, Mn, and Si contents which reflect the dissolution of the metallic elements at the anodic site during corrosion. W1 has the highest Fe dissolution rate, consistent with the electrochemical results. Moreover, selective Mn dissolution in the BM and welded joints did not occur in the NaCl solution. This explains the similar rates of initial pitting of the BM and the welded joints. As a relatively stable element, Si dissolved more from the welded joints than that from the BM. However, the corrosion products were similar, illustrating the heterogeneous distributions of the metals in the local areas.
Furthermore, the Cl content originating from the corrosion solution (3.5 wt.% NaCl) is higher in the sites containing corrosion products than those without corrosion products, suggesting the adsorption of Cl− on the surfaces. Interestingly, the Cl− content in the corrosion products of W1 was significantly higher than in those of W2. Cl−-containing media contributes to an automatic operation response, resulting in more severe pitting corrosion. On the joint surface, Cl− promotes the entry of the local aggregation into the exterior defect at the inhomogeneous grain boundary.
Cathodic reaction: O2 + 2H2O + 4e → 4OH−
Anodic reaction: 2Fe → 2Fe2+ + 4e
The O content in the sites with corrosion products is significantly higher than in sites without corrosion products, illustrating the oxidation reaction of the U71Mn rail joints. Compared with W2, higher O and C contents and a lower Fe content are noted in the corrosion products of W1, indicating that the Fe compound tends to form the hydroxides Fe–COOH and Fe–OOH rather than Fe2O3, FeO, and Fe–OH. Compared with the Fe oxides, Fe hydroxides are detrimental to corrosion resistance in NaCl solutions [15]. On the surfaces of the W1 welded joints, the coarse grains and heterogeneous distribution promote the unstable initiation of pits and preferential local accumulation of cathode sites, unlike in W2. For the W1 microzones, the interiors of the reaction sites are local areas of oxygen enrichment which can form stable corrosion products. Conversely, the defects of the exterior sites act as grain boundaries that form reactive sites and continue to react with Cl− acceleration, thereby increasing corrosion.

3.5. Corrosion Mechanism

For rail tracks in a corrosive environment, pits generally form on the surface of the rail, especially at the bottom of the rail foot [11,36]. This causes stress concentration under the superposition of internal stress and alternating axial loads, resulting in fatigue cracking [37]. Subsequently, the cracks experience sustained growth under service conditions above the crack growth threshold, which ultimately leads to the fatigue fracture of the rails [29]. The welded joints are the weakest sections of the railway owing to their heterogeneous chemical composition and microstructure [17,38]. This study focused on the corrosion mechanism of flash-butt-welded joints of U71Mn rail steel to improve the service life and quality of steel rails and develop corrosion-resistant joints.
Figure 9 shows a schematic of the determined corrosion mechanisms, including the combined effects of Cl− and O on the corrosion products. When these ions are adsorbed and accumulate locally, they form locally-corroded microbatteries that promote corrosion [39]. Pits generally initiate at surface inhomogeneities such as inter-metallic phases, non-metallic inclusions, grain boundaries, dislocations, defects, or mechanically damaged sites [18,40]. This readily occurs in the WM microzones of W1, with coarse grains and uneven grain distributions. In W2, well-distributed corrosion sites weaken the ion effect when exposed to the same aggressive medium. Moreover, fewer corrosion products were noted in W2 relative to W1. In addition, fewer O products and less Cl− response are concentrated on W2 relative to W1. As the cladding layer has a thicker passive film which provides better corrosion protection to the cladded component [12], the products on W2 show less corrosion resistance. These results agree with the findings regarding the polarisation curve and corrosion resistance. Compared with W1, W2, with its uniform grains, has a smaller self-corrosion current (1.71 × 10−4 A cm−2) and less negative corrosion potential (−0.857 mV), indicating its lower corrosion rate and better corrosion resistance. The total resistance of W2 (1088.83 Ω−1cm2) is higher than that of W1 (811.875 Ω−1cm2), suggesting the better corrosion resistance of W2 after the post-weld heat treatment.

