Abstract
This study deciphers the chloride-induced early-stage corrosion of Cr/RE-microalloyed HRB400 rebars in saturated Ca(OH)₂ pore solutions (0.5–3.5 wt% Cl⁻). Rare-earth addition transforms original MnS and Al₂O₃–MnO–CaO inclusions into RE–Al–O–S particles, many encapsulated by thin MnS shells. Preferential MnS dissolution creates occluded cells whose acidification simultaneously attacks the exposed RE–Al–O core and adjacent steel, yet the RE phase markedly retards this sequence. Across all chloride levels, HRB400-Cr-RE exhibits the highest pitting potential, lowest passive current density, largest charge-transfer resistance and thinnest passive-film donor density; after 7 d immersion its corrosion rate is one-third that of HRB400 and confocal microscopy confirms the shallowest pits with the lowest aspect ratios. Elevated Cl⁻ progressively lowers pitting potentials, raises passive currents, shrinks Nyquist arcs and increases donor densities in all steels, evidencing accelerated dissolution of inclusions and surrounding matrix under high-chloride conditions.
Similar content being viewed by others
Data availability
The datasets generated and/or analyzed during the current study are not publicly available due to the data are part of an ongoing study but may be available from the corresponding author on reasonable request.
References
Fu, C., Fang, D., Ye, H., Huang, L. & Wang, J. Bond degradation of non-uniformly corroded steel rebars in concrete. Eng. Struct. 226, 111392 (2021).
Hornbostel, K., Angst, U. M., Elsener, B., Larsen, C. K. & Geiker, M. R. Influence of mortar resistivity on the rate-limiting step of chloride-induced macro-cell corrosion of reinforcing steel. Corros. Sci. 110, 46–56 (2016).
Zhao, Y., Dong, J., Ding, H. & Jin, W. Shape of corrosion-induced cracks in recycled aggregate concrete. Corros. Sci. 98, 310–317 (2015).
Mundra, S., Criado, M., Bernal, S. A. & Provis, J. L. Chloride-induced corrosion of steel rebars in simulated pore solutions of alkali-activated concretes. Cem. Concr. Res. 100, 385–397 (2017).
Berrocal, C. G., Lundgren, K. & Löfgren, I. Corrosion of steel bars embedded in fibre reinforced concrete under chloride attack: state of the art. Cem. Concr. Res. 80, 69–85 (2016).
Tang, S. W., Yao, Y., Andrade, C. & Li, Z. Recent durability studies on concrete structure. Cem. Concr. Res. 78, 143–154 (2015).
Tran, D. T., Lee, H.-S., Singh, J. K. & Lee, D.-E. Corrosion prevention of steel rebar embedded in the cement mortar under accelerated conditions: combined effects of phosphate and chloride ions. Constr. Build. Mater. 365, 130042 (2023).
Xiong, C. et al. Preparation of phytic acid conversion coating and corrosion protection performances for steel in chlorinated simulated concrete pore solution. Corros. Sci. 139, 275–288 (2018).
Liu, Q. et al. A novel green reinforcement corrosion inhibitor extracted from waste Platanus acerifolia leaves. Constr. Build. Mater. 260, 119695 (2020).
Moffatt, E. G., Thomas, M. D. & Fahim, A. Performance of high-volume fly ash concrete in marine environment. Cem. Concr. Res. 102, 127–135 (2017).
Aguirre-Guerrero, A. M., Robayo-Salazar, R. A. & de Gutiérrez, R. M. A novel geopolymer application: coatings to protect reinforced concrete against corrosion. Appl. Clay Sci. 135, 437–446 (2017).
Calero, J. C., Llorca, M. C. & Terradillos, P. G. Influence of different ways of chloride contamination on the efficiency of cathodic protection applied on structural reinforced concrete elements. J. Electroanal. Chem. 793, 8–17 (2017).
Etteyeb, N., Dhouibi, L., Takenouti, H. & Triki, E. Protection of reinforcement steel corrosion by phenylphosphonic acid pre-treatment PART II: tests in mortar medium. Cem. Concr. Compos. 65, 94–100 (2016).
Etteyeb, N., Dhouibi, L., Takenouti, H. & Triki, E. Protection of reinforcement steel corrosion by phenyl phosphonic acid pre-treatment PART I: tests in solutions simulating the electrolyte in the pores of fresh concrete. Cem. Concr. Compos. 55, 241–249 (2015).
Liu, M., Cheng, X., Li, X. & Lu, T. J. Corrosion behavior of low-Cr steel rebars in alkaline solutions with different pH in the presence of chlorides. J. Electroanal. Chem. 803, 40–50 (2017).
Roventi, G., Bellezze, T., Giuliani, G. & Conti, C. Corrosion resistance of galvanized steel reinforcements in carbonated concrete: Effect of wet–dry cycles in tap water and in chloride solution on the passivating layer. Cem. Concr. Res. 65, 76–84 (2014).
Du, F. et al. Chloride ions migration and induced reinforcement corrosion in concrete with cracks: a comparative study of current acceleration and natural marine exposure. Constr. Build. Mater. 263, 120099 (2020).