4. Conclusions

In the present study, the microstructural evolution and corrosion performance of U71Mn welded joints prepared via flash welding and subjected to post-weld heat treatments were investigated and compared with those of the BM. The microstructures of the welded joints, the polarisation curves and resistances, corrosion product morphologies, and elemental distributions were examined to elucidate the corrosion mechanism. The main findings are summarised as follows:
  • The microstructural analysis revealed that the main structure of the U71Mn welded joints and the BM consisted of pearlite and a small amount of ferrite. Due to re-austenization after post-weld heat treatment, uniformly distributed fine grains can be found in the weld zones.
  • Because the microstructures of the welded joint were disrupted and then reconfigured after welding, the U71Mn welded joints exhibited a higher corrosion current density and smaller impedance value than the BM.
  • After the post-weld heat treatment, the grain microstructure of the U71Mn weld bead was finer and more homogeneous, resulting in a smaller corrosion current density, a larger absolute self-corrosion potential value, and improved corrosion resistance.
  • When the O and Cl− adsorbed and accumulated in local areas in the corrosion products of the weld microzones, these elements induced an inhomogeneous response, while a less severe corrosion response in zones after the post-weld heat treatment which were relieved with a compact and thick corrosion product layer.

Author Contributions

Investigation, H.Y., P.Z. and F.C.; Resources, X.Z.; Writing—original draft, T.L.; Writing—review & editing, X.Z. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Sichuan Science and Technology Department through the Commercialization of Research Findings project (grant number 2023ZHCG0038).

Institutional Review Board Statement

This study is not involving humans or animals.

Data Availability Statement

The raw/processed data required to reproduce the findings of this study cannot be shared at this time because they are part of an ongoing study.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Wang, Y.; Zhou, H.; Shi, Y.J.; Feng, B.R. Mechanical Properties and Fracture Toughness of Rail Steels and Thermite Welds at Low Temperature. Int. J. Miner. Metall. Mater. 2012, 19, 409–420. [Google Scholar] [CrossRef]
  2. Qin, Y.; Zheng, B. The Qinghai–Tibet Railway: A Landmark Project and Its Subsequent Environmental Challenges. Environ. Dev. Sustain. 2010, 12, 859–873. [Google Scholar] [CrossRef]
  3. Hu, Y.; Guo, L.C.; Maiorino, M.; Liu, J.P.; Ding, H.H.; Lewis, R.; Meli, E.; Rindi, A.; Liu, Q.Y.; Wang, W.J. Comparison of Wear and Rolling Contact Fatigue Behaviours of Bainitic and Pearlitic Rails under Various Rolling-Sliding Conditions. Wear 2020, 460–461, 203455. [Google Scholar] [CrossRef]
  4. Zhao, J.; Miao, H.; Kan, Q.; Fu, P.; Ding, L.; Kang, G.; Wang, P. Numerical Investigation on the Rolling Contact Wear and Fatigue of Laser Dispersed Quenched U71Mn Rail. Int. J. Fatigue 2021, 143, 106010. [Google Scholar] [CrossRef]
  5. Jian, H.; Wang, Y.; Yang, X.; Xiao, K. Microstructure and Fatigue Crack Growth Behavior in Welding Joint of Al-Mg Alloy. Eng. Fail. Anal. 2021, 120, 105034. [Google Scholar] [CrossRef]
  6. Liu, F.C.; Hovanski, Y.; Miles, M.P.; Sorensen, C.D.; Nelson, T.W. A Review of Friction Stir Welding of Steels: Tool, Material Flow, Microstructure, and Properties. J. Mater. Sci. Technol. 2018, 34, 39–57. [Google Scholar] [CrossRef]
  7. Yang, Z.Z.; Ji, P.; Wu, R.Z.; Wang, Y.; Turakhodjaev, N.; Kudratkhon, B. Microstructure, Mechanical Properties and Corrosion Resistance of Friction Stir Welded Joint of Al–Mg–Mn–Zr–Er Alloy. Int. J. Mater. Res. 2023, 114, 65–76. [Google Scholar] [CrossRef]
  8. Ma, R.; Huang, D.; Zhang, J.; Zhang, Y.; Lv, Q. Effects of Rail Flash-Butt Welding and Post-Weld Heat Treatment Processes Meeting Different National Standards on Residual Stresses of Welded Joints. Int. J. Mater. Res. 2020, 111, 780–787. [Google Scholar] [CrossRef]
  9. Wang, J.; Ma, C.; Han, J.; Jiang, Z.; Linton, V. Acquisition of HSLA Steel Weld Joints with Excellent Mechanical Performance through Flash Butt Welding Physical Simulation. Mater. Lett. 2021, 303, 130511. [Google Scholar] [CrossRef]
  10. Yang, Y.L.; Zhou, L.L.; Chen, H.B.; Wang, J.; Qiao, H.C.; Lu, Y.; Qin, G.W. Laser Shock Peening Fe-Based Coatings for Enhancing Wear and Corrosion Resistance. Mater. Sci. Technol. 2021, 37, 1214–1224. [Google Scholar] [CrossRef]
  11. Liu, C.P.; Zhao, X.J.; Liu, P.T.; Pan, J.Z.; Ren, R.M. Influence of Contact Stress on Surface Microstructure and Wear Property of D2/U71Mn Wheel-Rail Material. Materials 2019, 12, 3268. [Google Scholar] [CrossRef] [Green Version]
  12. Lei, X.; Nuam, V.L.; Deng, Y.; Yuan, Y.; Liu, M.; Yao, W.; Wang, N. Insight into the Passivation and Corrosion Behavior of Additive Manufacturing Repaired Single Crystal Superalloy. Corros. Sci. 2022, 203, 110340. [Google Scholar] [CrossRef]
  13. Park, J.H.; Ko, K.P.; Hagio, T.; Ichino, R.; Lee, M.H. Effect of Zn-Mg Interlayer on the Corrosion Resistance of Multilayer Zn-Based Coating Fabricated by Physical Vapor Deposition Process. Corros. Sci. 2022, 202, 110330. [Google Scholar] [CrossRef]
  14. Zhang, C.; Huang, G.; Cao, Y.; Li, Q.; Zhu, Y.; Huang, X.; Liu, Q. Investigation on Microstructure and Localized Corrosion Behavior in the Stir Zone of Dissimilar Friction-Stir-Welded AA2024/7075 Joint. J. Mater. Sci. 2020, 55, 15005–15032. [Google Scholar] [CrossRef]
  15. Ming, J.; Zhou, X.; Jiang, L.; Shi, J. Corrosion Resistance of Low-Alloy Steel in Concrete Subjected to Long-Term Chloride Attack: Characterization of Surface Conditions and Rust Layers. Corros. Sci. 2022, 203, 110370. [Google Scholar] [CrossRef]