Ida, N., Nishimoto, M., Muto, I. & Sugawara, Y. Role of MnS in the intergranular corrosion and depassivation of sensitized Type 304 stainless steel. npj Mater. Degrad. 8, 2 (2024).
Kuah, K. X. & Blackwood, D. J. Investigating molybdenum’s sulphur scavenging ability for MoS2 formation in preventing pitting corrosion of stainless steels. npj Mater. Degrad. 7, 80 (2023).
Li, Z. et al. Role of segregation behavior of Cu and Sb in the region of inclusions on initial corrosion. npj Mater. Degrad. 7, 29 (2023).
Liu, P., Zhang, Q.-H., Watanabe, Y., Shoji, T. & Cao, F.-H. A critical review of the recent advances in inclusion-triggered localized corrosion in steel. npj Mater. Degrad. 6, 81 (2022).
Saito, H., Nishimoto, M. & Muto, I. Pitting corrosion characteristics of sintered Type 316 L stainless steel: relationship between pores and MnS. npj Mater. Degrad. 8, 61 (2024).
Reformatskaya, I., Rodionova, I., Beilin, Y. A., Nisel’Son, L. & Podobaev, A. The effect of nonmetal inclusions and microstructure on local corrosion of carbon and low-alloyed steels. Prot. Met. 40, 447–452 (2004).
Szklarska-Smialowska, Z. Influence of sulfide inclusions on the pitting corrosion of steels. Corrosion 28, 388–396 (1972).
Domizzi, G., Anteri, G. & Ovejero-Garcıa, J. Influence of sulphur content and inclusion distribution on the hydrogen induced blister cracking in pressure vessel and pipeline steels. Corros. Sci. 43, 325–339 (2001).
Liu, M., Cheng, X., Li, X., Jin, Z. & Liu, H. Corrosion behavior of Cr modified HRB400 steel rebar in simulated concrete pore solution. Constr. Build. Mater. 93, 884–890 (2015).
Liu, M., Cheng, X. & Li, X. Corrosion propagation behavior of low-Cr steel Rebars in simulated concrete environments. Int. J. Electrochem. Sci. 14, 726–742 (2019).
Yuan, X., Wang, X., Cao, Y. & Yang, H. Natural passivation behavior and its influence on chloride-induced corrosion resistance of stainless steel in simulated concrete pore solution. J. Mater. Res. Technol. 9, 12378–12390 (2020).
Yan, L., Song, G.-L., Wang, Z. & Zheng, D. Crevice corrosion of steel rebar in chloride-contaminated concrete. Constr. Build. Mater. 296, 123587 (2021).
Liu, M., Cheng, X., Li, X., Pan, Y. & Li, J. Effect of Cr on the passive film formation mechanism of steel rebar in saturated calcium hydroxide solution. Appl. Surf. Sci. 389, 1182–1191 (2016).
Xu, L. et al. Structural characteristics and chloride intrusion mechanism of passive film. Corros. Sci. 207, 110563 (2022).
Liu, M. et al. Indoor accelerated corrosion test and marine field test of corrosion-resistant low-alloy steel rebars. Constr. Build. Mater. 5, 87–99 (2016).
Yang, D., Yan, C., Zhang, J., Liu, S. & Li, J. Chloride threshold value and initial corrosion time of steel bars in concrete exposed to saline soil environments. Constr. Build. Mater. 267, 120979 (2021).
Zhang, X. et al. Effects of niobium and rare earth elements on microstructure and initial marine corrosion behavior of low-alloy steels. Appl. Surf. Sci. 475, 83–93 (2019).
Wei, J., Dong, J., Ke, W. & He, X. Influence of inclusions on early corrosion development of ultra-low carbon bainitic steel in NaCl solution. Corrosion 71, 1467–1480 (2015).
An, H. et al. High corrosion resistance film on rebar by cerium modification. J. Mater. Sci. Technol. 64, 73–84 (2021).
Chen, T. et al. Insights into the role of the Cr and rare element in improving the corrosion resistance of HRB400 rebars in simulated SO2-polluted marine environment. J. Build. Eng. 97, 110807 (2024).
Chen, T. et al. Deterioration mechanism of passivation behavior of ductile iron induced by shrinkage defects in simulated concrete pore solution. J. Mater. Sci. Technol. 236, 136–149 (2025).
Chen, T. et al. The coupling mechanism of shrinkage defects and graphite on the corrosion resistance of ductile iron. Corros. Sci. 227, 111798 (2024).
Dong, B. et al. Corrosion failure analysis of low alloy steel and carbon steel rebar in tropical marine atmospheric environment: outdoor exposure and indoor test. Eng. Fail. Anal. 129, 105720 (2021).
Al-Amoudi, O. S. B., Rasheeduzzafar, A., Maslehuddin, M. & Abduljauwad, S. Influence of sulfate ions on chloride-induced reinforcement corrosion in portland and blended cement concretes. Cem. Concr. Aggreg. 16, 3–11 (1994).