  16. Sui, F.; An, T.; Zheng, S.; Chen, L.; Li, S. Influence of Effective Strain on the Corrosion Behavior of Nickel-Based GH4710 Superalloy in Chloride Solutions. Corros. Sci. 2022, 204, 110386. [Google Scholar] [CrossRef]
  17. Wang, Z.; Zhang, X.; Yu, H.; Liu, J.; Cheng, L.; Hu, S.E.; Wu, K. Effects of Pearlite on Corrosion Initiation and Propagation in Weathering Steels in Marine Environments. J. Mater. Sci. 2022, 57, 6039–6055. [Google Scholar] [CrossRef]
  18. Chaves, I.A.; Melchers, R.E. Pitting corrosion in pipeline steel weld zones. Corros. Sci. 2011, 53, 4026–4032. [Google Scholar] [CrossRef]
  19. Moshtaghi, M.; Loder, B.; Safyari, M.; Willidal, T.; Hojo, T.; Mori, G. Hydrogen trapping and desorption affected by ferrite grain boundary types in shielded metal and flux-cored arc weldments with Ni addition. Int. J. Hydrogen Energy 2022, 47, 20676–20683. [Google Scholar] [CrossRef]
  20. Lanzutti, A.; Andreatta, F.; Lekka, M.; Fedrizzi, L. Microstructural and Local Electrochemical Characterisation of Gr. 91 Steel-Welded Joints as Function of Post-Weld Heat Treatments. Corros. Sci. 2019, 148, 407–417. [Google Scholar] [CrossRef]
  21. Ding, J.; Zhang, Z.-M.; Wang, J.-Z.; Wang, J.-Q.; Han, E.-H. Corrosion Behavior of Different Parts of the Weld of 316L/52M/A508 Dissimilar Metal Welded Joint in Simulated Pressurized Water Reactor Primary Water. Mater. Corros. 2015, 66, 1435–1444. [Google Scholar] [CrossRef]
  22. Xu, Y.; Hou, X.; Shi, Y.; Zhang, W.; Gu, Y.; Feng, C.; Volodymyr, K. Correlation between the Microstructure and Corrosion Behaviour of Copper/316L Stainless-Steel Dissimilar-Metal Welded Joints. Corros. Sci. 2021, 191, 109729. [Google Scholar] [CrossRef]
  23. Li, B.; Wu, M.; Jin, W.; Zhou, Y.; Ma, C.; Wang, X. Corrosion Behavior of Weld Joints of Aluminum Alloy A7N01P-T4 for High-speed Trains. Corros. Sci. Prot. Technol. 2014, 26, 223–227. [Google Scholar] [CrossRef]
  24. Fattah-Alhosseini, A.; Naseri, M.; Gholami, D.; Imantalab, O.; Attarzadeh, F.R.; Keshavarz, M.K. Microstructure and Corrosion Characterization of the Nugget Region in Dissimilar Friction-Stir-Welded AA5083 and AA1050. J. Mater. Sci. 2019, 54, 777–790. [Google Scholar] [CrossRef]
  25. Hu, Y.; Watson, M.; Maiorino, M.; Zhou, L.; Wang, W.J.; Ding, H.H.; Lewis, R.; Meli, E.; Rindi, A.; Liu, Q.Y.; et al. Experimental Study on Wear Properties of Wheel and Rail Materials with Different Hardness Values. Wear 2021, 477, 203831. [Google Scholar] [CrossRef]
  26. Gong, L.; Liu, H.; Lv, C.; Zhao, L. Effect of Alloying Composition on Microstructure and Mechanical Properties of Ultranarrow Gap Welded Joints of U71Mn Rail Steel. Adv. Mater. Sci. Eng. 2021, 2021, 9282463. [Google Scholar] [CrossRef]
  27. Zhong, W.; Hu, J.J.; Li, Z.B.; Liu, Q.Y.; Zhou, Z.R. A Study of Rolling Contact Fatigue Crack Growth in U75V and U71Mn Rails. Wear 2011, 271, 388–392. [Google Scholar] [CrossRef]
  28. Pan, J.; Chen, L.; Liu, C.; Zhang, G.; Ren, R. Relationship between the Microstructural Evolution and Wear Behavior of U71Mn Rail Steel. J. Materi. Eng. Perform. 2021, 30, 1090–1098. [Google Scholar] [CrossRef]
  29. Yu, X.; Feng, L.; Qin, S.; Zhang, Y.; He, Y. Fracture Analysis of U71Mn Rail Flash-Butt Welding Joint. Case Stud. Eng. Fail. Anal. 2015, 4, 20–25. [Google Scholar] [CrossRef] [Green Version]
  30. TB/T 1632-2014; Railway Industry Standard of the People’s Republic of China, Railway Applications-Track-Flash Butt Welding of Rails. National Railway Administration: Beijing, China, 2014.
  31. TB/T 2344-2020; Railway Industry Standard of the People’s Republic of China. Rails—Part 1: 43 kg/m~75 kg/m Rails. National Railway Administration: Beijing, China, 2020.
  32. Sinhmar, S.; Dwivedi, D.K. A Study on Corrosion Behavior of Friction Stir Welded and Tungsten Inert Gas Welded AA2014 Aluminium Alloy. Corros. Sci. 2018, 133, 25–35. [Google Scholar] [CrossRef]
  33. Solmaz, R.; Altunbaş Şahin, E.A.; Döner, A.; Kardaş, G. The Investigation of Synergistic Inhibition Effect of Rhodanine and Iodide Ion on the Corrosion of Copper in Sulphuric Acid Solution. Corros. Sci. 2011, 53, 3231–3240. [Google Scholar] [CrossRef]
  34. Wen, M.; Sun, Y.; Yu, J.; Yang, S.; Hou, X.; Yang, Y.; Sun, X.; Zhou, Y. Amelioration of Weld-Crack Resistance of the M951 Superalloy by Engineering Grain Boundaries. J. Mater. Sci. Technol. 2021, 78, 260–267. [Google Scholar] [CrossRef]
  35. Dong, L.; Zhang, Y.; Han, Y.; Peng, Q.; Han, E.H. Environmentally Assisted Cracking in the Fusion Boundary Region of a SA508-Alloy 52M Dissimilar Weld Joint in Simulated Primary Pressurized Water Reactor Environments. Corros. Sci. 2021, 190, 109668. [Google Scholar] [CrossRef]
  36. Fang, X.Y.; Zhang, H.N.; Ma, D.W. Influence of Initial Crack on Fatigue Crack Propagation with Mixed Mode in U71Mn Rail Subsurface. Eng. Fail. Anal. 2022, 136, 106220. [Google Scholar] [CrossRef]
  37. Wang, Y.; Chai, P.; Ma, H.; Cao, X.; Zhang, Y. Formation Mechanism and Fracture Behavior in Extra-Filling Refill Friction Stir Spot Weld for Al–Cu–Mg Aluminum Alloy. J. Mater. Sci. 2020, 55, 358–374. [Google Scholar] [CrossRef]
  38. Singh, J.; Shahi, A.S. Microstructure and Corrosion Behavior of Duplex Stainless Steel Electron Beam Welded Joint. J. Mater. Sci. 2022, 57, 9454–9479. [Google Scholar] [CrossRef]
  39. Chen, G.; Liu, S.; Huang, C.; Ma, Y.; Li, Y.; Zhang, B.; Gao, L.; Zhang, B.; Wang, P.; Qu, X. In-Situ Phase Transformation and Corrosion Behavior of TiNi via LPBF. Corros. Sci. 2022, 203, 110348. [Google Scholar] [CrossRef]
  40. Xu, W.; Deng, Y.; Zhang, B.; Zhang, J.; Peng, Z.; Hou, B.; Duan, J. Crevice corrosion of U75V high-speed rail steel with varying crevice gap size by in-situ monitoring. J. Mater. Res. Technol. 2022, 16, 1856–1874. [Google Scholar] [CrossRef]
Materials 16 05437 g001
Figure 1. Sampling points on an U71Mn rail joint (mm).
Figure 1. Sampling points on an U71Mn rail joint (mm).
Materials 16 05437 g001
Materials 16 05437 g002
Figure 2. Representative optical micrographs of the metallographic microstructures of the (a) BM, (b) the HAZ of W1, (c) the WM of W1, (d) the HAZ of W2, and (e) the WM of W2. The scale bars (100, 50, and 20 μm) indicate the magnification (×100, ×200, and ×500, respectively).
Figure 2. Representative optical micrographs of the metallographic microstructures of the (a) BM, (b) the HAZ of W1, (c) the WM of W1, (d) the HAZ of W2, and (e) the WM of W2. The scale bars (100, 50, and 20 μm) indicate the magnification (×100, ×200, and ×500, respectively).
Materials 16 05437 g002
Materials 16 05437 g003
Figure 3. Cyclic potentio-dynamic polarisation curves of the microzones of the BM, W1, and W2.
Figure 3. Cyclic potentio-dynamic polarisation curves of the microzones of the BM, W1, and W2.
Materials 16 05437 g003
Materials 16 05437 g004
Figure 4. Corrosion potentials and currents of the BM and the welded joints after Tafel fitting. The black and red bars represent the corrosion currents and potentials, respectively.
Figure 4. Corrosion potentials and currents of the BM and the welded joints after Tafel fitting. The black and red bars represent the corrosion currents and potentials, respectively.
Materials 16 05437 g004
Materials 16 05437 g005
Figure 5. Nyquist plot of WM in a 3.5 wt.% NaCl solution. The equivalent circuit is shown in the inset.
Figure 5. Nyquist plot of WM in a 3.5 wt.% NaCl solution. The equivalent circuit is shown in the inset.
Materials 16 05437 g005
Materials 16 05437 g006
Figure 6. Bode plots of the U71Mn rail joints: (a) angle and (b) |Z| as functions of the frequency.