Zhang, Z., Zhang, P., Niu, G., Ding, C. & Wu, H. Enhanced passivation of Cr-modified rebar in simulated seawater sea-sand concrete chloride environment. J. Mater. Res. Technol. 35, 7051–7064 (2025).
Chen, T. et al. Understanding the mechanism of shrinkage defects on corrosion kinetics of ductile iron. Corros. Sci. 256, 113168 (2025).
Chen, T. et al. Comparative study on corrosion resistance of carbon steel and ductile iron: Implications for the development of corrosion-resistant steels. Corros. Sci. 255, 113127 (2025).
Chen, T. et al. Corrosion behavior of 650 MPa high strength low alloy steel in industrial polluted environment containing different concentration of Cl-. Int. J. Miner. Metall. Mater. https://doi.org/10.1007/s12613-025-3135-5 (2025).
Williams, D. E., Kilburn, M. R., Cliff, J. & Waterhouse, G. I. Composition changes around sulphide inclusions in stainless steels, and implications for the initiation of pitting corrosion. Corros. Sci. 52, 3702–3716 (2010).
Montemor, M., Simoes, A. & Ferreira, M. Chloride-induced corrosion on reinforcing steel: from the fundamentals to the monitoring techniques. Cem. Concr. Compos. 25, 491–502 (2003).
Dehwah, H. A., Austin, S. A. & Maslehuddin, M. Chloride-induced reinforcement corrosion in blended cement concretes exposed to chloride-sulphate environments. Mag. Concr. Res. 54, 355–364 (2002).
Zheng, S., Li, C., Qi, Y., Chen, L. & Chen, C. Mechanism of (Mg, Al, Ca)-oxide inclusion-induced pitting corrosion in 316L stainless steel exposed to sulphur environments containing chloride ion. Corros. Sci. 67, 20–31 (2013).
Chen, T. et al. Exploring trace Mg microalloying impact on corrosion mechanism of X70 Steel. Metall. Mater. Trans. A 56, 3518–3535 (2025).
Batista, W., Louvisse, A., Mattos, O. & Sathler, L. The electrochemical behaviour of INCOLOY 800 and AISI 304 steel in solutions that are similar to those within occluded corrosion cells. Corros. Sci. 28, 759–768 (1988).
Mikhailov, A. S., Scully, J. R. & Hudson, J. L. Nonequilibrium collective phenomena in the onset of pitting corrosion. Surf. Sci. 603, 1912–1921 (2009).
Chen, T. et al. Insights into multiple coupling mechanisms of SO42−/Cl− and Cr/RE elements on the corrosion resistance of rebar in simulated carbonated concrete pore solution. Constr. Build. Mater. 485, 141957 (2025).
Chen, T. et al. Assessing the durability of low-alloy rebars in China plateau environment by outdoor exposure and on-site online monitoring. Constr. Build. Mater. 468, 140475 (2025).
Liu, C. et al. Effect of inclusions modified by rare earth elements (Ce, La) on localized marine corrosion in Q460NH weathering steel. Corros. Sci. 129, 82–90 (2017).
Liu, C. et al. Role of Al2O3 inclusions on the localized corrosion of Q460NH weathering steel in marine environment. Corros. Sci. 138, 96–104 (2018).
Che, Z. C. et al. Role of Te-RE alloying on the passive film and pitting corrosion behavior of 316L stainless steel. Corros. Sci. 240, 112457 (2024).
Liu, C. et al. New insights into the mechanism of localised corrosion induced by TiN-containing inclusions in high strength low alloy steel. J. Mater. Sci. Technol. 124, 141–149 (2022).
Liu, C. et al. Influence of rare earth metals on mechanisms of localised corrosion induced by inclusions in Zr-Ti deoxidised low alloy steel. Corros. Sci. 166, 108463 (2020).
Acknowledgements
The authors acknowledge the National Natural Science Foundation of China (No. 52374323).
Author information
Authors and Affiliations
Contributions
R.Z.: writing-original draft & editing; T.C.: data curation; L.H.: investigation; W.Y., C.G., X.Z., and X.C.: methodology; C.L.: methodology, supervision, writing-review & editing; X.L.: supervision, methodology. All authors read and approved the final version.
Corresponding authors
Ethics declarations
Competing interests
X.L. serves as editor of this journal and had no role in the peer review or decision to publish this manuscript. The remaining authors declare no competing interests.
Additional information
Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Supplementary information
Rights and permissions
Open Access This article is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License, which permits any non-commercial use, sharing, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if you modified the licensed material. You do not have permission under this licence to share adapted material derived from this article or parts of it. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by-nc-nd/4.0/.
About this article
Cite this article
Zhu, R., Chen, T., Hao, L. et al. Enhancement mechanisms of Cr and RE on the corrosion resistance of HRB400 rebar in chloride-containing concrete pore solution. npj Mater Degrad (2026). https://doi.org/10.1038/s41529-026-00746-3
Received:
Accepted:
Published:
DOI: https://doi.org/10.1038/s41529-026-00746-3