Figure 6. Bode plots of the U71Mn rail joints: (a) angle and (b) |Z| as functions of the frequency.
Materials 16 05437 g006
Materials 16 05437 g007
Figure 7. Macromorphologies of the BM and welded joints.
Figure 7. Macromorphologies of the BM and welded joints.
Materials 16 05437 g007
Materials 16 05437 g008
Figure 8. Locations selected of EDS results for the (a) BM, (b) W1, and (c) W2, and EDS elemental mapping of (d) BM, (e) W1, and (f) W2.
Figure 8. Locations selected of EDS results for the (a) BM, (b) W1, and (c) W2, and EDS elemental mapping of (d) BM, (e) W1, and (f) W2.
Materials 16 05437 g008
Materials 16 05437 g009
Figure 9. Mechanism of the corrosion response of U71Mn welded joints.
Figure 9. Mechanism of the corrosion response of U71Mn welded joints.
Materials 16 05437 g009
Table 1. Chemical composition of U71Mn rails (wt.%).
Table 1. Chemical composition of U71Mn rails (wt.%).
CompositionCSiMnSPFe
Standard requirements [31]0.65–0.80.15–0.580.70–1.20≤0.025≤0.025Remaining
Test result0.690.300.990.0100.015Remaining
Table 2. Fitting results of representative data from the Nyquist and corresponding Bode plots.
Table 2. Fitting results of representative data from the Nyquist and corresponding Bode plots.
SampleR1
(Ω)		Y0-Q1 (Ω−1cm−2Sn)n-Q1R2
(Ω cm2)		Y0-Q2 (Ω−1cm−2Sn)n-Q2R3
(Ω cm2)		X2
Chi-Square		R2 + R3 (Ω cm2)
BM2.5193.55 × 10−50.91124189.92 × 10−40.8636914193.42 × 10−31437
HAZ of W11.8645.32 × 10−50.937817.641.59 × 10−30.6248985.41.03 × 10−41003.04
WM of W11.7531.85 × 10−50.92955.991.25 × 10−30.58445823.91.13 × 10−3829.89
HAZ of W22.5054.69 × 10−50.885519.31.03 × 10−30.8604610424.22 × 10−31061.3
WM of W22.1793.66 × 10−50.9100419.169.10 × 10−40.7712110372.36 × 10−31056.16
R1, R2, and R3 are the solution, film, and double-layer resistances corresponding to the interfacial charge transfer reactions, respectively. Q represents the constant-phase elements representing the non-ideal capacitances of the electrical double layer. n < 1 indicates a frequency-dependent capacitor which shows the characteristic behaviour of an oxide film. X2 (chi-square) is the error of the electrical equivalent circuit fitting.
Table 3. Main elemental compositions of the corrosion products of the BM and the welded joints (wt.%).
Table 3. Main elemental compositions of the corrosion products of the BM and the welded joints (wt.%).
Weight Percentage (wt.%)FeMnSiClCO
Corrosion-product-free site of BM70.481.250.130.098.9118.48
Products of BM60.720.510.10.116.5631.4
Corrosion-product-free site of W187.181.260.270.027.853.23
Products of W153.940.550.110.478.0736.03
Corrosion-product-free site of W288.771.630.220.027.131.12
Products of W263.80.480.090.353.5331.13
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Liao, T.; Zhang, X.; Yang, H.; Zhou, P.; Chen, F. Microstructural Evolution and Micro-Corrosion Behaviour of Flash-Welded U71Mn Joints as a Function of Post-Weld Heat Treatment. Materials 2023, 16, 5437. https://doi.org/10.3390/ma16155437

AMA Style

Liao T, Zhang X, Yang H, Zhou P, Chen F. Microstructural Evolution and Micro-Corrosion Behaviour of Flash-Welded U71Mn Joints as a Function of Post-Weld Heat Treatment. Materials. 2023; 16(15):5437. https://doi.org/10.3390/ma16155437

Chicago/Turabian Style

Liao, Tingting, Xi Zhang, He Yang, Pan Zhou, and Fei Chen. 2023. "Microstructural Evolution and Micro-Corrosion Behaviour of Flash-Welded U71Mn Joints as a Function of Post-Weld Heat Treatment" Materials 16, no. 15: 5437. https://doi.org/10.3390/ma16155437

APA Style

Liao, T., Zhang, X., Yang, H., Zhou, P., & Chen, F. (2023). Microstructural Evolution and Micro-Corrosion Behaviour of Flash-Welded U71Mn Joints as a Function of Post-Weld Heat Treatment. Materials, 16(15), 5437. https://doi.org/10.3390/ma16155437

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop